JP6904188B2 - Switching power supply - Google Patents

Description

The present invention relates to a switching power supply device.

Switching power supplies used in electrical equipment include, for example, a primary rectifying and smoothing circuit that rectifies and smoothes commercial AC power on the primary side and outputs primary DC power, and turns the obtained primary DC power current on and off. A switching element that switches to a state, a transformer in which a current switched between an on state and an off state flows in the primary winding, a rectifying and smoothing circuit on the secondary side connected to the secondary winding of the transformer, and the secondary. It has a constant voltage control circuit that pulse width modulates the drive pulse of the switching element in order to stabilize the output voltage of the rectifying and smoothing circuit on the side.

Such power supply devices are required to be designed in compliance with the safety standards of each country. For example, in the safety standard IEC61010, there is a method of conforming to a 9.4 energy restricted circuit in order to reduce the ignition risk in the device. This energy-limited circuit standard requires that the output current be limited below a specified level. When the adjustment network is used to limit the maximum available current, it is necessary to satisfy the requirement even if a part of the adjustment network fails.

In addition, the UL standard, which is an American safety standard, conforms to a limited power supply (LPS) and a limited voltage / current circuit (Limited Voltage / Current) in order to reduce the risk of ignition of equipment and diffusion of flames. There is a way to make it. According to the UL standard, finite power supplies and limited voltage / current circuits have a requirement to limit the output power and output current to below the specified level, and even if a part of the circuit fails, the requirement is satisfied. There is a need to. In addition, according to the requirements of these safety standards, it is necessary to limit the current and power to the level required by the safety standards even if a part of the circuit that limits the output voltage or output current fails. There is.

As a method for limiting the output voltage, output current, and output power in a switching power supply device, for example, a method for limiting the output power by limiting the peak value of the drain current of the switching element on the primary side of the switching power supply has been proposed. (See, for example, Patent Document 1).
Further, in the switching power supply device, as a method of limiting the output voltage, output current, and output power, for example, a method of providing an overcurrent protection device such as a fuse in the output path on the secondary side, and detecting the output current on the secondary side. Then, a method of controlling the switching element on the primary side has been proposed.

Japanese Unexamined Patent Publication No. 2006-034045

However, in the prior art described in Patent Document 1, since the circuits that limit the output voltage, the output current, and the output power are not duplicated, the safety standard cannot be satisfied. Further, Patent Document 1 does not suggest or disclose a method for duplicating. Further, the conventional technique described in Patent Document 1 has a problem that the current limit value on the secondary side varies depending on the type of converter to be controlled. It should be noted that such variation depends on, for example, the detection accuracy of the drain current of the switching element. In particular, for example, in a switching power supply device that can handle commercial AC voltages of 100V system and 200V system, there is a problem that the variation of the peak value of the drain current becomes larger.
As described above, in the prior art, since the variation of the current limit value on the secondary side is large, the rated current of the device must be set low in order to satisfy the current limit value on the secondary side required by the safety standard. There was a problem that it had to be done.
In addition, in the method of providing an overcurrent protection device such as a fuse for overcurrent protection, the variation in the operating time and operating point of the overcurrent protection device and the influence of the ambient temperature increase the variation in the overcurrent protection operating point. There is a problem that the rated current of the device must be set lower than the current limit value on the secondary side required by the safety standard.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a switching power supply device that can comply with safety standards and can obtain a larger rated current than before.

(1) In order to achieve the above object, the switching power supply device according to one aspect of the present invention includes a primary side winding to which a switching element is connected, a first secondary side winding to be connected to an output unit, and the like. A transformer having a second secondary winding, a first overcurrent protection unit that detects an overcurrent flowing through the first secondary winding by comparing it with a first threshold, and the first two. A second overcurrent protection unit that detects the overcurrent flowing in the next winding by comparing it with a second threshold value different from the first threshold value, a detection result of the first overcurrent protection unit, and the second overcurrent protection. A control unit that controls the switching element is provided based on at least one of the detection results of the unit, and the first overcurrent protection unit is supplied with electric power from the second secondary winding side. To.

(2) Further, in the switching power supply device according to one aspect of the present invention, the second overcurrent protection unit may be supplied with electric power from the first secondary winding side.

(3) Further, in the switching power supply device according to one aspect of the present invention, the transformer includes a third secondary winding, and the second overcurrent protection unit includes the third secondary winding. Power may be supplied from the side.

(4) Further, in the switching power supply device according to one aspect of the present invention, the first threshold value is equal to or lower than the second threshold value, and the output of the first overcurrent protection unit is a signal indicating an output current suppression request. , An error of comparing the voltage value based on the voltage generated in the first secondary winding with the first predetermined value and generating an output voltage error as a feedback signal for controlling the output voltage to a constant voltage. An amplification unit is provided, and the output of the first overcurrent protection unit and the output of the error amplification unit, whichever has the stronger output suppression request, is output as the detection result of the first overcurrent protection unit. You may.

(5) Further, in the switching power supply device according to one aspect of the present invention, the output of the second overcurrent protection unit is a binary signal, and the voltage value based on the voltage generated in the first secondary winding. The overvoltage detection unit is provided with an overvoltage detection unit that compares the second predetermined value with the second predetermined value to detect the overvoltage state and outputs the detected result as a binary signal, and the output of the second overcurrent protection unit and the overvoltage detection unit. When one of the outputs is detected, it may be output as the detection result of the second overcurrent protection unit.

(6) Further, in the switching power supply device according to one aspect of the present invention, the control unit stops or suppresses the output for the first period based on the detection result of the first overcurrent protection unit. The switching element may be controlled.

(7) Further, in the switching power supply device according to one aspect of the present invention, the control unit has a failure in the first overcurrent protection unit and the power supply system that supplies power to the first overcurrent protection unit. In this case, the switching element may be controlled so as to stop or suppress the output for a second period different from the first period based on the detection result of the second overcurrent protection unit.

(8) Further, in the switching power supply device according to one aspect of the present invention, the control unit sets the signal level of the output of the first overcurrent protection unit and the output of the error amplification unit, whichever has the stronger output suppression request. The output may be suppressed accordingly, and the switching element may be controlled so as to suppress the output current to a predetermined current value when an overcurrent state occurs.

(9) Further, in the switching power supply device according to one aspect of the present invention, the control unit compares the voltage value based on the voltage generated in the first secondary winding with the second predetermined value. An overvoltage detection unit that detects an overvoltage state and outputs the detected result as a binary signal. When one of the output of the second overvoltage protection unit and the output of the overvoltage detection unit is detected, the output is stopped. The switching element may be controlled so as to do so.

According to the present invention, it is possible to provide a switching power supply device that can comply with safety standards and can obtain a larger rated current than before.

It is a block diagram which shows the structural example of the switching power supply device which concerns on 1st Embodiment. It is a figure which shows the operation of the switching power supply apparatus which concerns on 1st Embodiment, and the waveform example of each part. It is a flowchart of the protection processing procedure example at the time of overcurrent occurrence performed by the switching power supply device which concerns on 1st Embodiment. It is a block diagram which shows the other configuration example of the switching power supply device which concerns on 1st Embodiment. It is a block diagram which shows the structural example of the switching power supply device which concerns on 2nd Embodiment. It is a figure which shows the operation of the switching power supply device which concerns on 2nd Embodiment, and the waveform example of each part. It is a flowchart of the protection processing procedure example at the time of overcurrent occurrence performed by the switching power supply device which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration example of the switching power supply device 1 according to the present embodiment. As shown in FIG. 1, the switching power supply device 1 includes a DC power supply 2, a power supply input unit 3, a converter unit 4, a secondary winding N22 (second secondary winding), a diode D22, a capacitor C22, and a second. 1 The overcurrent protection unit 5, the second overcurrent protection unit 6, the first transmission unit 53, the second transmission unit 63, and the control unit 7 are provided.

The converter unit 4 includes a transformer T1, a capacitor C1, a switching element Q1, a diode D21, a capacitor C21, and a resistor R1.
The transformer T1 includes a primary winding N11, a secondary winding N21 (first secondary winding), and a secondary winding N22.

The first overcurrent protection unit 5 includes a resistor R21, a Vref 51, and a comparator 52.
The second overcurrent protection unit 6 includes a resistor R22, Vref61, and a comparator 62.
The control unit 7 includes a first output stop circuit 71, a second output stop circuit 72, and a PWM control unit 73.

Next, the connection relationship of the switching power supply device 1 will be described.
In the DC power supply 2, the positive electrode is connected to the first input unit of the power input unit 3, and the negative electrode is connected to the second input unit of the power input unit 3.

In the power input unit 3, the first output unit is connected to the positive electrode of the capacitor C1 and one end of the primary winding N11 of the transformer T1, and the second output unit is grounded to GND (ground) on the primary side.

In the transformer T1, the other end of the primary winding N11, which is the start of winding, is connected to the drain of the switching element Q1.

The switching element Q1 is, for example, an N-channel field effect transistor, in which the source is connected to one end of the resistor R1 and the CS signal input unit of the PWM control unit 73, and the gate is connected to the output unit of the PWM control unit 73. The diode D1 is a parasitic diode and is included in the switching element Q1.

The other end of the resistor R1 is grounded to the GND on the primary side.
The negative electrode side of the capacitor C1 is grounded to the primary side GND.

One end of the secondary winding N21 of the transformer T1 at the start of winding is connected to the anode of the diode D21, and the other end is grounded to the secondary GND. Further, the other end of the secondary winding N21 of the transformer T1 is connected to one end of the resistor R21, the negative power supply V-terminal of the Vref 51, and the negative power supply V-terminal of the comparator 52.
The other end of the resistor R21 is connected to one end of the resistor R22, the positive input portion of the comparator 52, the V-terminal of the Vref 61, and the negative power supply V-terminal of the comparator 62.
The other end of the resistor R22 is connected to the GND output of the switching power supply 1 and the positive input portion of the comparator 62.

The cathode of the diode D21 is connected to the positive electrode of the capacitor C21, the output unit Vout of the switching power supply device 1, and the positive power supply V + of the comparator 62.
The negative electrode of the capacitor C21 is grounded to the COM on the secondary side.

One end of the secondary winding N22 of the transformer T1 is connected to the anode of the diode D22, and the other end, which is the start of winding, is grounded to the COM on the secondary side.
The cathode of the diode D22 is connected to the positive electrode of the capacitor C22, the positive power supply V + of the comparator 52, and the positive power supply V + of the Vref 51.
The negative electrode of the capacitor C22 is grounded to the COM on the secondary side.

In the comparator 52, the negative input unit is connected to the output unit of Vref 51, the positive input unit is connected to the other end (point A) of the resistor R21, and the output unit is connected to the input unit of the first transmission unit 53. ..
In the comparator 62, the negative input unit is connected to the output unit of Vref 61, the positive input unit is connected to the other end (point B) of the resistor R22, and the output unit is connected to the input unit of the second transmission unit 63. ..

In the first transmission unit 53, the output unit (point C) is connected to the input unit of the first output stop circuit 71.
In the second transmission unit 63, the output unit (point D) is connected to the input unit of the second output stop circuit 72.

The output unit of the first output stop circuit 71 is connected to the first input unit of the PWM control unit 73.
The output unit of the second output stop circuit 72 is connected to the second input unit of the PWM control unit 73.

Next, the outline of the operation of each component will be described.
The power input unit 3 outputs the power output by the DC power supply 2 to the transformer T1.

The converter unit 4 transforms the voltage output by the power input unit 3 into a voltage corresponding to the turns ratio between the primary side and the secondary side of the transformer T1. The converter unit 4 generates pulse-shaped electric power on the secondary side by controlling the pulse width between the on state and the off state of the switching element Q1 according to the control of the PWM control unit 73.
The converter unit 4 rectifies and smoothes the electric power generated on the secondary side by the diode D21 and the capacitor C21.
The electric power generated in the secondary winding N22 is rectified and smoothed by the diode D22 and the capacitor C22.

In the first overcurrent protection unit 5, the Vref 51 generates the first threshold value Vref1 by using the voltage generated in the secondary winding N22 as a power source. The comparator 52 of the first overcurrent protection unit 5 is driven by the voltage value generated in the secondary winding N22. The comparator 52 compares the first threshold value Vref1 generated by Vref 51 with the voltage value at point A, which is the other end of the resistor R21, and outputs the comparison result to the first transmission unit 53. The outputs of the comparator 52 are H (high) level and L (low) level. Therefore, the comparator 52 outputs the L level when the voltage value at point A is less than the first threshold value Vref1, and outputs the H level when the voltage value at point A is greater than or equal to the first threshold value Vref1. The first transmission unit 53 is an isolator between the secondary side and the primary side, and is, for example, a photocoupler. The first transmission unit 53 outputs the information (H level, L level) output by the comparator 52 to the first output stop circuit 71.

In the second overcurrent protection unit 6, the Vref 61 generates the second threshold value Vref2 by using the voltage generated in the secondary winding N21 as a power source. The comparator 62 of the second overcurrent protection unit 6 is driven by the voltage value generated in the secondary winding N21. The comparator 62 compares the second threshold value Vref2 generated by Vref61 with the voltage value at point B, which is the other end of the resistor R22, and outputs the comparison result to the second transmission unit 63. The outputs of the comparator 62 are H level and L level. Therefore, the comparator 62 outputs the L level when the voltage value at point B is less than the second threshold value Vref2, and outputs the H level when the voltage value at point B is greater than or equal to the second threshold value Vref2. The second transmission unit 63 is an isolator between the secondary side and the primary side, and is, for example, a photocoupler. The second transmission unit 63 outputs the information (H level, L level) output by the comparator 62 to the second output stop circuit 72.

The control unit 7 controls the drive state of the switching element Q1 of the converter unit 4 according to the outputs of the first overcurrent protection unit 5 and the second overcurrent protection unit 6. When the first overcurrent protection unit 5 outputs the H level, the first output stop circuit 71 determines that an overcurrent has occurred, and outputs an instruction to stop the output to the PWM control unit 73. When the second overcurrent protection unit 6 outputs the H level, the second output stop circuit 72 determines that an overcurrent has occurred, and outputs an instruction to stop the output to the PWM control unit 73. When the first output stop circuit 71 outputs an instruction to stop the output, the PWM control unit 73 controls the switching element Q1 so as to stop the output for the first predetermined time T1. When the second output stop circuit 72 outputs an instruction to stop the output, the PWM control unit 73 controls the switching element Q1 so as to stop the output for the second predetermined time T2. Further, the PWM control unit 73 controls the duty ratio of the switching element Q1 in the on state and the off state in response to a feedback signal (not shown) based on the output Vout. The control unit 7 detects the current value flowing through the switching element Q1 by the CS signal, compares the detected value with the predetermined value, and as a result of comparison, determines that an overcurrent has flowed when the detected value is equal to or greater than the predetermined value. To limit the upper limit of output. As a result, the control unit 7 limits the peak value of the drain current of the switching element Q1 and suppresses the secondary output current to I_olp_conv, which is the overcurrent protection operating point. Overcurrent protection by drain current detection is a circuit generally provided in a general feedback-controlled switching power supply.

As described above, in the switching power supply device 1, the first overcurrent protection unit 5 generates the first threshold value Vref1 by using the voltage generated in the secondary winding N22 different from the output Vout, and detects the overcurrent. The comparator 52 is driven. Then, the second overcurrent protection unit 6 uses the voltage generated in the same secondary winding N21 as the output Vout to generate the second threshold value Vref2 and drives the comparator 62 that detects the overcurrent. .. With this configuration, according to the present embodiment, two systems of overcurrent protection units (first overcurrent protection unit 5 and second overcurrent protection unit 6) are driven by different power sources, so that one system fails. Even in this case, the remaining overcurrent protection unit can be used to detect the occurrence of overcurrent and stop the output.

In this embodiment, the secondary winding N21 is the output of the device, and the load is connected to the secondary winding N21. It is conceivable that the output is short-circuited and an overcurrent that cannot maintain the output voltage Vout flows. In this case, the overcurrent protection of the first overcurrent protection unit 5 and the second overcurrent protection unit 6 does not function, and the overcurrent protection by drain current detection functions. The overcurrent protection by the drain current detection is to detect the overcurrent immediately by comparing with a predetermined value for each switching pulse in order to prevent the switching element Q1 from being damaged.

Here, the operation when the output is short-circuited and an overcurrent that cannot maintain the output voltage Vout flows will be described. The PWM control unit 73 performs an operation of widening the on-pulse width of the switching element Q1 in response to a feedback signal (not shown). The on-pulse width is widened, and the drain current of the switching element Q1 is increased. When the drain current increases and the CS signal exceeds a predetermined value, the PWM control unit 73 narrows the pulse width and limits the drain current peak value of the switching element Q1. As a result, the output current Io is limited to the overcurrent protection operating point I_olp_conv. After a relatively short predetermined time has elapsed from the occurrence of the overcurrent state, the PWM control unit 73 stops the hi-cup operation or the output. Here, the hi-cup operation is an operation in which the output is temporarily cut off and then automatically restored.
Therefore, when the output is short-circuited and an overcurrent that cannot maintain the output voltage Vout flows, the first overcurrent protection unit 5 and the second overcurrent protection unit 6 do not operate.

In FIG. 1, a constant voltage circuit may be provided between the cathode of the diode D22 and the Vref 51 and the comparator 52.

Next, the voltage value output by the Vref 51 of the first overcurrent protection unit 5 and the voltage value output by the Vref 61 of the second overcurrent protection unit 6 will be described. The current limit value required by the safety standard is I_limit.
Assuming that the threshold value of the detected current value in the first overcurrent protection unit 5 is I_olp1, the first threshold value Vref1 output by the Vref 51 has the relationship of the following equation (1).

Assuming that the threshold value of the detected current value in the second overcurrent protection unit 6 is I_olp2, the second threshold value Vref2 output by Vref61 has the relationship of the following equation (2).

It is assumed that the resistance values of the resistor R21 and the resistor R22 are the same. The resistance values of the resistors R21 and R22 may be different as long as the relationship with the threshold value is satisfied. Further, it is assumed that the second threshold value Vref2 is a voltage larger than the first threshold value Vref1.

Next, the operation of the switching power supply device 1 and an example of waveforms of each part will be described.
FIG. 2 is a diagram showing an operation of the switching power supply device 1 and a waveform example of each part according to the present embodiment. In FIG. 2, the horizontal axis represents time and the vertical axis represents signal level.

<1. Operation when neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 has failed>
First, an example in which an overcurrent occurs when neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 has failed will be described. Before time t1, it is assumed that the output current value is a constant current, I1 and the voltage value is V1.

At time t1, an overcurrent occurs and the output current value becomes equal to or greater than I_olp1, which is the detection current threshold value of the first overcurrent protection unit 5. As a result, the output current I ₀ flowing through the resistor R21 increases, and the voltage value at point A becomes higher than the first threshold value Vref 1. Therefore, the comparator 52 operates, and the signal at point C changes from the L level to the H level.
Since the current value generated by the overcurrent is I_olp2 or less, the voltage value is the second threshold value Vref2 or less. Therefore, the comparator 62 does not operate.
Here, the period T3 from the time t1 to the time t2 is the time from the occurrence of the overcurrent until the signal at the output C point of the first transmission unit 53 changes from the L level to the H level, and the output during this period is Since it is not protected, the output current is I_olp1 or more and I_olp_conv or less. For example, the time of the period T3 can be set longer by delaying the output of the detection signal in an integrator circuit or the like in order to allow a temporary overload. The upper limit of the set time of the period T3 is set so as to meet the requirements of the safety standard.

Since the current value I_olp_conv is a current value limited by detecting the drain current of the switching element Q1, there is a large variation. When I_olp_conv is larger than the threshold value I_olp1, the comparator 52 operates, so that the operation shown in FIG. 2 is obtained.
On the other hand, when the current value I_olp_conv is smaller than the threshold value I_olp1, the PWM control unit 73 limits the overcurrent to I_olp_conv in response to the CS signal on the primary side, so that the comparator 52 does not operate, but the output is limited to within I_limit. Therefore, it satisfies the safety standard. Therefore, the current value I_olp_conv may be equal to or greater than the output rated current value of the switching power supply device 1.

At time t2, the first output stop circuit 71 gives an instruction to the PWM control unit 73 to stop the output during the period of T1 in response to the H level signal output by the comparator 52 via the first transmission unit 53. Output. As a result, the PWM control unit 73 controls the switching element Q1 so as to stop the output during the period of T1. As a result, the output voltage Vout becomes 0 [V] when the output is stopped during the period of T1, and the output current also becomes 0 [A].

At time t3 after the period from time t2 to T1, the first output stop circuit 71 outputs an instruction to restart the output to the PWM control unit 73. As a result, the PWM control unit 73 controls the switching element Q1 so as to restart the output. As a result, as shown in FIG. 2, the output voltage Vout and the output current I ₀ are restored.

For example, in the IEC61010 standard 9.4 energy restricted circuit, the output current limit value is limited by an AC effective value or a DC value. Therefore, the period T1 is set so that the effective value of the output current is equal to or less than the limit current I_limit required by the safety standard even if an overcurrent occurs again when the converter unit 4 starts the output. ..
That is, by presetting the duty ratio of the pulse composed of the period T3 and the period T1, the output effective current becomes I_limit or less even when the overcurrent occurs again. Therefore, the output effective current can meet the requirements of the safety standard. The control unit 7 may be configured so that after the comparator 52 receives the H level signal output via the first transmission unit 53, the output stop state is maintained without restarting.

In the example shown in FIG. 2, the first output stop circuit 71 outputs the H level at time t2, but the second output stop circuit 72 also outputs the H level depending on the magnitude of the overcurrent. May be output. The PWM control unit 73 may control the output to be stopped when at least one of the first output stop circuit 71 and the second output stop circuit 72 outputs the H level.

<2. Operation when a failure occurs in a part of the path of the second overcurrent protection unit 6>
Next, an example in which an overcurrent occurs when a part of the second overcurrent protection unit 6, the power supply unit thereof, the second transmission unit 63, or the second output stop circuit 72 has a failure will be described. The power supply unit of the second overcurrent protection unit 6 is a secondary winding N21, a diode D21, and a capacitor C21.
In this case, the first overcurrent protection unit 5 operates in the same manner as the operation described in the case where neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 of FIG. 2 has failed. This operating state is the same as the operation when neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 has failed.

Therefore, even if a part of the second overcurrent protection unit 6, the power supply unit thereof, the second transmission unit 63, or the second output stop circuit has a failure, the operation of the first overcurrent protection unit 5 is affected. Not reachable. If a failure occurs in which the resistor R22 is opened, the resistor R21 and the resistor R22 are connected in series with the path to which the output current is supplied from the converter unit 4, so that the output current path is cut off and the resistor R21 is connected. The flowing current becomes 0 [A]. As a result, no current flows through the load connected to the switching power supply device 1, so that the overcurrent state is eliminated.
Therefore, according to the present embodiment, the limit value of the output current satisfies the requirement of the safety standard even if a failure occurs in a part of the second overcurrent protection unit 6 or the power supply unit thereof.

<3. Operation when a failure occurs in a part of the path of the first overcurrent protection unit 5>
Next, an example in which an overcurrent occurs when a part of the first overcurrent protection unit 5, the power supply unit thereof, the first transmission unit 53, or the first output stop circuit 71 has a failure will be described. The power supply unit of the first overcurrent protection unit 5 is a secondary winding N22, a diode D22, and a capacitor C22.

For example, when a failure occurs in a part of the first overcurrent protection unit 5 or its power supply unit, the comparator 52 operates even if the current value exceeds I_olp1, that is, exceeds the first threshold value Vref1, but the comparator 52 operates but is excessive. Current protection does not work.
At time t7, an overcurrent occurs. As a result, the output current I ₀ flowing through the resistor R22 increases, and the voltage value at point B becomes higher than the second threshold value Vref2. Therefore, the comparator 62 operates, and the signal at point C changes from the L level to the H level.

Here, the period from the time t7 to the time t8 is the time from the occurrence of the overcurrent until the signal at the output D point of the second transmission unit 63 changes from the L level to the H level, and during this period, the output is Since it is not protected, the output current is I_olp2 or more and I_olp_conv or less. For example, the period from time t7 to time t8 can be set longer by delaying the output of the detection signal in an integrator circuit or the like in order to allow a temporary overload, but the upper limit of the set time is Set to meet the requirements of safety standards.

Since the current value I_olp_conv is a current value limited by detecting the drain current of the switching element Q1, there is a large variation. When I_olp_conv is larger than the threshold value I_olp2, the comparator 62 operates, so that the operation shown when a failure occurs in a part of the path of the first overcurrent protection unit 5 in FIG.
On the other hand, when the current value I_olp_conv is smaller than the threshold value I_olp2, the PWM control unit 73 limits the overcurrent to I_olp_conv in response to the CS signal on the primary side, so that the comparator 62 does not operate, but the output is limited to within I_limit. Therefore, it satisfies the safety standard. Therefore, the current value I_olp_conv may be equal to or greater than the output rated current value of the switching power supply device 1.

At time t8, the second output stop circuit 72 gives an instruction to the PWM control unit 73 to stop the output during the period of T2 in response to the H level signal output by the comparator 62 via the second transmission unit 63. Output. As a result, the PWM control unit 73 controls the switching element Q1 so as to stop the output during the period of T2. As a result, the output voltage Vout becomes 0 [V] when the output is stopped during the period of T2, and the output current also becomes 0 [A].

At time t9 after the period from time t8 to T2 has elapsed, the second output stop circuit 72 outputs an instruction to restart the output to the PWM control unit 73. As a result, the PWM control unit 73 controls the switching element Q1 so as to restart the output. As a result, as shown in FIG. 2, the output voltage Vout and the output current I ₀ are restored.

Here, the period T2 is set so that the effective value of the output current is equal to or less than the limit current I_limit required by the safety standard even if an overcurrent occurs again when the converter unit 4 starts the output. ..
That is, by presetting the duty ratio of the pulse composed of the period t7 to t8 and the period T2, the effective output current is I_limit or less even when the overcurrent occurs again. Therefore, the output effective current can meet the requirements of the safety standard.

As described above, even if a part of the first overcurrent protection unit 5, the power supply unit thereof, the first transmission unit 53, or the first output stop circuit 71 has a failure, the operation of the second overcurrent protection unit 6 is performed. Does not affect. If a failure occurs in which the resistor R21 is opened, the resistor R21 and the resistor R22 are connected in series with the path to which the output current is supplied from the converter unit 4, so that the output current path is cut off and the resistor R22 is connected. The flowing current becomes 0 [A]. As a result, no current flows through the load connected to the switching power supply device 1, so that the overcurrent state is eliminated.
Therefore, according to the present embodiment, the limit value of the output current satisfies the requirement of the safety standard even if a failure occurs in a part of the first overcurrent protection unit 5 or the power supply unit thereof.

<4. Operation when the output is short-circuited and an overcurrent that cannot maintain the output voltage Vout flows (when the output is short-circuited, there is no circuit failure)>
In this case, as in time t10 or later, the PWM control unit 73 sets the peak value of the drain current of the switching element Q1 on the primary side when the CS signal is equal to or higher than a predetermined value, that is, an overcurrent is generated in the switching element Q1. By controlling to limit, the output current I ₀ is limited to the overcurrent protection operation point I_olp_conv. After a predetermined time has elapsed from the occurrence of the overcurrent state, the PWM control unit 73 controls to perform the hi-cup operation. Here, the hi-cup operation is an operation in which the output is temporarily cut off and then automatically restored. The I_olp_conv, the cycle of the hicup operation, the detail ratio of the output and stop pulses, and the like are set in advance so that the effective output current during the hicup operation is equal to or less than the limit current I_limit required by the safety standard. By setting in this way, the output execution current in the hi-cup operation can meet the requirements of the safety standard.
Further, during the hi-cup operation after the time t10, a point A waveform signal is generated at both ends of the resistor R21, and a B point waveform signal is generated at both ends of the resistor R22. Since the signal of the point A waveform is input to the comparator 52, the comparator 52 outputs the signal of the point C waveform via the first transmission unit 53. The width of the signal output by the comparator 52 after the time t10 is shorter than the period T3. Although the signal of the point B waveform is input to the comparator 62, the comparator 62 does not operate because the power supplied to the comparator 62 is lost.
In FIG. 2, the output current I ₀ exceeds I_limit, but the period exceeding I_limit is short, and it is equal to or less than the overcurrent protection operating point I_olp_conv, and the effective output current is required by the safety standard. Since it is below the limit current I_limit (for example, rated output current), it meets the requirements of safety standards. Alternatively, the output may be stopped.
The hi-cup operation continues until the output short-circuit state is released, and returns to the steady operation when the output short-circuit state is released.

As described above, the first overcurrent protection unit 5 and the second overcurrent protection unit 6, their power supply units, the first output transmission unit 53, the second output transmission unit 63, the first output stop circuit 71, and the second output stop circuit 71. Even if any component of the output stop circuit 72 fails or the output is short-circuited, the output current limit value satisfies the safety standard as described above. That is, the overcurrent protection operation according to the present embodiment can satisfy the safety standard after duplicating the detection circuit and the protection circuit.

Next, an example of the processing procedure performed by the switching power supply device 1 will be described.
FIG. 3 is a flowchart of an example of a protection processing procedure when an overcurrent occurs, which is performed by the switching power supply device 1 according to the present embodiment.

(Step S1) The PWM control unit 73 determines whether or not the CS signal level is equal to or higher than a predetermined value. When the PWM control unit 73 determines that the CS signal level is equal to or higher than a predetermined value (step S1; YES), the PWM control unit 73 proceeds to step S2. When the PWM control unit 73 determines that the CS signal level is not equal to or higher than a predetermined value (step S1; NO), the PWM control unit 73 proceeds to step S3.

(Step S2) The PWM control unit 73 controls the switching element Q1 so as to limit the _{output current value I 0 to I_olp_conv.} After the processing, the PWM control unit 73 returns the processing to step S1.

(Step S3) The PWM control unit 73 determines whether or not at least one of the first output stop circuit 71 and the second output stop circuit 72 has output an instruction to stop the output. When the PWM control unit 73 determines that at least one of the first output stop circuit 71 and the second output stop circuit 72 has not output an instruction to stop the output (step S3; NO), the PWM control unit 73 processes in step S1. Return. When the PWM control unit 73 determines that at least one of the first output stop circuit 71 and the second output stop circuit 72 has output an instruction to stop the output (step S3; YES), the PWM control unit 73 proceeds to the process in step S4. ..

(Step S4) The PWM control unit 73 determines which of the first output stop circuit 71 and the second output stop circuit 72 outputs an instruction to stop the output. When the PWM control unit 73 determines that the first output stop circuit 71 has output an instruction to stop the output (step S4; first), the PWM control unit 73 proceeds to the process in step S5. When the PWM control unit 73 determines that the second output stop circuit 72 has output an instruction to stop the output (step S4; second), the PWM control unit 73 proceeds to the process in step S6.

(Step S5) The PWM control unit 73 controls the switching element Q1 so as to stop the output during the period of T1, and then restarts the output. After the processing, the PWM control unit 73 returns the processing to step S1.

(Step S6) The PWM control unit 73 controls the switching element Q1 so as to stop the output during the period of T2, and then restarts the output. After the processing, the PWM control unit 73 returns the processing to step S1.

Thereby, according to the present embodiment, the rated output current of the switching power supply device 1 capable of conforming to the energy limited circuit in the IEC6101 standard, the finite power supply (LPS) in the UL standard, and the limited voltage / current circuit (Limited Voltage / Current) can be obtained. , It is possible to realize an overcurrent protection circuit that can approach these required values. Further, according to the present embodiment, it is possible to provide a switching power supply device 1 that satisfies the above safety standard and has a rated output current larger than that of the conventional one. The reason why the rated output current can be supplied larger than before is that in the conventional method, it is necessary to set the rated output low in consideration of the detection accuracy of the current flowing through the switching element and the variation of the overcurrent protection device. It was. On the other hand, according to the present embodiment, since the overcurrent can be detected with high accuracy by the configuration shown in FIG. 1, it is not necessary to increase the margin as in the conventional case, and the output can be performed as rated, which is larger than the conventional value. It can supply the rated output current.

The 9.4 energy-limited circuit in the IEC61010 standard, which is a safety standard, and the power supply circuit and power supply device that conform to the finite power supply and limited voltage / current circuit in the UL standard reduce the risk of ignition and the spread of flames to the outside. Is considered to be. Therefore, according to the present embodiment, the switching power supply 1 conforming to the standard relaxes the structural requirements as a fire protection enclosure required for the housing of the switching power supply 1, and as a result, the switching power supply 1 It can reduce costs and improve design flexibility. In addition, the switching power supply device 1 conforming to the standard is switched so that the safety standard requirements for the circuits and devices connected to the load side, for example, the assessment of fire risk becomes easy and the verification test does not need to be performed. The design time of the power supply device 1 can be shortened. Further, according to this embodiment, it is not necessary to carry out the requirement test according to the safety standard for the circuit and the device connected to the load side, and the load current is increased more than before while maintaining the convenience of design. While supplying it, it can contribute to the improvement of the added value of the entire device.

In the example shown in FIG. 1, an example in which power is supplied from the secondary winding N21 to the Vref 61 and the comparator 62 of the second overcurrent protection unit 6 is shown, but the present invention is not limited to this. As shown in FIG. 4, the switching power supply unit 1A may further include a secondary winding N23, a diode D23, and a capacitor C23. FIG. 4 is a block diagram showing another configuration example of the switching power supply device 1A in the present embodiment.

As shown in FIG. 4, the transformer T1A includes a primary winding N11, a secondary winding N21 (first secondary winding), and a secondary winding N22 (second secondary winding). , Secondary side winding N23 (third secondary side winding) is provided.

In the example shown in FIG. 4, one end of the secondary winding N23 of the transformer T1A is connected to the anode of the diode D23, and the other end at the beginning of winding is grounded to the COM on the secondary side.
The cathode of the diode D23 is connected to the positive electrode of the capacitor C23, the positive power supply V + of the comparator 62, and the positive power supply V + of the Vref 61.
The negative electrode of the capacitor C23 is grounded to the COM on the secondary side.

According to the configuration shown in FIG. 4, in addition to the configuration shown in FIG. 1, the Vref 61 of the second overcurrent protection unit 6 and the comparator 62 are secondary independently of the secondary winding N21 side and the secondary winding N22. Power is supplied from the winding N23. As a result, according to the modified example of the present embodiment, when the secondary winding N21 side is short-circuited, or when a failure occurs in the first overcurrent protection unit 5 and a part of the power supply unit, the primary side Even if there is no overcurrent protection circuit by detecting the drain current, the second overcurrent protection unit 6 can detect and protect the overvoltage state and the overcurrent state.

In FIG. 4, a constant voltage circuit may be provided between the cathode of the diode D22 and the Vref 51 and the comparator 52, and similarly, between the cathode of the diode D23 and the Vref 61 and the comparator 62. It may be provided with a constant voltage circuit.

As described above, even with the switching power supply device 1A having the configuration shown in FIG. 4, according to the switching power supply device 1A capable of obtaining the same effect as the switching power supply device 1 having the configuration shown in FIG. 1, the secondary Even if any of the winding N21, the diode D21, and the capacitor C21 fails, the Vref 61 and the comparator 62 of the second overcurrent protection unit 6 have an N23 different from the secondary windings N21 and N22. Since the power is supplied from the overcurrent, it is possible to more appropriately protect against the overcurrent when an overcurrent occurs.

[Second Embodiment]
FIG. 5 is a block diagram showing a configuration example of the switching power supply device 1B according to the present embodiment. As shown in FIG. 5, the switching power supply device 1B includes a DC power supply 2, a power supply input unit 3, a converter unit 4, a secondary winding N22, a diode D22, a capacitor C22, a first overcurrent protection unit 5B, and a first transmission. Section 53, second overcurrent protection section 6B, second transmission section 63, control section 7B, resistor R31, resistor R32, resistor R33, resistor R34, diode D81, OR circuit 64, overvoltage detection section 83, and error amplification section 84. To be equipped. The functional unit having the same function as that of the switching power supply device 1 will be described by using the same reference numerals.

Further, the first overcurrent protection unit 5B includes a resistor R21, a Vref 51, a comparator 52B, a diode D51, a resistor R51, a resistor R52, a resistor R53, and a capacitor C51.
The second overcurrent protection unit 6B includes a resistor R22, a Vref61, a comparator 62, a resistor R61, and a capacitor C61.
The control unit 7B includes a PWM control unit 73B, a comparator 75, a latch protection unit 76, and a buffer circuit 77.

Next, the connection relationship of the switching power supply device 1B, which is different from that of the switching power supply device 1, will be described.
The other end of the resistor R21 is connected to one end of the resistor R22, one end of the resistor R51, the V-terminal of the Vref 61, and the negative power supply V-terminal of the comparator 62.
The other end of the resistor R22 is connected to the GND output of the switching power supply 1 and one end of the resistor R61.

The other end of the resistor R51 is connected to one end of the capacitor C51 and the negative input portion of the comparator 52B.
The output unit of Vref 51 is connected to one end of the resistor R52.
In the comparator 52B, the negative input portion is connected to the other end of the resistor R51 and one end of the capacitor C51, the positive input portion is connected to the other end of the resistor R52 and one end of the resistor R53, and the output portion is connected to the other end of the capacitor C51. It is connected to the other end of the resistor R53 and the cathode of the diode D51. An integrator is formed by a resistor R51, a resistor R52, a resistor R53, a capacitor C51, and a comparator 52B. The comparator 52B does not have to include an integrator circuit.

One end of the resistor R33 is connected to the cathode of the diode D21, the positive electrode of the capacitor C21, and the power supply unit of the error amplification unit 84.
The output unit of the error amplification unit 84 is connected to the cathode of the diode D81.
The anode of the diode D51 is connected to the anode of the diode D81 and the input unit (point E) of the first transmission unit 53. The diode D51 and the diode D81 form an adder circuit.
In the first transmission unit 53, the output unit (FB) is connected to the second input unit of the PWM control unit 73B.

The other end of the resistor R61 is connected to one end of the capacitor C61 and the positive input portion of the comparator 62.
The other end of the capacitor C61 is connected to one end of the resistor R22, the V-terminal of Vref61, and the negative power supply V-terminal of the comparator 62.
In the comparator 62, the negative input unit is connected to the output unit of the Vref 61, the positive input unit is connected to the other end of the resistor R61, and the output unit is connected to one input unit of the OR circuit 64.

The overvoltage detection unit 83 has an input unit connected to the other end of the resistor R31 and one end of the resistor R32, and an output unit connected to the other input unit of the OR circuit 64.
In the OR circuit 64, the output unit (point F) is connected to the input unit of the second transmission unit 63.
In the second transmission unit 63, the output unit (OVP) is connected to the second input unit of the comparator 75.

In the comparator 75, the first input unit is connected to the comparison voltage source, and the output unit is connected to the input unit of the latch protection unit 76.
The output unit of the latch protection unit 76 is connected to the first input unit of the PWM control unit 73B.
In the PWM control unit 73B, the third input unit is connected to the source of the switching element Q1 of the converter unit 4 and one end (CS) of the resistor R1, and the output unit is connected to the input unit of the buffer circuit 77.
The output unit of the buffer circuit 77 is connected to the gate of the switching element Q1.

Next, the outline of the operation of each component will be described.
The comparator 52B outputs the result of comparing the voltages of the first threshold value Vref1 and the other end of the resistor R21 to the first transmission unit 53 via the diode D51. The comparator 52B outputs the comparison result as an analog value instead of the H and L levels. The comparator 52B delays the reaction time for overcurrent protection by means of an integrator.

As shown in FIG. 5, the comparator 52B is connected to the error amplification unit 84 via the diodes D51 and D81. Therefore, when the comparator 52B operates, the constant current I_olp1 continues to flow under the control of the PWM control unit 73B as described later with reference to FIG. 6, and the output voltage is the voltage V1 when no overcurrent occurs. It becomes a low voltage. Here, it is assumed that the Vref 51 includes, for example, two first threshold values Vref1 and a first'threshold value Vref1'with a value smaller than the first threshold value Vref1. The comparator 52B first outputs an H level in comparison with the first threshold value Vref1, and based on this, switches the threshold value from the first threshold value Vref1 to the first'threshold value Vref1'. As a result of switching the threshold value to the first'threshold value Vref1', the constant current is controlled to be a constant current having a current value smaller than I_olp2. When the plurality of threshold values are switched in this way, the protection state after the overcurrent is detected can be controlled to a safer state. The comparator 52B may have a hysteresis function and perform the above operation.

The error amplification unit 84 amplifies this error by dividing the output voltage between the resistor R33 and the resistor R34 and using the voltage generated in the resistor R34 as an error of the output voltage. Further, the error amplification unit 84 generates a feedback signal with appropriate phase compensation, and outputs the generated feedback signal to the first transmission unit 53 via the diode D81. The error amplification unit 84 is a circuit generally provided in a switching power supply for general feedback control, and outputs a feedback signal as an analog value instead of H and L levels.

The lower voltage value of the result of comparison by the comparator 52B and the output of the error amplification unit 84 is input to the first transmission unit 53 by the diode D51 and the diode D81. In other words, the first transmission unit 53 functions as a feedback signal path for controlling the output Vout at a constant voltage during normal operation, but functions as a path for transmitting an overcurrent detection signal when an overcurrent occurs.

The comparator 62 outputs the result of comparing the voltages of the second threshold value Vref2 and the other end of the resistor R22 to the OR circuit 64. The comparator 62 outputs the comparison result at the H and L levels.

The overvoltage detection unit 83 compares the voltage value generated in the resistor R32 with the predetermined voltage value when the output voltage is divided by the resistor R31 and the resistor R32. The overvoltage detection unit 83 detects that an overvoltage has occurred when the divided voltage is equal to or higher than a predetermined voltage value, and outputs an H level detection signal to the OR circuit 64. The overvoltage detection unit 83 detects that no overvoltage has occurred when the divided voltage is less than a predetermined voltage value, and outputs an L level detection signal to the OR circuit 64. The overvoltage detection unit 83 is a circuit generally provided in a switching power supply having output overvoltage protection.

The second transmission unit 63 outputs the H level when one of the output of the overvoltage detection unit 83 and the result of comparison by the comparator 62 is the H level by the OR circuit 64.

The comparator 75 compares a predetermined voltage value of the comparison voltage source with the voltage value of the OVP signal, and if the voltage value of the OVP signal is equal to or higher than the predetermined voltage value, outputs an H level signal to the latch protection unit 76. When the voltage value of the OVP signal is less than a predetermined voltage value, the comparator 75 outputs an L level signal to the latch protection unit 76.

When the comparator 75 outputs an H level, that is, when an overvoltage is detected, the latch protection unit 76 outputs a latch signal that stops the output for a predetermined period (also referred to as latch stop) to the PWM control unit 73B.

The PWM control unit 73B controls the switching element Q1 so as to limit the peak value of the drain current of the switching element Q1 according to the CS signal and suppress the output current on the secondary side to the overcurrent protection operating current I_olp_conv. The PWM control unit 73B controls the switching element Q1 so as to stop the output current on the secondary side in response to the latch signal output by the latch protection unit 76. Further, the PWM control unit 73B controls the switching element Q1 according to the level of the FB signal output by the first transmission unit 53, so that the output voltage Vout becomes constant according to the output of the error amplification unit at normal times. _{Control is performed, and the switching element Q1 is controlled so that the output current I 0} becomes a constant current limited to the threshold value I_olp 1 according to the output of the first overcurrent protection unit 5B when an overcurrent occurs.

The buffer circuit 77 outputs the signal output by the PWM control unit 73B to the gate of the switching element Q1.

As described above, in the switching power supply device 1B, the first transmission unit 53 also serves as the output transmission of the detection signal of the comparator 52B and the detection signal of the error amplification unit 84, and the second transmission unit 63 is the detection signal of the comparator 62. And the output transmission of the detection signal of the overvoltage detection unit 83. Further, in the switching power supply device 1B, power is supplied to the Vref 51 of the first overcurrent protection unit 5B and the comparator 52B from the secondary side winding N22 side different from the secondary side winding N21.

The voltage value output by the Vref 51 of the first overcurrent protection unit 5B and the voltage value output by the Vref 61 of the second overcurrent protection unit 6B are the same conditions as those of the equations (1) and (2) of the first embodiment. Is. Further, the current limit value required by the safety standard is set to I_limit.

In the example shown in FIG. 5, an example in which the overvoltage detection unit 83 and the error amplification unit 84 are provided has been described. However, the switching power supply device 1B may include the error amplification unit 84, and the overvoltage detection unit 83 may be provided. It does not have to be prepared. When the switching power supply device 1B does not include the overvoltage detection unit 83, the output of the comparator 62 may be directly connected to the input unit of the second transmission unit 63. Further, the comparator 62 may have an integrator circuit and a hysteresis function.
When the output of the detection signal is delayed by an integrator circuit or the like, it is preferable that the output timing of the comparator 62 is delayed with respect to the comparator 52B. The reason for this is that when the comparator 62 operates, it is necessary to turn off the input and release the latch after the overcurrent state of the load is resolved, and automatic recovery cannot be performed. Further, also in FIG. 5, the first threshold value Vref1 of Vref51 is smaller than the second threshold value Vref2 of Vref61, as in the first embodiment.

Further, the switching power supply device 1B may include a secondary winding N23, a diode D23, and a capacitor C23 as a power supply unit of the Vref 61 and the comparator 62, as in FIG.
When power is obtained from a system different from that of the secondary winding N21 side, Vref 51 and the comparator 52B are preferable. The reason for this is that, as will be described later with reference to FIG. 6, the output voltage Vout is controlled to be a constant voltage even if the error amplification unit 84 operates, so that the output voltage Vout does not decrease, but when the comparator 52B operates. , The voltage value of the output voltage Vout becomes low. Therefore, when power is supplied from Vout to the Vref 51 or the comparator 52B when an overcurrent is generated and the protect state is in effect, the operation of the Vref 51 or the comparator 52B is not guaranteed. The comparator 52B needs to continue to output the detection signal even after the detection. Therefore, in the present embodiment, power is supplied to the Vref 51 and the comparator 52B from the secondary winding N22 side different from the secondary winding N21 side. On the other hand, since the outputs of the Vref 61 and the comparator 62 are stopped after the detection, it is sufficient that the power is supplied at the time of the detection. Therefore, the electric power supplied to the Vref 61 and the comparator 62 may be from the secondary winding N21 side.

Next, the operation of the switching power supply device 1B and an example of waveforms of each part will be described.
FIG. 6 is a diagram showing an operation of the switching power supply device 1B and a waveform example of each part according to the present embodiment. In FIG. 6, the horizontal axis represents time and the vertical axis represents signal level. Further, the waveform g101 represents the output waveform of the comparator 52B, the waveform g102 represents the output waveform of the error amplification unit 84, and the waveform g103 is the waveform of point E input to the first transmission unit 53 (hereinafter, E). (Also called a point waveform). As shown in the waveform g101, the output signal of the comparator 52B is a signal indicating an output current suppression request, and when the output current suppression request is high, the signal level is low. Further, as shown in the waveform g102, the output signal of the error amplification unit 84 is a signal indicating an output voltage suppression request, and when the output voltage suppression request is high, the signal level becomes low.

<1. Operation when neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 has failed>
First, an example in which an overcurrent occurs when neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 has failed will be described. Before time t101, it is assumed that the output current value is a constant current, I1 and the voltage value is V1.

During the period from time t101 to time t102, the output current I ₀ rises from I 1 and an overcurrent occurs.
At time t102, the output current value becomes equal to or higher than I_olp1, which is the detection current threshold value of the first overcurrent protection unit 5. As a result, the output current I ₀ flowing through the resistor R21 increases, and the comparator 52B outputs an analog signal so that the voltage value of the negative input portion of the comparator 52B becomes equal to the first threshold value Vref1. As a result, the output current maintains I_olp1. Since the first threshold value Vref1 is set lower than the second threshold value Vref2, the comparator 62 does not operate. As a result, the output of the comparator 52B is reduced as in the waveform g101. At this time, since the output voltage decreases due to the overcurrent, the output of the error amplification unit 84 increases as in the waveform g102. As a result, the E-point waveform becomes a waveform obtained by adding the waveform g101 and the waveform g102 as shown in the waveform g103. The FB signal waveform, which is the output signal of the first transmission unit 53, is equivalent to the E point waveform. As a result of the PWM control unit 73B controlling the switching element Q1 in response to the FB signal output by the first transmission unit 53, the output current I ₀ becomes a constant current limited to the threshold value I_olp 1.

During the period from time t102 to time t103, the output current I ₀ is limited (suppressed) to the threshold value I_olp1 by the control of the PWM control unit 73B, and as a result, the output voltage Vout drops to a voltage value lower than V1.
In this way, the output voltage Vout drops during the operation of the first overcurrent protection unit 5. However, since the secondary winding N22 is configured so that the rectifying diode D22 conducts when the switching element Q1 is turned on, if the switching element Q1 is in the switching operation, the first error occurs. Power continues to be supplied to the current protection unit 5B. As a result, the overcurrent protection operation is maintained.

At time t103, when the overcurrent state is resolved and the output current I ₀ falls below the threshold value I_olp 1, the level of the analog output signal of the comparator 52B becomes high. The PWM control unit 73B controls the switching element Q1 so as to cancel the constant current control. As a result, the voltage value of the output voltage Vout rises, and the error amplification unit 84 returns to the constant voltage control state. In the example shown in FIG. 6, the waveform when the integrator circuit of the comparator 52B is not provided is shown. When the comparator 52B includes an integrator circuit, the operation of the first overcurrent protection unit 5B operates more slowly according to the integration time constant than when the comparator 52B does not have an integrator circuit. Further, when the comparator 52B has hysteresis, when the comparator 52B operates, the detection threshold value is lowered accordingly, so that the output suppression of the converter unit 4 is further strengthened. Therefore, the output voltage Vout is the comparator. It drops sharply as compared to the case where 52B does not have hysteresis.

According to the present embodiment, in the series of operations described above, the threshold value I_olp1 is set so as not to exceed the required value I_limit of the safety standard, so that the output current I ₀ becomes I_limit or less.

<2. Operation when a failure occurs in a part of the path of the second overcurrent protection unit 6B>
Next, an example in which an overcurrent occurs when a part of the second overcurrent protection unit 6B or its power supply unit, or the second transmission unit 63, the comparator 75, and the latch protection unit 76 have a failure. explain.
In this case, the first overcurrent protection unit 5B operates in the same manner as the operation described with reference to FIG. This operating state is the same as the operation when neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 has failed.

<3. Operation when overvoltage occurs (when overvoltage occurs, no circuit failure)>
Next, the operation when an overvoltage is generated will be described.
At time t104, the overvoltage detection unit 83 operates when the output voltage Vout exceeds a predetermined voltage value and an overvoltage state occurs. Then, at times t104 to t105, the overvoltage detection unit 83 switches the output signal from the L level to the H level. In this case, the output of the comparator 62 is the L level. As a result, the PWM control unit 73B controls the switching element Q1 so as to stop the output in response to the OVP signal output by the second transmission unit 63. As a result, the output voltage Vout is latched and stopped. In this case, the E point waveform and the FB signal are 0V signals.
The output stop due to the latch stop continues until the power supply of the switching power supply device 1B is turned off.

<4. Operation when a failure occurs in a part of the path of the first overcurrent protection unit 5B>
Next, an example in which an overcurrent occurs when a failure occurs in a part of the first overcurrent protection unit 5B, the power supply unit thereof, or the first transmission unit 53 will be described. In this case, since the power supply units of the first overcurrent protection unit 5B and the second overcurrent protection unit 6B are separate, even if a failure occurs in the first overcurrent protection unit 5B and a part of the power supply. , Does not affect the operation of the second overcurrent protection unit 6B. As shown in the waveform g102, the output of the malfunction amplification unit 84 is in a high impedance state because the power supply is lost. Further, in the E-point waveform, the waveform g101 and the waveform g102 are added as shown in the waveform g103 in the same manner as in the operation when neither the first overcurrent protection unit 5 nor the second overcurrent protection unit 6 has failed. It becomes a waveform. The FB signal waveform, which is the output signal of the first transmission unit 53, is equivalent to the E point waveform. Further, as shown in the F point waveform, the second overcurrent protection unit 6 does not operate. Therefore, the OVP signal is also an L level signal.
The output stop due to the latch stop continues until the power supply of the switching power supply device 1B is turned off.

At time t106, the _{comparator 62 operates when the output current I 0} flowing through the resistor R22 increases and the threshold value I_olp2 is exceeded and an overcurrent state occurs. Then, at times t106 to t107, the comparator 62 switches the output signal from the L level to the H level. In this case, the output of the overvoltage detection unit 83 is L level. As a result, the PWM control unit 73B controls the switching element Q1 so as to stop the output in response to the OVP signal output by the second transmission unit 63. As a result, the output voltage Vout is latched and stopped. In this case, since the threshold value I_olp2 is also set to the required value I_limit or less of the safety standard, the output current Io is also set to I_limit or less. In FIG. 6, the output current I ₀ exceeds I_limit, but the period exceeding I_limit is short, and the effective output current is equal to or less than the limit current I_limit required by the safety standard. Therefore, it is safe. Meets the requirements of the standard.

<5. Operation when the output is short-circuited and an overcurrent that cannot maintain the output voltage Vout flows (when the output is short-circuited, there is no circuit failure)>
Next, the operation when the output is short-circuited will be described.
In this case, as in time t108 or later, the PWM control unit 73B sets the peak value of the drain current of the switching element Q1 on the primary side when the CS signal is equal to or higher than a predetermined value, that is, an overcurrent is generated in the switching element Q1. By controlling to limit, the output current I ₀ is limited to the overcurrent protection operation point I_olp_conv. After a predetermined time has elapsed from the occurrence of the overcurrent state, the PWM control unit 73B controls to perform the hi-cup operation. Here, the hi-cup operation is an operation in which the output is temporarily cut off and then automatically restored. The I_olp_conv, the cycle of the hicup operation, the detail ratio of the output and stop pulses, and the like are set in advance so that the effective output current during the hicup operation is equal to or less than the limit current I_limit required by the safety standard. By setting in this way, the output execution current in the hi-cup operation can meet the requirements of the safety standard. In FIG. 6, the output current I ₀ exceeds I_limit, but the period exceeding I_limit is short, and it is equal to or less than the overcurrent protection operating point I_olp_conv, and the effective output current is required by the safety standard. Since it is below the limit current I_limit (for example, rated output current), it meets the requirements of safety standards.
The hi-cup operation continues until the output short-circuit state is released, and returns to the steady operation when the output short-circuit state is released.

Next, an example of the processing procedure performed by the switching power supply device 1B will be described.
FIG. 7 is a flowchart of an example of a protection processing procedure when an overcurrent occurs, which is performed by the switching power supply device 1B according to the present embodiment.

(Step S101) The PWM control unit 73B determines whether or not the CS signal is equal to or higher than a predetermined value. When the PWM control unit 73B determines that the CS signal is equal to or higher than a predetermined value (step S102; YES), the PWM control unit 73B proceeds to the process of step S107. When the PWM control unit 73B determines that the CS signal is less than a predetermined value (step S102; NO), the PWM control unit 73B proceeds to the process of step S102.

(Step S102) The PWM control unit 73B determines whether or not the latch signal is at the H level. When the PWM control unit 73B determines that the latch signal is at the H level (step S102; YES), the PWM control unit 73B proceeds to the process in step S103. When the PWM control unit 73B determines that the latch signal is at the L level (step S102; NO), the PWM control unit 73B proceeds to step S105.

(Step S103) The PWM control unit 73B controls the switching element Q1 so as to stop the output. After the process, the PWM control unit 73B proceeds to the process of step S104.

(Step S104) The PWM control unit 73B controls so that the latch is stopped. The latch stop state is a state in which the output voltage Vout is 0V and the output current I ₀ is 0A.

(Step S105) The PWM control unit 73B determines whether or not the level of the FB signal is lowered. When the PWM control unit 73B determines that the level of the FB signal has decreased (step S105; YES), the PWM control unit 73B proceeds to the process of step S106. When the PWM control unit 73B determines that the level of the FB signal has not decreased (step S105; NO), the PWM control unit 73B returns to the process of step S101.

(Step S106) The PWM control unit 73B controls the _{switching element Q1 so that the output current I 0} becomes a constant current limited to the threshold value I_olp1. After the process, the PWM control unit 73B returns to the process of step S101.

_{(Step S107) The PWM control unit 73B limits the output current I 0} to the overcurrent protection operating point I_olp_conv by controlling so as to limit the peak value of the drain current of the switching element Q1 on the primary side. Subsequently, after a predetermined time has elapsed from the occurrence of the overvoltage state, the PWM control unit 73B controls to perform the hi-cup operation.

The CS signal monitors the current of the switching element Q1 for each switching pulse. Then, as soon as the CS signal exceeds a predetermined value, the control unit 7B limits the switching element switching element Q1 to I_olp_conv regardless of the state of the FB signal. Since the overcurrent protection by the CS signal is performed for each switching pulse, it is the overcurrent protection that functions with the highest priority. The FB signal is used for output constant voltage control in steady operation, and the FB signal level decreases as the output voltage increases. Therefore, in the steady state, the control unit 7B suppresses the pulse width by comparing the FB signal with the CS signal. In the present embodiment, when the secondary side becomes an overcurrent state by using this principle, the control unit 7B performs overcurrent protection by lowering the FB signal level and suppressing the pulse width.

Further, in the present embodiment, since the operation by the CS signal is prioritized, when the overcurrent is detected in the CS signal and the operation shifts to the hi-cup operation, the protection circuit on the secondary side does not operate. Therefore, the latch signal does not reach the H level during the output suppression operation by the CS signal. That is, on the secondary side, since the detection time is long, the output is stopped by the hi-cup before the detection.

As described above, even if any of the parts of the first overcurrent protection unit 5B, the second overcurrent protection unit 6B, and their power supply units fails, according to the present embodiment, the overcurrent state or Even if an overvoltage state occurs, the output current limit value satisfies the requirements of the safety standard, so that the requirements of the safety standard can be satisfied.

As described above, in the present embodiment, the detection signal of the overcurrent protection by the comparator 52B and the output signal of the error amplification unit 84 are added by the diodes D51 and D81, so that one first transmission unit 53 can be used in common. did. Further, in the present embodiment, the detection signal for overcurrent protection by the comparator 62 and the output signal of the overvoltage detection unit 83 are shared by one second transmission unit 63 via the OR circuit 64. Thereby, according to the present embodiment, it is possible to reduce the number of parts of the switching power supply device 1B, and further reduce the cost and the mounting area.

In the above-described embodiment, an example of protecting the switching power supply device 1 (1A, 1B) according to the following policies (I.) to (V.) has been described. Not as far as I explained. Any device that meets the intended use and safety standards of the switching power supply 1 (1A, 1B) may be used.
(I.) When an overcurrent flows due to an output short circuit and the output voltage drops, the overcurrent protection on the primary side operates with the highest priority.
(II.) When an overcurrent is generated but the output voltage is maintained, one of the two overcurrent protection circuits on the secondary side operates.
(III.) The power supply to be supplied to the two overcurrent protection circuits on the secondary side needs to be generated from different windings in case of one failure.
(IV.) When the power of the overcurrent protection circuit on the secondary side is supplied from the output winding, there is a problem that the overcurrent protection circuit cannot operate if the output is short-circuited. , It is necessary to provide an overcurrent protection function on the primary side.
(V.) If the output windings are not used for the power supply to the two overcurrent protection circuits on the secondary side and they are generated from different windings, the overcurrent protection function on the primary side is not necessary. ..

A program for realizing all or part of the functions of the control unit 7 (7B) in the present invention is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into the computer system. , All or part of the processing performed by the control unit 7 (7B) may be performed by executing. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. Further, the "computer system" shall also include a WWW system provided with a homepage providing environment (or display environment). Further, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM, or a storage device such as a hard disk built in a computer system. Furthermore, a "computer-readable recording medium" is a volatile memory (RAM) inside a computer system that serves as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, it shall include those that hold the program for a certain period of time.

Further, the program may be transmitted from a computer system in which this program is stored in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting a program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. Further, the above program may be for realizing a part of the above-mentioned functions. Further, it may be a so-called difference file (difference program) that can realize the above-mentioned function in combination with a program already recorded in the computer system.

Although the embodiments for carrying out the present invention have been described above using the embodiments, the present invention is not limited to these embodiments, and various modifications and substitutions are made without departing from the gist of the present invention. Can be added.

1,1A, 1B ... Switching power supply device, 2 ... DC power supply, 3 ... Power supply input unit, 4 ... Converter unit, 5,5B ... 1st overcurrent protection unit, 6,6B ... 2nd overcurrent protection unit, 7, 7B ... control unit, 51 ... Vref, 52, 52B ... comparator, 53 ... first transmission unit, 61 ... Vref, 62 ... comparator, 63 ... second transmission unit, 71 ... first output stop circuit, 72 ... first 2 output stop circuit, 73, 73B ... PWM control unit, 83 ... overvoltage detection unit, 84 ... error amplification unit, T1, T1A ... transformer, C1. C21, C22, C51, C61 ... Capacitor, Q1 ... Switching element, D1, D21, D22 ... Diode, R1, R31, R32, R33, R34, R51, R52, R53, R61 ... Resistance, N11 ... Primary winding, N21, N22 ... Secondary winding

Claims (9)

A primary winding to which a switching element is connected, a first secondary winding connected to an output unit, and a transformer having a second secondary winding.
A first overcurrent protection unit that detects the overcurrent flowing through the first secondary winding by comparing it with the first threshold value.
A second overcurrent protection unit that detects the overcurrent flowing through the first secondary winding by comparing it with a second threshold value different from the first threshold value.
A control unit that controls the switching element based on at least one of the detection result of the first overcurrent protection unit and the detection result of the second overcurrent protection unit.
With
The first overcurrent protection unit is supplied with electric power from the second secondary winding side.
Switching power supply. The second overcurrent protection unit is supplied with electric power from the first secondary winding side.
The switching power supply device according to claim 1. The transformer comprises a third secondary winding.
The second overcurrent protection unit is supplied with electric power from the third secondary winding side.
The switching power supply device according to claim 1. The first threshold value is equal to or lower than the second threshold value.
The output of the first overcurrent protection unit is a signal indicating an output current suppression request.
Error amplification that compares the voltage value based on the voltage generated in the first secondary winding with the first predetermined value and generates an error of the output voltage as a feedback signal for controlling the output voltage to a constant voltage. Department, equipped with
Of the output of the first overcurrent protection unit and the output of the error amplification unit, the output with the stronger output suppression request is output as the detection result of the first overcurrent protection unit.
The switching power supply device according to any one of claims 1 to 3. The output of the second overcurrent protection unit is a binary signal,
It is provided with an overvoltage detection unit that compares a voltage value based on the voltage generated in the first secondary winding with a second predetermined value, detects an overvoltage state, and outputs the detected result as a binary signal. ,
When one of the output of the second overcurrent protection unit and the output of the overvoltage detection unit is detected, the output is output as the detection result of the second overcurrent protection unit.
The switching power supply device according to claim 4. The control unit controls the switching element so as to stop or suppress the output during the first period based on the detection result of the first overcurrent protection unit.
The switching power supply device according to any one of claims 1 to 3. The control unit is based on the detection result of the second overcurrent protection unit when a failure occurs in the first overcurrent protection unit and the power supply system that supplies power to the first overcurrent protection unit. The switching element is controlled so as to stop or suppress the output for a second period different from the first period.
The switching power supply device according to any one of claims 1 to 3. The control unit suppresses the output according to the signal level of the output of the first overcurrent protection unit and the output of the error amplification unit, whichever has the stronger output suppression request, and when an overcurrent state occurs. , The switching element is controlled so as to suppress the output current to a predetermined current value.
The switching power supply device according to claim 4 or 5. The control unit compares a voltage value based on the voltage generated in the first secondary winding with a second predetermined value, detects an overvoltage state, and outputs the detected result as a binary signal. The detection unit controls the switching element so as to stop the output when one of the output of the second overcurrent protection unit and the output of the overvoltage detection unit is detected.
The switching power supply device according to claim 8.

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