JP3501147B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device, and more particularly to a switching power supply device that can supply a large output capacitance while using a plurality of transformers and can protect the device safely. Regarding power supply.

[0002]

2. Description of the Related Art Normally, for a switching power supply,
In order to increase the output capacity in response to a request, the capacity of the transformer has been increased or a plurality of transformers have been connected. However, when increasing the capacity of the transformer, the bobbin used for the transformer is used each time.
There was a problem that new cores and molds were needed, which resulted in higher costs and time required for procurement. Therefore, in the conventional switching power supply device, as shown in FIG. 5, a plurality of existing transformers are connected to increase the total capacitance and one switching element Q1 is used for driving. .

In the conventional switching power supply device 100,
Primary winding P11 of each of the transformers T11 and T12,
P12 are commonly connected in parallel, and the primary windings P11, P1
2 connects the drain of the switching element Q1 in series,
Secondary windings S11, T11 of the transformers T11, T12,
Both ends of S12 are commonly connected, and one ends of the secondary windings S11 and S12 are connected to the anode of the diode D1.
The other ends of 11, S12 are commonly connected to the negative side of the capacitor C1, the cathode of the diode D1 is connected to the positive side of the capacitor C1, and the anode of the diode D3 is connected to the tertiary winding B11 of the transformer T11. It is configured.

When a DC voltage is applied from the DC power supply 1 to the conventional switching power supply, first, a current starts to flow from the DC power supply 1 to the capacitor C3 via the starting resistor R1 and the voltage of the capacitor C3 rises. Then, the control unit 3 is activated, and PW that alternately repeats high level and low level
The M signal is output from the control unit 3 to the gate of the switching element Q1.

As a result, the switching element Q1 is on / off controlled and energy is sequentially induced from the primary windings P11, P12 provided in the transformers T11, T12 to the secondary windings S11, S12, and the secondary winding S11. , S12 induced energy is diode D1 and capacitor C1
The output voltage Vout is supplied to the load after being rectified and smoothed by.

Further, the output voltage Vout generated across the capacitor C1 is detected by the error amplifier 5, and the error signal is used as a photodiode PD1 constituting a photocoupler.
By feeding back from the phototransistor PT1 to the control unit 3, the control unit 3 controls the ON period of the switching element Q1 so that the output voltage Vout becomes constant.

According to such a conventional switching power supply device, there is an advantage that it is possible to supply a large output capacity while using a plurality of transformers, which is small in size.

[0008]

However, in the conventional switching power supply device, since the primary winding and the secondary winding are simply connected in parallel, the core characteristics of the transformers T11 and T12 are There is a problem of heat generation in the transformer due to current imbalance such that the current concentrates in one of the transformers due to the difference or the variation in the winding inductance and the leakage inductance. For example, even when two transformers are used, There is a problem that it is difficult to increase the output current by two.

Further, in the configuration in which the power source of the control unit 3 is obtained from the tertiary winding B11 magnetically coupled to the transformer T11, the transformer T12 which does not obtain the power source of the control unit 3 is used.
Even if the primary winding P12 or the secondary winding S12 of FIG. 2 goes into an open state for some reason, the control unit 3 continues to operate and supplies the output current required by the load, so that the transformer T11 generates excessive heat. It is thought that it will generate a great deal of stress and cause a dangerous state such as smoking or ignition.

The present invention has been made in view of the above, and an object thereof is to switch using a plurality of transformers.
If the power supply is configured as a
Can supply a large output capacity, and
Switching power supply for short circuit open abnormal test
An object of the present invention is to provide a switching power supply device capable of safely protecting a device.

[0011]

The invention according to claim 1 is
In order to solve the above problems, the DC input from the DC power supply
Switching power that converts voltage to another DC voltage and outputs
In the power supply unit, multiple sources connected in series with the DC power supply
For the primary winding of the lance and the primary winding of the transformers
Switching elements connected in series and a die for each
A plurality of transistors that are commonly connected in parallel via an ode.
Induced in the secondary winding of the transformer and the secondary windings of the transformers
A first rectifying / smoothing circuit for rectifying and smoothing the generated voltage;
Error between the voltage from the rectifying and smoothing circuit of No. 1 and the first reference voltage
Connect in series with the error amplifier that outputs the voltage as a feedback signal.
The tertiary windings of the plurality of transformers connected to each other,
Rectifying and smoothing the voltage induced in the tertiary winding of the transformer
The rectifying and smoothing circuit of No. 2 and the power from the second rectifying and smoothing circuit.
First stop when pressure becomes lower than lower limit reference voltage
A low voltage detection circuit for outputting a signal, and the second rectifying and smoothing circuit
If the voltage from the circuit exceeds the upper reference voltage
An overvoltage detection circuit that outputs a second stop signal when
Using the voltage from the rectifying and smoothing circuit of No. 2 as the operating power supply
The switching element is turned on according to the feedback signal from the amplifier.
Output voltage from the low voltage detection circuit
Output from the first stop signal or the overvoltage detection circuit
Of the switching element in response to the applied second stop signal.
The gist of the present invention is to include a control unit that stops the operation.

According to a second aspect of the present invention, in order to solve the above-mentioned problems, the control unit includes a primary winding of the transformer or
When a short circuit test is performed on the secondary winding or the tertiary winding
Is the first stop signal output from the low voltage detection circuit.
It is necessary to stop the operation of the switching element accordingly.
To the effect.

According to a third aspect of the present invention, in order to solve the above-mentioned problems, the control unit is connected to a primary winding of the transformer.
If the open test is performed by
The switching element according to the first stop signal output from
The main point is to stop the child's motion.

According to a fourth aspect of the present invention, in order to solve the above-mentioned problems, the control unit couples to a secondary winding of the transformer.
If the open test is performed by
The switching element according to the second stop signal output from
The main point is to stop the child's motion.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problems, the control unit is connected to a tertiary winding of the transformer.
If the open test is performed by
The switching element according to the first stop signal output from
The main point is to stop the child's motion.

[0016]

[0017]

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a switching power supply device according to an embodiment of the present invention.
The switching power supply device shown in FIG. 1 has the same or corresponding parts as those of the conventional switching power supply device shown in FIG.

The primary winding P1 of the transformer T1 is connected to the DC power source 1, and the primary winding P2 of the transformer T2 is further connected.
Is connected in series to the drain of the switching element Q1,
The source of the switching element Q1 is connected to the DC power supply 1. Secondary windings S1, S2 of transformers T1, T2
The anodes of the diodes D1 and D2 are connected to one of the terminals, and the cathodes of the diodes D1 and D2 are commonly connected to the positive electrode side of the capacitor C1. The other terminals of the secondary windings S1 and S2 of the transformers T1 and T2 are commonly connected to the negative side of the capacitor C1. Then, the diodes D1 and D2 and the capacitor C
By 1, the voltage induced in the secondary windings S1 and S2 is rectified and smoothed and output to the load as the output voltage Vout. The diodes D1 and D2 and the capacitor C1 form a first rectifying and smoothing circuit 7 that rectifies and smoothes the voltages induced in the secondary windings S1 and S2 of the transformers T1 and T2.

An error amplifier 5 which detects an error voltage between the voltage of the capacitor C1 and the reference voltage Vref and outputs a feedback signal from a photodiode PD1 and a phototransistor PT1 forming a photocoupler to the control section 3 is detected.
Is provided. In the above-mentioned transformers T1 and T2,
As shown in FIG. 1, the primary windings P1 and P2 and the tertiary windings B1 and B2 magnetically coupled to each other are connected in series and connected to the anode of the diode D3. Diode D3
A startup resistor R1, a capacitor C3, and a control unit 3 are connected to the cathode of, and the voltage induced in the tertiary windings B1 and B2 of the transformers T1 and T2 is rectified and smoothed by the diode D3 and the capacitor C3 to control the voltage. It outputs to the OVP (overvoltage detection circuit) 3a and UVLO (low voltage detection circuit) 3b provided in the section 3. The diode D3 and the capacitor C3 are connected to the tertiary winding B of the transformers T1 and T2.
1st and 2nd rectifying and smoothing the voltage induced in B2
A rectifying / smoothing circuit 9 is configured.

The OVP 3a has a Zener diode (not shown) that generates an upper limit reference voltage Voref that allows the control unit 3 to operate, and includes the tertiary windings B1 and B of the transformers T1 and T2.
When the voltage induced in 2 becomes larger than the upper limit reference voltage Voref of the Zener diode, the second stop signal is output to the inside of the control unit 3 because the overvoltage is input. UVLO
3b has a Zener diode (not shown) that generates a lower limit reference voltage Vuref with which the control unit 3 can operate, and the voltage induced in the tertiary windings B1 and B2 of the transformers T1 and T2 is the lower limit reference of the Zener diode. When the voltage becomes lower than the voltage Vuref, the low voltage is input, so that the first stop signal is output to the inside of the control unit 3.

The control section 3 controls the ON period of the switching element Q1 in accordance with the feedback signals from the photodiode PD1 and the phototransistor PT1 which constitute the photocoupler. In addition, the control unit 3 sets P in response to the second stop signal from the OVP 3a or the first stop signal from the UVLO 3b.
The oscillation operation of the WM signal is stopped and a low level signal is output to the gate of the switching element Q1 to stop the switching operation. In the present embodiment, the transformers T1 and T2 are used for simplification of the description, but three or more transformers may be used.

Next, the normal operation of the switching power supply according to the embodiment of the present invention will be described with reference to FIG. First, when a DC voltage is applied from the DC power supply 1 as t0 to t1 shown in FIG. 2, a current starts to flow from the DC power supply 1 to the capacitor C3 through the starting resistor R1 and the voltage Vc of the capacitor C3 gradually increases. Rise to.

Then, as t1 to t2 shown in FIG.
The voltage Vc of the capacitor C3 is lower than the lower limit reference voltage Vuref, and the semiconductor element forming the control unit 3 reaches a operable voltage,

## EQU1 ## When Vuref> Vc (1), the UVLO 3b outputs the first stop signal at a high level (a voltage substantially equal to the voltage Vc) to the inside of the control unit 3.
As a result, the control unit 3 stops the oscillation operation of the PWM signal according to the first stop signal and outputs a low level signal to the gate of the switching element Q1, so that the switching operation is continuously stopped.

Next, as t2 to t3 shown in FIG.
The voltage Vc of the capacitor C3 reaches a range higher than the lower limit reference voltage Vuref and lower than the upper limit reference voltage Voref,

## EQU00002 ## When Voref>Vc> Vuref (2), the high level first stop signal output from the UVLO 3b becomes low level, the control unit 3 is normally started, and the PWM signal is output from the control unit 3. It is periodically output to the gate of the switching element Q1. As a result, the switching element Q1 is on / off controlled and the transformers T1, T
2 from the primary windings P1 and P2 to the secondary windings S1
Energy is induced in S2, and the energy induced in the secondary windings S1 and S2 is rectified and smoothed by the diodes D1 and D2 and the capacitor C1, respectively, and the output voltage V
out is supplied.

The above lower limit reference voltage Vuref is higher than the upper limit reference voltage Voref.

[Formula 3] Vuref> Voref / 2 (3), and by setting the voltage higher than 1/2 of the upper limit reference voltage Voref, it is determined whether or not one of the transformers T1 and T2 cannot be used in the UVLO3b. Can be determined by.

As a result, the switching element Q1 is on / off controlled and energy is induced from the primary windings P1 and P2 provided in the transformers T1 and T2 to the secondary windings S1 and S2, and the secondary windings S1 and S2. The energy induced in the rectifier is rectified and smoothed by the diodes D1 and D2 and the capacitor C1, respectively, and the output voltage Vout is supplied to the load.

Further, the output voltage Vout generated across the capacitor C1 is detected by the error amplifier 5, and the error voltage is fed back to the control unit 3 as a feedback signal, so that the control unit 3 keeps the output voltage constant. Switching element Q1
Control the on period of.

Next, as indicated by t3 to t3 in FIG. 2, the voltage Vc of the capacitor C3 reaches a range higher than the upper limit reference voltage Voref for the reason described later,

## EQU00004 ## When Vc> Voref (4), the OVP 3a outputs a second stop signal at a high level (a voltage substantially equal to the voltage Vc) to the inside of the control unit 3. As a result, the control unit 3 stops its operation, and as shown in FIG.
Since the PWM signal oscillated from the control unit 3 is stopped, the drive signal output to the gate of the switching element Q1 is stopped and becomes low level, and the switching element Q1 is turned off.

As described above, in the switching power supply device which converts the DC voltage input from the DC power supply into a predetermined DC voltage by controlling the ON period of the switching element and outputs the DC voltage, the primary windings of a plurality of transformers are connected. By connecting in series, the secondary windings of a plurality of transformers are connected in parallel via diodes, and the tertiary windings of a plurality of transformers are connected in series. Due to the variation caused by the difference between the winding inductance and the leakage inductance, it is possible to eliminate the cause of current imbalance, such as current concentration in one of the transformers. For example, as in this embodiment, two transformers are used. By connecting the primary windings in series with each other, the energy stored in the two transformers is distributed in half and the secondary windings are By being connected in series, the energy emission periods of the transformers can be made almost the same, and the two transformers can share the energy almost the same, so that a power source with a larger output than a single transformer can be configured. it can.

In addition, a control unit for controlling the ON period of the switching element is provided, and the induced voltage is rectified and smoothed by connecting the tertiary windings of a plurality of transformers in series and used as the operating power supply of the control unit. The control unit can be configured not to operate normally only with the voltage induced in either one of the tertiary windings.

Further, in a switching power supply device which converts a DC voltage input from a DC power supply into another DC voltage and outputs the converted DC voltage, primary windings of a plurality of transformers are sequentially connected in series to the DC power supply, and A voltage is induced in the secondary windings of a plurality of transformers by connecting a switching element in series to the secondary winding and connecting the secondary windings of a plurality of transformers in parallel via diodes. Is rectified and smoothed by the first rectifying and smoothing circuit, and the error voltage between the voltage from the first rectifying and smoothing circuit and the first reference voltage is output as a feedback signal from the error amplifier, and the three
The secondary winding is connected in series, the voltage induced in this tertiary winding is rectified and smoothed by the second rectifying and smoothing circuit, and is used as the power supply of the control unit. By controlling the ON period by the control unit,
It is possible to solve the problem of heat generation due to current imbalance, such as current concentration in one of the transformers due to variations caused by the difference in transformer core characteristics and the difference in winding inductance. By connecting the primary windings of two transformers in series with each other, the energy accumulated in each of the two transformers is distributed by half, and the secondary windings are connected in parallel. The energy discharge period can be made substantially the same, and the two transformers can share the energy almost the same, so that a power source having a larger output than a single transformer can be configured.

As a result, the switching power supply device can be constructed by using a plurality of transformers, and it is possible to supply a large output capacity in spite of its small size. Moreover, as in the conventional switching power supply device, the transformer has an extra capacity. It is possible to prevent the generation of heat and give a great deal of stress, or to approach a dangerous state such as smoke or fire, and it is possible to safely protect the switching power supply device.

Next, the operation of the switching power supply device according to the embodiment of the present invention when the short circuit open abnormal test of the transformer consisting of the six types of test items shown in FIG. 3 is performed will be described.

(1) Short circuit of the primary winding As shown in FIG. 3 (1), the switch SWp1s is temporarily connected to the primary winding P1 in an open state, and the switching power supply device is in operation. When the switch SWp1s connected in parallel to the primary winding P1 of the transformer T1 is short-circuited, the inductance component L of the secondary winding S1 of the transformer T1 is minimized. At the same time, the third winding B1 of the transformer T1
Inductance component L has a minimum value. Therefore, when the switching element Q1 is on, the DC power supply 1
A current flows from the drain to the source of the switching element Q1 through the switch SWp1s and the primary winding P2 of the transformer T2.

Further, since the inductance L component of the tertiary winding B1 of the transformer T1 is minimized, only the energy induced in the tertiary winding B2 of the transformer T2 is supplied to the anode of the diode D3. Diode D
The cathode voltage Vc of No. 3 is about 1/2 of the normal value. That is, since the voltage Vc generated in the capacitor C3 is lower than the lower limit reference voltage Vuref and is expressed by the above-described formula (1), the first stop signal of high level (approximately the same voltage as the voltage Vc) is output from the UVLO 3b. It is output inside. As a result, the control unit 3 stops the oscillation operation of the PWM signal according to the first stop signal and outputs a low level signal to the gate of the switching element Q1, so that the switching operation is stopped.

As described above, the UVLO 3b (low voltage detection circuit) which outputs the first stop signal when the voltage Vc from the second rectifying / smoothing circuit 9 becomes lower than the lower limit reference voltage Vuref is provided and controlled. When the short circuit test is performed on the primary windings of the transformers T1 and T2, the part 3 is UVLO.
By stopping the operation of the switching element Q1 in response to the first stop signal output from 3b,
Even if the secondary winding is short-circuited, it is possible to prevent excessive heat generation in the transformer, apply a great deal of stress, and prevent dangerous situations such as smoke and ignition, and to safely protect the switching power supply device.

(2) Short-circuit of secondary winding As shown in FIG. 3 (2), the switch SWs1s is temporarily connected to the secondary winding S1 in an open state, and when the switching power supply device is in operation, When the switch SWs1s connected in parallel to the secondary winding S1 of the transformer T1 is short-circuited, the inductance component L of the primary winding P1 of the transformer T1 is minimized. At the same time, the third winding B1 of the transformer T1
Inductance component L has a minimum value. Therefore, when the switching element Q1 is on, the DC power supply 1
A current flows from the drain to the source of the switching element Q1 through the primary winding P1 of the transformer T1 (the inductance component L is minimum) and the primary winding P2 of the transformer T2.

Further, since the inductance L component of the tertiary winding B1 of the transformer T1 is minimized, only the energy induced in the tertiary winding B2 of the transformer T2 is supplied to the anode of the diode D3. Diode D
The cathode voltage Vc of No. 3 is about 1/2 of the normal value. That is, since the voltage Vc generated in the capacitor C3 is lower than the lower limit reference voltage Vuref and is expressed by the above-described formula (1), the first stop signal of high level (approximately the same voltage as the voltage Vc) is output from the UVLO 3b. It is output inside. As a result, the control unit 3 stops the oscillation operation of the PWM signal according to the first stop signal and outputs a low level signal to the gate of the switching element Q1, so that the switching operation is stopped.

As described above, the UVLO 3b (low voltage detection circuit) for outputting the first stop signal when the voltage Vc from the second rectifying / smoothing circuit 9 becomes lower than the lower limit reference voltage Vuref is provided. When the short-circuit test is performed on the secondary windings of the transformers T1 and T2, the control unit 3 causes the UVLO
By stopping the operation of the switching element Q1 in response to the first stop signal output from 3b
Even if the secondary winding is short-circuited, it is possible to prevent excessive heat generation in the transformer, apply a great deal of stress, and prevent dangerous situations such as smoke and ignition, and to safely protect the switching power supply device.

(3) Short circuit of the tertiary winding As shown in FIG. 3 (3), the switch SWb1s is temporarily connected to the tertiary winding B1 in an open state, and when the switching power supply device is in operation, When the switch SWb1s connected in parallel to the tertiary winding B1 of the transformer T1 is short-circuited, the inductance component L of the primary winding P1 of the transformer T1 is minimized. At the same time, the secondary winding S1 of the transformer T1
Inductance component L has a minimum value.

Therefore, while the switching element Q1 is on, the primary winding P1 of the transformer T1 is switched from the DC power supply 1 to the primary winding P1.
(Inductance component L is minimum), and current flows between the drain and source of the switching element Q1 via the primary winding P2 of the transformer T2. Since the tertiary winding B1 of the transformer T1 is short-circuited by the switch SWb1s, the tertiary winding B of the transformer T2 is connected to the anode of the diode D3.
Since only the energy induced in 2 is supplied, the cathode voltage Vc of the diode D3 is about half that in the normal state. That is, since the voltage Vc generated in the capacitor C3 is lower than the lower limit reference voltage Vuref and is expressed by the above-described formula (1), the first stop signal of high level (approximately the same voltage as the voltage Vc) is output from the UVLO 3b. It is output inside.
As a result, the control unit 3 stops the oscillation operation of the PWM signal according to the first stop signal and outputs a low level signal to the gate of the switching element Q1, so that the switching operation is stopped.

As described above, the UVLO 3b (low voltage detection circuit) for outputting the first stop signal when the voltage Vc from the second rectifying / smoothing circuit 9 becomes lower than the lower limit reference voltage Vuref is provided, When the short-circuit test is performed on the tertiary windings of the transformers T1 and T2, the control unit 3 causes the UVLO
By stopping the operation of the switching element Q1 in response to the first stop signal output from 3b,
Even if the secondary winding is short-circuited, it is possible to prevent excessive heat generation in the transformer, apply a great deal of stress, and prevent dangerous situations such as smoke and ignition, and to safely protect the switching power supply device.

(4) Opening of Primary Winding As shown in FIG. 3 (4), the switch SWp1o is temporarily connected to the primary winding P1 in a short-circuited state, and the switching power supply device is in operation. When the switch SWp1o connected in series to the primary winding P1 of the transformer T1 is opened, the DC power source 1, the primary winding P1 of the transformer T1, the transformer T2
The primary current winding P2, the drain of the switching element Q1, and the source of the switching element Q1 are disconnected from the current loop at the time of turning on, so that the switching operation is stopped. At the same time, from the DC power source 1 through the starting resistor R1
A current flows through the capacitor C3 and is generated in the capacitor C3
Voltage Vc, as t 1 ~t 2 shown in FIG. 2, capacitor
Since the voltage Vc of the capacitor C3 is lower than the lower limit reference voltage Vuref ,
The semiconductor element that composes the control unit 3 has reached an operable voltage.
Sometimes, when the above equation (1) is reached, UVLO3
The first stop signal from b to a high level (voltage almost equal to the voltage Vc)
No. is output to the inside of the control unit 3. As a result, the control unit 3
Stop the oscillation operation of the PWM signal according to the first stop signal
Output a low level signal to the gate of switching element Q1.
As a result, the switching operation is stopped.

Therefore, the operation of the switching element can be stopped when an open test is performed on the primary winding of the transformer, and extra heat is generated in the transformer as in the conventional switching power supply device. It is possible to prevent a large amount of stress from being applied and to approach a dangerous state such as smoking or ignition, and it is possible to safely protect the switching power supply device.

(5) Opening of secondary winding As shown in FIG. 3 (5), the switch SWs1o is temporarily connected to the secondary winding S1 in a short-circuited state, and the switching power supply device is in operation. When the switch SWs1o connected in series to the secondary winding S1 of the transformer T1 is opened, an excessive surge voltage is generated in the opened primary winding P1. This surge voltage is simultaneously generated in the tertiary winding B1 which is magnetically coupled to the primary winding P1.

When a surge voltage is induced in the tertiary winding B1 to generate an overvoltage, and the capacitor C3 is charged through the diode D3 to reach an overvoltage higher than the upper limit reference voltage Voref of the OVP 3a, the OVP 3a changes to the first voltage. 2 The stop signal is output to the inside of the control unit 3. As a result, the control unit 3 receives the OV
In response to the second stop signal from P3a, the oscillation operation of the PWM signal is stopped and the low-level signal is sent to the switching element Q1.
, The operation of the switching element Q1 is stopped.

As described above, the OVP 3a (overvoltage detection circuit) for outputting the second stop signal when the voltage Vc from the second rectifying / smoothing circuit 9 becomes overvoltage than the upper limit reference voltage Voref is provided and controlled. When the open test is performed on the secondary winding of the transformer, the unit 3 stops the operation of the switching element Q1 in response to the second stop signal output from the OVP 3a, and thereby the secondary winding of the transformer is stopped. It is possible to stop the operation of the switching element when an open test is performed on the wire, which causes excessive heat generation in the transformer like the conventional switching power supply device and gives great stress, smoke or ignition. It is possible to prevent such a dangerous situation from being approached and to safely protect the switching power supply device.

(6) Opening of the tertiary winding As shown in FIG. 3 (6), the switch SWb1o is temporarily connected to the tertiary winding B1 in a short-circuited state, and while the switching power supply device is operating, When the switch SWb1o connected in series to the tertiary winding B1 of the transformer T1 is opened, 3
The forward current flowing from the anode to the cathode of the diode D3 connected to the next winding B1 becomes zero. at the same time,
A voltage Vc generated in the capacitor C3 when a current flows from the DC power source 1 to the capacitor C3 via the starting resistor R1 is shown in FIG.
As shown by t1 to t2, the voltage Vc of the capacitor C3 is
Is lower than the lower limit reference voltage Vuref, and when the semiconductor element forming the control unit 3 reaches a voltage at which the semiconductor element can operate, if the above equation (1) is satisfied, the UVLO 3b outputs a high level (a voltage substantially equal to the voltage Vc). ), The first stop signal is output to the inside of the control unit 3. As a result, the control unit 3 stops the oscillation operation of the PWM signal according to the first stop signal and outputs a low level signal to the gate of the switching element Q1, so that the switching operation is stopped .

As described above, when the voltage from the second rectifying / smoothing circuit 9 becomes lower than the lower limit reference voltage Vuref, the first
When the UVLO 3b (low voltage detection circuit) that outputs a stop signal is provided and an open test is performed on the tertiary winding of the transformer, the switching element Q1 is output according to the first stop signal output from the UVLO 3b. By stopping the operation of, even if the third winding of one transformer is opened,
As in the conventional switching power supply device, it is possible to prevent excessive heat generation in the transformer to give a great deal of stress, and to prevent a dangerous state such as smoking or ignition from being approached, so that the switching power supply device can be protected safely. In addition, the above-mentioned transformer short circuit open abnormal test (1)-
Although (6) was performed on the transformer T1, it goes without saying that similar results can be obtained by performing the same test on the transformer T2.

(Modification) FIG. 4 is a circuit diagram showing a structure of a modification of the switching power supply device according to one embodiment of the present invention. As shown in FIG. 4, the feature of this modification is that the diode D connected to the secondary winding S1 of the transformer T1.
1, the capacitor C1 is connected in the immediate vicinity of the cathode of the diode D1, and the capacitor C2 is installed in the immediate vicinity of the cathode of the diode D2 with respect to the diode D2 connected to the secondary winding S2 of the transformer T2. Is to be connected. The diodes D1 and D2 and the capacitors C1 and C2 form a third rectifying and smoothing circuit 23 that rectifies and smoothes the voltages induced in the secondary windings S1 and S2 of the transformers T1 and T2, respectively.

By using such a third rectifying / smoothing circuit 23, the energy induced in the secondary winding S1 of the transformer T1 is generated in the output voltage Vout when rectified and smoothed via the diode D1 and the capacitor C1. The high frequency ripple voltage that has been generated can be reduced as compared with the conventional switching power supply device. Similarly, the secondary winding S of the transformer T2
The high frequency ripple voltage generated in the output voltage Vout when the energy induced in 2 is rectified and smoothed via the diode D2 and the capacitor C2 can be reduced as compared with the conventional switching power supply device.

[0053]

According to the present invention as set forth in claim 1, a DC power source is provided.
DC voltage input from the power source is converted to another DC voltage and output.
In a switching power supply device that supports
Connect the primary windings of the
The switching element is connected in series to the primary winding of
In addition, the secondary windings of multiple transformers are
Multiple transformers connected in parallel via an ion
The voltage induced in the secondary winding of the
Rectifying and smoothing the voltage from the first rectifying and smoothing circuit
The error voltage from the reference voltage is used as the feedback signal from the error amplifier.
Output and connect the tertiary windings of multiple transformers in series.
The voltage induced in the third winding of the
Rectified and smoothed, and used as the power supply for the control unit.
The ON period of the switching element is controlled according to the feedback signal from
Controlled by the control unit and low voltage detection by the control unit
First stop signal or overvoltage detection circuit output from the circuit
Switching element according to the second stop signal output from the switching element
By stopping the operation of the
For the difference between line inductance and leakage inductance
Due to the resulting variation, either one of the transformers will be energized.
The problem of heat generation due to current imbalance, such as concentrated current
Can be eliminated, for example, as in this embodiment, 2
2 by connecting the primary winding of each transformer in series
Half the energy stored in each transformer
It is distributed and the secondary windings are connected in parallel,
The energy release period of the lance can be made almost the same,
Since the transformers share the energy almost equally,
Can configure a power supply with a larger output than one transformer
It Also, the first stop signal output from the low voltage detection circuit
Alternatively, in response to the second stop signal output from the overvoltage detection circuit,
The switching element to stop the operation,
It is possible to safely protect the power supply unit. This conclusion
As a result, a switching power supply device is constructed using multiple transformers.
When supplied, it provides a large output capacity despite its small size.
Can and short-circuit open abnorm of transformer
Protect switching power supplies safely against
be able to.

[0054]

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a switching power supply device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the switching power supply device according to the embodiment of the present invention.

FIG. 3 is a diagram showing test items and test contents of a transformer short circuit open abnormal test performed on the switching power supply device.

FIG. 4 is a circuit diagram showing a configuration of a modified example of the switching power supply device according to the embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a conventional switching power supply device.

[Explanation of symbols]

1 DC power supply 3 control unit 3a OVP 3b UVLO 5 Error amplifier 7 First rectifying and smoothing circuit 9 Second rectifying and smoothing circuit C1, C2, C3 capacitors D1, D2, D3 diode P1, P2 primary winding PD1 photodiode PT1 phototransistor Q1 switching element R1 starting resistance S1, S2 secondary winding T1, T2 transformer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-60370 (JP, A) JP-A-6-339270 (JP, A) JP-A-7-274498 (JP, A) JP-A-2001-157450 (JP, A) JP 2001-161066 (JP, A) JP 2001-119949 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 3/28

Claims (5)

(57) [Claims] 1. A DC voltage input from a DC power supply
For switching power supplies that convert to DC voltage and output
And Primary winding of multiple transformers connected in series to DC power supply
When, The switches connected in series to the primary windings of the plurality of transformers.
A switching element, Before being commonly connected in parallel via diodes to each
Secondary windings of multiple transformers, Rectify the voltage induced in the secondary windings of the plurality of transformers
A first rectifying and smoothing circuit for smoothing, Between the voltage from the first rectifying and smoothing circuit and the first reference voltage
An error amplifier that outputs the error voltage as a feedback signal, A tertiary winding of the plurality of transformers connected in series, Rectify the voltage induced in the tertiary windings of the plurality of transformers
A second rectifying and smoothing circuit for smoothing, The voltage from the second rectifying / smoothing circuit is lower than the lower limit reference voltage.
Low voltage that outputs the first stop signal when the voltage also becomes low
A detection circuit, The voltage from the second rectifying / smoothing circuit is higher than the upper reference voltage.
Overvoltage that outputs the second stop signal when the overvoltage also occurs
A detection circuit, The voltage from the second rectifying / smoothing circuit is used as an operating power source, and
The switching element is responsive to the feedback signal from the error amplifier.
Controlling the ON period of the child, and the low voltage detection circuit
First stop signal output from the overvoltage detection circuit
Switching according to a second stop signal output from the
And a control unit for stopping the operation of the element,
Switching power supply. 2. The control unit includes: Pair with the primary winding, secondary winding, or tertiary winding of the transformer
If a short circuit test is performed by
The switching element according to the first stop signal output from
The suspension of claim 1, wherein the operation of the child is stopped.
Itching power supply. 3. The control unit comprises: When an open test is performed on the primary winding of the transformer
Is a first stop signal output from the low voltage detection circuit.
It is possible to stop the operation of the switching element according to
The switching power supply device according to claim 1, which is characterized in that. 4. The control unit comprises: When an open test is performed on the secondary winding of the transformer
Is a second stop signal output from the overvoltage detection circuit.
It is possible to stop the operation of the switching element according to
The switching power supply device according to claim 1, which is characterized in that. 5. The control unit includes: When an open test is performed on the third winding of the transformer
Is a first stop signal output from the low voltage detection circuit.
It is possible to stop the operation of the switching element according to
The switching power supply device according to claim 1, which is characterized in that.