JP4360152B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply apparatus that changes an output voltage by turning on and off a remote switch and stably secures a voltage induced in an auxiliary winding of a transformer.

  FIG. 9 shows a configuration of a flyback converter which is an example of a conventional switching power supply device. On the secondary side of the switching power supply device, a remote switch SW2 for remote control that changes the output voltage Vout is provided.

  In the figure, the switching element Q1 turns on and off the input voltage Vin applied to the primary winding N1 of the transformer T1. The voltage induced in the secondary winding N2 of the transformer T1 is rectified by the diode D1, smoothed by the capacitor C1, and becomes the output voltage Vout.

  The voltage induced in the auxiliary winding N3 of the transformer T1 is rectified by the diode D2, smoothed by the capacitor C2, and becomes the voltage Vcc. There is a correlation between the output voltage Vout and the voltage Vcc. The voltage Vcc based on the voltage induced in the auxiliary winding N3 of the transformer T1 is used as a power source for the on / off modulation means U1 and the like.

  The first error detection means 10 has an error amplifier U2, and is an output voltage Vout based on the voltage induced in the secondary winding N2 of the transformer T1 and a voltage Vr1 · (R6 + R7) / (R5 + R6 + R7) based on the reference voltage Vr1. The difference is compared and output as a feedback signal FB to the on / off modulation means U1 via the photocoupler OC1.

  The circuit constants of the capacitor C3 and the resistor R4 determine the frequency response characteristic of feedback. The circuit constant of the resistor R3 determines the gain of the photocoupler OC1.

  The on / off modulation unit U1 receives the feedback signal FB, generates the drive signal OUT of the switching element Q1 based on the magnitude thereof, and changes the ratio of time between the on and off (duty ratio).

  When the feedback signal FB is low, the ON / OFF time ratio (duty ratio) of the drive signal OUT of the switching element Q1 is reduced, and when the feedback signal FB is high, the drive signal OUT of the switching element Q1 is turned on and off. Increase the off time ratio (duty ratio).

The feedback signal FB is pulled up (not shown) in the on / off modulation means U1, and the phototransistor collector of the photocoupler OC1 is connected.
When the photocoupler OC1 is turned on, the feedback signal FB is decreased and the duty ratio is decreased. When the photocoupler OC1 is turned off, the feedback signal FB rises due to pull-up, and the duty ratio increases.

Remote switch SW2 is arranged in parallel with resistor R7.
When remote-on is selected, the remote switch SW2 selects open, and the positive input terminal of the error amplifier U2 becomes the voltage Vr1 · (R6 + R7) / (R5 + R6 + R7). When remote-off is selected, the remote switch SW2 selects short-circuit, and the positive input terminal of the error amplifier U2 becomes the voltage Vr1 · R6 / (R5 + R6).

The operation of the conventional example of FIG. 9 will be described. Note that the remote switch SW2 is open.
When the switching element Q1 is turned on / off and the output voltage Vout becomes higher than the voltage Vr1 · (R6 + R7) / (R5 + R6 + R7), the output of the error amplifier U2 decreases, the current of the photodiode in the photocoupler OC1 increases, The current of the phototransistor in the photocoupler OC1 increases. As a result, the feedback signal FB decreases, the on-time ratio (duty ratio) of the switching element Q1 decreases, and the output voltage Vout decreases.

  When the output voltage Vout becomes lower than the voltage Vr1 · (R6 + R7) / (R5 + R6 + R7), the output of the error amplifier U2 increases, the current of the photodiode in the photocoupler OC1 decreases, and the phototransistor in the photocoupler OC1. Current decreases. As a result, the feedback signal FB increases, the on-time ratio (duty ratio) of the switching element SW1 increases, and the output voltage Vout increases.

In this way, the output voltage Vout is controlled to a predetermined voltage.
When remote-on (the remote switch SW2 is open), the output voltage Vout becomes the voltage Vr1 · (R6 + R7) / (R5 + R6 + R7).
When remote-off (the remote switch SW2 is short-circuited), the output voltage Vout is the voltage Vr1 · R6 / (R5 + R6).

  The output voltage Vout when remote-off is lower than the output voltage Vout when remote-on.

  A high voltage is supplied to a load (not shown) connected to the output voltage Vout when the remote is on, and a low voltage is supplied when the remote is off. This has the effect that the power consumption of the load (not shown) connected to the output voltage Vout and the switching power supply device can be reduced during remote off (see, for example, Patent Document 3).

  For example, if the output voltage is 80%, the power consumption is 64% in the resistive load, and the power consumption is 80% in the constant current load.

  FIG. 10 is a characteristic diagram for explaining the operation of the conventional example of FIG. The horizontal axis represents the load current Io, and the vertical axis represents the voltage Vcc based on the auxiliary winding N3 of the transformer T1. At remote ON, the voltage Vcc at no load is set as the voltage V2, and the voltage Vcc at the rated load I1 is set as the voltage V1. When remote off, the voltage Vcc at no load is set to voltage V4, and the voltage Vcc at the rated load I1 is set to voltage V3.

  There is a correlation between the output voltage Vout and the voltage Vcc. When the output voltage Vout decreases at remote off, the voltage Vcc also decreases. When the output voltage increases at remote on, the voltage Vcc also decreases.

  Further, the coupling of the transformer T1 is not perfect and there is a leakage inductance. The leakage inductance affects the characteristics of the switching power supply device at a heavy load. If the load is changed from a light load to a heavy load while the output voltage Vout is controlled to be constant, the voltage Vcc rises due to the influence of leakage inductance.

  Therefore, the voltage V1 and the voltage V3 are larger than the voltage V2 and the voltage V4.

JP-A-4-368461 JP-A-6-178538 Japanese Patent No. 3415263

  However, such a switching power supply device has a trade-off problem that, when the effect of the remote switch is improved, the rated characteristics are deteriorated.

  Specifically, it is necessary to secure the voltage V4 in order to guarantee the operation of the on / off modulation means U1 and the like when the remote is off. When the voltage V4 is lowered, the operation becomes unstable.

  In order to obtain the effect of the remote switch, the voltage difference (V2−V4) and the voltage difference (V1−V3) between the voltage Vcc at the remote on and the voltage Vcc at the remote off need to be large. However, if this difference is increased while securing the voltage V4, the value of the voltage V1 increases.

  When the voltage V1 increases, the power consumption of the on / off modulation means U1 and the like when the rated load I1 is remote on increases. At this time, the switching power supply device has the maximum output, the conversion loss is also the maximum, and it may be desired to reduce the power consumption.

  That is, if the voltage V4 is secured and the voltage difference (V2-V4) and the voltage difference (V1-V3) are secured, the voltage V1 cannot be suppressed.

  An object of the present invention is to solve the above-described problems, and to provide a switching power supply device that appropriately suppresses power consumption and has stable operation over the entire operation range.

The present invention which achieves such an object is as follows.
[1] A switching element for turning on and off an input voltage applied to the primary winding of the transformer, a first error detecting means for comparing a difference between a voltage induced in the secondary winding of the transformer and a predetermined voltage, On-off modulation means that operates with a voltage induced in the auxiliary winding of the transformer and generates a drive signal for the switching element based on a feedback signal, and compares the difference between the voltage induced in the auxiliary winding and a predetermined voltage A second error detecting unit; and a circuit for connecting a feedback signal from the first error detecting unit and a feedback signal from the second error detecting unit in series, wherein the auxiliary winding includes the first error detecting unit. The auxiliary winding when the voltage induced in the auxiliary winding when the feedback signal from the means is selected selects the feedback signal from the second error detecting means And the first error detecting means includes a first error amplifier having an inverting input connected to a voltage induced in the secondary winding, and the second error detecting means. The means comprises a second error amplifier whose inverting input is connected to a voltage induced in the auxiliary winding, a cathode of a photodiode is connected to an output of the first error amplifier, and a collector of a phototransistor is turned on and off A photocoupler connected to the feedback signal of the modulation means, the emitter of the phototransistor connected to the output of the second error amplifier, and a switch for shorting the non-inverting input of the second error amplifier to a common potential The switching power supply device characterized by the above-mentioned.
[ 2 ] A switching element for turning on and off an input voltage applied to the primary winding of the transformer, a first error detecting means for comparing a difference between a voltage induced in the secondary winding of the transformer and a predetermined voltage, On-off modulation means that operates with a voltage induced in the auxiliary winding of the transformer and generates a drive signal for the switching element based on a feedback signal, and compares the difference between the voltage induced in the auxiliary winding and a predetermined voltage A second error detecting unit; and a circuit for connecting a feedback signal from the first error detecting unit and a feedback signal from the second error detecting unit in series, wherein the auxiliary winding includes the first error detecting unit. The auxiliary winding when the voltage induced in the auxiliary winding when the feedback signal from the means is selected selects the feedback signal from the second error detecting means And the first error detecting means includes a first error amplifier having an inverting input connected to a voltage induced in the secondary winding, and the second error detecting means. The means comprises a second error amplifier whose inverting input is connected to a voltage induced in the auxiliary winding, a cathode of a photodiode is connected to an output of the first error amplifier, and a collector of a phototransistor is turned on and off is connected to the feedback signal of the modulating means comprises a photocoupler emitter of the phototransistor is connected to the output of said second error amplifier, further comprising a switch for shorting the cathode of the photodiode to a common potential Switching power supply.
[ 3 ] The switch is open when the load current of the secondary winding is a heavy load, and the switch is shorted when the load current is a light load. [ 1 ] or [ 1 ] 2 ] The switching power supply device according to any one of the above.
[ 4 ] The switching power supply device according to any one of [ 1 ] and [ 2 ], wherein the switch is open when there is no abnormality and the switch is short-circuited when there is an abnormality.
[ 5 ] The switch is opened when the output voltage induced in the secondary winding is not decreased, and the switch is shorted when the output voltage is decreased. [ 1 ] or [ 1 ] 2 ] The switching power supply device according to any one of the above.
The features of the embodiment of the present invention are as follows.
(1) a switching element for turning on and off an input voltage applied to the primary winding of the transformer, a first error detecting means for comparing a difference between a voltage induced in the secondary winding of the transformer and a predetermined voltage; An on-off modulation unit that operates with a voltage induced in the auxiliary winding of the transformer and generates a drive signal for the switching element based on a feedback signal; and a voltage induced in the auxiliary winding and a predetermined voltage Switching comprising: a second error detecting means for comparing a difference from the voltage; and a remote switch for switching between a feedback signal from the first error detecting means and a feedback signal from the second error detecting means. Power supply.

(2) The switching power supply according to (1), wherein the remote switch is switched based on a determination based on a load current value.

(3) The switching power supply according to (1), wherein the remote switch is switched based on a determination based on detection of abnormality.

(4) The first error detection means and the second error detection means are connected in series, and the remote switch is arranged to short-circuit the first error detection means ( The switching power supply device according to any one of 1) to (3).

(5) The switching power supply device according to any one of (1) to (4), wherein an output switch that turns on and off an output based on the secondary winding is provided based on on / off of the remote switch.

(6) The switching power supply device according to any one of (1) to (5), wherein a state monitoring unit that operates with a voltage induced in the auxiliary winding and monitors an operation state is provided.

(7) a switching element for turning on and off the input voltage applied to the primary winding of the transformer;
The difference between the output voltage induced in the secondary winding of the transformer and a predetermined voltage is compared, and a first error detection means for generating a feedback signal and the voltage induced in the auxiliary winding of the transformer are operated and feedback A second error generating a feedback signal by comparing a difference between a voltage induced in the auxiliary winding and a reference voltage in a switching power supply device comprising on / off modulation means for generating a drive signal for the switching element based on the signal A detection unit; and a remote switch that selects a feedback signal from the first error detection unit when remote-on and selects a feedback signal from the second error detection unit when remote-off. A switching power supply device.

(8) The auxiliary winding is formed to have a smaller number of turns than the voltage induced in the auxiliary winding when remote-on and no load is induced. The switching power supply according to (7), characterized in that

(9) a switching element for turning on and off the input voltage applied to the primary winding of the transformer;
The difference between the output voltage induced in the secondary winding of the transformer and a predetermined voltage is compared, and a first error detection means for generating a feedback signal and the voltage induced in the auxiliary winding of the transformer are operated and feedback A second error generating a feedback signal by comparing a difference between a voltage induced in the auxiliary winding and a reference voltage in a switching power supply device comprising on / off modulation means for generating a drive signal for the switching element based on the signal A detecting circuit, a series circuit of a feedback signal from the first error detecting means and a feedback signal from the second error detecting means, and a feedback signal from the first error detecting means at remote off. A switching power supply comprising: a remote switch that is substantially short-circuited.

(10) The switching power supply according to (9), wherein the auxiliary winding is formed with a number of turns in which a voltage induced in the auxiliary winding when remote-on is larger than the reference voltage.

(11) The switching element that turns on and off the input voltage applied to the primary winding of the transformer is compared with the output voltage induced in the secondary winding of the transformer and a predetermined voltage to generate a feedback signal. A switching power supply comprising: first error detection means; and on-off modulation means that operates with a voltage induced in the auxiliary winding of the transformer and generates a driving signal for the switching element based on a feedback signal. The difference between the voltage induced in the reference voltage and the reference voltage is compared, and the second error detection means for generating a feedback signal, and the feedback signal from the first error detection means when the load is heavy, and the light load is selected. And a switch for selecting a feedback signal from the second error detecting means.

(12) The switching element for turning on and off the input voltage applied to the primary winding of the transformer and the difference between the output voltage induced in the secondary winding of the transformer and a predetermined voltage are compared to generate a feedback signal. A switching power supply comprising: first error detection means; and on-off modulation means that operates with a voltage induced in the auxiliary winding of the transformer and generates a driving signal for the switching element based on a feedback signal. Comparing the difference between the voltage induced in the reference voltage and the reference voltage, and selecting a feedback signal from the second error detecting means for generating a feedback signal, an abnormality monitoring means, and the first error detecting means when there is no abnormality, And a switch for selecting a feedback signal from the second error detecting means when there is an abnormality. Source apparatus.

(13) The switching power supply according to (12), further comprising: an output switch that cuts off an output when there is an abnormality; and a state monitoring unit that operates with a voltage induced in the auxiliary winding.

(14) The switching element that turns on and off the input voltage applied to the primary winding of the transformer is compared with the output voltage induced in the secondary winding of the transformer and a predetermined voltage to generate a feedback signal. A switching power supply comprising: first error detection means; and on-off modulation means that operates with a voltage induced in the auxiliary winding of the transformer and generates a driving signal for the switching element based on a feedback signal. The second error detecting means for comparing the difference between the voltage induced in the signal and the reference voltage and generating a feedback signal, the comparator for detecting the decrease in the output voltage, and the output being cut off when the output voltage is decreased Selecting an output switch and a feedback signal from the first error detecting means when the output voltage is not lowered, Reduction There switching power supply unit, characterized in that it comprises a switch for selecting a fee-back signal from the second error detecting means when the.

(15) A circuit that substantially limits the maximum value of the load current is provided, and the auxiliary winding is formed in a number of turns in which a voltage induced in the auxiliary winding at the time of detection by the comparator is smaller than the reference voltage. (14) The switching power supply device according to (14).

As is apparent from the above description, the present invention has the following effects.
The power consumption of the load and the switching power supply device such as the on / off modulation means can be suitably suppressed over the entire operation range. Further, the operation of the on / off modulation means and the like can be stably ensured, and a prompt switching response can be made.

  In addition, it is possible to secure a voltage based on the voltage induced in the auxiliary winding of the transformer at a light load, and to set a low voltage based on the voltage induced in the auxiliary winding of the transformer at the rated load. The power consumption of the load and the switching power supply device can be suitably suppressed.

  Further, when an abnormality is detected, a voltage based on the voltage induced in the auxiliary winding of the transformer can be stably secured, and the output power can be limited.

  Further, the configuration is simplified, the number of parts is reduced, and the switching power supply device can be reduced in size and cost.

  Further, the switching power supply device can be stably secured from the voltage induced in the auxiliary winding of the transformer while the switching power supply device is disconnected from the load at the time of remote off.

  In addition, the operation of the state monitoring unit can be secured stably.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a switching power supply device according to the present invention. In addition, the same code | symbol is attached | subjected to the same element as the prior art example of FIG. 9, and description is abbreviate | omitted.

  A feature of the embodiment of FIG. 1 is that a second error detecting means 20 for comparing a difference between a voltage Vcc based on a voltage induced in the auxiliary winding N3 of the transformer T1 and a predetermined reference voltage Vr2, and a first error detecting means 10 Is provided with a remote switch SW1 for switching the feedback signal A from the feedback signal B and the feedback signal B from the second error detecting means 20 and changing the output voltage Vout.

  The second error detection means 20 includes an error amplifier U3, compares the difference between the voltage Vcc and the reference voltage Vr2, and outputs the result as a feedback signal FB to the on / off modulation means U1 via the diode D3. Similar to the operation of the first error detection means 10, the voltage Vcc is controlled to the reference voltage Vr2 by the second error detection means 20.

  Then, the second error detection means 20 generates a feedback signal B. On the other hand, the first error detection means 10 generates a feedback signal A.

  The circuit constants of the capacitor C4 and the resistor R8 determine the frequency response characteristic of feedback.

  The operation of the embodiment of FIG. 1 will be described. When the remote switch is on, the remote switch SW1 selects the feedback signal A from the first error detection means 10 and stabilizes the output voltage Vout as in the conventional example of FIG. When the remote switch is off, the remote switch SW1 selects the feedback signal B from the second error detection means 20, and stabilizes the voltage Vcc as described above.

  2 and 3 are characteristic diagrams for explaining the operation of the embodiment of FIG. The description of the conventional example in FIG. 10 is omitted. FIG. 2 corresponds to FIG.

  In FIG. 2, the voltage Vcc at no load at the time of remote-on is assumed to be a voltage V6. That is, the voltage Vcc induced in the auxiliary winding N3 when remote-on and no load is set to the voltage V6. Further, the voltage Vcc at the rated load I1 at the time of remote-on is assumed to be the voltage V5. Furthermore, the voltage Vcc at the time of remote-off is set to the voltage V7. That is, the voltage Vcc induced in the auxiliary winding N3 when remote-off is set to the voltage V7.

  The voltage V7 (= Vr2) becomes a constant voltage by the feedback of the second error detection means 20. Further, similarly to the conventional example of FIG. 10, the voltage is higher than the voltage V6. That is, the voltage V5 in FIG. 2 is larger than the voltage V6, similarly to the voltages V1 and V3 in the conventional example in FIG.

In FIG. 3, the horizontal axis represents the load current Io, and the vertical axis represents the output voltage Vout.
In the figure, the output voltage Vout at the time of remote on is assumed to be a voltage V8. Further, the output voltage Vout at no load at the time of remote-off is assumed to be a voltage V9. Further, the output voltage Vout at the rated load I1 at the time of remote-off is assumed to be a voltage V10.

  The voltage V8 (= Vr1 · (R6 + R7) / (R5 + R6 + R7)) in FIG. 3 becomes a constant voltage as described in the conventional example in FIG.

  Further, the coupling of the transformer T1 in the embodiment of FIG. 1 is not perfect and there is a leakage inductance. Furthermore, the leakage inductance affects the characteristics of the switching power supply device at a heavy load. As a result, when the load is changed from a light load to a heavy load while the voltage Vcc is controlled to be constant, the output voltage Vout decreases due to the influence of leakage inductance.

  Therefore, in FIG. 3, the voltage V10 is smaller than the voltage V9. This limits the output power when remote off.

  In order to guarantee the operation of the on / off modulation means U1, etc., it is necessary to secure the voltage V6 and the voltage V7. When the voltage V6 and the voltage V7 are lowered, the operation becomes unstable.

  FIG. 2 shows that even if the voltage difference (V6-V7) between the voltage Vcc at remote on with no load and the voltage Vcc at remote off is small, the voltage difference between the light load and the rated load I1 ( V6-V7) can be greatly increased.

  Specifically, when the auxiliary winding N3 and the reference voltage Vr2 of the transformer T1 are set so that the voltage V6 and the voltage V7 are reduced within an allowable range, the voltage V5 is reduced. When the voltage V5 is suppressed, the power consumption of the on / off modulation means U1 and the like when the rated load I1 is remote on and is suppressed.

  Further, the output voltage Vout when the rated load I1 is remote off decreases to V10, and the power consumption of the load (not shown) connected to the output voltage Vout and the switching power supply is suppressed.

  As described above, the embodiment of FIG. 1 can favorably suppress the power consumption of the switching power supply device over the entire operation range.

  FIG. 4 is a block diagram of a second embodiment of the switching power supply device according to the present invention. Note that the same elements as those in the embodiment of FIG.

  The feature of the embodiment of FIG. 4 is that the remote switch (switch) SW3 is switched based on the determination based on the value of the load current Io, and the first error detection means 10 and the second error detection means 20 are switching power supplies. The remote switch SW3 is arranged such that the first error detecting means 10 is short-circuited on the secondary side of the switching power supply device.

  Specifically, the load current determination unit U4 is arranged in series with a load (not shown), the remote switch SW3 is arranged in parallel with the positive input terminal of the error amplifier U2, and the feedback signal FB of the on / off modulation unit U1 and the photocoupler OC1. The phototransistor, the diode D3, and the error amplifier U3 are arranged in series.

  That is, a series circuit of the feedback signal from the first error detection means 10 and the feedback signal from the second error detection means 20 is formed.

  When the load current Io is a heavy load, the load current determination unit U4 turns on remotely, and the remote switch SW3 selects open. When the load current Io is light, the remote switch SW3 is selected to be short-circuited.

  Further, when the load current Io is a heavy load (remote on, remote switch SW3 is open), the voltage Vcc is set to be higher than the reference voltage Vr2.

  That is, the auxiliary winding N3 is formed to have a number of turns in which the voltage Vcc induced in the auxiliary winding N3 when remote-on is larger than the reference voltage Vr2.

  On the other hand, if a hysteresis is provided for switching the remote switch SW3, the switching operation is stabilized.

  5 and 6 are characteristic diagrams for explaining the operation of the embodiment of FIG. 5 and 6 correspond to FIGS. 2 and 3, respectively. Description of the same components as those in FIGS. 2 and 3 is omitted. 5 and 6 show a case where the voltage V6 is set smaller than the voltage V7. On the other hand, FIGS. 2 and 3 show a case where the voltage V6 is set to be larger than the voltage V7.

  This setting can be adjusted by setting the auxiliary winding N3 of the transformer T1 and the reference voltage Vr2. That is, the auxiliary winding N3 of the embodiment of FIG. 4 is formed with a number of turns in which the voltage V6 is smaller than the voltage V7. When the voltage V6 is set smaller than the voltage V7, the voltage V9 becomes larger than the voltage V8.

  If the voltage V6 is set smaller than the voltage V7, the voltage V9 is larger than the voltage V8. However, there is an advantage that the voltage V5 is lowered. An increase in voltage V9 increases load stress. The decrease in the voltage V5 suppresses the power consumption of the on / off modulation means U1 and the like.

  Therefore, specifically, it is preferable to set the auxiliary winding N3 and the reference voltage Vr2 of the transformer T1 so that the voltage V5 is minimized within the voltage V9 range that the load can tolerate.

  FIG. 5 will be described. From the load I2 to the rated load I1 (heavy load) is remote-on, and the remote switch SW3 selects open. The voltage Vcc at the load I2 is set as the voltage V11, and the voltage Vcc at the rated load I1 is set as the voltage V5.

  As in the characteristic diagram of FIG. 2, the voltage V5 is larger than the voltage V11. That is, the voltage V5 in FIG. 5 is larger than the voltage V11, like the voltages V1 and V3 in FIG.

  In FIG. 5, from no load to load I2 (light load) is set to remote off, and the remote switch SW3 selects short. Further, voltage Vcc from no load to load I2 is set to voltage V7. As in the characteristic diagram of FIG. 2, the voltage V7 (= Vr2) is a constant voltage.

  FIG. 6 will be described. From the load I2 to the rated load I1 (heavy load) is remote-on, and the remote switch SW3 selects open. Further, the output voltage Vout from the load I2 to the rated load I1 is set to a voltage V8. As in the characteristic diagram of FIG. 3, the voltage V8 (= Vr1 · (R6 + R7) / (R5 + R6 + R7)) is a constant voltage.

  In FIG. 6, from no load to load I2 (light load) is set to remote off, and the remote switch SW3 selects short. Further, the output voltage Vout when there is no load is the voltage V9, and the output voltage Vout when the load is I2 is the voltage V12.

  As in the characteristic diagram of FIG. 3, the voltage V12 is smaller than the voltage V9. That is, the voltage V12 in FIG. 6 is smaller than the voltage V9, similarly to the voltage V10 in FIG.

  The operation of the second embodiment will be described with reference to FIGS. When the load current Io is from the load I2 to the rated load I1 (heavy load) (remote on, remote switch SW3 is open), the voltage Vcc is higher than the reference voltage Vr2, and the output of the error amplifier U3 is short-circuited. The diode D3 is turned on, and the voltage of the phototransistor of the photocoupler OC1 is generated in the feedback signal FB of the on / off modulation means U1.

  That is, when the remote is turned on, the remote switch SW3 substantially selects the feedback signal from the first error detection means 10.

  As a result, as in the embodiment of FIG. 1, the output voltage Vout of the embodiment of FIG. 4 is controlled to a constant voltage by the voltage V8 (= Vr1 · (R6 + R7) / (R5 + R6 + R7)).

  In the embodiment of FIG. 4, when the load current Io is from no load to the load I2 (light load) (remote off, the remote switch SW3 is short-circuited), the positive input terminal of the error amplifier U2 becomes zero. The output of the error amplifier U2 is short-circuited, the photodiode and the phototransistor of the photocoupler OC1 are turned on and saturated (short-circuited), and the output voltage of the error amplifier U3 is generated in the feedback signal FB of the on / off modulation means U1.

  That is, the remote switch SW3 substantially selects the feedback signal from the second error detection means 20 when the remote is off.

As a result, as in the embodiment of FIG. 1, the voltage Vcc of the embodiment of FIG. 4 is controlled to a constant voltage by the voltage V7 (= Vr2).
At this time, the output voltage Vout of the embodiment of FIG. 4 is lowered, and there is an effect that power consumption of a load (not shown) and a switching power supply device connected thereto can be reduced.

  As described above, in the embodiment of FIG. 4, similarly to the embodiment of FIG. 1, the power consumption of the switching power supply device can be suitably suppressed over the entire operation range.

  And a remote switch switches automatically by determination based on the value of load current.

  Further, in order to guarantee the operation of the on / off modulation means U1 and the like, it is necessary to secure the voltage V6 and the voltage V7 in the embodiment of FIG. 1, but in the embodiment of FIG. In some cases, it is not necessary to secure the voltage V6.

  As a result, the voltage V5 is further suppressed, and the power consumption of the on / off modulation means U1 and the like when the rated load I1 is remote on can be further suppressed.

  Further, in the embodiment of FIG. 4, the load current determining means U4 is formed so as to act on the secondary side load current Io. However, the load current determining means U4 is separated from the primary side primary winding. Even if it is formed so as to act based on the current of the line N1 and the switching element Q1, etc., the same operation is performed and the same effect is obtained.

  FIG. 7 is a block diagram of a third embodiment of the switching power supply device according to the present invention. The same elements as those in the embodiment of FIG. 4 are denoted by the same reference numerals and description thereof is omitted.

  The features of the embodiment of FIG. 7 are that the switching power supply device is configured by a forward converter, and that the remote switch (switch) SW3 is switched by determination based on detection of an abnormality on the secondary side of the switching power supply device, Based on the on / off of the remote switch SW3, an output switch SW4 for turning on / off the output based on the secondary winding N2 of the transformer T1 is provided, and the switching is performed by the voltage Vcc based on the voltage induced in the auxiliary winding N3 of the transformer T1. The point is that a state monitoring means U7 for monitoring the operation state of the primary side of the power supply device is provided.

  Specifically, the voltage induced in the secondary winding N2 of the transformer T1 is rectified by the diode D4 and the diode D5, smoothed by the inductor L1 and the capacitor C1, and becomes the output voltage Vout via the output switch SW4.

  The abnormality monitoring means U5 monitors the temperature of the diode D5 by the temperature detection means TH1, and determines that an abnormality occurs when the temperature of the diode D5 exceeds a predetermined value. The output is transmitted to the remote switch SW3 and the inverter U6 is connected to the inverter U6. To the output switch SW4.

  When the temperature of the diode D5 is equal to or lower than a predetermined value, the remote switch is turned on, the remote switch SW3 selects open, and the output switch SW4 selects short.

  At this time, the Zener diode D6 is set so that the transistor Q2 is saturated by the voltage Vcc.

  When the temperature of the diode D5 is equal to or higher than a predetermined value, the remote switch is turned off, the short switch is selected for the remote switch SW3, and the open switch is selected for the output switch SW4.

  The state monitoring means U7 monitors the input voltage Vin, and an output proportional to the magnitude is transmitted to the secondary side of the switching power supply device via the photocoupler OC2.

  The second error detecting means 20 and the first error detecting means 10 are arranged in series on the primary side of the switching power supply device. Specifically, the feedback signal FB of the on / off modulation means U1, the transistor Q2, the Zener diode D7, and the phototransistor of the photocoupler OC1 are connected in series.

  The remote switch SW3 is arranged so as to short-circuit the first error detection means 10 on the secondary side of the switching power supply device. Specifically, the remote switch SW3 is connected to the output terminal of the error amplifier U2.

  The second error detection means 20 has a transistor Q2, its base is connected to the voltage Vcc via the resistor 10 and a Zener diode D6, and a resistor R9 is disposed between its base and emitter.

  The operation of the second error detection means 20 will be described. When the voltage Vcc becomes excessively large, the base current of the transistor Q2 increases and the voltage between the collector and the emitter decreases. As a result, the feedback signal FB of the on / off modulation means U1 decreases, the on-time ratio (duty ratio) of the switching element Q1 decreases, and the voltage Vcc decreases.

  When the voltage Vcc becomes excessively small, the base current of the transistor Q2 decreases and the collector-emitter voltage increases. As a result, the feedback signal FB of the on / off modulation means U1 rises, the on-time ratio (duty ratio) of the switching element Q1 increases, and the voltage Vcc rises.

  In this way, the voltage Vcc in the embodiment of FIG. 7 is controlled to a predetermined voltage. The operation of the second error detection means 20 in the embodiment of FIG. 7 is substantially the same as the operation of the second error detection means 20 in the embodiment of FIG.

The operation of the third embodiment in FIG. 7 will be described.
First, when the temperature of the diode D5 is equal to or lower than a predetermined value (remote on, remote switch SW3 is open, and output switch SW4 is short), the transistor V2 is saturated (shorted) by the voltage Vcc, and the feedback of the on / off modulation means U1. In the signal FB, the voltage of the phototransistor of the photocoupler OC1 is generated.

  As a result, similarly to the embodiment of FIG. 4, the output voltage Vout of the embodiment of FIG. 7 is controlled to a constant voltage by the voltage V8 (= Vr1 · (R6 + R7) / (R5 + R6 + R7)).

  Next, when the temperature of the diode D5 is equal to or higher than a predetermined value (remote off, remote switch SW3 is short, output switch SW4 is open), the photodiode and phototransistor of the photocoupler are on and saturated (short), A voltage between the collector and the emitter of the transistor Q2 is generated in the feedback signal FB of the on / off modulation means U1.

  Thus, the voltage Vcc is controlled to a predetermined voltage. The output of the switching power supply device is open.

  In this manner, the embodiment of FIG. 7 can suitably suppress the power consumption of the switching power supply device over the entire operating range, as in the embodiment of FIG. In addition, the operation of the state monitoring unit U7 can be secured stably.

  Further, the Zener diode D7 has a function of limiting the upper limit of the voltage between the collector and the emitter of the transistor Q2. Thereby, the upper limit of the feedback signal FB of the on / off modulation means U1 can be limited, and the increase of the output voltage Vout can be suppressed.

  In particular, the case where the output voltage Vout increases at a light load as shown in the characteristic diagram of FIG. 6 is preferable because the increase in the output voltage Vout can be suppressed.

  In the above-described example, the abnormality monitoring unit U5 is arranged to measure the temperature of the diode D5. Alternatively, an output overvoltage and overcurrent may be detected. A control signal for remote control may be obtained from the load device (not shown).

  Furthermore, in the above-described example, the state monitoring unit U7 is arranged to monitor the voltage of the input voltage Vin. However, apart from this, monitoring of a commercial power supply further upstream of the input voltage Vin, switching element Q1, etc. You may make it monitor the temperature of others, etc.

Moreover, in the above-mentioned example, although it applied to a flyback converter and a forward converter, you may apply to a push pull converter, a bridge type converter, and other converters.
Furthermore, the output voltage Vout may be an alternating current.

  FIG. 8 is a block diagram of a fourth embodiment of the switching power supply device according to the present invention. The same components as those in the embodiment of FIG. 4 and the embodiment of FIG.

  The feature of the embodiment of FIG. 8 is the configuration of the comparator U8, the switch SW4, and the switch SW3.

  In the figure, the inverting input of the comparator U8 is connected to the output voltage Vout. The non-inverting input of the comparator U8 is connected to the connection point between the resistor R6 and the resistor R7. That is, the non-inverting input of the comparator U8 is connected to a reference voltage. Further, the output of the comparator U8 is connected to the control terminal of the output switch SW4 via the diode D15, and is connected to the control terminal of the switch SW3 via the resistor R17.

  The comparator U8 operates based on the voltage Vr1 · R7 / (R5 + R6 + R7). On the other hand, the output voltage Vout is controlled to the voltage Vr1 · (R6 + R7) / (R5 + R6 + R7) by the error amplifier U2. The voltage Vr1 · R7 / (R5 + R6 + R7) is smaller than the voltage Vr1 · (R6 + R7) / (R5 + R6 + R7).

  One end of the switch SW4 is connected to the secondary winding N2 via the diode D1. Further, the other end of the switch SW4 is connected to the output voltage Vout. The switch SW4 is formed by a P-channel MOSFET.

  Further, a resistor R16 is connected between the source of the switch SW4 and the drain of the switch SW4. The resistor R16 makes the starting characteristic of the embodiment of FIG. 8 suitable. A resistor R15 is connected between the source of the switch SW4 and the gate of the switch SW4. Further, a capacitor C15 is connected between the gate of the switch SW4 and the common potential GND.

  One end of the switch SW3 is connected to the output of the error amplifier U2 of the first error detecting means 10. Further, the other end of the switch SW3 is connected to the common potential GND. The switch SW3 is formed by an NPN transistor. Further, a resistor R18 is connected between the base of the switch SW3 and the emitter of the switch SW3.

  Further, the on / off modulation means U1 is formed by a current control type control circuit. A resistor R2 is connected between one end (source) of the switching element Q1 and the common potential COM. Further, the connection point between one end (source) of the switching element Q1 and the resistor R2 is connected to the signal CS of the on / off modulation means U1 through the filter F.

  Inside the on / off modulation means U1, the feedback signal FB is connected to the inverting input of the comparator U10 via a diode D10 and a resistor R11. A resistor R12 and a Zener diode D11 are connected to the inverting input of the comparator U10. Furthermore, the signal CS is connected to the non-inverting input of the comparator U10. The output of the comparator U10 is connected to the switching element Q1 via the drive signal OUT.

  The comparator U10 controls on / off of the drive signal OUT so that the feedback signal FB and the signal CS match. When the feedback signal FB rises, the ratio (duty ratio) of the on-time of the switching element SW1 increases to increase the signal CS, and when the feedback signal FB decreases, the ratio of the on-time (duty ratio) of the switching element SW1. Ratio) is reduced to reduce the signal CS.

  In this way, the embodiment of FIG. 8 controls the output voltage Vout to a predetermined voltage as in the embodiment of FIG. When the Zener diode D11 is turned on, the inverting input of the comparator U10 becomes constant, the signal CS becomes constant, the maximum value of the on-time ratio (duty ratio) of the switching element SW1 is limited, and the output (substantially) output ( The maximum value of Vout · Io) is limited.

Such a steady operation in the embodiment of FIG. 8 will be described.
The output voltage Vout is controlled to a voltage Vr1 · (R6 + R7) / (R5 + R6 + R7) by the error amplifier U2. Further, the output of the comparator U8 becomes low level, the diode D15 is turned on, the output switch SW4 is turned on, and the switch SW3 is turned off.

  Then, the voltage Vcc becomes larger than the reference voltage Vr2, the output of the error amplifier U3 becomes low level, the diode D3 is turned on, and the voltage of the phototransistor of the photocoupler OC1 is applied to the feedback signal FB. That is, the feedback signal FB becomes a feedback signal from the first error detection means 10.

Next, the operation when the output terminal is short-circuited in the embodiment of FIG. 8 will be described.
When the output terminal is short-circuited, the output voltage Vout decreases. When the output voltage Vout becomes Vr1 · R7 / (R5 + R6 + R7), the output of the comparator U8 becomes high level, the diode D15 is turned off, the output switch SW4 is turned off, and the switch SW3 is turned on.

  Then, the photodiode and the phototransistor of the photocoupler OC1 are turned on and saturated (short-circuited), and the output of the error amplifier U3 is applied to the feedback signal FB. That is, the feedback signal FB becomes a feedback signal from the second error detection means 20.

  Therefore, the comparator U8 detects a decrease in the output voltage Vout. The output switch SW4 is turned off to shut off the output when the output voltage Vout is lowered.

  Further, the switch SW3 substantially selects the feedback signal from the second error detection means 20 when the output voltage Vout is lowered.

  The embodiment of FIG. 8 can suitably suppress the power consumption of the switching power supply device over the entire operating range, as in the embodiment of FIG.

  Also, due to the action of the Zener diode D11, the output (Vout · Io) is substantially limited during the period from when the output terminal is short-circuited until the output switch SW4 is turned off. For this reason, the embodiment of FIG. 8 has high reliability and is suitable.

  Further, the auxiliary winding N3 is formed in a number of turns in which the voltage Vcc induced in the auxiliary winding N3 is smaller than the reference voltage Vr2 when the comparator detects, that is, when the output voltage Vout is the voltage Vr1 · R7 / (R5 + R6 + R7). Then, the operation of the embodiment of FIG. 8 becomes stable and preferable.

  Specifically, with this configuration, when the comparator U8 operates, the second error detection means 20 (error amplifier U3) immediately operates and the operation becomes stable.

It is a block diagram which shows one Example of this invention. It is a characteristic view for demonstrating operation | movement of the Example of FIG. It is a characteristic view for demonstrating operation | movement of the Example of FIG. It is a block diagram which shows the 2nd Example of this invention. It is a characteristic view for demonstrating operation | movement of the Example of FIG. It is a characteristic view for demonstrating operation | movement of the Example of FIG. It is a block diagram which shows the 3rd Example of this invention. It is a block diagram which shows the 4th Example of this invention. It is a block diagram of the conventional switching power supply device. It is a characteristic view for demonstrating the operation | movement of the prior art example of FIG.

Explanation of symbols

T1 Transformer N1 Primary winding N2 Transformer secondary winding N3 Transformer auxiliary winding Q1 Switching element 10 First error detection means 20 Second error detection means SW1, SW2, SW3 Remote switch (switch)
SW4 Output switch U1 On-off modulation means U4 Load current determination means U5 Abnormality monitoring means U7 Status monitoring means U8 Comparator

Claims (5)

A switching element for turning on and off the input voltage applied to the primary winding of the transformer;
First error detecting means for comparing a difference between a voltage induced in the secondary winding of the transformer and a predetermined voltage;
An on-off modulation means that operates at a voltage induced in the auxiliary winding of the transformer and generates a driving signal for the switching element based on a feedback signal;
Second error detection means for comparing a difference between a voltage induced in the auxiliary winding and a predetermined voltage;
A circuit for connecting in series the feedback signal from the first error detection means and the feedback signal from the second error detection means;
The auxiliary winding is connected to the auxiliary winding when the voltage induced in the auxiliary winding when the feedback signal from the first error detecting means is selected selects the feedback signal from the second error detecting means. Formed in a number of turns greater than the induced voltage ,
The first error detection means includes a first error amplifier connected to a voltage induced at the secondary winding by an inverting input;
The second error detecting means includes a second error amplifier whose inverting input is connected to a voltage induced in the auxiliary winding,
The cathode of the photodiode is connected to the output of the first error amplifier, the collector of the phototransistor is connected to the feedback signal of the on / off modulation means, and the emitter of the phototransistor is connected to the output of the second error amplifier. With a photocoupler,
A switching power supply device comprising: a switch for short-circuiting the non-inverting input of the second error amplifier to a common potential . A switching element for turning on and off the input voltage applied to the primary winding of the transformer;
First error detecting means for comparing a difference between a voltage induced in the secondary winding of the transformer and a predetermined voltage;
An on-off modulation means that operates at a voltage induced in the auxiliary winding of the transformer and generates a driving signal for the switching element based on a feedback signal;
Second error detection means for comparing a difference between a voltage induced in the auxiliary winding and a predetermined voltage;
A circuit for connecting in series the feedback signal from the first error detection means and the feedback signal from the second error detection means;
The auxiliary winding is connected to the auxiliary winding when the voltage induced in the auxiliary winding when the feedback signal from the first error detecting means is selected selects the feedback signal from the second error detecting means. Formed in a number of turns greater than the induced voltage,
The first error detection means includes a first error amplifier connected to a voltage induced at the secondary winding by an inverting input;
The second error detecting means includes a second error amplifier whose inverting input is connected to a voltage induced in the auxiliary winding,
The cathode of the photodiode is connected to the output of the first error amplifier, the collector of the phototransistor is connected to the feedback signal of the on / off modulation means, and the emitter of the phototransistor is connected to the output of the second error amplifier. With a photocoupler,
Switching power supply you further comprising a switch for shorting the cathode of the photodiode to a common potential. When the load current of the secondary winding is a heavy load, the switch is open,
Said load current switching power supply device according to any one of claims 1 or 2, wherein said that the switch is shorted when a light load. When there is no abnormality, the switch is open,
Abnormality said switch switching power supply device according to claim 1 or 2, characterized in that a short-circuit when the. The switch is open when there is no drop in the output voltage induced in the secondary winding,
Reduction there said switch switching power supply device according to claim 1 or 2, characterized in that a short-circuit when the output voltage.

Images