JP3453016B2 - Multi-output 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 having a plurality of outputs consisting of a main output and a sub output, and in particular, the sub output is always stable even when the main output is in a light load or no load state. DC-D capable of supplying power
The present invention relates to a multi-output switching power supply device using a C converter.

[0002]

2. Description of the Related Art FIG. 9 is a diagram showing an example of a switching power supply device using a conventional forward converter type DC-DC converter and having a choke input type multiple output on the secondary side. In the figure, 1 is an input power source, 2
Is a control circuit, 3 is an output transistor, 4 is a main transformer, 5 is a first rectifying diode, 6 is a choke transformer, 8 is a first rectifying capacitor, 9 is a main output load, and 10 is a main output load.
Is an error amplifier, 11 is a second rectifying diode, 12 is a third rectifying diode, 13 is a second rectifying capacitor,
14 is a third rectifying capacitor, 15 is a freewheeling diode,
Reference numeral 16 is a switch, and 17 is a resonance capacitor. The control circuit 2, the output transistor 3, and the main transformer 4
Configures an input voltage conversion unit that converts the DC voltage E input from the input power supply 1 into a pulsed voltage.

Next, the operation will be described. The winding Lp on the primary side of the main transformer 4 and the output transistor 3 that performs on / off switching operation are connected in series,
A DC voltage from the input power supply 1 is applied to both ends thereof. The control circuit 2 modulates the output pulse width according to the error signal of the error amplifier 10 that detects the fluctuation of the main output voltage V ₁ output to the main output load 9, and the so-called PWM (P
The output transistor 3 is turned on / off by the ULS WIDTH MODELATION control to make the output voltage V ₁ of the main output constant. The primary side winding Lp and the secondary side winding Ls of the main transformer 4 are connected with the same polarity, and power is transmitted to the secondary side while the output transistor 3 is on.

Energy is simultaneously stored in the primary winding L ₁ of the choke transformer 6, that is, the choke coil by the current flowing at this time, and the rectification of the first rectifying diode 5 and the first rectifying capacitor 8 is performed. The circuit rectifies the pulsed voltage generated in the secondary winding L _S of the main transformer 4, and charges the first rectifying capacitor to the main output voltage V ₁ . At this time, since the output voltage from the secondary winding L ₂ or L _{3 of} the choke transformer 6 is blocked by the second rectifying diode 1 and the third rectifying diode 12, no power is supplied. Next, when the output transistor 3 is turned off, a current due to the back electromotive force flows through the freewheeling diode 15 into the primary winding L ₁ and the secondary windings L ₂ and L ₃ of the choke transformer 6. Therefore, the secondary winding L ₂ or L of the choke transformer 6
_The output obtained from _{3 is} obtained by storing power in the primary winding L ₁ of the choke transformer 6 when the output transistor 3 is on, but when the output transistor 3 is off, the primary winding L _{1 of the} choke transformer 6 is It is obtained as the back electromotive force generated in the.

On the secondary side of the choke coil 6, when the main output load 9 is sufficiently larger than the load on the secondary winding side of the choke transformer 6, the voltage applied to the primary side winding of the choke transformer 6 Is clipped to the main output voltage by turning on the free wheeling diode 15, so that a voltage that is a multiple of the number of turns of the main output voltage (a winding ratio of the primary side and the secondary side of the choke transformer 6) can be obtained. . However, when the main output load becomes a light load, the freewheeling diode 15 stops conducting, and when the current in the primary winding L ₁ of the choke transformer 6 becomes discontinuous, the secondary side of the choke transformer 6 stabilizes. The power is lost and the secondary winding L _{2 of} the choke transformer 6
The voltage of the sub-output obtained by rectifying the voltage generated in the L _3,
That is, the voltage across the second or third rectifying capacitor drops significantly.

When the main output is unloaded, no current flows in the primary winding L ₁ of the choke transformer 6, so that no voltage is generated in the secondary winding and the sub output Is not obtained, and as a result, the operation is stopped despite the secondary load of the choke coil 6. Therefore, when a standby state with a light load such as a television receiver is required, a standby power source is separately provided.

[0007]

Since the conventional multi-output switching power supply device using the DC-DC converter having the choke transformer is constructed as described above, the main output becomes a light load and the primary side current of the choke transformer. If the current becomes discontinuous or there is no load, the freewheeling diode will turn off and the secondary winding voltage of the choke transformer will drop significantly or not be output, so choke the power (that is, the sub power). There was a problem that stable supply from the secondary side of the transformer became impossible. this is,
When a light load standby state is required like a television receiver, it means that another power source for standby is required.

The present invention has been made in order to solve the above-mentioned problems, and even if the main output is either light load or no load, the sub-supply supplied from the secondary side of the choke transformer. The purpose of the present invention is to obtain a multi-output switching power supply device using a DC-DC converter whose output can always be stably supplied.

[0009]

A multi-output switching power supply device according to claim 1 of the present invention is a voltage conversion device for converting an input DC voltage into a pulsed voltage by turning on / off at a predetermined timing by a switching operation. Means and a primary winding to which the output voltage from the voltage converting means is applied at one end
A choke transformer having a secondary winding coupled to the secondary winding and outputting a voltage induced as a secondary output voltage in the secondary winding, and a positive electrode of the choke transformer at the other end of the primary winding. Connected to the rectifying capacitor that generates the main output voltage from the output voltage from the voltage conversion means, and the choke transistor during the period when the pulsed output voltage is not output from the voltage conversion means.
Short the one end of the primary winding and the negative electrode of the rectifying capacitor.
If the main output load is light or no load due to
The rectifying capacitor to the choke transformer primary winding
And a short-circuit means for causing a current to flow back .

According to a second aspect of the present invention, in the first aspect of the invention, the voltage converting means is composed of an input voltage converting section of a forward type DC-DC converter.

According to a third aspect of the present invention, in the multi-output switching power supply device of the first aspect, the voltage converting means is constituted by an input voltage converting section of a step-down chopper type DC-DC converter.

According to a fourth aspect of the present invention, in the first aspect of the invention, the voltage converting means is constituted by an input voltage converting section of a half bridge type DC-DC converter.

According to a fifth aspect of the present invention, in the multi-output switching power supply device according to the first aspect, the voltage converting means comprises an input voltage converting section of a push-pull type DC-DC converter.

A multi-output switching power supply device according to a sixth aspect of the present invention is the multi-output switching power supply device according to any one of the first to fifth aspects of the invention, wherein the short-circuit means is composed of a free wheeling diode and a switch transistor connected in parallel therewith. Is.

According to a seventh aspect of the present invention, in the multi-output switching power supply device according to any one of the first to fifth aspects, the short-circuit means is composed of a switch transistor.

According to an eighth aspect of the present invention, in the multi-output switching power supply device according to the second aspect, the short-circuit means is a voltage of the secondary winding of the main transformer used as the voltage converting means. Is detected to detect the period during which the output voltage is not output from the voltage converting means, and one end of the primary winding of the choke transformer and the negative electrode of the rectifying capacitor are short-circuited during the detected period. It is a thing.

According to a ninth aspect of the present invention, in the multi-output switching power supply device according to any one of the first to fifth aspects of the invention, an error amplifier for detecting a variation in the main output voltage is provided, and the voltage converting means is an error amplifier. The timing of the switching operation is controlled based on the output of the.

[0018]

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1. An embodiment of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals indicate that they are the same as or equivalent to the conventional ones. FIG. 1 is a diagram showing a configuration of a multi-output switching power supply device according to the first embodiment.
In the figure, 1 is an input power source for applying a DC voltage E to an input terminal AA ', 2 is a control circuit, 3 is an output transistor,
4 is a main transformer, 5 is a first rectifying diode, 6 is a choke transformer, 7 is a switch transistor, 8 is a first rectifying capacitor, 9 is a main output load, 10 is an error amplifier, 11 is a second rectifying diode, 12 is the third rectifying diode, 13 is the second rectifying capacitor, and 14 is the third
Is a freewheeling diode, 16 is a switch, and 17 is a resonance capacitor. The present embodiment basically uses a forward converter type DC-DC converter similar to that shown in FIG. 9 of a conventional example, and uses a choke input type secondary side switching power supply device of multiple outputs. However, the difference is that the switch transistor 7 is arranged in parallel with the free wheeling diode 15.
Here, the control circuit 2, the output transistor 3, and the main transformer 4 form an input voltage conversion unit that converts the input DC voltage into a pulsed voltage.

Next, the operation will be described with reference to FIG.
In FIG. 2, (a) shows the gate voltage waveform of the output transistor 3, and (b) shows the primary winding (L of the main transformer 4).
p) current waveform, (c) current waveform of the secondary winding Ls of the main transformer 4, (d) switch transistor supplied from the winding L _D wound on the secondary side of the main transformer 4. 7 is a drive voltage waveform of the gate, (e) is a voltage waveform of the primary winding L ₁ of the choke transformer 6, (f) is a current waveform of the primary winding L ₁ of the choke transformer 6, and (g) is It is a current waveform of the secondary winding L ₂ of the choke transformer 6.

In FIG. 2, the output transistor 3 is on during the period from t _{0 to} t ₁ . At this time, a forward voltage is applied to the primary winding L ₁ of the choke transformer 6,
The current of the primary side winding L ₁ has a waveform that rises primarily.
During the period from t _{1 to} t ₂ , the output transistor 3 is turned off, the reverse voltage is applied to the first rectifier diode 5 and turned off, a positive voltage is applied to the gate of the switch transistor 7, and the switch transistor 7 is turned on. . As a result, the voltage of the primary winding L ₁ of the choke transformer 6 is maintained at the main output voltage. The switch transistor 7 can be driven by the auxiliary winding L _D provided in the main transformer 4 in the case of a forward converter type switching power supply.

When the main output load is above a certain level in the switch transistor 7 and the primary winding L ₁ of the choke transformer 6, a current flows from the source to the drain of the switch transistor 7 when the main output load is light, or when there is no main output load. Even under load, the electric charge stored in the first rectifying capacitor 8 for main output rectification causes a current to flow from the drain to the source. Therefore, even when the main output is light load or no load,
Since current always flows continuously through the primary winding L ₁ of the choke transformer 6, the secondary output voltage excited in the secondary winding of the choke transformer 6 does not decrease. That is, the voltage of the sub output can be stably obtained.

Further, when the output transistor 3 is off, the voltage generated across the primary winding L ₁ of the choke coil 6 is always the main output voltage. Therefore, the voltage of the sub output generated on the secondary side of the choke transformer 6 is always a voltage proportional to the winding ratio of the primary side and the secondary side of the choke transformer 6 regardless of the load of the main output. Therefore, the error amplifier 10 detects a variation error of the main output load voltage V ₁ ,
By controlling the output pulse width of the control circuit 2 so that the main output voltage becomes constant, all output voltages including the sub output can be made constant. Although the switch transistor 7 is provided in parallel with the free wheeling diode 15 in the present embodiment, it goes without saying that the free wheeling diode 15 may be removed and the same operation and effect can be obtained by using only the switch transistor 7. .

Embodiment 2. Embodiment 2 of the present invention
Will be described with reference to the drawings. FIG. 3 is a diagram showing a configuration of a choke input type switching power supply device having multiple outputs using a step-down chopper method. In the figure, 1 is an input power source for applying a DC voltage E to an input terminal AA ', 2 is a control circuit, 3 is an output transistor, 6 is a choke transformer, 7 is a switch transistor, 8 is a first rectifying capacitor, 9 Is a main output load, 10 is an error amplifier, 11 is a second rectifying diode, 12 is a third rectifying diode, 13 is a second rectifying capacitor, 14 is a third rectifying capacitor, 15 is a freewheeling diode, and 16 is a switch. Is. Here, the control circuit 2 and the output transistor 3 configure an input voltage conversion unit that directly converts the input DC voltage into a pulsed voltage.

Next, the operation will be described. The output transistor 3 and the switch transistor 7 are ON / OFF driven by the output pulse signal of the control circuit 2, and as shown in FIG. 4, the switch transistor 7 is controlled to be OFF while the output transistor 3 is ON. When the output transistor 3 is turned on, a voltage in the forward direction is applied to the winding L ₁ on the primary side of the choke transformer 6, and the current flowing through the winding L ₁ on the primary side has a waveform that primarily increases.
Next, while the output transistor 3 is off, the control circuit 2 controls the switch transistor 7 to be on, so that the primary winding voltage of the choke transformer 6 is almost the main output voltage V _1. Maintained at.

When the main output load is above a certain level,
A current flows from the source to the drain of the switch transistor 7, and this current also flows in the primary side winding of the choke transformer 6, so that the first output for generating the main output voltage is generated even when the main output load is light or no load is applied. The electric charge stored in the rectifying capacitor 8 flows from the drain to the source. Therefore, as in the case of the first embodiment, even when the main output is lightly loaded or unloaded, a continuous current always flows in the primary winding L ₁ of the choke transformer 6, so that the choke is performed. The decrease in the secondary output voltage excited in the secondary winding of the transformer 6 is eliminated. That is, the voltage of the sub output can be stably obtained.
The voltage generated across the primary winding L ₁ of the choke coil 6 when the output transistor 3 is off is almost the main output voltage. Therefore, the secondary output voltage generated on the secondary side of the choke transformer 6 is always a voltage proportional to the winding ratio of the primary side and the secondary side of the choke transformer 6, regardless of the load of the main output.

Therefore, the error amplifier 10 detects the variation error of the main output load voltage V ₁ and controls the output pulse width of the control circuit 2 so that the main output voltage becomes constant, so that all the sub outputs including the sub output are detected. The output voltage of can be made constant. In the present embodiment, since the step-down chopper method is used as the converting means for converting the input DC voltage into the pulsed voltage, the main transformer 4 as shown in the first embodiment is not required, It has a feature that it is suitable for downsizing and weight reduction of the device. Although the switch transistor 7 is provided in parallel with the free wheeling diode 15 also in the present embodiment, it is needless to say that the same operation and effect can be obtained by removing the free wheeling diode 15 and using only the switch transistor 7.

Embodiment 3. FIG. 5 shows a configuration of a multi-output switching power supply device according to a third embodiment of the present invention. In the present embodiment, a so-called half-bridge type DC-DC converter is used and a secondary side has a choke input. In this type of switching power supply device, the sub output obtained from the secondary side of the choke transformer is stably supplied even when the main load is light load or no load. Hereinafter, a third embodiment of the present invention
Will be described with reference to the drawings. In FIG. 5, 1 is an input power source for applying a DC voltage E to input terminals A-A ', 2 is a control circuit, 4 is a main transformer, 5 is a first rectifying diode, 6 is a choke transformer, 7 is a switch transistor, 8 is the first rectifying capacitor, 9 is the main output load, 10
Is an error amplifier, 11 is a second rectifying diode, 12 is a third rectifying diode, 13 is a second rectifying capacitor,
14 is a third rectifying capacitor, 15 is a freewheeling diode,
Reference numeral 16 is a switch, 18 and 19 are bypass capacitors, 20 is a coupling capacitor, 21 is a fifth rectifying diode, 30 is a first output transistor, and 31 is a second output transistor. The control circuit 2, the main transformer 4, the output transistors 30 and 31, the bypass capacitors 18 and 19, and the coupling capacitor 20 form an input voltage conversion unit that converts the input DC voltage into a pulsed voltage.

Next, the operation will be described. Control circuit 2
As shown in FIG. 6, the first output transistor 30 and the second output transistor 31 are alternately turned on, and the switch transistor 7 is turned off while one of them is on. The output transistors 30 and 31 and the switch transistor 7 are controlled in operation. Therefore, while either the first output transistor 30 or the second output transistor 31 is on, a forward voltage is applied to the primary winding L ₁ of the choke transformer 6 and the primary voltage is applied. The current flowing through the side winding L ₁ has a waveform that rises primarily. Next, while the first output transistor 30 and the second output transistor 31 are both off, the control circuit 2 controls the switch transistor 7 to be on. The secondary winding voltage is maintained at approximately the main output voltage.

Therefore, when the main output load is above a certain level in the switch transistor 7 and the primary winding L ₁ of the choke transformer 6, a current flows from the source to the drain direction, and when the main output load is light or no load is applied. At some times, the electric charge stored in the first rectifying capacitor 8 for generating the main output voltage flows as a current from the drain to the source. As in the case of the first or second embodiment, even when the main output is lightly loaded or unloaded, a current continuously flows through the primary winding L ₁ of the choke transformer 6, The drop in the secondary output voltage induced in the secondary winding of the choke transformer 6 is eliminated. That is, the voltage of the sub output can be stably obtained. Further, the voltage generated at both ends of the primary winding L ₁ of the choke coil 6 when the output transistor 30 or 31 is off is almost the main output voltage. Therefore, the voltage of the sub output generated on the secondary side of the choke transformer 6 is always a voltage proportional to the winding ratio of the primary side and the secondary side of the choke transformer 6 regardless of the load of the main output.

Therefore, as in the case of the first or second embodiment, the main output load voltage V _{1 is set} by the error amplifier 10.
By controlling the output pulse width of the control circuit 2 so that the main output voltage becomes constant, all output voltages including the sub output can be made constant.
The present embodiment is a half-bridge type DC-D.
Since it is based on the switching power supply device using the C converter, there is an effect that the main output voltage and the sub output voltage with less ripple can be obtained as compared with the first or second embodiment. Further, also in the present embodiment, the switch transistor 7 is provided in parallel with the free wheeling diode 15, but it goes without saying that the free wheeling diode 15 may be removed and the same operation and effect can be obtained by using only the switch transistor 7.

Fourth Embodiment FIG. 7 is a diagram showing the configuration of a multi-output switching power supply device according to Embodiment 4 of the present invention. In the fourth embodiment, the switch transistor 7 in the third embodiment is driven by detecting the voltage of the secondary winding of the main transformer 4. In FIG. 7, 25 is a detection transistor, 26, 2
Reference numerals 7 and 28 denote detection resistors for detecting the voltage of the secondary winding of the main transformer 4. The control circuit 2, the main transformer 4, the output transistors 30 and 31, the bypass capacitors 18 and 19, and the coupling capacitor 20 form an input voltage conversion unit that converts the input DC voltage into a pulsed voltage.

Detecting resistor 26, detecting resistor 27, detecting resistor 2
The voltage of the secondary winding of the main transformer 4 is detected by 8, and when the voltage of the secondary winding is negative, that is, both the first output transistor 30 and the second output transistor 31 are off. Only when this happens, the detection transistor 25 is turned off and the switch transistor 7 is turned on. Other configurations and operations are basically the same as those of the third embodiment. That is, according to the present embodiment, the timing output of the control circuit 2 can be simplified as compared with the case of the third embodiment shown in FIG.

Embodiment 5. FIG. 8 is a diagram showing a configuration of a multi-output switching power supply device according to a fifth embodiment of the present invention. Although the case of the half bridge type switching power supply device has been described in the third or fourth embodiment, the full bridge type or push-pull type may be used. In the fifth embodiment, the primary side circuit 29 in the fourth embodiment is replaced with the push-pull method, and the operation and effect are the same as those in the third or fourth embodiment.

[0034]

According to claim 1 of the present invention, the voltage converting means for converting the input DC voltage into a pulsed voltage by turning on / off at a predetermined timing by a switching operation, and the voltage converting means. It has a primary winding to which an output voltage is applied at one end and a secondary winding coupled to the primary winding,
A choke transformer that outputs the voltage induced in the secondary winding as a sub output voltage and a positive electrode are connected to the other end of the primary winding of the choke transformer, and the main output voltage is obtained from the output voltage from the voltage conversion means. During the period when the pulsed output voltage is not output from the rectifying capacitor to be generated and the voltage conversion means.
One end of primary winding of choke transformer and rectifying capacitor
By short-circuiting the negative electrode of
Is a rectifying capacitor to a choke transformer when there is no load
Since the primary winding of the choke transformer is equipped with a short-circuit means for circulating a current, a continuous current always flows in the primary winding of the choke transformer even when the main output is lightly loaded or unloaded. The secondary output supplied from the secondary winding of the choke transformer has the effect of realizing a multi-output switching power supply device using a DC-DC converter that can always supply power stably.

According to a second aspect of the present invention, in the first aspect of the invention, the voltage converting means is a forward type DC-
Since it is composed of the input voltage converter of the DC converter, the forward method D has a sub output that can always supply power stably even if the main output is light load or no load.
There is an effect that a multi-output switching power supply device for a C-DC converter can be realized.

According to claim 3 of the present invention, in the invention of claim 1, the voltage converting means is a step-down chopper type DC.
-Because it is composed of the input voltage converter of the DC converter, it does not require a main transformer,
The secondary output supplied from the secondary winding can always stably supply electric power, and has an effect that a switching power supply device using a compact and lightweight DC-DC converter can be realized.

According to a fourth aspect of the present invention, in the first aspect of the invention, since the voltage converting means is composed of the input voltage converting section of the half-bridge type DC-DC converter, the main output is a light load. Alternatively, a half-bridge type D that has a secondary output that can always supply power stably even under no load and that also reduces the ripple of the output voltage
There is an effect that a multi-output switching power supply device for a C-DC converter can be realized.

According to a fifth aspect of the present invention, in the first aspect of the invention, the voltage converting means is a push-pull type DC.
-Because it is composed of the input voltage converter of the DC converter, it has a sub output that can always supply power stably even if the main output is light load or no load, and the ripple of output voltage is reduced. Pull system DC-DC
There is an effect that a multi-output switching power supply device for a converter can be realized.

According to claim 6 or 7 of the present invention,
In the invention according to any one of claims 1 to 5, since the short-circuit means uses the switch transistor, the DC-DC has a sub output capable of always supplying electric power stably even if the main output is light load or no load. There is an effect that a multi-output switching power supply device using a converter can be realized with a simple configuration.

According to claim 8 of the present invention, claim 2,
In any one of the inventions 4 and 5, the short-circuiting means detects the voltage of the secondary winding of the main transformer used for the voltage converting means to detect a period during which the output voltage is not output from the voltage converting means. Since the one end of the primary winding of the choke transformer and the negative electrode of the rectifying capacitor are short-circuited during this detected period, the configuration of the control circuit for controlling the switching operation of the voltage conversion means is simplified. effective.

According to a ninth aspect of the present invention, in any one of the first to fifth aspects of the present invention, an error amplifier for detecting the fluctuation of the main output voltage is provided, and the voltage converting means is based on the output of the error amplifier. Since the timing of the switching operation is controlled by using this, it has a sub output that can always supply power stably even when the main output is light load or no load, and the output voltage of the main output and the sub output is stable. There is an effect that a multi-output switching power supply device using a high quality DC-DC converter can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing operation waveforms in the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a second embodiment of the present invention.

FIG. 4 is a diagram showing operation waveforms in the second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a third embodiment of the present invention.

FIG. 6 is a diagram showing operation waveforms in the third embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a fifth embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a conventional multi-output switching power supply device.

[Explanation of symbols]

1 Input Power Source 2 Control Circuit 3 Output Transistor 4 Main Transformer 5 First Rectifying Diode 6 Choke Transformer 7 Switch Transistor 8 First Rectifying Capacitor 9 Main Output Load 10 Error Amplifier 11 Second Rectifying Diode 12 Third Rectifying Diode 13 2nd rectifying capacitor 14 3rd rectifying capacitor 15 freewheeling diode 16 switch
17 Resonance Capacitors 18, 19 Bypass Capacitor 20 Coupling Capacitor 21 Fifth Rectifying Diode 23, 24 Bypass Resistor 25 Detection Transistor 26, 27, 28
Detection resistor 27 Detection resistor 28 Detection resistor 29 Primary side circuit 30 First output transistor 31 Second output transistor

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 G05F 1/24 H02M 3/155

Claims (9)

(57) [Claims] 1. A voltage converting means for converting an inputted DC voltage into a pulsed voltage by turning on / off at a predetermined timing by a switching operation, and an output voltage from the voltage converting means is applied to one end.
A choke transformer having a secondary winding and a secondary winding coupled to the primary winding, which outputs a voltage induced in the secondary winding as a sub output voltage, and a positive electrode of the choke transformer. is the connection to the other end of the primary winding, above the output voltage and the rectifier capacitor to generate a main output voltage, not pulsed output voltage from the voltage conversion means is outputted during the period from the voltage converting means Above the primary winding of the choke transformer
By shorting one end to the negative electrode of the rectifying capacitor
If the main output load is light or no load,
Current from the capacitor to the primary winding of the above choke transformer
Multiple-output switching power supply device being characterized in that a shorting means for recirculating. 2. The voltage converting means is a forward type DC
The multi-output switching power supply device according to claim 1, wherein the multi-output switching power supply device comprises an input voltage conversion unit of a DC converter. 3. The voltage converting means is a step-down chopper type D
The multi-output switching power supply device according to claim 1, wherein the multi-output switching power supply device comprises an input voltage conversion unit of a C-DC converter. 4. The multi-output switching power supply device according to claim 1, wherein the voltage conversion means is composed of an input voltage conversion unit of a half bridge type DC-DC converter. 5. The voltage conversion means is a push-pull type D.
The multi-output switching power supply device according to claim 1, wherein the multi-output switching power supply device comprises an input voltage conversion unit of a C-DC converter. 6. The multi-output switching power supply device according to claim 1, wherein the short-circuit means includes a free wheeling diode and a switch transistor connected in parallel with the free wheeling diode. 7. The multi-output switching power supply device according to claim 1, wherein the short-circuit means is composed of a switch transistor. 8. The short-circuiting means detects the period of time when the output voltage is not output from the voltage converting means by detecting the voltage of the secondary winding of the main transformer used in the voltage converting means, and this is detected. 6. The multi-output switching power supply device according to claim 2, wherein one end of the primary winding of the choke transformer and the negative electrode of the rectifying capacitor are short-circuited during the above period. 9. The method according to claim 1, further comprising an error amplifier for detecting a fluctuation of the main output voltage, wherein the voltage conversion means controls the timing of the switching operation based on the output of the error amplifier. The multi-output switching power supply device according to any one of claims.