JPH11225474A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter capable of obtaining sufficient auxiliary power supply output with a small loss, even when a DC output to be supplied to a load is lowered depending on an output characteristic of the converter. SOLUTION: In this DC-DC converter, when a DC output voltage V0 to be supplied to a load 8 is lowered and a voltage generated on an auxiliary coil 4b of a transformer 4 become lower than the breakdown voltage, namely the specified voltage of a constant voltage diode 22 in a coil voltage detecting circuit 20 by the output characteristic of the converter, a transistor 19 is turned on, a voltage generated on the other auxiliary coil 4d is superimposed on the voltage generated on the auxiliary coil 4b, and a voltage higher than the voltage usually supplied from the auxiliary coil 4b is supplied to the power supply terminral of a control circuit 9. As a result, even when a DC output to be supplied to the load is lowered by the output characteristic of the converter, the sufficient power for driving the control circuit 9 is obtained with a small loss.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter, and more particularly to a DC-DC converter capable of obtaining a sufficient auxiliary power output with low loss even when the DC output supplied to a load is reduced due to the output characteristics of the converter. It is.

[0002]

2. Description of the Related Art DC-DC which has been widely used conventionally
FIG. 5 shows an example of the converter. This DC-DC converter includes a DC power supply 1 such as a battery or a capacitor input type rectifier circuit, and first and second switching elements connected between one end and the other end of the DC power supply 1 as first and second switching elements. Two FETs (field effect transistors) 2, 3; a transformer 4 having a primary winding 4a, a secondary winding 4c, and an auxiliary winding 4b; and a series connection with each of the first and second FETs 2, 3. A resonance circuit 6 composed of a primary winding 4a of a transformer 4, a resonance capacitor 5 and a resonance inductor formed integrally with the primary winding 4a, and a secondary of the transformer 4 A load 8 connected to the winding 4c via a rectifying / smoothing circuit 7, and an auxiliary winding 4b of the transformer 4;
, And control pulse signals V _G1 , V 2 having opposite phases to the gate terminals of the first and second FETs 2, 3.
_And a control circuit 9 for applying _G2 to alternately turn on / off the first and second FETs 2 and 3. Although not shown, the control circuit 9 first and second PWM (pulse width to control the pulse width of the control pulse signal V _G1, V _G2 to be applied to the gate terminals of FET2,3 depending on the terminal voltage of the load 8 Modulation) control means. The rectifying / smoothing circuit 7 includes rectifying diodes 10 and 11 and a smoothing capacitor 12. The voltage generated in the auxiliary winding 4b of the transformer 4 is used as driving power for the control circuit 9 through the rectifying diode 13 and the smoothing capacitor 14. Is supplied to the power supply terminal of.

In the DC-DC converter shown in FIG. 5, the DC input voltage E of the DC power supply 1 is intermittently turned on and off by turning on and off the first and second FETs 2 and 3 alternately. The DC voltage applied to the winding 4a, thereby rectifying and smoothing the voltage induced in the secondary winding 4c of the transformer 4 by the rectifying and smoothing circuit 7, is different from the DC input voltage E of the DC power supply 1. _While supplying _O to the load 8,
The voltage generated in the auxiliary winding 4b of the transformer 4 is rectified and smoothed by the rectifier diode 13 and the smoothing capacitor 14, and drive power is supplied to the control circuit 9. When the terminal voltage of the load 8 is low, the pulse widths of the control pulse signals V _G1 and V _G2 applied to the gate terminals of the first and second FETs 2 and 3 are reduced by the PWM control means in the control circuit 9. Widened,
When the terminal voltage of the load 8 is high, the first and second FETs
A control pulse signal V _{G1 applied} to each of the gate terminals 2 and 3;
The pulse width of V _G2 becomes narrow. Thereby, the DC output voltage V _O supplied to the load 8 is stabilized. Furthermore,
Due to the resonance action of the resonance circuit 6, the first and second FETs
Since the rising and falling of the switching voltage waveforms or the switching current waveforms of the second and third FETs are sinusoidal, zero voltage switching (ZVS) and zero current switching (ZCS) are performed when the first and second FETs 2 and 3 are turned on and off. ), And the switching loss is reduced.

[0004]

In the DC-DC converter shown in FIG. 5, the characteristic of the DC output supplied to the load 8 is a constant current characteristic as shown in FIG. 6 or a constant power characteristic as shown in FIG. In the case of having the characteristics, etc., the DC output voltage V _O supplied to the load 8 according to the increase of the current I _O flowing through the load 8
The first and second FETs 2 and 3 are turned on so that
Controlled off. Accordingly, the voltage generated in the primary winding 4a of the transformer 4 decreases, so that the voltage generated in the auxiliary winding 4b also decreases. Therefore, in the DC-DC converter shown in FIG. 5 in the above case, the voltage generated in the auxiliary winding 4b of the transformer 4 decreases in proportion to the decrease in the DC output voltage V _O supplied to the load 8, so that the control circuit However, there was a disadvantage that sufficient power could not be obtained to drive No. 9.
In order to solve such a defect, conventionally, for example, as shown in FIG. 8, the voltage of the auxiliary winding 4b of the transformer 4 is set high, and the voltage generated in the auxiliary winding 4b is adjusted by the rectifier diode 13 and the smoothing capacitor 14. After the rectification and smoothing, the voltage was adjusted to a voltage sufficient for driving the control circuit 9 by the dropper circuit 15. In FIG. 8, reference numeral 16 denotes a capacitor for coping with a steep voltage change that cannot be handled by the dropper circuit 15. However, the DC shown in FIG.
In the DC converter, the product of the difference voltage between the voltage generated in the auxiliary winding 4b of the transformer 4 and the set voltage of the dropper circuit 15 and the current flowing in the circuit between the auxiliary winding 4b and the dropper circuit 15 of the transformer 4 is There was a drawback of power loss.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a DC-DC converter capable of obtaining a sufficient auxiliary power supply output with low loss even when the DC output supplied to a load is reduced due to the output characteristics of the converter.

[0006]

SUMMARY OF THE INVENTION DC-DC according to the present invention
The converter applies the DC voltage of the DC power supply to the primary winding of the transformer intermittently or alternately by the on / off operation of at least one switching element, and outputs the voltage generated in the primary winding of the transformer or the transformer. Rectifying and smoothing the voltage induced in the secondary winding by a rectifying and smoothing circuit to supply a DC output of a voltage different from the DC voltage of the DC power supply to a load, and a voltage generated in an auxiliary winding of the transformer. From the auxiliary power supply. In one embodiment of the DC-DC converter, another auxiliary winding that generates a voltage higher than the voltage generated in the auxiliary winding of the transformer is provided in the transformer, and is normally generated in the auxiliary winding. The auxiliary power supply output is supplied by a voltage, and a voltage generated in the other auxiliary winding when a voltage generated in the auxiliary winding of the transformer becomes equal to or less than a specified value due to a decrease in a DC output supplied to the load. The auxiliary power supply output is supplied in a superimposed manner. When the DC output supplied to the load is normal, the auxiliary power supply output is supplied by the voltage generated in the auxiliary winding of the transformer, and the DC output supplied to the load decreases to specify the voltage generated in the auxiliary winding of the transformer. When the voltage is less than the value, the voltage of the other auxiliary winding that generates a voltage higher than the voltage generated in the auxiliary winding is superimposed on the voltage generated in the auxiliary winding and the auxiliary power supply output is supplied, so the supply to the load Regardless of the DC output to be performed, an auxiliary power supply output always exceeding a specified value can be obtained. Therefore, a voltage adjusting means such as a dropper circuit that generates a power loss becomes unnecessary, and even when the DC output supplied to the load is reduced due to the output characteristics of the converter, a sufficient auxiliary power supply output can be obtained with low loss. .

In a modified embodiment of the DC-DC converter according to the present invention, another auxiliary winding for generating a voltage having the same polarity as the voltage generated in the auxiliary winding of the transformer is provided in series with the auxiliary winding. At this time, the auxiliary power supply output is supplied by a voltage generated in the auxiliary winding, and the auxiliary power supply output is supplied when the voltage generated in the auxiliary winding of the transformer becomes lower than a specified value due to a decrease in the DC output supplied to the load. The auxiliary power supply is supplied by a sum voltage of a voltage generated in the winding and a voltage generated in the other auxiliary winding. When the DC output supplied to the load is normal, the auxiliary power supply output is supplied by the voltage generated in the auxiliary winding of the transformer, and the DC output supplied to the load decreases to specify the voltage generated in the auxiliary winding of the transformer. If the value is less than the value, the auxiliary power supply output is supplied by the sum voltage of the voltage generated in the auxiliary winding and the voltage generated in the other auxiliary windings. The above auxiliary power output can be obtained.
Therefore, a voltage adjusting means such as a dropper circuit that generates a power loss becomes unnecessary, and even when the DC output supplied to the load is reduced due to the output characteristics of the converter, a sufficient auxiliary power supply output can be obtained with low loss. . Furthermore,
In this embodiment, the voltages generated in the two auxiliary windings are rectified and smoothed by a rectifying element and a smoothing capacitor, respectively.
When an auxiliary power supply output is obtained from one or both of the smoothing capacitors, there is an advantage that the withstand voltage of each smoothing capacitor can be reduced.

In another embodiment of the DC-DC converter according to the present invention, a plurality of rectified voltages having different voltage levels are formed from the voltage generated in the auxiliary winding of the transformer, and the rectified voltages having different voltage levels are normally formed. The auxiliary power supply output is supplied by the rectified voltage having a low voltage level, and when the voltage generated in the auxiliary winding of the transformer due to a decrease in the DC output supplied to the load becomes equal to or less than a specified value, the plurality of different powers are output. The auxiliary power supply output is supplied by the rectified voltage having a higher voltage level among the voltage levels. When the DC output supplied to the load among the rectified voltages of a plurality of different voltage levels formed from the voltage generated in the auxiliary winding of the transformer is normal, the auxiliary power supply output is supplied by the rectified voltage of the low voltage level, When the DC output supplied to the transformer drops and the voltage generated in the auxiliary winding of the transformer falls below the specified value, the auxiliary power supply output is supplied by a high voltage level rectified voltage, so regardless of the DC output supplied to the load It is possible to always obtain an auxiliary power supply output exceeding a specified value. Therefore, a voltage adjusting means such as a dropper circuit that generates a power loss becomes unnecessary, and even when the DC output supplied to the load is reduced due to the output characteristics of the converter, a sufficient auxiliary power supply output can be obtained with low loss. . Further, in this embodiment, there is no need to add another auxiliary winding to the transformer, so that there is an advantage that the transformer can be reduced in size and weight and the circuit configuration can be simplified.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a DC-DC converter according to the present invention will be described below with reference to FIGS. However, in FIG. 1, substantially the same parts as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted. DC of this embodiment
As shown in FIG. 1, the DC converter shown in FIG.
In C-DC converter, the other auxiliary winding 4d of turns N ₁ of the auxiliary winding often turns N ₂ than 4b provided in the transformer 4, the other auxiliary winding 4d rectifier diode 17, a smoothing capacitor 18 and transistor 19, it is connected to both ends of the smoothing capacitor 14 to detect a voltage generated in the auxiliary winding 4b, and when the detected voltage becomes equal to or lower than a specified value, gives an output signal to a base terminal of the transistor 19 to thereby provide a transistor 19 Is provided with a winding voltage detection circuit 20 for turning on the power supply. In FIG. 1, 20a and 20b indicate winding voltage input terminals, and 20c indicates a signal output terminal. As shown in FIG. 2, the winding voltage detection circuit 20 includes a resistor 21, a constant voltage diode 22, and a current limiting resistor 23 connected in series between the winding voltage input terminals 20a and 20b, and a base terminal. A transistor 24 connected to a connection point between the resistor 21 and the constant voltage diode 22 and having an emitter terminal connected to the winding voltage input terminal 20a and a collector terminal connected to the signal output terminal 20c; It comprises a resistor 25 connected between the connection point of the voltage input terminal 20b and the collector terminal of the transistor 24. By appropriately selecting the breakdown voltage of the constant voltage diode 22, the auxiliary winding 4
The specified value of the voltage generated in b can be set. The other configuration is substantially the same as the DC-DC converter shown in FIG.

In the above configuration, when the DC output voltage V _O supplied to the load 8 is normal, the voltage generated in the auxiliary winding 4b of the transformer 4 is a specified value, that is, a constant value in the winding voltage detection circuit 20. Since the voltage is higher than the breakdown voltage of the voltage diode 22, the transistor 24 is in the ON state, and nothing is output from the signal output terminal 20c of the winding voltage detection circuit 20. Therefore, since the transistor 19 is off, the voltage generated in the auxiliary winding 4b of the transformer 4 normally includes the rectifier diode 13 and the smoothing capacitor 14.
Is supplied to the power supply terminal of the control circuit 9 through the
Is driven. The output characteristics of the DC-DC converter, such as the constant current characteristic and the constant power characteristic, depend on the first and second FETs 2,
When the DC output voltage V _O supplied to the load 8 decreases, the voltage generated in the auxiliary winding 4b of the transformer 4 also decreases. The voltage generated in the auxiliary winding 4b of the transformer 4 is equal to the winding voltage detection circuit 2.
When the voltage falls below the breakdown voltage of the constant voltage diode 22 within 0, the transistor 24 is turned off, and a signal is output from the signal output terminal 20c. At this time, the transistor 19 is turned on, and the voltage generated in the other auxiliary winding 4d of the transformer 4 is superimposed on the smoothing capacitor 14 via the rectifier diode 17 and the smoothing capacitor 18. Here, the number of turns N ₂ of other auxiliary winding 4d auxiliary winding 4b
For more than the number of turns N _1, it becomes higher than the voltage voltage generated in the other auxiliary winding 4d is generated in the auxiliary winding 4b. As a result, a voltage higher than the voltage supplied by the auxiliary winding 4b is generated across the smoothing capacitor 14, and this voltage is supplied to the power supply terminal of the control circuit 9, and the control circuit 9 is driven.

As described above, in this embodiment, when the DC output voltage V _O supplied to the load 8 is normal, the voltage generated in the auxiliary winding 4b of the transformer 4 is
The power is supplied to the power supply terminal of the control circuit 9 via the smoothing capacitor 14. The DC output voltage V _O supplied to the load 8 is reduced due to the output characteristics of the DC-DC converter, and the voltage generated in the auxiliary winding 4 b of the transformer 4 breaks down the constant voltage diode 22 in the winding voltage detection circuit 20. Voltage,
That is, when the voltage falls below the specified value, the voltage generated in the other auxiliary winding 4d is superimposed on the voltage generated in the auxiliary winding 4b, and a voltage higher than the voltage normally supplied is supplied to the power supply terminal of the control circuit 9. You. Therefore, regardless of the DC output voltage V _O supplied to the load 8, the driving power of the control circuit 9 which is always equal to or higher than the specified value can be obtained, so that the dropper circuit 15 which generates the power loss as shown in FIG. This eliminates the need for the voltage adjusting means, so that even if the DC output supplied to the load 8 decreases due to the output characteristics of the converter, sufficient power for driving the control circuit 9 can be supplied with low loss.

The DC-DC converter of the embodiment shown in FIG. 1 can be changed. For example, the DC-DC converter of the embodiment shown in FIG. 3 includes another auxiliary winding 4 that generates a voltage having the same polarity as the voltage generated in the auxiliary winding 4b of the transformer 4.
e is provided in series with the auxiliary winding 4b, and a rectifier diode 17 and a smoothing capacitor 18 are connected in series between the other auxiliary winding 4e and a connection point of the rectifier diode 13 and the smoothing capacitor 14. The transistor 1 is connected between the connection point of the capacitor 18 and the power supply terminal of the control circuit 9.
9 and the rectifier diode 13 and the smoothing capacitor 1
A short-circuit prevention diode 26 is connected between the connection point 4 and the emitter terminal of the transistor 19. Other configurations are substantially the same as those of the embodiment shown in FIG.

[0013] In the circuit of FIG. 3, when the DC output voltage V _O supplied to the load 8 is normal, since the transistor 24 the same manner as in the case in winding voltage detecting circuit 20 of FIG. 1 is in the ON state, No signal is output from the signal output terminal 20c, and the transistor 19 is off. For this reason, the voltage generated in the auxiliary winding 4b of the transformer 4 is normally supplied to the power supply terminal of the control circuit 9 via the rectifier diode 13 and the smoothing capacitor 14, and the control circuit 9 is driven.
The DC output voltage V _O supplied to the load 8 decreases due to the output characteristics such as the constant current characteristic and the constant power characteristic of the DC-DC converter, and the voltage generated in the auxiliary winding 4 b of the transformer 4 is changed to the winding voltage detection circuit 20. When the voltage falls below the breakdown voltage of the constant voltage diode 22, the transistor 24 is turned off and a signal is output from the signal output terminal 20c. As a result, the transistor 19 is turned on, and the sum of the voltages of the smoothing capacitors 14 and 18 connected to the auxiliary winding 4b and the other auxiliary winding 4e of the transformer 4 is supplied to the power supply terminal of the control circuit 9. , The control circuit 9 is driven. Therefore, in the embodiment shown in FIG.
As in the case shown in (1), the voltage adjusting means such as the dropper circuit 15 is unnecessary, and even when the DC output supplied to the load 8 is reduced due to the output characteristics of the converter, sufficient power for driving the control circuit 9 is reduced. Can be supplied with loss. Further, the embodiment shown in FIG. 3 has an advantage that the withstand voltage of each of the smoothing capacitors 14 and 18 can be reduced as compared with the case shown in FIG.

The DC-DC converter of the embodiment shown in FIG. 4 is the same as the DC-DC converter shown in FIG.
The rectifier diode 27 and the smoothing capacitor 28 are connected in series between the connection point of the transformer 4 and the connection point of the auxiliary winding 4b and the rectifier diode 13, and the connection point of the rectifier diode 27 and the smoothing capacitor 28 and the rectifier diode 13 and The voltage doubler rectifier diode 29 and the transistor 19 are connected in series between the connection point of the smoothing capacitor 14 and the connection point of the voltage multiplier rectifier diode 29 and the transistor 19 and the connection point of the rectifier diode 27 and the smoothing capacitor 14. The doubler smoothing capacitor 30 is connected. The rectifier diode 27, the smoothing capacitor 28, the voltage doubler rectifier diode 29, and the voltage doubler smoothing capacitor 30 in FIG. 4 are connected to the voltage level of the sum of the voltage of the auxiliary winding 4b of the transformer 4 and the charging voltage of the smoothing capacitor 28, The voltage doubler rectifier circuit generates a rectified voltage having a voltage level approximately twice the voltage of the auxiliary winding 4b from both ends of the voltage doubler smoothing capacitor 30. Other configurations are substantially the same as those of the embodiment shown in FIG.

In the circuit shown in FIG. 4, when the potential at the upper end of the auxiliary winding 4b of the transformer 4 is a positive half cycle with respect to the lower end, a smoothing capacitor 28 through the rectifier diode 27 has a polarity shown in FIG. Is charged to approximately the maximum value.
Next, in the half cycle in which the potential of the upper end of the auxiliary winding 4b of the transformer 4 is negative with respect to the lower end, the sum voltage of the voltage of the auxiliary winding 4b and the charging voltage of the smoothing capacitor 28 is doubled through the voltage doubler rectifier diode 29. The pressure smoothing capacitor 30 is charged. Therefore, the doubler smoothing capacitor 30 is charged with a voltage that is approximately twice the maximum value of the voltage of the auxiliary winding 4b of the transformer 4. At this time, the rectifier diode 13 becomes conductive, so that the rectifier diode 13
Through the auxiliary winding 4 with the polarity shown in FIG.
The battery is charged to almost the maximum value of the voltage of b. As described above, rectified voltages of two different voltage levels are formed from the voltage generated in the auxiliary winding 4b of the transformer 4, and the voltages of the rectified voltages from the smoothing capacitor 14 and the doubler smoothing capacitor 30 are substantially the same as those of the auxiliary winding 4b. And a rectified voltage of approximately twice the voltage level is output.

Here, when the DC output voltage V _O supplied to the load 8 is normal, the transistor 24 in the winding voltage detection circuit 20 is on, so that the signal output terminal 20 c
Does not output anything, and the transistor 19 is off. Therefore, a rectified voltage having substantially the same voltage level as the voltage generated in the auxiliary winding 4b of the transformer 4 is normally supplied from the auxiliary winding 4b to the rectifier diode 13 and the smoothing capacitor 14b.
Is supplied to the power supply terminal of the control circuit 9 through the
Is driven. The DC output voltage V _O supplied to the load 8 decreases due to the output characteristics such as the constant current characteristic and the constant power characteristic of the DC-DC converter, and the voltage generated in the auxiliary winding 4 b of the transformer 4 is changed to the winding voltage detection circuit 20. Constant voltage diode 2 inside
When the voltage falls below the breakdown voltage of transistor 2, transistor 2
4 is turned off, and a signal is output from the signal output terminal 20c. As a result, the transistor 19 is turned on, and the voltage generated in the auxiliary winding 4b of the transformer 4 becomes approximately 2
The rectified voltage of the double voltage level is supplied from the voltage doubler smoothing capacitor 30 to the power supply terminal of the control circuit 9, and the control circuit 9 is driven. Therefore, also in the embodiment shown in FIG.
As in the case shown in FIG. 1, no voltage adjusting means such as the dropper circuit 15 is required, and the load 8
Even when the DC output supplied to the power supply decreases, sufficient power for driving the control circuit 9 can be supplied with low loss. Further, in the embodiment shown in FIG.
As shown in the figure, another auxiliary winding 4d (4
Since it is not necessary to add e), there is an advantage that the transformer 4 can be reduced in size and weight and the circuit configuration can be simplified as compared with the cases shown in FIGS.

The embodiments of the present invention are not limited to the above three embodiments, and various modifications are possible. For example,
In the embodiment shown in FIG. 4, a voltage doubler rectifier circuit including a rectifier diode 27, a smoothing capacitor 28, a voltage doubler rectifier diode 29, and a voltage doubler smoothing capacitor 30 is added between the auxiliary winding 4b of the transformer 4 and the transistor 19. When the transistor 19 is turned on, the rectifier diode 13 and the smoothing capacitor 14
Although the form in which the rectified voltage of a voltage level higher than the rectified voltage generated through the power supply terminal is supplied to the power supply terminal of the control circuit 9 is shown, the present invention is not limited to the voltage doubled rectifier circuit,
It is also possible to use a multiple voltage rectifier circuit such as a Cockcroft-Walton circuit. Also, depending on the operating voltage of the control circuit 9, a voltage doubler rectifier circuit is connected instead of the rectifier circuit composed of the rectifier diode 13 and the smoothing capacitor 14, and a triple voltage rectifier is connected between the auxiliary winding 4b of the transformer 4 and the transistor 19. It is also possible to connect the above multiple voltage rectifier circuit. Further, in each of the above-described embodiments, the resonance reactor constituting the resonance circuit 6 is configured by the inductance formed integrally with the primary winding 4a of the transformer 4, but the resonance reactor is an independent inductance. You may comprise. Further, in each of the above embodiments, the mode in which the FET is used as the switching element has been described, but another switching element such as a bipolar transistor or a thyristor may be used. Further, in each of the above embodiments, the example in which the present invention is applied to the half-bridge type resonant DC-DC converter is shown.
The present invention can also be applied to a C-DC converter or a flyback or forward resonance DC-DC converter having one switching element. Further, the present invention is not limited to the resonance type converter, but includes a normal DC having a transformer.
Needless to say, the present invention can be applied to a DC converter.

[0018]

As described above, according to the present invention, a sufficient auxiliary power supply output can be obtained with low loss even when the DC output supplied to the load is reduced due to the output characteristics of the converter. Regardless of the state, the internal loss of the DC-DC converter can be reduced, and the DC-DC converter can always be operated stably.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a DC-DC converter according to the present invention.

FIG. 2 is an electric circuit diagram showing an internal configuration of a winding voltage detection circuit.

FIG. 3 is an electric circuit diagram showing a modified embodiment of the present invention.

FIG. 4 is an electric circuit diagram showing another embodiment of the present invention.

FIG. 5 is an electric circuit diagram showing a conventional DC-DC converter.

FIG. 6 is a graph showing a constant current output characteristic of the converter.

FIG. 7 is a graph showing constant power output characteristics of a converter.

8 is an electric circuit diagram showing an example of improvement of an auxiliary power supply output in the circuit of FIG.

[Explanation of symbols]

1. . . DC power supply, 2. . . 2. first FET (first switching element); . . 3. second FET (second switching element); . . Transformer, 4a. . . Primary winding, 4b. . . Auxiliary winding, 4c. . . Secondary winding, 4d, 4
e. . . 4. other auxiliary windings; . . Resonance capacitor,
6. . . 6. resonance circuit; . . 7. rectifying and smoothing circuit; . . Load, 9. . . Control circuit, 10, 11. . . Rectifier diode, 12. . . 12. smoothing capacitor; . . Rectifier diode, 14. . . 14. smoothing capacitor; . . Dropper circuit; 16. . . Capacitor, 17. . . Rectifier diode, 18. . . Smoothing capacitor, 19. . . Transistor, 20. . . Winding voltage detection circuit, 20a, 20b. . .
Winding voltage input terminal, 20c. . . Signal output terminal, 2
1. . . Resistance, 22. . . Constant voltage diode, 2
3. . . 24. current limiting resistor; . . Transistor, 2
5. . . Resistance, 26. . . Diode for short circuit prevention, 2
7. . . Rectifier diode, 28. . . Smoothing capacitor,
29. . . Doubler rectifier diode, 30. . . Doubler smoothing capacitor

Claims (3)

[Claims] A DC voltage of a DC power supply is intermittently or alternately applied to a primary winding of a transformer by an on / off operation of at least one switching element, and a voltage generated in the primary winding of the transformer or The voltage induced in the secondary winding of the transformer is rectified and smoothed by a rectifying / smoothing circuit to supply a DC output of a voltage different from the DC voltage of the DC power supply to a load, and to be generated in an auxiliary winding of the transformer. In a DC-DC converter for extracting an auxiliary power supply output from a voltage to be applied, another auxiliary winding that generates a voltage higher than a voltage generated in an auxiliary winding of the transformer is provided in the transformer. The auxiliary power supply output is supplied by the voltage generated in the transformer, and the voltage generated in the auxiliary winding of the transformer due to the decrease in the DC output supplied to the load becomes lower than a specified value. By superimposing the voltage generated in the other auxiliary winding and supplying the auxiliary power output DC-
DC converter. 2. A DC voltage of a DC power supply is intermittently or alternately applied to a primary winding of a transformer by an on / off operation of at least one switching element, and a voltage generated in the primary winding of the transformer or The voltage induced in the secondary winding of the transformer is rectified and smoothed by a rectifying / smoothing circuit to supply a DC output of a voltage different from the DC voltage of the DC power supply to a load, and to be generated in an auxiliary winding of the transformer. A DC-DC converter for extracting an auxiliary power supply output from a voltage to be applied, wherein another auxiliary winding that generates a voltage having the same polarity as the voltage generated in the auxiliary winding of the transformer is provided in series with the auxiliary winding;
Normally, the auxiliary power supply output is supplied by the voltage generated in the auxiliary winding, and when the voltage generated in the auxiliary winding of the transformer becomes equal to or less than a specified value due to a decrease in the DC output supplied to the load, A DC-DC converter, wherein the auxiliary power supply output is supplied by a sum voltage of a voltage generated in an auxiliary winding and a voltage generated in the another auxiliary winding. 3. A DC voltage of a DC power supply is intermittently or alternately applied to a primary winding of a transformer by an on / off operation of at least one switching element, and a voltage generated in the primary winding of the transformer or The voltage induced in the secondary winding of the transformer is rectified and smoothed by a rectifying / smoothing circuit to supply a DC output of a voltage different from the DC voltage of the DC power supply to a load, and to be generated in an auxiliary winding of the transformer. A rectified voltage of a plurality of different voltage levels is formed from a voltage generated in an auxiliary winding of the transformer, and a lower voltage of the plurality of different voltage levels is normally used. The auxiliary power supply output is supplied by the rectified voltage of a level, and a voltage generated in the auxiliary winding of the transformer due to a decrease in the DC output supplied to the load is defined. DC-DC, characterized by supplying the auxiliary power output by the rectified voltage of the high voltage level of the plurality of different voltage levels when the following
converter.