JP2002291248A - Flyback switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an apparatus and improve the converting efficiency. SOLUTION: A power supply 1 is provided with transformers 13, 24, rectifier circuits 11, 12, 21 for generating pulse voltage VP1 , VP2 , a filter circuit 23 for filtering the pulse voltage VP2 and generating a DC voltage VDC, a switching element 14 connected to a primary winding 13a of the transformer 13 in series and synchronized with a drive signal SD1 and switching the pulse voltage VP1 , and a switching element 25 connected to a primary winding 24a of the transformer 24 in series and synchronized with a drive signal SD2 and switching the DC voltage VDC. The power supply 1 rectifies and combines voltages induced in secondary windings 13b, 24b of the transformers 13, 24 and generates an output voltage V0 , and is also provided with a control circuit 16 for controlling the pulse width of the drive signal SD1 in response to the voltage of the output voltage V0 and a control circuit 27 for controlling a pulse width of the drive signal SD2 in response to the voltage of the pulse voltage VP2 .

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 for converting power from AC to DC, and more particularly to a flyback switching power supply capable of converting power at a high power factor.

[0002]

2. Description of the Related Art Generally, in a capacitor-input type switching power supply, input current harmonics are generated when an input current flows in a pulse shape. Therefore, when the power of the switching power supply is large or when a plurality of switching power supplies are used at the same time, the effect of this harmful harmonic component on the commercial power system cannot be ignored, and power equipment due to the occurrence of harmonic induction failure or voltage waveform distortion is not negligible. It causes various problems such as heating. For this reason, in recent years, reduction of input current harmonics has been demanded, and various switching power supplies of a power factor improvement type capable of reducing input current harmonics have been proposed. As this type of switching power supply, there are many proposed two-converter and one-converter systems.
The two-converter method has a problem that the overall conversion efficiency is low even if the efficiency of each stage is high, and the one-converter method has a problem that the output ripple is large. Therefore, a power supply device 31 shown in FIG. 3 has been developed to solve these problems while reducing input current harmonics.

[0003] As shown in FIG.
A flyback type configuration is provided which includes a step-up / step-down converter circuit 32 for power factor improvement and a step-up / step-down converter circuit 33 of a capacitor input type, and one circuit is commonly used by both circuits 32 and 33. Specifically, the power supply device 31 includes first and second transformers 35 and 36 for switching, and a circuit constituting a part of the step-up / step-down converter circuit 32 on the primary circuit side of both transformers 35 and 36. And diodes 11 and 12 for rectifying the AC voltage VAC of the AC power supply PS to generate a first pulsating voltage VP1. Further, on the primary circuit side, as a circuit constituting a part of the buck-boost converter circuit 33, the AC voltage VAC
A diode stack 21 that rectifies the current to generate a second pulsating voltage VP2 having the same phase and the same voltage waveform as the first pulsating voltage VP1, a current limiting resistor 22, and a second pulsating voltage VP2.
And a switching element (for example, FET) 34 for smoothing the voltage to a DC voltage VDC.

On the other hand, on the secondary circuit side of the first transformer 35, a rectifying diode 15 and a smoothing capacitor 1 are provided.
7 is provided, and a rectifying diode 26 is provided on the secondary circuit side of the second transformer 36. Also,
A switching control circuit 37 for PWM controlling the pulse width of the drive signal SD for the switching element 34 based on the output voltage VO is provided between the secondary circuit and the primary circuit of each of the transformers 35 and 36.

In this power supply device 31, a diode 11,
12 rectifies the AC voltage VAC shown in FIG. 4A to generate a first pulsating voltage VP1 shown in FIG.
The diode stack 21 and the capacitor 23 generate a DC voltage VDC by rectifying and smoothing the AC voltage VAC. Also, during the high voltage period (peak period) of the first pulsating voltage VP1, the buck-boost converter circuit 32 mainly generates the output voltage VO. In this case, the first pulsating voltage V
At the maximum voltage VMAX of P1, the ratio of the current value of the current I11 flowing through the primary winding 35a of the first transformer 35 to the current value of the current I12 flowing through the primary winding 36a of the second transformer 36 is, for example, It is specified in advance so as to be 9: 1. For this purpose, the two transformers 35 and 36 have, for example, the inductance and the number of turns of the primary winding 35a of the first transformer 35 as L35a and N35a, respectively, and the inductance and the winding of the secondary winding 35b of the first transformer 35, respectively. The number of turns is L35b and N35b, respectively, the inductance and number of turns of the primary winding 36a of the second transformer 36 are L36a and N36a, respectively, and the inductance and number of turns of the secondary winding 36b of the second transformer 36 are respectively. When L36b and N36b are set, the following equation and the specification satisfying the equation are manufactured. L35a: L36a = 1: 9 Expression N35a: N35b = N36a: N36b Expression

Under such specifications, for example, if the switching element 34 is turned on when the first pulsating voltage VP1 is at the maximum voltage VMAX during the positive cycle of the AC voltage VAC (the drive signal SD) Is output), the current I11 is supplied to the diode 11, the primary winding 35 of the transformer 35.
a, a switching element 34, and a current path including a diode in the diode stack 21. Thereby, energy is stored in the transformer 35. Next, when the switching element 34 is controlled to be turned off (when the drive signal SD is stopped), the diode 15 and the capacitor 17 generate the output voltage VO by rectifying and smoothing the induced voltage of the secondary winding 35b. I do.

On the other hand, when the voltage of the first pulsating voltage VP1 gradually decreases, the buck-boost converter circuit 32 outputs the output voltage VO.
The input voltage for generating is reduced. Therefore, the buck-boost converter circuit 33 gradually contributes to the generation of the output voltage VO. Eventually, during the low voltage period (valley period) of the first pulsating voltage VP1, the first pulsating voltage VP1
Is the output voltage VO of the buck-boost converter circuit 32
Is lower than the threshold voltage VS at which the output voltage VO can be generated, the generation of the output voltage VO by the buck-boost converter circuit 32 becomes almost impossible. Therefore, during this low voltage period, the buck-boost converter circuit 33 mainly generates the output voltage VO.

Therefore, during the low voltage period of the first pulsating voltage VP1, the current I12 based on the charging voltage of the capacitor 23 is controlled when the switching element 34 is turned on.
Flows through a current path including the positive terminal of the capacitor 23, the primary winding 36a of the second transformer 36, the switching element 34, and the negative terminal of the capacitor 23. Thereby, energy is stored in the second transformer 36. Next, when the switching element 34 is turned off, the diode 26 and the capacitor 17 rectify and smooth the induced voltage of the secondary winding 36b to generate the output voltage VO. As a result, during the period when the voltage of the first pulsating voltage VP1 exceeds the threshold voltage VS, the output voltage VO is mainly generated by the current I11 shown in FIG. 4C, and the voltage of the first pulsating voltage VP1 is Threshold voltage VS
During the lower voltage period, the output voltage VO is mainly generated by the current I12 shown in FIG. The switching control circuit 37 stabilizes the output voltage VO to a predetermined voltage over one cycle of the AC voltage VAC by PWM controlling the pulse width of the drive signal SD for the switching element 34.

On the other hand, as shown in FIG. 4E, the input current I12IN for charging the capacitor 23 has the second pulsating voltage V
Near the point where P2 reaches the maximum voltage VMAX, it flows into the capacitor 23 in a pulsed manner. Therefore, the input current IIN flowing into the power supply device 31 is a combination of the current I11 shown in FIG. 3C and the input current I12IN shown in FIG. Becomes Therefore, the current IIN flows over almost one cycle of the AC voltage VAC. As a result, a good power factor improvement effect of an input power factor of about 0.85 to 0.9 can be obtained. The output voltage VO can be generated with extremely high efficiency.

[0010]

However, the conventional power supply device 31 has the following problems. That is, in the power supply device 31, in order to sufficiently improve the power factor, the buck-boost converter circuit 32 generates most of the power converted by the power supply device 31 in the period near the maximum voltage VMAX of the first pulsating voltage VP1. There is a need. Therefore, in order to make it difficult for the current to flow through the primary winding 36a of the second transformer 36 during the period near the maximum voltage VMAX, the inductance of the primary winding 36a in the second transformer 36 is
The inductance of the primary winding 35a in the transformer 35 is extremely large as described above.
For this reason, the number of turns of the primary winding 36a of the second transformer 36 must be very large, which results in an increase in the size of the second transformer 36, and accordingly, the size of the power supply device 31 itself increases. There is a problem.

The primary winding 36a of the transformer 36 is
Since the inductance is large, the winding resistance is also large. Therefore, in order to reduce the power loss caused by the current passing through the primary winding 36a of the large winding resistance, originally, during the period near the maximum voltage VMAX of the first pulsating voltage VP1, , Buck-boost converter circuit 32
It is preferable that only the buck-boost converter circuit 33 operates and the buck-boost converter circuit 33 stops operating. However, even in this period, a current corresponding to the inductance ratio between the primary winding 35a of the transformer 35 and the primary winding 36a of the transformer 36 flows through the primary winding 36a, and as a result, a corresponding power loss occurs. There is also a problem that the conversion efficiency of the power supply device 31 is reduced. Further, the primary winding 36a of the transformer 36
, The power loss caused by the current passing through the primary winding 36 a reduces the conversion efficiency of the power supply device 31 during the entire operation of the buck-boost converter circuit 33. There are also problems.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a flyback switching power supply device capable of reducing the size of the device and improving the conversion efficiency while maintaining a sufficient input power factor improvement effect. The purpose is to provide.

[0013]

To achieve the above object, a flyback type switching power supply according to claim 1 is
First and second transformers respectively having a primary winding and a secondary winding, a first rectifier circuit for rectifying an input AC to generate a first pulsating voltage, and a second rectifier for rectifying the input AC and a A second rectifier circuit for generating a pulsating voltage, a smoothing circuit for smoothing the second pulsating voltage to generate a DC voltage, and a series connection to a primary winding of the first transformer. The first drive signal is transmitted through the primary winding in synchronization with the first drive signal.
A second switching signal connected in series with a primary winding of the second transformer and having a switching cycle equal to the switching cycle of the first drive signal. Switching the DC voltage through the primary winding in synchronization with
A switching element, and rectifies and combines voltages induced in respective secondary windings of the first and second transformers by switching the first and second switching elements, thereby providing an output. A flyback type switching power supply for generating a voltage,
A first control circuit that controls a pulse width of the first drive signal in accordance with a voltage value of the output voltage, and a first control circuit that controls a pulse width in accordance with the voltage value of the first pulsating voltage or the second pulsating voltage. Second
And a second control circuit for controlling the pulse width of the drive signal.

According to a second aspect of the present invention, in the flyback type switching power supply of the first aspect, the second control circuit responds to the pulse width of the first drive signal. The pulse width of the second drive signal is controlled to be wide or narrow.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a flyback switching power supply according to the present invention will be described below with reference to the accompanying drawings. The same components as those of the conventional flyback type switching power supply device 31 are denoted by the same reference numerals, and redundant description will be omitted, and redundant description of the same operation will be omitted.

First, the configuration of a flyback type switching power supply (hereinafter, also simply referred to as "power supply") 1 will be described with reference to FIG. The power supply 1 has an AC /
A DC converter, which includes a step-up / step-down converter circuit 10 for power factor improvement and a step-up / step-down converter circuit 20 of a capacitor input type, and has a high pulsating voltage VP1 similar to the conventional power supply device 31. During the voltage period (peak period), the buck-boost converter circuit 10 mainly generates the output voltage VO, and during the low voltage period of the first pulsating voltage VP1 (valley period), the buck-boost converter circuit 20 mainly generates the output voltage VO.
Generates the output voltage VO, thereby improving the input power factor.

The buck-boost converter circuit 10 includes a diode 11, which forms a part of the first rectifier circuit of the present invention,
12, first transformer 13, first switching element 1
4, a diode 15, a first control circuit 16, and a capacitor 17. In this case, the diodes 11, 1
2 rectifies the AC voltage VAC of the AC power supply PS to generate a first pulsating voltage VP1. The first transformer 13 includes a primary winding 13a (inductance value: L13a) and a secondary winding 1
3b, and the first transformer 3 in the power supply device 31.
5 and the same specifications. The first switching element 14 is constituted by, for example, an FET and
3a, and switches the first pulsating voltage VP1 generated by the diodes 11 and 12 in synchronization with the first drive signal SD1. Specifically, the first switching element 14 is turned on when the first drive signal SD1 is output from the first control circuit 16, and the first switching element 14 is turned on.
A first pulsating voltage VP1 is applied between both ends of 3a. The diode 15 rectifies the AC voltage induced in the secondary winding 13b of the first transformer 13 to generate a pulsating voltage. The capacitor 17 smoothes the pulsating voltage generated by the diode 15 and a diode 26 described later, and
Generate O. The first control circuit 16 operates in the same manner as the control circuit 37 in the conventional power supply device 31, generates the first drive signal SD1, and outputs the detected output voltage VO.
Is higher, the pulse width TW1 of the first drive signal SD1 is higher.
By controlling (PWM control) the pulse width TW1 of the first drive signal SD1 to be wider (PWM control) as the voltage value of the output voltage VO decreases (see FIG. 2B), the output voltage VO becomes a predetermined voltage value. Stabilize. In this case, the first drive signal SD1
Is set to a frequency sufficiently higher than the frequency of the AC voltage VAC.

The buck-boost converter circuit 20 includes a part of the first rectifier circuit according to the present invention, a diode stack 21 forming a second rectifier circuit, a resistor 22, a capacitor 23 forming a smoothing circuit according to the present invention, Transformer 2
4, a second switching element 25, a diode 26, and a second control circuit 27. In this case, the diode stack 21 rectifies the AC voltage VAC of the AC power supply PS to generate a second pulsating voltage VP2. The resistor 22 is connected in series to the capacitor 23 and limits the inrush current to the capacitor 23. The capacitor 23 has a second pulsating voltage V
P2 is smoothed to DC voltage VDC. The second transformer 24 is
A primary winding 24a (inductance value: L24a) and a secondary winding 24b are provided. This primary winding 24a is connected in series to the second switching element 25,
4a and the second switching element 25 are connected to the capacitor 2
3 are connected in parallel. In addition, both transformers 13 and 24
For example, they are manufactured with the same specifications. Therefore, in this example, the inductance value L24a and the inductance value L13a are defined to be equal. The second switching element 25 is composed of, for example, an FET, and switches the DC voltage VDC in synchronization with the second drive signal SD2. Specifically, the second switching element 25
When the drive signal SD2 is output from the second control circuit 27, the state shifts to the ON state, and the DC voltage VDC is applied across the primary winding 24a. The diode 26 rectifies the AC voltage induced in the secondary winding 24b of the second transformer 24 to generate a pulsating voltage. The diode 26 is diode-OR-connected to the diode 15 and outputs the generated pulsating voltage to the capacitor 17.

The second control circuit 27 controls the first drive signal S
D1 and the second pulsating voltage VP2 are input, and FIG.
As shown in (c), a second drive signal SD2 whose rising is synchronized with the rising of the first drive signal SD1 is generated, and a second pulsating voltage VP2 (first pulsating voltage VP1) is generated.
May be detected), the level of the voltage value, and the detected pulse width TW1 of the first drive signal SD1
The pulse width TW2 of the second drive signal SD2 is controlled according to the width of the second drive signal SD2. Specifically, as shown in FIG. 3C, the second control circuit 27 sets the second pulsating voltage VP2 to the second pulsating voltage VP2 in the period near the peak (point A in FIG. 4A). The pulse width TW2 of the drive signal SD2 is reduced to a minimum (almost zero),
The pulse width TW2 is gradually increased in accordance with the drop of the pulsating voltage VP2 (see the pulse width TW2 near point B in FIG. 3A), and the second pulsating voltage VP2 is near zero volt (FIG. 3A). In the period (point C), the pulse width TW2 is increased to the maximum, and the pulse width TW2 is gradually narrowed toward the minimum pulse width in accordance with the rise of the second pulsating voltage VP2. That is,
The second control circuit 27 controls the second drive signal SD2 so that the higher the voltage value of the second pulsating voltage VP2 is, the narrower the voltage value becomes (in inverse proportion to the voltage value of the second pulsating voltage VP2). The pulse width TW2 is controlled. Further, the second control circuit 27 also detects the pulse width TW1 of the first drive signal SD1, and when the pulse width TW1 is reduced, the pulse width TW2 of the second drive signal SD2 is reduced. 1 pulse width T of the drive signal SD1
When W1 is widened, the pulse width TW2 is widened. That is, the second control circuit 27 controls the pulse width TW2 so as to be proportional to the pulse width TW1 of the first drive signal SD1.

Further, in the power supply device 1, unlike the conventional power supply device 31, the buck-boost converter circuit 10 mainly performs the second drive during the high voltage period of the second pulsating voltage VP2 for generating the output voltage VO. The pulse width TW2 of the signal SD2 is narrowed to suppress generation of power by the buck-boost converter circuit 20. Therefore, the inductance L24a of the primary winding 24a of the second transformer 24 is changed to the inductance L36a of the primary winding 36a of the conventional second transformer 36.
It can be set to a value that is sufficiently smaller than. Further, as a result of reducing the inductance L24a of the primary winding 24a, the inductance L24 of the secondary winding 24b is reduced.
Similarly, the secondary winding 3 of the conventional transformer 36 is
6b can be set to a value smaller than the inductance L36b. Therefore, the second transformer 24
Since the number of turns of the primary winding 24a and the secondary winding 24b is reduced, the size is sufficiently smaller than that of the second transformer 36 in the conventional power supply device 31.

Next, the operation of the power supply 1 will be described with reference to FIGS.

In the power supply device 1, when the power is turned on, the diode stack 21 rectifies the AC voltage VAC to the second pulsating voltage VP2 and supplies the rectified voltage to the capacitor 23 via the resistor 22. At this time, the resistor 22 suppresses the occurrence of the inrush current by limiting the current value of the current I12IN flowing into the capacitor 23 to a predetermined value.

Next, when the switching by the first switching element 14 and the second switching element 25 is started, during the high voltage period of the first pulsating voltage VP1 (and the second pulsating voltage VP2), the voltage rises and falls. Pressure converter circuit 10
However, it operates basically in the same manner as the buck-boost converter circuit 32 in the power supply device 31. Specifically, the first control circuit 16 stabilizes the output voltage VO by PWM controlling the pulse width TW1 of the first drive signal SD1 based on the fluctuation of the output voltage VO. On the other hand, during this period, the buck-boost converter circuit 20 outputs the second drive signal SD2
Is narrowed to a minimum by the second control circuit 27, thereby maintaining a state that hardly contributes to the generation of the output voltage VO. Therefore, the input power factor of the power supply device 1 is improved accordingly. At this time, even if the step-up / step-down converter circuit 20 operates for a short period of time, the inductance value L24a of the primary winding 24a in the second transformer 24 is small.
Can be reduced. Therefore, it is possible to reduce the winding resistance by that amount, thereby avoiding a decrease in the conversion efficiency in the power supply device 1.

On the other hand, as the voltage value of the first pulsating voltage VP1 decreases, the pulse width TW2 of the second drive signal SD2 is gradually widened by the second control circuit 27, so that the buck-boost converter circuit 20 Gradually contributes to the generation of the output voltage VO. Thereafter, the buck-boost converter circuit 10
During which the generation of the output voltage VO by the
In a low voltage period in which the pulsating voltage VP1 (and the second pulsating voltage VP2) of the second drive signal SD2 is lower than the threshold voltage VS, the buck-boost converter circuit 20 sets the pulse width TW2 of the second drive signal SD2 to The output voltage VO is mainly generated in place of the buck-boost converter circuit 10 by being expanded to the vicinity of the maximum pulse width by the circuit 27. In this period, the second control circuit 27 increases or decreases the pulse width TW2 of the second drive signal SD2 in accordance with the width of the pulse width TW1 of the first drive signal SD1 output from the first control circuit 16. Control. Accordingly, the buck-boost converter circuit 20 stabilizes the output voltage VO by being subjected to PWM control according to the pulse width TW2 of the second drive signal SD2. in this case,
In the power supply device 1, in FIG. 4D, the input current I flowing into the power supply device 1 except that the current I12 hardly flows in the period near the maximum voltage VMAX of the second pulsating voltage VP2 is shown.
IN, the current I11 flowing into the buck-boost converter circuit 10, and the input current I12IN flowing into the capacitor 23 have basically the same current waveform as the corresponding current in the power supply device 31.

As described above, according to the power supply device 1, the first control circuit 16 controls the pulse width of the first drive signal SD1 according to the level of the voltage value of the output voltage VO, and the second control circuit Since the circuit 27 controls the pulse width of the second drive signal SD2 according to the level of the second pulsating voltage VP2, the inductance of the primary winding 24a in the second transformer 24 can be reduced. Thus, the size of the second transformer 24 and the size of the power supply device 1 can be reduced. Also, the primary winding 24a of the second transformer 24
As described above, when the output voltage VO is generated by the buck-boost converter circuit 20, the power loss caused by the current flowing through the primary winding 24a can be sufficiently reduced. The conversion efficiency of the device 1 can be improved. Also, the second control circuit 27 controls the width of the pulse of the second drive signal SD2 in accordance with the width of the pulse of the first drive signal SD1, thereby increasing the pulse width of the first drive signal SD1. When the load is heavy, the pulse width of the second drive signal SD2 is increased, and conversely, when the pulse width of the first drive signal SD1 is reduced, when the load is light, control is performed so as to reduce the pulse width of the second drive signal SD2. be able to. Therefore, the amount of output voltage VO generated by the second transformer 24 can be appropriately reduced or increased according to the load of the load, so that the conversion efficiency of the power supply device 1 can be further improved.

It should be noted that the flyback switching power supply of the present invention is not limited to the configuration of the power supply 1 described above, and can be appropriately changed. For example, the second control circuit 2
7 may be configured to change the pulse width TW2 of the second drive signal SD2 based on only the second pulsating voltage VP2. In the embodiment of the present invention described above, the second control circuit 27 controls the pulse width TW2 of the second drive signal SD2 so as to be inversely proportional to the voltage value of the second pulsating voltage VP2. For example, the pulse width TW2 in one cycle of the second pulsating voltage VP2 is obtained in advance by an experiment or the like, and stored as pulse width data in a memory or the like, and the pulse width TW2 is changed based on the stored pulse width data. A configuration can also be employed. In the embodiment of the invention described above, the second control circuit 27 generates the second drive signal SD2 in synchronization with the rise of the first drive signal SD1, but the second drive signal SD2 May be any timing as long as it is generated during one cycle of the first drive signal SD1. For example, not only during the output period of the first drive signal SD1, but also during the stop period of the first drive signal SD1.
Can be generated. Further, in the embodiment of the present invention, an example has been described in which the first drive signal SD1 and the second drive signal SD2 are positive logic, but it is needless to say that the first drive signal SD1 and the second drive signal SD2 may be negative logic. Further, the first switching element 14 and the second switching element 25 are not limited to FETs, and various switching elements such as transistors can be employed.

[0027]

As described above, according to the flyback type switching power supply device of the first aspect, the second control circuit operates according to the voltage value of the first pulsating voltage or the second pulsating voltage. By controlling the pulse width of the second drive signal, the pulse width of the second drive signal during a period in which the output voltage is generated by the first transformer is mainly independent of the pulse width of the first drive signal. It can be minimized or narrowed to zero. Therefore, unlike the conventional power supply device 31, it is not necessary to set a large ratio of the inductance of the primary winding of the first transformer to the inductance of the primary winding of the first transformer. If the same core material is used, the number of turns of the primary winding can be significantly reduced as compared with the conventional transformer. Therefore, the size of the second transformer can be reduced, and the size of the switching power supply itself can be reduced. In addition, since the inductance of the primary winding in the second transformer can be reduced, the winding resistance can be reduced accordingly, whereby the electric power caused by the current flowing through the primary winding of the second transformer can be reduced. As a result, the conversion efficiency of the switching power supply can be improved.

According to the flyback type switching power supply of the second aspect, the second control circuit controls the pulse width of the second drive signal in accordance with the pulse width of the first drive signal. Accordingly, when the load in which the pulse width of the first drive signal spreads is heavy, the pulse width of the second drive signal is widened, and when the load in which the pulse width of the first drive signal narrows is light, the second drive signal is used. Since the pulse width of the drive signal can be controlled to be reduced, the amount of output voltage generated by the second transformer can be appropriately reduced or increased according to the load of the load, and as a result, the conversion efficiency of the power supply device can be reduced. It can be further improved.

[Brief description of the drawings]

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

FIGS. 2A and 2B are waveform diagrams for explaining the operation of the power supply device 1, wherein FIG. 2A is a voltage waveform diagram of a second pulsating voltage VP2;
(B) is a voltage waveform diagram of the first drive signal SD1, and (c) is a voltage waveform diagram of the second drive signal SD2.

FIG. 3 is a circuit diagram of a conventional power supply device 31.

FIGS. 4A and 4B are waveform diagrams for explaining the operation of the power supply device 31, wherein FIG. 4A is a waveform diagram of an AC voltage VAC, FIG. 4B is a waveform diagram of a first pulsating voltage VP1, and FIG. ) Is a current waveform diagram of the current I11, (d) is a current waveform diagram of the current I12, (e) is a current waveform diagram of the input current I12IN, and (f) is a current waveform diagram of the input current IIN.

[Explanation of symbols]

 Reference Signs List 1 switching power supply device 10 step-up / step-down converter circuit 11, 12 diode 13 first transformer 13a primary winding 13b secondary winding 14 first switching element 16 first control circuit 20 step-up / step-down converter circuit 21 diode stack 23 capacitor 24 Second transformer 24a Primary winding 24b Secondary winding 25 Second switching element 27 Second control circuit SD1 First drive signal SD2 Second drive signal VAC Input AC VO Output voltage VP1 First pulsating voltage VP2 Second pulsating voltage

Claims (2)

[Claims] 1. A first and a second transformer having a primary winding and a secondary winding, respectively, a first rectifier circuit for rectifying an input alternating current to generate a first pulsating voltage, and an input alternating current. A second rectifier circuit that rectifies to generate a second pulsating voltage;
A smoothing circuit for smoothing the second pulsating voltage to generate a DC voltage, and a primary circuit connected in series to a primary winding of the first transformer and synchronized with a first drive signal; A first switching element for switching the first pulsating voltage via the first transformer, and a first switching element connected in series to a primary winding of the second transformer, and a switching cycle of which is set to the first cycle.
A second switching element that switches the DC voltage via the primary winding in synchronization with a second drive signal equal to the switching cycle of the drive signal of the first drive signal.
Flyback switching power supply device that generates an output voltage by rectifying and combining voltages induced in respective secondary windings of the first and second transformers by switching a second switching element. A first control circuit that controls a pulse width of the first drive signal according to a voltage value of the output voltage; and a voltage value of the first pulsating voltage or the second pulsating voltage. Controlling the pulse width of the second drive signal in accordance with
A flyback type switching power supply device comprising: 2. The apparatus according to claim 1, wherein the second control circuit controls the width of the pulse of the second drive signal in accordance with the width of the pulse of the first drive signal. Flyback type switching power supply.