JP3478693B2 - 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 improving the efficiency of a power factor correction circuit for a switching power supply.

[0002]

2. Description of the Related Art FIG. 4 shows an embodiment of a conventional switching power supply with a power factor correction circuit. In the figure, 1 is a commercial AC power supply, 2, 3, 4, and 5 are rectifying diodes, 6 is a power factor correction circuit, for example, an active filter, 7 is a first transformer, and 8 is a primary transformer of the first transformer ( 2) Winding, 9 is the secondary winding of the first transformer, and 10 is the first
Switch element, 11 is a rectifying diode, 12 is a flywheel diode, 13 is a choke coil, 14 is a smoothing capacitor, 15 is a load, 16 is an error amplifier for detecting output voltage, 17 is a reference voltage, 18 is an oscillator, and 19 is driving. Circuit. Since this circuit is a known circuit, detailed description of its operation is omitted. This method, in order to improve the power factor,
The power factor correction circuit 6 is inserted between the rectifier circuit and the DC-DC converter. The power factor correction circuit has the same configuration as the step-up chopper type switching power supply even by itself, and it means that two switching power supplies are connected in series, and although the power factor can be improved, there is no reduction in efficiency. I cannot escape.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to improve the efficiency of a switching power supply with power factor correction in order to solve the above problems.

[0004]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention.
The same parts as the conventional circuit are indicated by the same numbers. 21
Is a second transformer, 22 is a primary winding of the first transformer, 23 is a secondary winding of the first transformer, 24 is a first switch element, 24a is a parasitic diode of the first switch element, 25 Is a second switch element, and 25a is a parasitic diode of the second switch element. Reference numeral 26 is a rectifying diode, and the same ON / OFF signal is applied to the first switch element 24 and the second switch element 25 by the drive circuit 19. In addition, the first transformer 7 and the second transformer 21
The winding start of each winding is indicated by a dot in FIG.

That is, the first capacitor 20 is connected in parallel with the commercial power source 1, and the winding start of the primary winding 8 of the first transformer 7 is connected in parallel with the first capacitor 20. At the end of the winding of the primary winding 8 of the transformer 7
The primary winding (3) 22 of the transformer 21 is connected to the beginning of the winding, and the first switching element 2 is connected to the winding end of the primary winding 22 of the second transformer 21.
4 and the second switch element 25 is connected to the other end of the first switch element 24, and a series circuit connected to the first switch element 24 is connected to the first switch element 24. The first diode 24a, which is a parasitic diode of the first switch element 24, is connected so as to be in the opposite direction in a cycle, and the first diode 24a is connected in parallel with the second switch element 25 in the opposite direction in a negative half cycle. The second diode 25a, which is a parasitic diode of the second switch element 25, is connected, and the anode of the third diode 11 is connected to the winding start of the secondary winding 9 of the first transformer 7.

A secondary winding 9 of the first transformer 7 is also provided.
Connect the second capacitor 14 at the end of winding
The cathode of the third diode 11 is connected to the other end of the second capacitor 14, and the second capacitor 14
A load 15 is connected in parallel with the second transformer 21, and an anode of a fourth diode 26 is connected to the end of the secondary winding 23 of the second transformer 21 to connect the fourth diode 26 to the third diode 11. The cathode of the fourth diode 26 is connected to the cathode of the second transformer 21.
The winding start of the secondary winding 23 is connected to the winding end of the secondary winding 9 of the first transformer 7.

Next, the operation of this circuit will be described with reference to FIG. In the figure, (a) is the input commercial voltage waveform,
(B) is a drive signal of the first switching element 24 and the second switching element 25, (c) is a current of the primary winding 8 of the first transformer 7 and the primary winding 22 of the second transformer 21. It is a waveform. First, the positive half cycle operation of the commercial power supply will be described. During the period A in FIG. 3, the signal turned on by the drive circuit 19 is the first switch element 24 and the second switch element 25.
When turned on, each switch element is turned on. Then, the current is the commercial power supply 1-the primary winding 8 of the first transformer 7-the primary winding 2 of the second transformer 21 (4) 2 -the first switching element 24 -the second switching element 25
And its parasitic diode 24a.

At this time, the primary winding 8 of the first transformer 7
Is applied with a voltage lower than the voltage nVo determined by the winding ratio of the first transformer 7 to the secondary winding 9, so that energy is not transferred to the secondary side. Next, when an off signal is applied from the drive circuit 19 to the first switch element 24 and the second switch element 25, the first switch element 24 and the second switch element 25 are turned off, respectively. Then, the current flows through the route of the secondary winding 23 of the second transformer 21, the rectifying diode 26, and the load 15, and the power is supplied to the load.

Next, when the ON signal is applied from the drive circuit 19 to the first switch element 24 and the second switch element 25 in the period B in FIG. 3, the respective switch elements are turned on. Then, the current is the commercial power supply 1-the primary winding 8 of the first transformer 7-the primary winding 22 of the second transformer 21-the first switch element 24-the second switch element 25 and its parasitic diode 24a. And the first route
The secondary winding 9 of the transformer, the rectifying diode 11 and the load 15 flow through the route. Next, when an off signal is applied from the drive circuit 19 to the first switch element 24 and the second switch element 25, the first switch element 24 and the second switch element 25 are turned off, respectively. And
The current flows through the route of the secondary winding 23 of the second transformer 21, the rectifying diode 26, and the load 15, and the power is supplied to the load.

Next, the operation during the period C in FIG. 3 will be described. The operation in this period is the same as that in the period A.

Next, the operation during the periods D, E and F in FIG. 3 will be described. The operations in these periods are shown in FIG. 3 except that the first transformer 7 and the second transformer 21, and the first switch element 24 and the second switch element 25 play relative roles. A,
(5) It is the same as the operation in the periods B and C.

With the above-described operation, the first transformer 7 functions as a forward winding in a positive half cycle and functions as a choke coil in a negative half cycle. Further, the second transformer 21 functions as a choke coil in the positive half cycle and functions as a forward winding in the negative half cycle. Then, the current supplied from the input commercial power supply to the switching power supply has a waveform similar to the input voltage as shown by the dotted line in FIG. 3C, and the power factor is improved. Further, in the conventional circuit shown in FIG. 4, two diodes are used when the input current is rectified, but since only one diode is used in this method, the efficiency can be improved.

FIG. 2 shows a second embodiment of the present invention. Figure 2
The circuit configuration and operation of the circuit will be described. 2, the same components as those described in FIG. 1 are designated by the same reference numerals.

In FIG. 2, the oscillator 18 is an error amplifier 1
When the DC output voltage becomes larger than the reference voltage 17, the first switch element 24 and the second switch element are used as the first input and the output of the input current detection circuit 27 as the second input. When the DC output voltage becomes shorter than the reference voltage 17 by shortening the ON time of 25, a pulse for increasing the ON time of the first switch element 24 and the second switch element 25 is generated to output the DC output. The voltage is stabilized, and the on / off time of the switch element is controlled so that the waveform of the input current becomes similar to the waveform of the input voltage.

With the configuration shown in FIG. 2, the loss due to the rectification on the primary side can be further reduced. As a result, the power factor and efficiency can be improved as compared with the conventional power factor improving switching power supply.

[0016]

【The invention's effect】

(6) According to the present invention, it is possible to realize a power factor correction type switching power supply with higher efficiency than ever before. Further, by reducing the number of parts, it is possible to realize a switching power supply with power factor correction, which is downsized and reduced in cost.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a second embodiment of the power factor improving switching power supply of the present invention.

FIG. 3 is an operation waveform of each part of the switching power supply of the present invention.

FIG. 4 is a circuit diagram of an example of a conventional power factor improving switching power supply.

[Explanation of symbols]

1 AC power supply 2 Rectifier diode 3 Rectifying diode 4 Rectifying diode 5 Rectifier diode 6 Power factor correction circuit 7 First Transformer 8 Primary winding of the first transformer 9 Primary winding of the first transformer 10 Main switch element 11 Rectifying diode 12 Flywheel diode 13 choke coil 14 Smoothing capacitor (7) 15 load 16 Error amplifier 17 Reference voltage 18 oscillators 19 Drive circuit 20 capacitors 21 Second Transformer 22 Primary winding of the second transformer 23 Secondary winding of the second transformer 24 First switch element 24a Parasitic diode of first switch element 25 Second switch element 25a Parasitic diode of second switch element 26 Rectifier diode 27 Current detection circuit

Claims (3)

(57) [Claims] 1. A first transformer 7 functioning as a forward winding in a positive half cycle in parallel with a commercial power source 1 and as a choke coil in a negative half cycle, and as a choke coil in a positive half cycle. , A second transformer 21 that functions as a forward winding in a negative half cycle, a first switch element 24, and a reverse polarity with respect to the first switch element.
The series circuit comprising the second switching element 25 is connected comprising, as well as connect the rectifier circuit in each of the transformer secondary winding 9, 23, are each anodes for the first and second switching elements Reverse polarity to connect
Two diodes 24a and 25a arranged in parallel are connected in parallel, and the secondary windings of the first and second transformers are connected in parallel via rectifier diodes 11 and 26, respectively, and supplied to the load 15. A switching power supply characterized in that 2. The switching power supply according to claim 1, wherein the diodes 24a and 25a are parasitic diodes of the first switch element 24 and the second switch element 25. 3. The switching power supply according to claim 1, wherein the switching frequencies of the first switching element 24 and the second switching element 25 are higher than the commercial frequency.