JPH104684A - Switching power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of voltage distortion and harmonic currents in a power line by increasing the power factor by connecting a rectifier diode to the voltage adding winding of a switch transformer and, further, to a smoothing capacitor. SOLUTION: A voltage V2 , rectified by means of a rectifier diode bridge 4, passes through a voltage adding winding 63 and the output voltage V3 of the winding 63 charges a smoothing capacitor 5 through a rectifier diode 15. When the charging voltage V4 of the capacitor 5 becomes a switching operation voltage or higher, switching operation is started by means of a winging 61 for primary-side switching, switching transistor 7, and switching control circuit 8. Namely, a switching transistor 7 is turned on/off by the on/off signal of a switching signal, outputted from the control circuit 8, and electric power is transmitted to the secondary side from the primary side, according to the windings of a switching transformer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply used for electronic equipment, and more particularly to a switching power supply having improved power factor.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing a conventional capacitor input type switching power supply.

When the switch 2 is turned on, the AC power supply 1 is connected to the rectifier diode bridge 4 via the fuse 3.
The AC voltage is rectified by the rectifier diode bridge 4 and supplied to the smoothing capacitor 5 to be smoothed. The smoothed voltage passes through the switching transformer 6 and is connected to the switching transistor 7.

The switching transistor 7 is turned on / off by an on / off signal of a switching signal output from a switching control circuit 8 connected to the base. The power is transmitted from the primary side to the secondary side according to the winding of the switching transformer 6 by the switching operation of the switching transistor 7.

The voltage transmitted to the secondary side of the switching transformer 6 is rectified by rectifier diodes 9 and 10.
The rectified voltage is smoothed by a smoothing circuit including a smoothing coil 11 and a smoothing capacitor 12 connected to the rectifying diodes 9 and 10. The switching control circuit 8 is controlled so that the smoothed voltage becomes the rated voltage, and the voltage having the rated voltage is supplied to the load circuit 13 through the output terminal.

FIGS. 5A and 5B are voltage / current waveform diagrams of a conventional circuit, wherein FIG. 5A shows an AC voltage of an AC power supply, and FIG. 5B shows waveforms of a rectified voltage V and an input current i.

[0007]

However, in a conventional switching power supply having a capacitor input type rectifier circuit, the input current i flows as shown in FIG. Is mostly a current flowing through the smoothing capacitor 5 in a short time,
Its flow angle t is very narrow.

[0008] Accordingly, there is a problem that the power factor becomes low and voltage distortion of the power supply line and harmonic current are generated. The voltage distortion and the harmonic current have a bad influence on other electronic devices through a power supply line of a commercial power supply.

It has also been proposed to add a step-up type active filter circuit to increase the power factor. However, in this case, there is a problem that the power supply device becomes large.

[0010]

In order to solve the above-mentioned problems, the present invention connects a rectifying diode bridge to an output of a rectifying diode bridge, and connects a rectifying diode to the voltage adding winding. A diode is connected to a smoothing capacitor and a primary-side switching winding of a switching transformer, and a switching transistor controlled by a switching control circuit is connected to the switching winding.

[0011]

FIG. 1 is a circuit diagram of a switching power supply according to the present invention, and the same parts as those in FIG. 4 are denoted by the same reference numerals.

The AC power supply 1 is connected to a switch 2 for turning on and off the power supply, and is connected to a rectifier diode bridge 4 for converting the AC power supply to a DC power supply through a noise filter 14 and an input overcurrent prevention fuse 3.

The output of the rectifier diode bridge 4 is connected to the voltage addition winding 63 of the switching transformer 6, and the output of the voltage addition winding 63 is connected to the anode of the rectifier diode 15. The cathode of the rectifier diode 15 is connected to the smoothing capacitor 5 and to the primary-side switching winding 61 of the switching transformer 6. The other end of the switching winding 61 is connected to the switching transistor 7.
It is connected to the.

A switching control circuit 8 for turning on / off the transistor 7 is connected to a base of the switching transistor 7. Switching transistor 7 is set to M
In the case of using an OSFET, the switching control circuit 8
Is connected to the gate.

Rectifier diodes 9 and 10 are connected to the secondary output voltage winding 62 of the switching transformer 6, and a smoothing circuit including a smoothing coil 11 and a smoothing capacitor 12 is connected to the rectifier diodes 9 and 10. . The smoothing circuit is connected to the switching control circuit 8 and to the output load circuit 13.

The diode 16 connected to the voltage addition winding 63 is for releasing high-frequency components generated in the voltage addition winding 63.

FIG. 2 is a voltage / current waveform diagram in the present invention. (A) is an input voltage V ₁ of the AC power supply 1, (b) is a rectified voltage V ₂ which is an output of the rectifier diode bridge 4,
(C) shows the voltage V ₆₃ across the voltage addition winding ₆₃ , and (d) shows the output voltage V ₃ of the voltage addition winding 63 and the charging voltage V ₄ of the smoothing capacitor 5.

FIG. 3 is a diagram showing the relationship between input voltage and input current in the present invention. (D) is an enlarged view of a part of (d) in FIG. 2, wherein the output voltage V ₃ and the charging voltage V ₄ ,
(E) is the current i ₂ obtained by rectifying the input current i ₁ and the current i ₃ of the output voltage V ₃ , and (f) is the input voltage V ₁ and the input current i ₁
Shows the relationship.

The operation of the circuit will be described with reference to FIGS.
When the switch 2 connected to the AC power supply 1 is turned on, the AC voltage V ₁ is input, and the noise filter 14 and the fuse 3
And is connected to the rectifier diode bridge 4.

The voltage V ₂ rectified by the rectifier diode bridge 4 passes through the voltage addition winding 63 of the switching transformer 6, and the output voltage V ₃ of the voltage addition winding 63 passes through the rectification diode 15 to charge the smoothing capacitor 5. I do.

[0021] charging voltage V ₄ of the smoothing capacitor 5 becomes equal to or higher than the switching operation voltage, switching transformer 6
The switching operation is started by the primary-side switching winding 61, the switching transistor 7, and the switching control circuit 8. That is, the switching transistor 7 is turned on / off by the on / off signal of the switching signal output from the switching control circuit 8, and from the primary side to the secondary side (the output voltage winding) according to the winding of the switching transformer 6. 62).

The voltage transmitted to the secondary side of the switching transformer 6 is rectified by rectifier diodes 9 and 10, and the rectified voltage is smoothed by a smoothing circuit including a smoothing coil 11 and a smoothing capacitor 12. The switching control circuit 8 is controlled so that the smoothed voltage becomes the rated voltage,
The voltage that has become the rated voltage is supplied to the load circuit 13 through the output terminal.

At this time, a voltage V ₆₃ across the terminal as shown in FIG. 2C is generated in the voltage addition winding 63 of the switching transformer 6, and the rectified current i ₂ is superimposed on the winding 63. 2, the output voltage V ₃ of the winding 63 is
As shown in (d), V ₃ = V ₂ + V ₆₃ .

The output voltage V ₃ passes through the diode 15 and is smoothed by the smoothing capacitor 5 to become a DC voltage V _{4 as shown} in FIG. DC voltage V ₄ is the average voltage of the charging voltage V _4, and the pulsed output voltage V ₃ of the smoothing capacitor 5.

As shown in FIG. 3D, the output voltage V ₃
Becomes a pulse with the same frequency as the switching frequency,
Since the current i ₃ flows through a portion where the output voltage V ₃ becomes higher than the average voltage V _4, the current i ₃ becomes as shown in FIG. This current i ₃ becomes a charging current for the smoothing capacitor 5.

The average of the current i ₃ becomes the current i _{2 as} shown in FIG. The current i ₃ is a pulsed current having the same frequency as the switching frequency.
By suppressing the switching frequency component by the inductance of the voltage addition winding 63 of the switching transformer 6 and the noise filter 14 included in the input part, the pulse-like current i ₃ becomes an average current,
Comprising an input current i ₁ as shown in (e) as rectified current i ₂ flows.

From the above, as shown in FIG. 3F, the input current i ₁ has no phase difference with the input voltage V _1, and the flow angle t ₁ thereof can be widened, so that the power factor is reduced. Be improved.

[0028]

As described above, according to the present invention, the rectifier diode is connected to the voltage adding winding of the switching transformer, and this is connected to the smoothing capacitor.
The flow angle of the input current is widened and the power factor can be increased,
Voltage distortion of the power supply line and generation of high-frequency current can be suppressed.

Further, since the voltage adding winding of the switching transformer is used without adding a boost type active filter circuit, there is an advantage that the shape and size of the power supply device need not be increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a switching power supply device of the present invention.

FIG. 2 is a voltage / current waveform diagram according to the present invention.

FIG. 3 is a diagram showing a relationship between an input voltage and an input current in the present invention.

FIG. 4 is a circuit diagram of a conventional switching power supply device.

FIG. 5 is a voltage / current waveform diagram in a conventional circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 4 Rectifier diode bridge 5 Smoothing capacitor 6 Switching transformer 61 Primary-side switching winding 62 Secondary-side output voltage winding 63 Voltage addition winding 7 Switching transistor 8 Switching control circuit 14 Noise filter 15 Rectifier diode

Claims (2)

[Claims] 1. A switching power supply having a rectifier diode bridge for converting AC to DC, a switching transformer, a switching transistor, and a switching control circuit, wherein a voltage adding winding of the switching transformer is connected to an output of the rectifier diode bridge. A rectifier diode is connected to the other end of the voltage addition winding, a smoothing capacitor and a primary-side switching winding of the switching transformer are connected to the rectifier diode, and the switching control circuit is connected to the other end of the switching winding. A switching power supply device, wherein the switching transistor controlled by the switching power supply is connected. 2. The switching power supply according to claim 1, wherein a noise filter is connected to an input side of the rectifier diode bridge.