JPH0678541A - Power supply equipment improved in power factor - Google Patents

Abstract

PURPOSE:To provide a DC power supply equipment having an improved power factor, whereby its AC input current can be suppressed to a low value, without altering the constants of parts used in a conventional DC power supply equipment, by only adding a small number of parts to conventional ones, in the stabilized DC power supply equipment used for various electronic apparatuses. CONSTITUTION:In a DC power supply equipment, a transformer 4 which follows conventionally the rectifier for an AC input power supply 1 is provided. The series circuit comprising a second switching element 13 and a capacitor 14 is connected in parallel with the series circuit comprising a primary winding 4a of the transformer 4 and a first switching element 5. In this configuration, when the AC input voltage is not lower than a certain voltage level V1, a current is fed from the AC input power supply 1, and when being not higher than the level V1, the current is fed from the capacitor 14 which has been charged to the peak value of the AC input voltage beforehand. Thereby, the power factor of the DC power supply equipment can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power factor improving power supply device capable of widening the conduction angle of an AC input current.

[0002]

2. Description of the Related Art FIG. 3 shows a circuit diagram of a conventional feedforward type power factor correction power supply device, which is shown in Japanese Patent Publication No. 3-79948. In FIG. 3, 1 is an AC input power source, 2 is a noise filter, 3 is a rectifier circuit, 4 is a transformer, 5 is a switching element, 6, 7, 11, 18 are diodes, 8 is a choke, 9 and 14 are capacitors, 10 Is a control circuit.

The operation of the power supply device configured as described above will be described below. The AC input power source 1 is converted into a pulsating flow by the rectifier circuit 3 via the noise filter 2. The pulsating voltage is applied to the primary winding 4a of the transformer 4 by the high frequency switching operation of the switching element 5, and a rectangular wave output stepped down or boosted to a desired voltage is obtained in the secondary winding 4b of the transformer 4. Rectification and smoothing is performed by the rectangular wave output diodes 6 and 7, the choke 8 and the capacitor 9, and a DC output is obtained.

The control circuit 10 receives a DC output and outputs a control signal for switching the switching element 5 at a high frequency to stabilize the DC output.

By the feedback winding 4c of the transformer 4, the excitation energy when the switching element 5 is turned on passes through the diode 11 when the switching element 5 is turned off and the capacitor 14
To charge. The output voltage of the rectifier circuit 3 is the capacitor 14
The AC input current flows through the rectifier circuit 3 to the primary winding 4a of the transformer 4 during a period higher than the voltage across the capacitor, and the diode 18 is connected to the capacitor 18 via the capacitor 14 while the output voltage of the rectifier circuit 3 is lower than the voltage across the capacitor 14. A current flows through the primary winding 4a of the transformer 4.

If the voltage across the capacitor 14 is set to be much lower than the peak value of the output voltage of the rectifier circuit 3, the AC input current flows for a longer period than in a normal feedforward power source in which the diode 18 is short-circuited. Therefore, the conduction angle increases and the power factor increases.

The set value of the voltage across the capacitor 14 changes depending on the turn ratio between the primary winding 4a and the feedback winding 4c of the transformer 4, and if the number of turns of the feedback winding 4c is less than that of the primary winding 4a, the capacitor The voltage across 14 becomes lower than the peak value of the output voltage of the rectifier circuit 3.

An AC input voltage waveform and a AC input current waveform of such a conventional power supply device are shown in FIG. 4 (a) and FIG. 4 (b), respectively.

[0009]

However, in the above-mentioned conventional configuration, the feedback winding 3 of the transformer 4 is used to increase the power factor.
If the number of turns of c is considerably smaller than the number of turns of the primary winding 4a and the voltage across the capacitor 14 is much lower than the peak value of the output voltage of the rectifier circuit 3, the DC output stabilization holding time after a momentary interruption or interruption of the AC input power supply The capacitor 14 required a large-capacity electrolytic capacitor for the purpose of ensuring.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a power factor improving power supply device capable of widening the conduction angle of an AC input current.

[0011]

In order to achieve the above object, a power factor improving power supply device of the present invention is connected between a rectifier circuit to which an AC input power source is connected via a noise filter and an output terminal of the rectifier circuit. Of the two circuits, one is a series circuit of the primary winding of the transformer and the first switching element, and the other is a capacitor and a diode connected in parallel to turn on below a certain voltage level of the AC input voltage. The second done
And a rectifying / smoothing circuit connected to the secondary winding of the transformer for obtaining a DC output.

[0012]

According to the present invention, of the absolute value sine wave voltage obtained by rectifying the sine wave AC input voltage, it is divided into a voltage period higher than a certain voltage level V1 and a voltage period lower than a certain voltage level V1. A current flows through the primary winding, and during a voltage period lower than V1, the second switching element is turned on, and the primary winding of the transformer is passed from the capacitor connected in series with the second switching element through the second switching element. Allow current to flow. The output of the secondary winding of the transformer is rectified and smoothed to obtain a DC output.

When the diode connected in parallel with the second switching element or the second switching element is a field effect transistor, the built-in diode causes the capacitor to have a peak voltage near the peak value of the AC input voltage of the sine wave. I'm charging.

By operating in this way, the capacitor is charged to the peak value of the sine wave AC input voltage, and the AC input voltage is irrespective of the magnitude of the sine wave AC input voltage and the voltage across the capacitor. Is applied to turn on the second switching element only during the period when the first switching element has the maximum duty ratio so as not to reach the maximum duty ratio, the DC output is stabilized and the conduction angle of the AC input current spreads and the power factor increases. Can be improved. If the maximum duty ratio of the first switching element continues, stabilization of the DC output cannot be maintained and the commercial ripple voltage increases, so the ON period of the second switching element is required to some extent.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit of a power factor correction power supply device according to an embodiment of the present invention. In FIG. 1, 1 is an AC input power supply, 2 is a noise filter, 3 is a rectifier circuit, 4 is a transformer, 5 is a first switching element, 13 is a second switching element, 19 is a third switching element, and 6 and 7. ，
11, 18 are diodes, 8 is a choke, 9, 12, 1
4 is a capacitor, 10 is a control circuit, 15 and 16 are resistors,
Reference numeral 17 is a Zener diode.

The operation of the power factor correction power supply device configured as described above will be described. The AC input power supply 1 is turned on, and the rectifying circuit 3 converts it into a pulsating flow through the noise filter 2. The rectangular wave of the pulsating voltage level is applied to the primary winding 4a of the transformer 4 by the high frequency switching of the first switching element 5. The voltage appearing on the secondary winding 4b of the transformer 4 is rectified and smoothed by the diodes 6 and 7, the choke 8 and the capacitor 9 to obtain a DC output.

The control circuit 10 generates a control signal to the first switching element 5 for stabilizing the voltage of the DC output, and inputs the AC input voltage to perform full-wave rectification for a period higher than a certain voltage level V1. Is a high level, and alternately outputs a signal that is a low level during a period lower than V1 and is input to the base of the third switching element 19.

The excitation energy accumulated during the ON period of the first switching element 5 is charged into the capacitor 12 through the diode 11 during the OFF period. Near the peak value of the AC input voltage of the sine wave, it passes through the built-in diode 13a of the second switching element 13 and is charged in advance to the peak value of the AC input voltage of the sine wave.

When the signal from the control circuit 10 becomes low level, the third switching element 19 turns off and the capacitor 1
The current from 2 flows through the resistor 15 and the diode 18 to the gate of the second switching element 13, is turned on, and the current flows from the capacitor 14 to the primary winding 4 a of the transformer 4. When the signal from the control circuit 10 becomes high level, the third switching element 19 is turned on, and the current from the capacitor 12 flows through the resistor 15 to the third switching element 19 and is accumulated in the gate of the second switching element 13. The electric charge is discharged through the resistor 16, the second switching element 13 is turned off, and a current flows from the rectifier circuit 3 to the primary winding 4a of the transformer 4.

The resistor 15 includes a Zener diode 17 and a third resistor.
It is a current limiting resistance to the switching element 19 of. This is because the diode 18 prevents a large negative voltage from being applied to the gate of the second switching element 13 when the third switching element 19 is turned on. The Zener diode 17 is for preventing a large positive voltage from being applied to the gate of the second switching element 13 when the third switching element 19 is off.

If an AC input voltage is applied to the voltage of V1 and the second switching element 13 is turned on only during the period when the first switching element has the maximum duty ratio, the AC input voltage of FIG. On the other hand, the AC input current shown in FIG. 2B flows, the conduction angle is widened, and the power factor is improved as compared with the conventional example. FIG. 2C shows the current of the second switching element 13, where the positive direction is the drain current and the negative direction is the current of the built-in diode. Although FIG. 1 shows a feedforward type, a flyback type can also be used.

[0022]

As described above, according to the present invention, the alternating current input voltage is applied to cause the current to flow from the precharged capacitor to the transformer only during the period when the first switching element has the maximum duty ratio to continue the oscillation. By doing so, the DC output can be stabilized, low commercial ripple voltage, and the holding time after input cutoff can be secured without increasing the capacity of the capacitor to secure the DC output holding time. Power factor can be improved without loss.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram for explaining the operation of the power factor correction power supply device in the embodiment.

FIG. 3 is a circuit diagram of a conventional feedforward power factor correction power supply device.

4A and 4B are waveform diagrams for explaining the operation of the power factor correction power supply device in the conventional example.

[Explanation of symbols]

 1 AC input power source 2 Noise filter 3 Rectifier circuit 4 Transformer 5 First switching element 6,7,11,18 Diode 8 Choke 9,12,14 Capacitor 10 Control circuit 13 Second switching element 15,16 Resistor 17 Zener diode 19 Third switching element

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H02M 7/217 9180-5H

Claims (1)

[Claims] 1. A rectifier circuit to which an AC input power source is connected via a noise filter, and one of two circuits connected between the output terminals of the rectifier circuit is a primary winding of a transformer and a first switching circuit. A series circuit of elements, another series circuit of a second switching element in which a diode and a diode are connected in parallel so as to turn on a capacitor and an AC input voltage below a certain voltage level, and the transformer for obtaining a DC output. Power factor correction power supply device comprising a rectifying and smoothing circuit connected to the secondary winding of the power supply.