JP3027284B2 - 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 a switching type stabilized DC power supply having an AC input.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration of a conventional AC input switching power supply. The configuration of a conventional AC input switching power supply includes a commercial AC power supply 1, a full-wave rectifier 2, diodes 3, 4, 5, 6, a smoothing capacitor 7, a transformer 8, and a primary winding 9 constituting the same. It comprises a secondary winding 10, a switch element 11, a rectifying and smoothing circuit 12, a load 13, and a control circuit 14. In the operation of the conventional configuration, the input of the commercial AC power supply 1 is rectified by the full-wave rectifier 2 and smoothed by the smoothing capacitor 7 to DC with little ripple, and then the switch element 11 is operated at a frequency higher than the input commercial AC frequency. By turning on and off (2), an AC voltage is applied to the primary winding 9 of the transformer 8 and the output thereof is output to the secondary winding 10 of the transformer 8.
Is supplied to a rectifying / smoothing circuit, rectified and smoothed, and supplied to a load 13 as a DC output voltage. Here, the control circuit 14 detects the output voltage of the rectifying / smoothing circuit 12, and turns on and off the switch element 11 so that the output voltage becomes a predetermined voltage. As described above, this configuration has a function of replacing the input of the commercial AC power supply 1 with a stable DC voltage and outputting the DC voltage.

[0003]

[Problems of the prior art] However, in the conventional configuration,
There are the following problems. FIG. 4 shows operation waveforms of the conventional configuration. In the drawing, Vin (1) indicates the output voltage of the full-wave rectifier 2 with respect to the voltage of the commercial AC power supply 1, and Iin (1) indicates the waveform of the input current from the commercial AC power supply 1. As can be seen from the figure, the conventional configuration has a problem that the input current is surged and the power factor is extremely low.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a high power factor AC input switching power supply having a simple configuration comprising a set of switch elements and a control circuit.

[0005]

According to the present invention, a series circuit of a first transformer and a switch element is connected to the output of a full-wave rectifier connected to an AC power supply, and the output side of the first transformer is connected to the output side of the first transformer. In a switching power supply in which a load is connected via a rectifying / smoothing circuit, both terminals of the AC power supply are connected by diode to one of the primary windings of a second transformer, and the other is connected to the switch element. And the secondary winding of the second transformer is connected to a smoothing capacitor via a diode, and a diode is connected between the terminals of the smoothing capacitor.
And connected between the output terminals of the full-wave rectifier through a resistor.

(3)

1 and 2 are circuit diagrams of an embodiment of the present invention and operation waveform diagrams of respective parts thereof. The configuration of the embodiment of the present invention comprises a commercial AC power supply 15, a full-wave rectifier 16, diodes 17, 18, 19, and 20 constituting the same, a first transformer 21 and a primary winding 22 constituting the same. , Secondary winding 23, switch element 24, rectifying / smoothing circuit 25, and diodes 26, 27, inductor 28, capacitor 29, load 3 constituting the same.
0, control circuit 31, diodes 32 and 33, second transformer 34, and primary winding 35 and secondary winding 3 constituting the same.
6, diodes 37 and 38, and a smoothing capacitor 39.

In this operation, the switch element 24 is turned on and off at a frequency higher than the input commercial AC frequency, and during the ON period, the diode 32 or 33 and the second transformer are supplied from the input commercial power supply 15. 34 primary winding 35
And a current flows through the switch element 24 to store power in the second transformer 34, and during the off period,
The above power is supplied to the smoothing capacitor 3 through the diode 37.
Send to 9. When the voltage Va (FIG. 2A) of the smoothing capacitor 39 is set higher than the minimum operating voltage for performing the constant voltage control of the switching power supply in this manner, the input voltage Vin becomes the voltage Va of the smoothing capacitor 39. Above the first transformer 21 via the full-wave rectifier 16.
, A predetermined input current I1 flows, and during this period, the diode 38 is off. Next, when the input voltage Vin becomes lower than Va, the full-wave rectifier 16 is turned off, and instead, the current Ia flows from the smoothing capacitor 39 to the first transformer 21 via the diode 38 (FIG. 2C). Flows.

In this manner, the voltage applied to the primary winding 22 of the transformer 21 is always maintained higher than the minimum operating voltage for performing the constant voltage control over the entire period of the commercial cycle. Is done. On the other hand, AC input power supply 15
Therefore, the current flowing to the second transformer 34 via the diode 32 or 33 is as follows: (4) Ic in FIG. 4d over the entire period of the commercial cycle. Therefore, the input current Iin (2) is Ib in FIG.
And Ic, and the current waveform is substantially as shown in FIG. 2eIin (2). As described above, in the circuit of the present invention, since the smoothing capacitor 39 is not directly connected to the input, there is no inrush current, and a current like Iin (2) in FIG. Can be realized.

[0009]

As described above, according to the present invention, a power supply having a high power factor and no inrush current can be realized in comparison with a conventional AC input switching power supply.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is an operation waveform diagram of each part of the present invention.

FIG. 3 is a conventional circuit diagram.

FIG. 4 is an operation waveform diagram of each part of the conventional circuit.

[Explanation of symbols]

 15 Commercial AC power supply 16 Full-wave rectifier 21 First transformer 24 Switch element 25 Rectifier smoothing circuit 30 Load 31 Control circuit 34 Second transformer (5) 39 Smoothing capacitor

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 7/06 H02M 7/217

Claims (1)

(57) [Claims] 1. A series circuit of a primary winding of a first transformer and a switch element is connected between output terminals of a full-wave rectifier connected to an AC power supply, and a diode and a smoothing capacitor are connected in parallel with the series circuit. Are connected, and the first transformer 2
A rectifying / smoothing circuit is connected to the next winding, and power is supplied to a load connected between the output terminals of the rectifying / smoothing circuit. A control circuit for controlling the elements is provided, and a first diode and a second diode are respectively connected from both terminals of the AC power supply.
Connected to one terminal of the primary winding of the second transformer, and the other terminal of the primary winding of the second transformer is connected to the primary winding of the first transformer. A switching power supply connected to a connection point of the switch element, wherein a secondary winding of the second transformer is connected between terminals of a smoothing capacitor via a third diode.