JPH0723560A - Switching power supply - Google Patents

Abstract

PURPOSE:To provide an AC input switch power supply in which the duty ratio of switch element can be set freely at high power factor for the input and output voltage ratio through a simple constitution comprising a set of switch element and control circuit. CONSTITUTION:A series circuit of an inductor 21 having a center tap and a switch element 24 is connected between the output terminals of a full-wave rectifier 16 connected with an AC power supply 15. A control circuit feeds power from the center tap of the inductor through a rectifying/smoothing circuit 25 to a load 28 and, at the same time, detects the output voltage of the rectifying/smoothing circuit 25 and turns the switch element 24 ON/OFF to produce a predetermined voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type DC stabilized power supply device which receives AC as an input.

[0002]

2. Description of the Related Art FIG. 4 shows the configuration of a conventional AC input switching power supply. The conventional AC input switching power supply is composed of a commercial AC power supply 1, a full-wave rectifier 2, diodes 3, 4, 5, and 6 constituting the commercial AC power supply 2, a smoothing capacitor 7, a transformer 8 and a primary winding 9 thereof. The secondary winding 10, the switching element 11, the rectifying / smoothing circuit 12, the load 13, and the control circuit 14. The operation of this conventional configuration is such that 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 a DC with less ripple (2), and then the switch element 11 is switched from the input commercial AC frequency. By turning on and off at a high frequency, an AC voltage is applied to the primary winding 9 of the transformer 8, and its output is applied to the primary winding 9 of the transformer 8, and its output is
The secondary winding 10 of the transformer 8 applies the rectifying and smoothing circuit to rectify and smooth the rectifying and smoothing circuit, and the DC output voltage is applied to the load 13. Here, the control circuit 14 detects the output voltage of the rectifier circuit 12 and turns on and off the switch element 11 so that it becomes a predetermined voltage. As described above, this configuration has a function of exchanging the input of the commercial AC power supply 1 with a stable DC voltage and outputting the DC voltage.

[0003]

[Problems of Prior Art] However, in the conventional configuration,
There are the following problems. FIG. 5 shows operation waveforms of the conventional configuration. In the figure, Vin (1) shows the output voltage of the full-wave rectifier 2 with respect to the voltage of the commercial AC power supply 1, and Iin (1) shows 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 becomes a surge 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 a simple structure including a pair of switch elements and a control circuit, and has a high power factor and a switch element with respect to an input / output voltage ratio. It is an object of the present invention to provide an AC input switching power supply whose duty ratio can be freely set.

[0005]

According to the present invention, a series circuit of an inductor having a center tap and a switching element is connected between the output terminals of a full-wave rectifier connected to an AC power source, and the center of the inductor is connected. A power supply is provided from the tap to the load through the rectifying / smoothing circuit, and at the same time, a control circuit is provided for detecting the output voltage of the rectifying / smoothing circuit and turning on / off the switch element so that the output voltage becomes a predetermined voltage. To do. (3)

[0006]

1 and 3 are a circuit diagram of a first embodiment of the present invention and operation waveform diagrams of respective parts thereof. This configuration includes a commercial AC power source 1, a full-wave rectifier 16 and a diode that constitutes the rectifier.
Inductors 17, 18, 19, 20 and an inductor 21 having a center tap, and a front winding 22 constituting the inductor 21.
And the rear winding 23, switch element 24, rectifying and smoothing circuit 2
5, a diode 26 constituting the same, a smoothing capacitor 27, a load 25, and a control circuit 29. Let the inductance of the inductor 21 having a center tap be L
1, the number of turns of the front winding 22 is N1, and the number of turns of the rear winding 2 is 2.
If the number of turns of 3 is N2, the inductance L2 of the winding 22 at the front is

[Equation 1] become that way. When the switch element 34 is turned on and off at a frequency higher than that of the AC input power supply 15, the input current Iin
The current waveform of (2) is as shown in FIG. 3b. In the figure, ton
Is the ON period t off−1 of the switch element 24, the period t 0 from when the switch element 24 is turned OFF until the input current Iin (2) becomes zero amperes, the ON / OFF cycle of the switch element 24, Ip− 1 is the current value of the input current Iin (2) immediately before the switch element 24 is turned off, and Ip-2 is the current value immediately after it is turned off. If the input voltage is Vin (2), Ip-1 is

[Equation 2] And Ip-2 is

[Equation 3] It is represented by.

Therefore, the output voltage of the rectifying / smoothing circuit 25 is set to V
out will be toff-1

[Equation 4] become that way.

As can be seen from the equation (4), in the first embodiment of the present invention, the turn ratio of the front portion and the rear portion of the inductor 21 having the center tap with respect to the voltage conversion ratio of an arbitrary input / output (4) force. , The duty ratio (ton / to) of the switch element 24 can be freely set. Also, the input current Iin (2)
The average value of the high frequency switching cycle of

[Equation 5] And the waveform is as shown in FIG. 3c. Therefore, as can be seen from FIG. 3, if a low-pass filter for removing high-frequency ripple is used immediately before or after the full-wave rectifier 16 with respect to the input current Iin (2), the input current waveform becomes Iin (2) above. (2) It becomes like ave, and its waveform is almost similar to a sine wave, and the power factor can be increased.

FIG. 2 is a block diagram of another embodiment of the present invention. In the figure, the same components as those in FIG.
The description is omitted. The portion different from FIG. 2 shows an example using a DC-DC converter as a load, which includes an inductor 27 having a center tap and a switch element 24.
A diode 30 is inserted between the two, and a rectifying / smoothing circuit 25
A series circuit of the primary winding 32 of the transformer 31 and the switch element 24 is connected to the output terminal of the transformer 31.
The load 39 is connected to the secondary winding 33 of the second rectifying / smoothing circuit 34 through the second rectifying / smoothing circuit 34, and the control circuit 40 controls the switch element 24 so that the output voltage of the second rectifying / smoothing circuit becomes a predetermined voltage. Turn on and off. The operation of this embodiment of the present invention is performed independently while the switch element 24 shares the operation of the switching element of the DC-DC converter, and the effect of the present invention is the same, so the description thereof is omitted. To do.

[0009]

As described above, according to the present invention, the duty ratio of the switching element can be freely set with respect to the voltage ratio of input and output with a high power factor in the conventional AC input switching power supply. It is possible to realize a switching power supply with an AC input. (5)

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 is an operation waveform diagram of each part of the present invention (FIG. 1)

FIG. 4 Conventional circuit diagram

FIG. 5 is an operation waveform diagram of each part of a conventional circuit

[Explanation of symbols]

 15 Commercial AC power supply 16 Full-wave rectifier 21 Inductor 24 Switch element 25 Rectifier smoother 28, 39 Load 31 Transformer 40 Control circuit

Claims (4)

[Claims] 1. A series circuit of an inductor having a center tap and a switch element is connected between output terminals of a full-wave rectifier connected to an AC power source, and the center tap of the inductor is connected to a load via a rectifying / smoothing circuit. A switching power supply having a control circuit for detecting the output voltage of the rectifying / smoothing circuit and turning on / off the switch element so that the output voltage becomes a predetermined voltage at the same time as supplying electric power. 2. A D provided with a switching element as a load.
2. A C-DC converter is used.
Switching power supply described. 3. A switch element having a function of a switching element for a converter as well.
Switching power supply described. 4. The switching power supply according to claim 3, wherein the control circuit detects the output voltage of the converter and controls the switching element to be turned on and off.