JPH07312871A - D.c. power supply - Google Patents

Abstract

PURPOSE:To miniaturize a capacitor for service interruption compensation in a DC power supply. CONSTITUTION:An inverting amplifier 21, connected between a control circuit 12 and a first MOS-FET 4, inverts control pulse signals applied to the first MOS-FET 4 relative to those applied to a second MOS-FET 9. As a result, when the pulse width of control pulse signals applied to the second MOS-FET 9 is reduced due to light load or the like, the on-duty of control pulse signals applied to the first MOS-FET 4 is increased. This increases voltage applied to a capacitor 6 for service interruption compensation, and thus allows use of a capacitor 6 of a small capacitance, which enables the miniaturization of capacitors 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply device, and more particularly to a DC power supply device having a power factor improving function.

[0002]

2. Description of the Related Art A conventional DC power supply device, for example, as shown in FIG. 5, is an AC power supply 1 for generating an AC voltage having a commercial frequency.
A diode bridge circuit 3 as a rectifier circuit connected to the filter circuit 2 and a first MOS-FET 4, a reactor 5, and a capacitor 6 as a first switching element connected to the output end of the diode bridge circuit 3. A series circuit, a main freewheeling diode 7 as a main freewheeling rectifying element connected in parallel to a reactor 5 and a capacitor 6 connected in series, and a first MOS-F
Auxiliary freewheeling diode 13 as an auxiliary freewheeling rectifying element connected in parallel with ET4 and reactor 5,
A transformer 8 having a primary winding 8a and a secondary winding 8b, a primary winding 8a of the transformer 8 connected to the output end of the diode bridge circuit 3, and a second MOS-FET 9 as a second switching element. And a series circuit with 2 of transformer 8
A control pulse signal is applied to the load 11 connected to the next winding 8b through the rectifying / smoothing circuit 10 and the gate terminals (control terminals) of the first and second MOS-FETs 4 and 9 to provide the first and the first. The control circuit 12 controls ON / OFF of the two MOS-FETs 4 and 9. The first MOS-FET 4,
The reactor 5, the capacitor 6, the main freewheeling diode 7, and the auxiliary freewheeling diode 13 form a step-down chopper circuit 20. Further, 14 is a rectifying diode, 15 is a smoothing capacitor, 16 is an operational amplifier (operational amplifier), 17 is a reference power source, and 18 and 19 are light emitting diodes and light receiving transistors which constitute a photocoupler.

In the above structure, the AC voltage of the commercial frequency generated by the AC power supply 1 is converted into the DC voltage which is full-wave rectified by the diode bridge circuit 3 through the filter circuit 2. The full-wave rectified DC voltage is supplied to the step-down chopper circuit 20, and the step-down chopper circuit 20 controls the voltage of the capacitor 6. That is, the step-down chopper circuit 20 controls the ON / OFF operation of the first MOS-FET 4 by controlling the pulse width of the control pulse signal applied to the gate terminal of the first MOS-FET 4 by the control circuit 12. Controls the charging voltage V _C of the capacitor 6. Therefore, while the output voltage of the diode bridge circuit 3 is lower than the charging voltage V _C of the capacitor 6, the charging voltage V _C of the capacitor 6 is applied to the primary winding 8a of the transformer 8 and the series circuit of the second MOS-FET 9. To be done. Also,
While the output voltage of the diode bridge circuit 3 is higher than the charging voltage V _{C of the} capacitor 6, the output voltage of the diode bridge circuit 3 is the primary winding 8a of the transformer 8 and the second M
It is directly applied to the series circuit of the OS-FET 9. At this time, the primary winding 8a of the transformer 8 and the second MOS-FET 9
6A shows the waveform of the input voltage V _IN of the series circuit of FIG. In the voltage waveform of FIG. 6A, the flat part is the capacitor 6
Charging voltage V _C , and the sinusoidal portion becomes the output voltage of the diode bridge circuit 3. This widens the conduction angle of the diode bridge circuit 3, so that the input current I
The waveform of _IN becomes the waveform shown in FIG. 6 (B), and the power factor is improved.

The input voltage V _IN shown in FIG. 6 (A) is the second M
When the OS-FET 9 is turned on / off, the voltage is intermittently applied to the primary winding 8a of the transformer 8, and an AC voltage is generated in the primary winding 8a of the transformer 8. Primary winding 8a of transformer 8
An AC voltage proportional to the winding ratio is induced in the secondary winding 8b by the AC voltage generated in the. Secondary winding 8b of transformer 8
The AC voltage induced in the load is rectified and smoothed by the rectifying diode 14 and the smoothing capacitor 15 of the rectifying and smoothing circuit 10, and the reduced or boosted DC voltage is supplied to the load 11. The operational amplifier 16 compares the DC voltage supplied to the load 11 with the voltage V _REF of the reference power source 17, and causes the light emitting diode 18 of the photocoupler to emit light according to the comparison output. As a result, the light receiving transistor 19 of the photocoupler
The control circuit 12 controls the pulse width of the control pulse signal applied to each gate terminal of the first and second MOS-FETs 4 and 9 by the output of the light receiving transistor 19. As a result, the DC voltage supplied to the load 11 is kept constant.

[0005]

By the way, in the DC power supply device of FIG. 5, the on-duty of the control pulse signal generated from the control circuit 12, that is, the ratio of one period of the pulse signal to the on-period of the pulse signal is generally. The maximum is about 50%. Therefore, the capacitor 6 of the step-down chopper circuit 20
The voltage V _C charged to is characterized by being lower than the voltage charged to the capacitor of a capacitor input type rectifier circuit that rectifies commercial alternating current with a rectifier and smoothes it with a capacitor. In particular, in the case of a light load, the pulse width of the control pulse signal becomes very narrow and the on-duty becomes considerably small, so that the charging voltage applied to the capacitor 6 drops significantly. Therefore, in order to sufficiently compensate for the instantaneous power failure of the output voltage of the diode bridge circuit 3 under a light load, the electrostatic capacity of the capacitor 6 for power failure compensation must be sufficiently increased to increase the charging energy. There is a drawback that the outer shape of the capacitor 6 becomes large.

Therefore, an object of the present invention is to provide a DC power supply device which can use a capacitor having a small electrostatic capacity and can miniaturize a capacitor for power failure compensation.

[0007]

A DC power supply device according to the present invention is a rectifier circuit connected to an AC power supply, and a series circuit of a first switching element, a reactor and a capacitor connected to an output terminal of the rectifier circuit. And a step-down chopper circuit composed of a main return rectifier element connected in parallel to the reactor and the capacitor connected in series, a transformer having a primary winding and a secondary winding, and the step-down chopper circuit. A series circuit of the primary winding of the transformer and a second switching element connected to the output terminal, and a load connected to the secondary winding of the transformer via a rectifying and smoothing circuit,
And a control circuit for applying a control signal to each control terminal of the first and second switching elements to control ON / OFF of the first and second switching elements. This DC power supply device is provided with control signal inverting means for inverting the control signal applied to the first switching element and the control signal applied to the second switching element. In the embodiment of the present invention, the control signal inverting means is provided either between the control circuit and the first switching element or between the control circuit and the second switching element. In one embodiment shown, the control signal inverting means is an inverting amplifier, and an auxiliary return rectifying element is connected in parallel to the first switching element and the reactor connected in series. In another embodiment shown in the figure, the control signal inverting means is composed of a drive transformer and a voltage dividing capacitor having two windings whose winding directions are opposite to each other.

[0008]

The control signal inverting means inverts one of the control signal given to the first switching element and the control signal given to the second switching element with respect to the other and gives it to the first switching element. Increase the on-duty of the control signal. As a result, the voltage applied to the power failure compensation capacitor becomes high, so that a capacitor having a small capacitance can be used as the power failure compensation capacitor. For this reason, the capacitor for power failure compensation can be downsized.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a DC power supply device according to the present invention will be described below with reference to FIG. However, in FIG. 1, the same parts as those shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. As shown in FIG. 1, the DC power supply device of the present embodiment is
The output terminal of the control circuit 12 and the first MOS-
An inverting amplifier 21 as control signal inverting means is connected between the gate terminal of the FET 4 and the gate terminal. Other configurations are the same as those of the circuit of FIG. In the above configuration, the control pulse signal applied from the control circuit 12 to the gate terminal of the first MOS-FET 4 is inverted by the inverting amplifier 21 and applied from the control circuit 12 to the gate terminal of the second MOS-FET 9. The control pulse signal is inverted.
Therefore, when the on-duty of the control pulse signal output from the control circuit 12 is reduced to about 10% due to a light load or the like, the on-duty of the control pulse signal applied to the gate terminal of the first MOS-FET 4 is reduced. Is 9
It will be considerably large, around 0%. Therefore, the first MOS
-Since the on-duty of the control pulse signal applied to the gate terminal of the FET 4 is a value of 50% at the minimum and close to 100% at the maximum, the charging voltage applied to the capacitor 6 of the step-down chopper circuit 20 at the time of light load. Can be raised. Further, since the voltage applied to the capacitor 6 at the time of overload can also be increased, the capacitor 6 for power failure compensation may have a small capacitance. Therefore, the capacitor 6
It is possible to reduce the outer shape of the. Regarding the power factor improving effect and the operation of supplying the DC output to the load 11,
Since the operation is basically the same as the circuit operation shown in FIG. 5, the description thereof will be omitted.

The DC power supply device of the embodiment shown in FIG.
It can be changed as shown in. That is, in the DC power supply device shown in FIG. 2, instead of the inverting amplifier 21 in the circuit of FIG. 1, a primary winding 22a and a secondary winding 2 having winding directions opposite to each other are provided.
2b and a driving transformer 22 and a voltage dividing capacitor 23 are connected to constitute a control signal inverting means, and the circuit configuration of the step-down chopper circuit 20 in FIG. It is omitted. Other configurations are the same as those of the circuit of FIG. 1 or FIG.
In the above configuration, when the control pulse signal output from the control circuit 12 is on, that is, when the control pulse signal is a high level voltage, it is applied to the signal line from the control circuit 12 to the gate terminal of the first MOS-FET 4. The high level voltage is divided by the voltage dividing capacitor 23 and the primary winding 22a of the driving transformer 22, and the voltage dividing capacitor 23 is charged. At this time, the secondary winding 22 of the drive transformer 22
Since a voltage having a reverse polarity to the voltage applied to the primary winding 22a is induced in b, the control pulse signal applied to the gate terminal of the first MOS-FET 4 is off, that is, the control pulse signal is It becomes a low level voltage. On the other hand, the second MOS-F
The control pulse signal output from the control circuit 12 is directly applied to the gate terminal of ET9. Next, the control circuit 12
When the control pulse signal from the ON state is turned off, that is, when the control pulse signal changes from the high level voltage to the low level voltage, the voltage dividing capacitor 23 is discharged and a voltage having a polarity opposite to the above is applied to the primary winding of the driving transformer 22. 22a. As a result, a voltage having a polarity opposite to that of the voltage of the primary winding 22a is induced in the secondary winding 22b of the driving transformer 22 and the first MO
The control pulse signal of the S-FET 4 changes from off to on, that is, the control pulse signal changes from a low level voltage to a high level voltage.
Therefore, even in the embodiment shown in FIG.
First MOS-F for control pulse signal of S-FET 9
Since the control pulse signal of ET4 is inverted, the same effect as the embodiment shown in FIG. 1 can be obtained.

The embodiment of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made. For example, in the above embodiment, an example in which a MOS-FET is used as a switching element is shown, but other switching elements such as a bipolar transistor, J-FET (junction field effect transistor), SCR (reverse blocking 3-terminal thyristor), etc. Can also be used. Further, in the above embodiment, an example in which the control signal inverting means is connected between the output terminal of the control circuit 12 and the gate terminal of the first MOS-FET 4 has been shown, but the output terminal of the control circuit 12 and the second A control signal inverting means may be connected to the gate terminal of the MOS-FET 9. The auxiliary free wheeling diode 13 of the circuit of FIG. 1 can be omitted. Further, the step-down chopper circuit 20 in the circuit of the embodiment of FIG.
Alternatively, it may be configured as shown in FIG. In particular, the step-down chopper circuit 20 shown in FIG. 4 has the basic configuration of a step-down chopper. In addition, in the circuit of FIG.
The step-down chopper circuit 20 may be configured by replacing the connection positions of the FET 4 and the capacitor 6 with each other and omitting the diode 7. In the above embodiment, the second MOS-
An example of application to a so-called flyback converter in which the rectifier diode 14 is in the off state when the FET 9 is in the on period has been shown, but the rectifier diode 14 is in the on state when the second MOS-FET 9 is in the on period. It can also be applied to a so-called forward converter.

[0012]

According to the present invention, since the on-duty of the control signal applied to the first switching element is increased, the voltage applied to the capacitor for power failure compensation can be increased. Therefore, the capacitor for power failure compensation may have a small capacity, and therefore there is an advantage that the capacitor can be downsized.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a DC power supply device according to the present invention.

FIG. 2 is an electric circuit diagram showing another embodiment of the present invention.

FIG. 3 is an electric circuit diagram showing a modified embodiment of the circuit of FIG.

FIG. 4 is an electric circuit diagram showing a modified embodiment of the circuit of FIG.

FIG. 5 is an electric circuit diagram showing a conventional DC power supply device.

6 is an input voltage V _IN and an input current I _IN of the circuit of FIG.
Waveform diagram showing

[Explanation of symbols]

1. ． ． AC power supply, 2. ． ． , Filter circuit, 3. ． ．
Diode bridge circuit (rectifier circuit), 4. ． ． First MOS-FET (first switching element), 5. ． ．
Reactor, 6. ． ． Capacitor, 7. ． ． Main freewheeling diode (main freewheeling rectifier), 8. ． ． Transformer, 8
a. ． ． Primary winding, 8b. ． ． Secondary winding, 9. ． ． Second MOS-FET (second switching element), 1
0. ． ． Rectifying and smoothing circuit, 11. ． ． Load, 12. ． ． Control circuit, 13. ． ． Auxiliary freewheeling diode (auxiliary freewheeling rectifying element), 20. ． ． Step-down chopper circuit, 21. ． ．
Inverting amplifier (control signal inverting means), 22. ． ． Drive transformer, 23. ． ． Capacitor for voltage division

Claims (5)

[Claims] 1. A rectifier circuit connected to an AC power supply, a series circuit of a first switching element connected to an output end of the rectifier circuit, a reactor and a capacitor, and the reactor and the capacitor connected in series. A step-down chopper circuit composed of a main circulation rectifying element connected in parallel to the transformer, a transformer having a primary winding and a secondary winding, and one of the transformers connected to the output terminals of the step-down chopper circuit.
Controlling a series circuit of a secondary winding and a second switching element, a load connected to the secondary winding of the transformer via a rectifying and smoothing circuit, and control terminals of the first and second switching elements. In a DC power supply device comprising a control circuit for applying a signal to control ON / OFF of the first and second switching elements, a control signal applied to the first switching element and the second switching element A DC power supply device comprising a control signal inverting means for inverting the control signal to be applied. 2. The "claim 1" wherein the control signal inverting means is provided between the control circuit and the first switching element or between the control circuit and the second switching element. DC power supply. 3. The DC power supply device according to claim 2, wherein the control signal inverting means is an inverting amplifier. 4. The DC power supply device according to claim 2, wherein the control signal inverting means includes a drive transformer having two windings whose winding directions are opposite to each other and a voltage dividing capacitor. 5. The direct current according to claim 1, wherein an auxiliary return rectifying element is connected in parallel to the first switching element and the reactor connected in series. Power supply.