JPH07264865A - Switching power circuit - Google Patents

Abstract

PURPOSE:To provide a small-sized switching circuit that enables the improvement of power factor and the holding of output in power interruption, as a power supply that converts commercial power into stable direct current and outputs the obtained direct current. CONSTITUTION:The title switching power supply consists of a rectifying circuit 2 that rectifies a.c. input; a first switching means 3 that switches the output of the rectifying circuit; a transformer 4 that outputs the switched output of the rectifying circuit 2 to the secondary side; a smoothing section 5 that smooths the output of the transformer 4; a first control circuit 6 that controls on/off of the switching means 3; a serial circuit means composed of a diode 8 and a capacitor 7, connected in parallel with the rectifying circuit 2; a second switching means 9 connected in parallel with the diode 8; and a second control circuit 10 that controls on/off of the switching means 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for converting a commercial power supply into a stable direct current and outputting the same, and more particularly to improving the power factor of a switching power supply.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram of a capacitor input type forward switching power supply according to the prior art. In FIG. 4, 100 is an AC power supply, 200 is a rectifier circuit, 300 is a switch element, 400 is a transformer,
Reference numeral 500 is a smoothing circuit, 600 is a control circuit, and 700 is a smoothing capacitor.

The operation of this circuit will be described below. The power supplied from the AC power supply 100 is supplied to the four diodes 201.
To 204 are converted into full-wave rectified waves (waveform A in FIG. 6), and the full-wave rectified waves are smoothed by the smoothing capacitor 700 to obtain smoothed voltage (waveform B in FIG. 6). The smoothed voltage is chopped in a pulse shape by the switch element 300 that repeatedly turns on / off in accordance with a signal from the control circuit 600, and is converted into a stable DC voltage by the smoothing unit 25 via the transformer 24.

The control circuit 600 detects the output voltage and performs on / off control of the switch element 300 so as to stabilize the output voltage. However, the charging current for charging the smoothing capacitor 700 does not flow for the entire period of the AC cycle, and a sudden current (waveform C in FIG. 6) flows within a short time. This current contains a large amount of harmonic components. Since the power factor decreases as more harmonic components are included, the decrease in power factor has been a problem in the circuit shown in FIG.

FIG. 5 is a circuit configuration diagram of a forward type switching power supply for the purpose of improving the power factor in order to solve the problem in FIG. The operation of this circuit is as follows. The voltage supplied from the AC power supply 100 is converted into a full-wave rectified wave (waveform A in FIG. 7) by the rectifier circuit 200 including the four diodes 201 to 202. This full-wave rectified wave is turned on / off according to the signal from the control circuit 601.
It is switched by the switching means 300 which is repeatedly turned off.

The control circuit 601 detects the output voltage, stabilizes the output voltage, monitors the voltage and current of the AC power supply 100, and controls the on / off of the switch element 300 so that the input current Iin has a sine wave shape. I do. The waveform of the switched input current is the waveform C shown in FIG.
However, when the average value is taken, it becomes a sine wave like a waveform C2.

The switched full-wave rectified wave is converted into a stable DC output by the smoothing circuit 25 via the transformer 24. As described above, the circuit shown in FIG.
00 is removed and the input current is made sinusoidal to improve the power factor.

[0008]

The circuit shown in FIG. 5 cannot hold the output voltage when the AC power supply 1 fails. In order to maintain the output, it is possible to insert a capacitor for energy storage on the primary side or the secondary side. However, when a capacitor is inserted in the primary side, it becomes like the capacitor input type switching power supply shown in FIG. 4, which causes a decrease in power factor. In addition, when a capacitor is inserted in the secondary side, the secondary side voltage is lower than the primary side voltage, so that a large capacity capacitor is required and the volume of the power source becomes large.

[0009] Therefore, an object of the present invention is to provide a small-sized switching power supply which can improve the power factor and can maintain the output during a power failure.

[0010]

FIG. 1 shows the principle of the present invention. That is, the switching power supply of the present invention is the AC power supply 1
The rectifier circuit 2 for rectifying the alternating current from the rectifier, the first switch means 3 for switching the output of the rectifier circuit 2, and the output of the rectifier circuit 2 switched by the switch means 3 are input to the primary side for conversion. 4 to output to the secondary side
A smoothing section 5 for smoothing the secondary side output of the transformer 4, and a first control circuit 6 for controlling the opening / closing of the switching means 5.
And a capacitor 7 connected in parallel to the output of the rectifier circuit 2.
And a diode 8 in series circuit means, a second switch means 9 connected in parallel to the diode 8, and a switch means 9
The second control circuit 10 controls the opening and closing of the.

[0011]

In normal operation, the second switch means 9 is off, and when the voltage from the AC power supply 1 is applied, it is rectified by the rectifier circuit 2 and the capacitor 7 is charged through the diode 8. When the capacitor 7 is charged to the peak value of the voltage of the AC power supply 1, the diode 8 is turned off, the capacitor is disconnected from the circuit, and the input current has a sine wave shape, so that the power factor is improved.

When the second control circuit 10 detects a power failure, the switch 9 is turned on and the capacitor 7 is discharged, so that the output voltage can be maintained for a certain period of time.

[0013]

FIG. 2 is a circuit diagram of the first embodiment of the present invention. FIG. 3 is a circuit configuration diagram in the second embodiment of the present invention. 2 and 3, parts that are the same as or correspond to those shown in FIG. 1 will be described using the same reference numerals.

Reference numeral 1 is an AC power supply, which supplies commercial power of AC100V. Reference numeral 2 denotes a rectifier circuit, in which four diodes 21 to 24 are bridge-connected. The output of the AC power supply 1 is converted into a full-wave rectified wave through the rectifier circuit 2. Reference numeral 3 is a transistor as a switch means, and ON / OFF is controlled based on a control signal from a control circuit 6 described later.

Reference numeral 4 denotes a transformer, which is the switch means 3 described above.
The output of the rectifier circuit 2 switched by is transformed and output to the secondary side circuit. A smoothing circuit 5 is composed of diodes 51 and 52, a coil 53, and a capacitor 54, and the output of the smoothing circuit 5 becomes the DC output of the switching power supply. Although the forward type circuit configuration is adopted in the present embodiment, a flyback type circuit configuration may be adopted.

Reference numeral 6 is a first control circuit which detects the output voltage of the smoothing circuit 5 so that the output voltage becomes stable DC, and rectifies it through the output voltage of the AC power supply 1 and the current transformer 61. The output current of the circuit is input, and the on / off of the switching transistor 3 is controlled so that the input current Iin has a sine wave shape. Here, the output voltage of the AC power supply 1 is used as a reference sine wave when the input current Iin is controlled to be a sine wave, and the output current is incorporated in order to recognize the current value.

Reference numeral 7 denotes a capacitor which serves as an energy supply source when the AC power supply 1 fails. Reference numeral 8 is a diode, which is connected in a direction in which the input current Iin is conducted. Reference numeral 9 denotes a switch, which is adapted to release the energy stored in the capacitor when turned on.

The connection positions of the parallel circuit composed of the diode 8 and the switch 9 and the capacitor 7 may be exchanged. Although a mechanical switch is shown in this figure, a semiconductor switch such as a transistor or a photocoupler may be used. 10 is a second control circuit, the power failure detection circuit 11 monitors the output voltage of the AC power supply 1, and according to the voltage value,
The switch on / off circuit 12 controls on / off of the switch 9. Although the power failure detection circuit 11 monitors the power failure of the AC power supply 1 here, it may be configured to monitor the rectifier circuit 2 or the voltage drop of the output of the smoothing circuit 5 as shown in FIG.

The operation of this embodiment will be described below. When power is supplied from the AC power supply 1, the rectifier circuit 2 converts the power into a full-wave rectified wave. Switch 9 during normal operation
Is in the off state, and the full-wave rectified wave charges the capacitor 7 via the diode 8. When the voltage across the capacitor 7 reaches the peak voltage of the AC power source 1, the charging is completed and the diode 8 is turned off, so that the capacitor 7 is disconnected from the circuit.

The equivalent circuit in this state is the same as the circuit shown in FIG. 5, and since the control circuit 6 controls the on / off of the switching transistor 3 so that the input current Iin has a sine wave shape, the power factor is improved. It Further, the switched full-wave rectification is transmitted through the transformer 24 to the smoothing unit 2
5 and is converted into a stable DC output.

However, when the power failure detection circuit 11 detects the power failure of the AC power supply 1, the switch on / off circuit 12 turns on the switch 9, so that the capacitor starts discharging. The discharged electric power is transmitted to the secondary side circuit via the transformer 4 and converted into a stable DC output by the smoothing circuit 5. In this way, a stable output can be maintained even during a power failure.

[0022]

As described above, according to the present invention, it is possible to provide a switching power supply that improves the power factor and is compact and lightweight and has a recovery function in the event of an input power failure.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional capacitor input type switching power supply.

FIG. 5 is a circuit diagram of a conventional power factor improving switching power supply.

FIG. 6 is an operation explanatory diagram of a capacitor input type switching power supply.

FIG. 7 is an operation explanatory diagram of a conventional power factor correction type switching power supply.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Rectifier circuit 3 ... 1st switch means 4 ... Transformer 5 ... Smoothing circuit 6 ... 1st control circuit 7 ... Capacitor 8 ... Diode 9 ... Second switch means 10 ... Second switch control circuit

Claims (4)

[Claims] 1. A rectifier circuit (2) for rectifying an input from an AC power source (1), a first switch means (3) for switching an output of the rectifier circuit (2), and a transformer for converting the switching output. A transformer (4) for transmitting to the secondary side, a smoothing circuit (5) for smoothing the output of the transformer (4) and converting it to a stable DC output, and controlling the opening and closing of the switch means (3). In a switching power supply circuit having a first control circuit (6), a series circuit means of a diode (8) and a capacitor (7) connected in parallel to the output of the rectifier circuit (2), and the diode (8 ) Is connected in parallel with the second switch means (9), and a second control circuit (10) for controlling the opening and closing of the switch means (9), a switching power supply circuit. 2. The second control circuit (10) controls opening / closing of the second switch means (9) according to an output voltage of the smoothing circuit (5). The switching power supply circuit described. 3. The second control circuit (10) controls opening and closing of the second switch means (9) according to an output voltage of the AC power supply (1). The switching power supply circuit described. 4. The second control circuit (10) controls opening / closing of the second switch means (9) according to an output voltage of the rectifier circuit (2). The switching power supply circuit described.