JPH0522931A - Switching power supply device - Google Patents

Abstract

PURPOSE:To contrive to lengthen the life of a smoothing capacitor by intermittently supplying the smoothing capacitor with the output from a rectifier. CONSTITUTION:Power rectified by a diode bridge 1 is smoothed by a power supply circuit 12 and supplied to a control circuit 11. Consequently, the output of PWM control circuit 3 is supplied to a switching circuit 10 by the control circuit 11 and the switch-ing circuit 10 starts switching. Switched power is supplied to and smoothed by a capacitor 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device.

[0002]

2. Description of the Related Art Conventionally, an electronic device using an AC 100V of a commercial power source as an input source requires a rectifier circuit, and in a small device, a power transformer reduces the voltage to several V to several tens V to perform rectification. You have a DC power supply. However, recently, after directly rectifying in the state of 100 V AC, several hundred KH
Switching power supply devices that perform power conversion by high-frequency switching of z or more have been widely used. Most of these adopt the capacitor input method using a diode bridge.

A conventional switching power supply device will be described below with reference to FIG. In FIG. 3, 1 is a diode bridge, 2 is a capacitor for smoothing the output of the diode bridge 1, 3 is a capacitor 3a and a resistor 3b.
PW oscillating at an oscillation frequency determined by the time constant of
The M control unit 4 is a voltage dividing resistor that divides the output of the capacitor 2, and is configured by connecting resistors 4a and 4b in series, and the connection unit 4c is the power supply terminal 3 of the PWM control unit 3.
It is connected to d. Reference numeral 5 denotes a switching transistor which is connected to the output terminal 3c of the PWM control unit and performs switching according to the oscillation of the PWM control unit. Reference numeral 6 denotes a transformer, the primary side 6a of which is connected in series with the switching transistor 5 and is connected to the capacitor 2. 7 extracts the electric power from the transformer 6 and performs waveform shaping and PWM
The power supply unit that supplies power to the control unit 3 includes an extraction unit 7a that extracts power from the transformer 6, a diode 7b that rectifies the extracted power, and a capacitor 7c that smoothes the rectified power. Reference numeral 8 is a diode for rectifying the electric power transformed by the transformer 6, 9 is a capacitor for smoothing the electric power rectified by the diode 8, and an electrolytic capacitor having a large capacity is used to improve smoothness.

The operation of the switching power supply device configured as described above will be described below with reference to the time chart of FIG.

When the current from the AC power source is input to the diode bridge 1, it is full-wave rectified as shown in FIG. 4 (a), smoothed by the capacitor 2 as shown in FIG. 4 (b), and converted into direct current. To be done. As a result, the voltage dividing resistor 4
Since a current flows through the terminal, a voltage is generated at the connection end 4c, the PWM control unit 3 is activated, and switching of the switching transistor 5 is started. This switched electric power is supplied to the primary side of the transformer 6 to transform it. The transformed electric power is converted into direct current by the diode 8 and the capacitor 9. When power is supplied to the transformer 6, the power supply unit 7 supplies power to the PWM control unit 3.

[0006]

However, in the above-mentioned conventional configuration, since the capacitor 2 has a large capacity and the resistance value when not charged is low, the rectifying section is configured as shown in FIG. 4 (c). A large current flows through the capacitor 2 every cycle of the output of the diode bridge 1, which shortens the life of the capacitor.

[0007]

In order to solve the above-mentioned conventional problems, the present invention has a switching unit for intermittently supplying the output of the rectifying unit to the capacitor.

[0008]

According to the present invention, the peak value of the current flowing through the smoothing capacitor is reduced by the above configuration.

[0009]

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

In FIG. 1, 1 is a diode bridge,
2 is a capacitor, 3 is a PWM control unit, 4 is a voltage dividing resistor, 5
Is a switching transistor, 6 is a transformer, 7 is a power supply unit, 8 is a diode, and 9 is a capacitor.

A switching circuit 10 is provided between the capacitor 2 and the diode 1, and includes a switching transistor 10a, a diode 10b for preventing backflow from the capacitor 2 to the diode 1, and a switching transistor 10a when the switching transistor 10a is in an ON state. It is formed of a coil 10c that stores energy and supplies the stored energy to the capacitor 2 when it is off. Reference numeral 11 causes the switching circuit 10 to perform switching using the oscillation of the PWM control unit 3 and outputs the output of the PWM control unit 3 when the voltage from the power supply unit 7 does not reach the regulated supply voltage of the PWM control unit 3. This is a control unit that prevents transmission to the switching transistor 5. Reference numeral 12 denotes a power supply circuit provided in the preceding stage of the switching circuit 10 and connected to the respective power supply terminals of the control unit 11 and the PWM control unit 3.

The operation of the switching power supply device configured as described above will be described below.

When the current from the AC power source is input to the diode bridge 1, it is full-wave rectified. The output from the diode bridge 1 is divided and smoothed by the power supply circuit 12 and supplied to the control circuit 11 and the PWM control unit 3. Therefore, the PWM control unit 3 starts oscillation. This PW
The output from the M control unit 3 is also supplied to the switching circuit 10 via the control unit 11, the switching circuit 10 starts the switching operation, and the current from the diode 1 is interrupted as shown in FIG. To the capacitor 2. Therefore, a current having a low peak value intermittently flows through the capacitor 2 as shown in FIG.

The power supplied from the power supply unit 7 is the PWM control unit 3
When the supply regulation voltage is reached, the control unit 11 controls the output of the PWM control unit 3 to be transmitted to the switching transistor 5.

The output from the capacitor 2 is intermittently supplied to the primary side of the transformer 6 by the switching of the switching transistor 5, so that the transformer 6 transforms and outputs from the secondary side. The output from the secondary side of the transformer is converted into direct current by the diode 8 and the capacitor 9.

When a current is supplied to the transformer 6, an output is obtained from the extraction unit 7a, so that the power supply unit 7 outputs PW.
Power supply to the M control unit 3 is started.

As described above, according to this embodiment, since the capacitor 2 is intermittently supplied with power at a high cycle, the peak value of the current flowing through the capacitor becomes small, so that the load on the smoothing capacitor is reduced. Becomes smaller, and the life of the smoothing capacitor can be extended.

[0018]

According to the present invention, since the switching section for intermittently supplying the output of the rectifying section to the capacitor is provided, the peak value of the current flowing through the capacitor is reduced, so that the load on the smoothing capacitor is reduced and the smoothing capacitor is reduced. The life of the capacitor can be extended.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram of a voltage supplied to a capacitor 2 of the device.

FIG. 3 is a circuit diagram of a conventional switching power supply device.

FIG. 4 is a waveform diagram of a voltage supplied to the capacitor 2 of the device 1 diode bridge 2 capacitor 3 PWM control unit 4 voltage dividing resistor 5 PWM control unit 6 transformer 7 power supply unit 8 diode 9 capacitor 10 switching circuit 11 control unit 12 Power supply circuit

Claims (1)

Claim: What is claimed is: 1. A rectifying unit for rectifying, a capacitor for smoothing voltage and current, a first switching unit for intermittently supplying the output of the rectifying unit to the capacitor, and a voltage. A switching power supply that includes a transformer that converts the output of the capacitor, a second switching unit that intermittently supplies the output of the capacitor to the primary side of the transformer, and a DC conversion unit that converts the output of the secondary side of the transformer to DC. apparatus.