JPH1169785A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power factor improved power supply, which can prevent the generation of excessive output voltage at the time of power input or instantaneous stop. SOLUTION: This circuit is provided with a reference voltage increase circuit 15 which increases reference voltage 16 connected to a voltage error amplifying circuit 12 gradually, at the time of power input or after returning from instantaneous stop, and a reset circuit 22 which sets the output voltage of the reference voltage increase circuit 15 to zero at the time of instantaneous stop. For the reference voltage to rise gradually at the time of power input or after returning from instantaneous stop, the output voltage is also raised gradually. By setting the rising time constant C2.R4 of the reference voltage to be larger than the time constants C1.R3 of the feedback cut-off frequency of the output voltage, it is possible to prevent the generation of excessive voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for a color television receiver, a color display device and the like, and more particularly, to a power factor correction power supply circuit for preventing an overvoltage of an output voltage at the time of turning on the power and at the time of a momentary power failure. It is about.

[0002]

2. Description of the Related Art Conventionally, a power factor improving power supply is provided in a chopper circuit with a voltage error amplifier circuit for comparing an output voltage and a reference voltage, a multiplied output of the error amplifier circuit and an input half-wave rectified voltage, and an input current. A current error amplifier circuit for comparing
The on / off period of the switching element is controlled by the output of the current error amplifier circuit, and the input current is made similar to the input half-wave rectified voltage so that the power factor is maintained at approximately 1. Such a known example is described in JP-A-7-87744.

[0003]

In the above prior art, when the cutoff frequency of the output voltage feedback voltage is increased, the effect of improving the power factor is lost, so that the frequency needs to be as low as 10 (Hz) or less. Also, the rise and convergence of the output voltage at the time of a momentary power failure are slow, and an overvoltage may occur.

[0004] It is an object of the present invention to provide a power factor correction power supply which prevents overvoltage at power-on and momentary power failure.

[0005]

In order to achieve the above object, according to the present invention, the value of a reference voltage connected to a voltage error amplifier circuit is gradually increased at the time of power-on and after recovery from a momentary power failure. In addition to the provision of a circuit, a reset circuit for setting the value of the reference voltage connected to the voltage error amplifier circuit to 0 at the time of a momentary power failure is provided to prevent an overvoltage of the output voltage.

[0006] When the power is turned on and after the recovery from the momentary power failure, the reference voltage gradually increases, so that the output voltage also gradually increases. Overvoltage can be prevented by setting the rising time constant of the reference voltage larger than the time constant of the feedback cutoff frequency of the output voltage.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In FIG. 1, when a switch 2 is turned on, a voltage obtained by full-wave rectification of an AC power supply 1 by a bridge diode 3 is input to a chopper circuit including a chopper coil 4, a switching FET 5, a switching diode 6, and a smoothing capacitor 7. The output is supplied to the load 21. Divided value Eo · R2 of output voltage Eo by voltage dividing circuit 13
/ (R1 + R2) and the voltage value Er of the reference voltage 16 are compared by the voltage error amplifier circuit 12. If the divided value of the output voltage Eo is higher, the output of the voltage error amplifier circuit 6 lowers the output voltage Eo of the chopper circuit. If the divided value of the output voltage Eo is lower, the output of the voltage error amplifier circuit 6 is equal to the output voltage E of the chopper circuit.
Acts to raise o. Therefore, the output voltage Eo supplied to the load 21 is Er · (R1 + R2) / R2.

Further, in order to make the input current similar to the input half-wave rectified voltage and to bring the power factor close to 1, the output of the voltage error amplifier circuit 12 and the input half-wave rectified voltage are multiplied by the multiplication circuit 11, and the multiplication circuit 11 The output of the current error amplifier circuit 10 is compared with the voltage detected by the detection resistor 8 and the output of the current error amplifier circuit 10 is input to the on / off circuit 9 and the switching F
Controls the on / off ratio of ET5.

Immediately after the switch 2 is turned on, the voltage E2 inputted to the voltage error amplifier circuit 12 by the reference voltage raising circuit 15
Is 0, the output voltage Eo is also 0. Thereafter, the reference voltage E2 input to the voltage error amplifier circuit 12 gradually increases and finally becomes Er, and the output voltage also becomes Er · (R1 + R2).
/ R2. At this time, the reference voltage raising circuit 1 is obtained from the time constant C1 · R3 of the feedback cutoff frequency circuit 14.
When the time constant C2 · R4 of 5 is increased, no overvoltage occurs.

During an instantaneous interruption, the output E1 of the rectifying and smoothing circuit comprising the rectifying diode 17 and the smoothing capacitor 18 becomes 0, so that the bias circuit 20 turns on the transistor 19 and discharges the capacitor C2 of the reference voltage raising circuit 15. After the recovery from the momentary power failure, the voltage E1 rises and the bias circuit 20 cuts off the transistor 19, so that the reference voltage E2 input to the voltage error amplifier circuit 12 gradually rises.

FIG. 2 shows vin, E in the circuit of FIG.
It is a graph which shows the transient response at the time of power-on of 1, E2, and Eo and at the time of a momentary power failure. In FIG. 2, the switch 2 is turned on at time to, and there is an instantaneous blackout during the period from time t1 to t2. Eo
The graph indicated by the dashed line is a graph when the reference voltage E2 input to the voltage error amplifier circuit 12 does not gradually increase when the power is turned on and after the recovery from the momentary power failure according to the present invention. Indicates that it will occur.

[0013]

According to the present invention, in a power factor improving power supply having a low feedback cut-off frequency, an overvoltage of an output voltage at the time of power-on and at a momentary power failure can be prevented, and a load can be protected from overvoltage.

[Brief description of the drawings]

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

FIG. 2 shows vin, E1, E2 and Eo in the circuit of FIG.
6 is a graph showing transient response at power-on and momentary power failure.

[Explanation of symbols]

1: AC power supply, 2: Switch, 3: Bridge diode, 4: Chopper coil, 5: Switching F
ET, 6: switching diode, 7: smoothing capacitor, 8: detection resistor, 9: on / off circuit, 1
0: current error amplifier circuit, 11: multiplier circuit, 12
... voltage error amplifier circuit, 13 ... voltage divider circuit, 14 ... feedback cutoff frequency circuit, 15 ... reference voltage rise circuit, 16 ... reference voltage, 17 ... rectifier diode, 18 ... smoothing capacitor, 19 ... transistor,
20: bias circuit, 21: load, 22: reset circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 5/63 H04N 5/63 A

Claims (1)

[Claims] 1. A chopper circuit for inputting a voltage obtained by rectifying and smoothing a commercial AC power supply, wherein a voltage obtained by dividing an output voltage of the chopper circuit to a constant value is input to one of an error amplifier circuit and a reference voltage is supplied to the other. In the chopper circuit for controlling the output voltage to a constant value multiple of the reference voltage, after turning on the reference voltage applied to the error amplifier, an integrating circuit for gradually increasing the reference voltage is connected to the error amplifier and the reference voltage reference. A power supply circuit provided between the power supply circuit and a reset circuit that detects a voltage rectified and smoothed separately from the input of the chopper circuit and discharges the output of the integration circuit when the commercial AC power supply stops momentarily.