JPH03239115A - Switching power supply device - Google Patents

Abstract

PURPOSE:To improve safety and a service function by connecting the secondary- output voltage-dividing means of a switching transformer and the relay driver circuit of a power switch relay-driven in the power circuit of a TV receiver. CONSTITUTION:A power switch 1 is paired with a relay 21 in the power circuit of a TV receiver. The relay 21 is controlled by a relay driver circuit 20 connected to split resistors 16 for detecting abnormal voltage on the output side of a switching transformer 9. When secondary side voltage intends to rise by the abnormality of a feedback circuit, secondary side voltage is inhibited to approximately 130V through control windings B1, B2, a diode 13 and a Zener diode 19. The relay driver circuit 20 is operated by secondary side voltage suppressed at 130V, the relay 21 is driven an the power switch 1 is turned OFF. That is, a circuit after the operation of the protective circuit can be checked without generating a secondary defective.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switching power supply device for a television receiver, and more particularly to an overvoltage protection circuit thereof.

2. Description of the Related Art In recent years, the display CRTs of television receivers have become larger, and the power supply circuits for driving them have also become larger in output. Of course, in response to such increased output, it is also necessary to improve security functions, and many circuit configurations have been proposed for protection circuits that can be used in the event of abnormalities in switching power supply circuits.

Hereinafter, a conventional switching power supply protection circuit for a television receiver will be described with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of a conventional switching power supply device. In FIG. 2, 1 is a power switch, 2 is a power rectifier circuit that rectifies alternating current and converts it into direct current, and 3 is a voltage control section for controlling the output voltage of the switching power supply device. The voltage control section 3 is composed of an oscillation section that performs self-excited oscillation, a control section that performs comparison control to maintain the output voltage at a predetermined voltage, and an output section. 4 is a drive circuit that drives the voltage control section 3. Reference numeral 6 designates a bow cutout portion for removing transient pulses generated during switching off, when the drive circuit is off and the oscillation section is off. 6
is a NuNano ζ circuit for suppressing whisker-like pulses generated by switching the switching transformer 7.9. 7 is an opto-isolator that transmits the control voltage of the secondary side of the switching transformer 90 to the primary side;
It also serves as an isolation between the primary and secondary sides. 8
An error detection circuit detects voltage fluctuations on the secondary side of the switching transformer 9 and generates an error voltage according to the difference from a predetermined voltage. 9 is a switching transformer with primary windings p1. p2.Secondary winding S5゜S6, control winding B1. B
It has 2. 10 is a rectifier diode on the secondary side, 11 is a t'Nh capacitor that serves as a bulb letter, and 12 is an avalanche diode. 13 is a diode for generating negative voltage, and 14 is an electrolytic capacitor for filtering the diode 13.

The operation of the conventional switching power supply device for a television receiver configured as described above will be described below.

First, when the switch 1 is turned on, a DC output is obtained by the rectifier circuit 2, and the DC output is applied to the voltage control section 3.

Automatic oscillation of about 60 kHz is started in the oscillation section of the voltage control section 3, and the winding P1. The voltage generated at P2 is applied to the control winding B1°B and the secondary winding S6. It is transmitted to S6. Control winding B1. Due to the voltage generated in B2,
The drive circuit 4 is driven, and the voltage control section 3 is further driven to maintain oscillation. The energy generated on the primary side is transmitted to the secondary side of the switching transformer 9, and the secondary winding S5. A voltage is generated at S6 and rectified by a diode 10° capacitor 1 to obtain a voltage output DC 116V. Voltage fluctuations on the secondary side are detected by the error detection circuit 8 and compared with a reference voltage, after which a signal indicating the error component is output. A signal indicating the error component is input to the opto-isolator 7 and fed back to the primary side, and a button is pressed to the voltage control section 3 to control the oscillation frequency and control the rectified output voltage on the secondary side to a specified value.

Next, using this circuit, we will explain the operation of the protection circuit in an abnormal state where the control range is exceeded. For example, when an optoisolator breaks down, the feedback loop is severed. In this case, frequency control becomes impossible, and the output voltage on the secondary side increases abnormally, destroying the circuit connected to the secondary side. An avalanche diode 12 is provided as a protection circuit for such abnormal conditions.

The avalanche diode 12 has a characteristic that if the avalanche voltage exceeds its own avalanche voltage and the supplied energy is large, it will cause energy destruction (like a power auto) and short-circuit. Conventional protection circuits take advantage of this characteristic by short-circuiting the avalanche diode 12, causing excessive short-circuit current to flow, and activating the overcurrent protection circuit included in the voltage control section on the primary side. .

Problems to be Solved by the Invention However, in the above-mentioned protection circuit, when a serviceman attempts to repair a fault, he finds that the avalanche diode 12 is shorted, so if he removes the avalanche diode 12 and turns on the switch f1, There was a possibility of a secondary failure in which excessive voltage was generated on the secondary side, destroying parts connected to the secondary side. Therefore, it has been desired to develop a protection circuit in case of feedback circuit abnormality.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a switching power supply device having a power protection function that does not cause secondary failures.

Means for Solving the Problem In order to remotely achieve this object, the switching power supply device of the present invention includes an abnormal voltage detection circuit provided on the secondary side of a switching transformer, and a relay drive circuit operated by the detection output of the abnormal voltage detection circuit. , consists of a relay part that controls opening and closing of the power switch according to the output of this relay drive circuit.

Depending on the configuration, it is possible to suppress the voltage rise in the event of an abnormality in the feedback loop, detect the voltage, drive the relay, and quickly turn off the power to protect the circuit.

Embodiment Hereinafter, a switching power supply device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a switching power supply device for a television receiver according to an embodiment of the present invention. Looking at Figure 1,
2 is a rectifier circuit, 3 is a voltage control section, 4 is a drive circuit, 5
1 is a control current extraction unit, 6 is a snubber circuit, 7 is an opto-isolator, 8 is an error detection circuit, 9 is a switching transformer, 10 is a rectifier diode, 11 is an electrolytic capacitor for puller, 13 is a diode for generating negative voltage, 1
Reference numeral 4 designates an electrolytic capacitor, which has the same structure as that shown in FIG. 2, and will be given the same reference numerals and detailed explanation thereof will be omitted.

Now, in FIG. 1, 18 is a resistor, and 19 is a Zener diode that protects the primary side of the opto-isolator 7. 16 (16a, 16b) is a dividing resistor for abnormal voltage detection, and 1 is a Zener diode. A relay drive circuit 20 drives a relay 21 that is paired with the power switch 1.

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

First, when an abnormality occurs and the secondary voltage attempts to rise, the control winding B1. As the voltage of B2 increases 9, the negative voltage generated by the diode 13 also increases.Then, the Zener diode 19 turns on, and the input voltage of the voltage control section 3 is pulled in the negative direction by the action of the Zener diode. The voltage increase is suppressed to a certain value. Although p is determined by the voltage value of the Zener diode 19, the secondary voltage of the switching transformer is suppressed to about 130V. Next, when the secondary side of Tranne 9 is held down to 130V, the voltage divided by dividing resistor 16 is detected by Zener diode 17, which activates relay drive circuit 20, turns off relay 21, and turns off power switch 1. It is. Therefore, since the relay does not drive very quickly, the relay is driven and the power is turned off after allowing the rising voltage to settle down to a level that will not destroy the components.

Effects of the Invention According to the present invention, compared to conventional protection circuits, when a service person checks the circuit after the protection circuit operates, it is possible to do so without the occurrence of secondary failures. We can provide excellent products.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a switching power supply according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional switching power supply.

Claims (1)

[Claims] A power supply rectifier circuit that rectifies an AC power input through a relay-driven switching means, a voltage control section that switches and outputs the rectified output, a switching transformer, a secondary output of the switching transformer, and the voltage control section. an error detection circuit connected between the two, a voltage dividing means for dividing the voltage of the secondary side output voltage section, and a relay driving connected between the voltage dividing means and the switching means driven by the relay. A switching power supply device with a circuit.