JPH0993452A - Television receiver protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop the operation of a switching power supply circuit completely when intermittent oscillation of the switching power supply circuit due to the operation of an overcurrent limit circuit continues. SOLUTION: A secondary output voltage of a switching power supply circuit is given to a microcomputer 13. When the voltage given to the microcomputer 13 repeats ON/OFF due to intermittent oscillation of the switching power supply circuit, the microcomputer 13 provides an output of a signal to deenergize a power supply relay 9 to stop supply of power to the switching power supply circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a television receiver.

[0002]

2. Description of the Related Art In recent years, the manufacturer's responsibility has been highlighted as to the safety of a television receiver when the circuit is abnormal, and an effective protection circuit is required from the viewpoint of multiple protection when the circuit is abnormal.

A conventional protection circuit for a television receiver will be described below with reference to the drawings.

FIG. 3 is a block diagram of a conventional protection circuit of a television receiver. In FIG. 3, 1 is a power supply rectifying bridge diode, 2 is a smoothing capacitor, 3 is a switching transformer, 4 is a switching power supply IC for driving and controlling a switching transistor, 5 is a switching transistor, and 6 is an overcurrent for detecting an overcurrent of the switching transistor. Detecting resistor, 7 is a rectifying diode for the control winding voltage of the switching transformer, 8 is a smoothing capacitor, 9 is a power relay for opening and closing the power supply to the switching power supply circuit, and 10 is a rectifying diode for the secondary side output voltage of the switching power supply circuit. , 11 is a smoothing capacitor, 12 is an overcurrent detection circuit for detecting an overcurrent of the secondary side output voltage of the switching power supply circuit to the load circuit, 13 is a microcomputer, 1
Reference numeral 4 is a load circuit for the secondary side output voltage of the switching power supply circuit.

The contents of the protection circuit of the television receiver configured as above will be described below.

In order to protect the switching power supply circuit in the case of an abnormality and the switching power supply circuit load 14 in the case of an abnormality, three types of protection circuits are introduced according to each abnormal state.

First, the overcurrent detection circuit 12 detects that the current to the load circuit 14 has increased due to an abnormality of the load circuit 14, inputs this detection signal to the microcomputer 13, and turns off the power supply relay 9. Then, the power supply to the switching power supply circuit is stopped.

Second, the overcurrent detection resistor 6 detects that an overcurrent has flown into the switching transistor 5 due to an abnormal state of the switching power supply circuit, and this detection voltage is limited to an overcurrent in the switching power supply IC 4. Input to the circuit to limit the current of switching transistor 5,
The switching power supply operation is stopped depending on the level of overcurrent.

Thirdly, when the output voltage of the control winding of the switching transformer 3 rises due to an abnormal state of the switching power supply circuit, the overvoltage protection circuit inside the switching power supply IC4 is operated to stop the switching power supply operation.

[0010]

However, in such a conventional protection method, a switching power supply IC is used.
The internal overcurrent limiting circuit 4 is a self-recovery type circuit that is not designed to maintain the operation of the protection circuit in order to protect the circuit by operating the switching power supply circuit even in a normal transient state. Therefore, even if the overcurrent limiting circuit operates due to the circuit abnormality and the switching power supply operation is stopped, the overcurrent does not flow after the stop and the protection operation is canceled. After that, since the overcurrent flows again, an intermittent oscillation state in which the operation of the overcurrent limiting circuit is repeated is repeated.

For this reason, although the abnormal circuit portion does not instantaneously cause expansion damage, there is a problem that if it is left in the intermittent oscillation state for a long time, it may cause expansion damage. .

The present invention solves the above problem by completely stopping the operation of the switching power supply when the overcurrent limiting circuit in the switching power supply IC operates and the intermittent oscillation state of the switching power supply circuit continues. The purpose is to prevent the expansion damage when the circuit is abnormal.

[0013]

In order to achieve the above-mentioned object, the first means of the present invention inputs the secondary side output voltage of a switching power supply circuit to a voltage conversion circuit and then inputs this output voltage to a microcomputer. However, it has a function to count the input voltage so that the microcomputer can judge that this input voltage is in the intermittent input state, and a function to output a signal to turn off the power relay from the microcomputer when the intermittent input state continues. The power relay OFF signal is connected to the power relay.

Further, in order to achieve the above object, the second means of the present invention inputs the input voltage to the overcurrent limiting circuit of the switching power supply IC having the built-in overcurrent limiting circuit and the overvoltage protection circuit to the integrating circuit. The output voltage of this integration circuit is input to the overvoltage protection circuit inside the switching power supply IC.

[0015]

According to the present invention, with the configuration of the first means, when the switching power supply circuit is in the intermittent oscillation state, the secondary side output voltage of the switching power supply circuit repeats ON / OFF. Is counted, and if this state continues for a certain period of time, it is determined that the circuit is abnormal, and the power supply relay is turned off to stop the power supply to the switching power supply circuit.

With the configuration of the second means, when the switching power supply circuit is in the intermittent oscillation state, the input voltage to the overcurrent limiting circuit inside the switching power supply IC is HIGH.
In order to repeat T / LOW, this voltage is integrated, and when the integrated voltage exceeds a certain value, it is determined that the intermittent oscillation state has continued, and this determination signal operates the overvoltage protection circuit inside the switching power supply IC. , Stop the switching power supply circuit operation completely.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a configuration block diagram of a protection circuit of a television receiver according to a first embodiment of the present invention.

In FIG. 1, 1 is a power supply rectifying bridge diode, 2 is a smoothing capacitor, 3 is a switching transformer, 4 is a switching power supply IC for driving and controlling a switching transistor, 5 is a switching transistor, 6
Is an overcurrent detection resistor for detecting an overcurrent of a switching transistor, 7 is a rectifier diode of a control winding voltage of a switching transformer, 8 is a smoothing capacitor, 9 is a power relay for opening and closing power supply to a switching power circuit, and 10 is switching. Rectifier diode for secondary output voltage of power supply circuit, 11 smoothing capacitor, 12 overcurrent detection circuit for detecting overcurrent of secondary output voltage of switching power supply circuit to load circuit, 13 microcomputer, 14 switching A load circuit for the secondary output voltage of the power supply circuit, and 15 is a voltage conversion circuit for converting the secondary output voltage of the switching power supply circuit into a voltage that can be input to the microcomputer.

The contents of the protection circuit of the television receiver configured as described above will be described below.

Depending on the abnormal state of the switching power supply circuit,
When the switching power supply circuit is in the intermittent oscillation state, the secondary side output voltage of the switching power supply circuit repeats ON / OFF, and this voltage is input to the voltage conversion circuit 15, and the microcomputer 1
After being converted into a voltage that can be input to 3, the output voltage is input to the microcomputer 13. The input voltage is counted so that the microcomputer 13 can determine that the input voltage is in the intermittent input state, and when a certain number of times of ON / OFF is repeated, it is determined that an abnormality has occurred in the switching power supply circuit. Further, a signal for turning off the power supply relay 9 is output and the power supply to the switching power supply circuit is stopped by turning off the power supply relay 9.

(Embodiment 2) FIG. 2 is a block diagram showing the configuration of a protection circuit of a television receiver according to a second embodiment of the present invention.

In FIG. 2, 1 is a power supply rectifying bridge diode, 2 is a smoothing capacitor, 3 is a switching transformer, 4 is a switching power supply IC for driving and controlling a switching transistor, 5 is a switching transistor, and 6
Is an overcurrent detection resistor for detecting an overcurrent of a switching transistor, 7 is a rectifier diode of a control winding voltage of a switching transformer, 8 is a smoothing capacitor, 9 is a power relay for opening and closing power supply to a switching power circuit, and 10 is switching. Rectifier diode for secondary output voltage of power supply circuit, 11 smoothing capacitor, 12 overcurrent detection circuit for detecting overcurrent of secondary output voltage of switching power supply circuit to load circuit, 13 microcomputer, 14 switching A load circuit for the secondary side output voltage of the power supply circuit, 16 is an integrating circuit for integrating the input voltage to the overcurrent limiting circuit inside the switching power supply IC, and 17 and 18 are diodes for preventing current in the reverse direction.

The contents of the protection circuit of the television receiver configured as above will be described below.

Depending on the abnormal state of the switching power supply circuit,
When the switching power supply circuit enters the intermittent oscillation state, the input voltage to the overcurrent limiting circuit of the switching power supply IC4 becomes HIG.
In order to repeat HT / LOW, this voltage is applied to the integration circuit 16
When the intermittent oscillation state is maintained for a certain period of time and the integrated voltage exceeds a certain value by inputting the voltage to the integrated circuit 15, the integrating circuit 15 outputs an abnormal detection voltage, and this abnormal detection output voltage is protected against overvoltage in the switching power supply IC4. By inputting the signal to the circuit and operating the overvoltage protection circuit inside the switching power supply IC4, the operation of the switching power supply circuit is completely stopped.

[0026]

As is apparent from the above description, when the switching power supply circuit is abnormal, the operation of the switching power supply can be completely stopped and the damage caused by the expansion of the circuit can be prevented.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a protection circuit of a television receiver according to a first embodiment of the present invention.

FIG. 2 is a configuration block diagram of a protection circuit of a television receiver according to a second embodiment of the present invention.

FIG. 3 is a configuration block diagram of a protection circuit of a conventional television receiver.

[Explanation of symbols]

 1 Power Rectifier Bridge Diode 2 Smoothing Capacitor 3 Switching Transformer 4 Switching Power Supply IC 5 Switching Power Transistor 6 Overcurrent Detection Resistor 7 Rectifier Diode 8 Smoothing Capacitor 9 Power Relay 10 Rectifier Diode 11 Smoothing Capacitor 12 Overcurrent Detection Circuit 13 Microcomputer 14 Load Circuit 15 Voltage conversion circuit 16 Integration circuit 17 Diode 18 Diode

Claims (2)

[Claims] 1. An input voltage for inputting a secondary side output voltage of a switching power supply circuit to a voltage conversion circuit and then to a microcomputer so that the microcomputer can determine that the input voltage is in an intermittent input state. The count function and the power relay is turned off from the microcomputer when the intermittent input state continues.
A protection circuit for a television receiver that has a function to output a signal that turns off the signal and connects the power relay OFF signal from the microcomputer to the power relay. 2. An input voltage to an overcurrent limiting circuit of a switching power supply IC having a built-in overcurrent limiting circuit and an overvoltage protection circuit is input to an integrating circuit, and an output voltage of the integrating circuit is overvoltage protected inside the switching power supply IC. A protection circuit for the television receiver that is input to the circuit.