JPH066627A - Fault state protection circuit - Google Patents

Abstract

PURPOSE:To provide the inexpensive fault state protection circuit with less number of components by superimposing an output signal of a fault detection circuit on a signal of one photocoupler so as to stop the power supply. CONSTITUTION:When an overcurrent or overvoltage or the like takes place due to a damaged circuit or the like, a fault state detection circuit 13 detects the occurrence and outputs a high level fault signal while usually outputting a low level signal. Then a transistor (TR) 16 is turned on, a terminal No2 of a photocoupler 12 is grounded, a voltage at a primary terminal No3 of the photocoupler 12 changes from a low to a high level. The photocoupler 12 is in operation in a voltage range from A to B normally, but since the TR 16 is turned on by a fault signal and a low level voltage is superimposed, a voltage C is obtained and the output of the photocoupler in the operating range between D and E changes into a voltage F. The voltage is used for a fault signal and inputted to a power supply stop circuit 11 to stop the power supply.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, television receivers and the like have a circuit for detecting an abnormal condition and stopping the power supply in order to prevent smoke and ignition caused by overcurrent, overvoltage, etc. that have flown due to circuit breakdown or the like. There is.

A conventional abnormal state protection circuit will be described below. FIG. 3 shows a configuration of a conventional abnormal state protection circuit. In FIG. 3, reference numeral 11 is a power supply stop circuit for actually stopping the power supply. Reference numeral 12 is a photocoupler for power source stabilization feedback. Reference numeral 13 is an abnormal state detection circuit, and 14 is a photocoupler for transmitting the output signal to the power supply primary side and inputting it to the power supply stop circuit.

The operation of the conventional abnormal state protection circuit configured as described above will be described below. First, when an abnormal state such as overcurrent or overvoltage occurs due to circuit breakdown or the like, the abnormal state detection circuit 13 outputs an abnormal signal. When the No. 1 terminal of the photocoupler 14 receives the output signal, a current flows from the No. 1 terminal to the No. 2 terminal.
The current depends on the characteristics of the photocoupler, and the photocoupler 1
It is output to the 4th terminal. It becomes an abnormal signal,
When input to the power supply stop circuit 11, the power supply is stopped.

[0005]

However, the above-mentioned conventional structure has two photocouplers, which is difficult to mount on a printed circuit board and has a problem of high cost.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an abnormal state protection circuit which is space-saving, has a small number of parts, and is inexpensive.

[0007]

The abnormal state protection circuit of the present invention has a structure in which the output signal of the abnormal state detection circuit is superimposed on one photocoupler to stop the power supply.

[0008]

With this configuration, the number of photocouplers can be reduced, the printed circuit board can have a small area, the number of parts can be reduced, and an inexpensive abnormal state protection circuit can be realized.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 11 is a power supply stop circuit for actually stopping the power supply. Reference numeral 12 is a photocoupler, which is used for feedback of power source stabilization and which transmits an abnormal signal to the primary side. An abnormal state detection circuit 13 outputs an abnormal signal. Reference numeral 15 is a diode and 16 is a transistor.

The operation of the abnormal state protection circuit configured as described above will be described with reference to FIG. First, as in the conventional example, when an overcurrent, an overvoltage, or the like occurs due to the breakdown of the circuit, the abnormal state detection circuit 13 detects it,
Normally, the LOW signal outputs a HIGH abnormal signal. Then, the transistor 16 is turned on, and the photocoupler 1
The 2nd terminal of 2 is grounded and the primary side of the photocoupler 3
The voltage of the No. terminal changes from LOW to HIGH. The photocoupler 12 normally operates in the voltage range of A to B in FIG. 2, but since the transistor 16 is turned on by an abnormal signal and the LOW voltage is superimposed, the voltage of the C becomes and the output of the photocoupler also becomes D. The operating range from to E becomes the voltage of F. This voltage is input to the power supply stop circuit as an abnormal signal to stop the power supply.

[0012]

As described above, according to the present invention, an abnormal state of a circuit such as an overcurrent or an overvoltage is detected, and the abnormal signal is superposed on a photocoupler for feedback for stabilizing a power supply which is presently used. It is possible to realize an excellent abnormal state protection circuit that does not occupy an area, has a small number of parts, and can reduce cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an abnormal state protection circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation range of the photocoupler in the embodiment of FIG.

FIG. 3 is a block diagram of a conventional abnormal state protection circuit.

[Explanation of symbols]

 11 Power Stop Circuit 12 Photo Coupler 13 Abnormal State Detection Circuit 15 Diode 16 Transistor

Claims (1)

[Claims] 1. An abnormal condition protection circuit comprising a photocoupler for power supply stabilization feedback, and a function for superimposing an output signal of the abnormality detection circuit to stop oscillation on the primary side of the power supply.