JP3505981B2 - Protection circuit for television receiver - Google Patents

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 As a device having this type of function, one described in Japanese Patent Laid-Open No. 9-93452 is known. The conventional technique will be described below with reference to FIG. FIG. 3 shows a protection circuit of a conventional television receiver.

In FIG. 3, the secondary side output voltage of the switching power supply circuit is input to the count circuit of the microcomputer 13,
When this input voltage is repeatedly turned on / off due to intermittent oscillation of the switching power supply circuit, a signal for turning off the power supply relay 9 is output from the microcomputer 13 to stop the power supply to the power supply circuit.

[0004]

However, in this conventional protection circuit for a television receiver, when the AC input power supply voltage continuously repeats a momentary drop, or when the AC input power supply voltage slows up or slows down, Often the secondary output voltage of the switching power supply circuit also fluctuates,
When the intermittent oscillation state should be detected for a certain period, the microcomputer counts the number of times this voltage change occurs, and if it exceeds the set number of times, it makes a false decision as a circuit abnormality and turns off the power relay.
There was a problem that caused F.

The present invention is intended to solve the above-mentioned problems.
When the input power supply voltage continuously decreases instantaneously,
Even when the C input power supply voltage slows up or slows down, the count line in the microcomputer has two output lines, one line has a latch circuit, and each line is input to the AND circuit. OFF
It is an object of the present invention to provide a protection circuit for a television receiver in which the detection accuracy of the intermittent oscillation state can be improved and the erroneous determination as a circuit abnormality can be reduced by adopting the configuration of outputting the signal.

[0006]

A television receiver protection circuit according to the present invention is a conventional television receiver protection circuit in which the output line of the count circuit in the microcomputer is two systems, and one line is provided. Latch circuits are provided and input to each AND circuit, and as a result, the power relay is turned off.
It is characterized in that a signal for causing the output is output.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A first aspect of the present invention is a power supply rectifying bridge diode, a smoothing capacitor, a switching transformer, a switching power supply IC for driving and controlling a switching transistor, a switching transistor, and a switching transistor. Overcurrent detection resistor for detecting overcurrent, rectifier diode of voltage control winding of switching transformer, power relay, its smoothing capacitor, and overcurrent of secondary side output voltage of switching power circuit to load circuit There are two output lines of the overcurrent detection circuit and the count circuit for detecting the current, and a latch circuit is provided on one of the lines to input to the AND circuit, the secondary side load circuit, and the secondary side. And a voltage conversion circuit that converts the output voltage into a voltage that can be input to the microcomputer. In, slow-up of the AC input power supply voltage, even if at the time of slow-down, can realize the protection circuit less television receiver of that erroneous determination circuit fault.

A protection circuit for a television receiver according to an embodiment of the present invention will be described below with reference to FIG.

(First Embodiment) FIG. 1 shows a protection circuit of a television receiver according to a first embodiment of the present invention. The difference from the conventional example shown in FIG. 3 is that an AND circuit 17 is provided in the microcomputer 13, the output result of the count circuit is two systems, a latch circuit is provided on one line, and each line is input to the AND circuit 17. Then, as a result, a signal for turning off the power relay 9 is output.

First, the microcomputer 13 observes the secondary side output voltage from the switching power supply circuit with a counting circuit. The counting circuit divides the count every fixed period and processes the count. The specifications are such that it counts, and if a certain number of times is exceeded, it is detected as abnormal for a certain period. One of the detected results is directly input to the AND circuit 17. The other is input to the latch circuit 16 and then to the AND circuit 17, and the latch circuit 16 controls so as to hold until the next fixed period passes.

The lines that do not pass the latch circuit 16 and the lines that pass the latch circuit 16 are input to the AND circuit 17, so that the output thereof is compared with the current state held by the latch circuit 16 for a certain period before. It becomes 1 within the fixed period
The fact that the abnormality is detected only once is invalidated by the AND circuit 17. Therefore, it is possible to eliminate erroneous determinations in the count circuit that are held in the latch circuit 16 and occur within a certain period.

As a result, in the conventional example, an AC that causes a malfunction
When the input power supply voltage continuously decreases instantaneously,
Even when the C input power supply voltage is slowed up or slowed down, it is less likely to erroneously determine that the circuit is abnormal, and the detection accuracy of the intermittent oscillation state can be improved.

(Second Embodiment) FIG. 2 shows a protection circuit for a television receiver according to a second embodiment of the present invention. The output line of the count circuit of the microcomputer according to the first embodiment has two or more lines, each of which is provided with a latch circuit 16, and a plurality of lines provided with the latch circuit 16 are provided. 17 and the power relay 9 is turned on from the microcomputer 13A as a result.
Output as a signal for FF. With this configuration, as in the case of the first embodiment, even when the AC input power supply voltage continuously and instantaneously drops, or when the AC input power supply voltage slows up or slows down, it is less likely to be erroneously determined as a circuit abnormality, and the intermittent operation is intermittent. The accuracy of oscillation state detection can be improved.

[0014]

As described above, according to the television receiver protection circuit of the present invention, in the conventional television receiver protection circuit, the output line of the count circuit of the microcomputer is further divided into two systems, one of which is provided. By providing a latch circuit on each line and a microcomputer inputting to each AND circuit, a television that is not erroneously determined to be a circuit abnormality even when the AC input power supply voltage slows up or slows down A protection circuit for the John receiver can be realized.

[Brief description of drawings]

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

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

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

[Explanation of symbols]

1 Power rectification bridge diode 2,8,11 Smoothing capacitor 3 switching transformer 4 Switching power supply IC 5 switching transistors 6 Overcurrent detection resistor 7, 10 Rectifying diode 9 power relay 12 Overcurrent detection circuit 13, 13A microcomputer 14 load circuit 15 Voltage conversion circuit 16 Latch circuit 17 AND circuit

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Claims (2)

(57) [Claims] 1. A secondary side output voltage of a switching power supply circuit
A voltage conversion circuit for converting the voltage value of the switching
It is arranged on the power supply line that supplies the power supply voltage to the power supply circuit.
Power relay and the voltage output from the voltage conversion circuit
The number of on / off times is counted at regular intervals to make the
When the number of voltage on / off times exceeds
Counting circuit for outputting an abnormality detection signal, and the counting
A latch circuit for holding the output of the circuit for a certain period of time,
The output of the input circuit and the output of the latch circuit are input.
Power supply circuit according to the output of the AND circuit and the AND circuit.
Relay control that outputs an off signal to control the relay off
Circuit, and the abnormality detection signal is continuously output from the count circuit.
When it is continuously output, the power relay is turned off.
Protection circuit of the television receiver, characterized in that the the like. 2. A secondary side output voltage of a switching power supply circuit.
Voltage conversion circuit for converting the voltage value of the
It is arranged on the power supply line that supplies the power supply voltage to the power supply circuit.
Power relay and the voltage output from the voltage conversion circuit
The number of on / off times is counted at regular intervals to make the
When the number of voltage on / off times exceeds
Counting circuit for outputting an abnormality detection signal, and the counting
A first latch circuit for holding the output of the circuit for a certain period, and 2
The output of the (k-1) th latch circuit at the k
n configured to hold for a certain period by a latch circuit of k
-One latch circuit, the output of the count circuit and the
AND circuit to which outputs of n latch circuits are input,
The power relay is turned off according to the output of the AND circuit.
With a power relay control circuit that outputs an off signal to
Abnormality detection signal is output n times continuously from the counting circuit
A protection circuit for a television receiver , wherein the power relay is turned off when the protection circuit is turned on .