JPH0759038B2 - Protection device for television receiver - Google Patents

Description

TECHNICAL FIELD The present invention relates to a protection device in a television receiver.

2. Description of the Related Art In a television receiver, a short circuit test of parts is carried out based on the Electrical Appliance and Material Control Law, and a circuit design satisfying this test is made.

Now, in FIG. 3, between the terminals A of the heater winding 2 on the secondary side of the flyback transformer 1 whose primary side and secondary side are insulated.
Consider the case where the short circuit test of -B is performed. More current than usual flows in the primary side power supply + B _{2, and} when the voltage drop across the resistor 8 exceeds 0.7V, the transistor 7 turns on via the base resistor 9 and the collector of the transistor 7 + B ₂
Occurs. This is divided through resistors 10 and 11 to make zener diode 12 conductive, and thyristor 14 is turned on via drive resistor 13. Then, the transistor 16 becomes conductive through the base resistor 15 and the point D becomes low level. As a result, the pulse output from the horizontal oscillation circuit (not shown) and applied to the terminal C is passed through the resistors 3 and 4 to the insulating transformer 5
However, since the output of the isolation transformer 5 becomes low level, the transistor 6 is cut off, the horizontal output circuit stops operating, and the flyback transformer 1 stops functioning.

Problems to be Solved by the Invention However, in the case of this protection circuit, the number of parts is large and there is a problem in terms of cost. Further, since the + B ₂ current increase is detected, there is a problem that malfunctions occur even in normal operation due to variations.

The present invention solves such a problem, and configures a protection circuit at a low cost so that no malfunction occurs.

Means for Solving the Problems A protective device according to the present invention is provided with a circuit for rectifying and smoothing the voltage of a heater winding, and when a main power switch and a power switch are turned on, a predetermined time generated from a microcomputer is generated. An output pulse having a width is obtained, and the operation of the horizontal output circuit is controlled by using this output pulse and the rectified voltage.

Operation According to the present invention, when the heater winding terminals are short-circuited,
The horizontal output circuit stops its operation immediately, and there is an advantage that there is no malfunction due to a normal increase in current.

Embodiment A protective device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, 17 is a rectifying diode, 18 is a smoothing capacitor, 19 and 20 are switching diodes, and 21 and 22 are switching transistors. E is the power supply voltage, and G is the output pulse of the microcomputer.

Voltage F rectified and smoothed by diode 17 and capacitor 18
And the output pulse G of the microcomputer, the switching diode
19 and 20 are connected to the anode side respectively, and the cathode side is commonly connected to the base of the transistor 21 through the base resistance of the switching transistor 21, the collector of the transistor 21 is connected to the base of the transistor 22, and the collector of the transistor 22 is It is connected to the isolation transformer 5.

In FIG. 1, first, the voltage of the heater winding 2 is changed to a diode.
It is rectified by 17 and smoothed by the capacitor 18. The voltage at this point is F. Regarding the time relationship of the voltage at point G, point E, and point F,
This is as shown in FIG. First, when the main power switch is turned on, the power supply voltage E is at a high level until it is turned off. The output pulse G is a high level pulse of about 600 ms after the main power switch is turned on. Even if the main power switch is turned on after the power switch is turned off, a high level pulse is output and the output pulse G Holds a high level, and when the power switch is turned on again, the pulse becomes a low level and disappears a predetermined time after the power switch is turned on. The predetermined time in this case is 600ms, which is the same as when the main power switch was turned on.
The level is high until about 600 ms after the power switch is turned on. On the other hand, the rectified / smoothed voltage F is
It occurs after the power is turned on.

First, in the period of G1 and G2, the output pulse G from the microcomputer is
Is high, the diode 20 is turned on, the transistor 21 is turned on, the transistor 22 is cut off, and the isolation transformer 5 continues normal operation. During the period of H ₁ and H ₂ , the diodes 19 and 20 are both turned on, and the same movement as above is performed. During the period of I ₁ and I ₂ , the diode 19 is turned on and the same movement as above is performed.

Here, when the short circuit test of the terminals A and B is performed in a state where the television receiver is operating, this is a rectification / compression during the period of I ₁ and I _2.
This is a case where the smoothed voltage F becomes low level. In this case, both the diodes 19 and 20 are turned off and the transistor 21
Is cut off, the transistor 22 is turned on, the point H becomes low level, the transistor 6 is turned off, and the horizontal output circuit stops operating.

As described above, if the main power switch is on and the television receiver is operating normally, the rectified voltage of the heater winding is always set and the short circuit occurs when there is no microcomputer output pulse. At this time, the operation of the horizontal output circuit is stopped if the rectified voltage disappears.Therefore, due to the relationship between the presence or absence of the microcomputer output pulse and the presence or absence of the rectified voltage, there is no malfunction in current increase other than when the heater winding is short-circuited. When the heater winding is short-circuited, the operation of the horizontal output circuit can be stopped without fail.

As described above, according to the present invention, by using the rectified voltage of the heater winding on the secondary side of the flyback transformer and the output pulse of the microcomputer, the short circuit test of the heater winding can be performed.
Be sure to stop the horizontal output circuit. Further, since the present circuit operates only during the short-circuit test of the heater winding, there is no problem of malfunction due to a normal current increase, and the circuit can be constructed at low cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a protection device for a television receiver according to an embodiment of the present invention, FIG. 2 is a timing chart diagram of the device, and FIG. 3 is a circuit diagram of a protection device of a conventional example. 1 ... Flyback transformer, 2 ... Heater winding, 17 ...
… Rectifying diode, 18… Smoothing capacitor, 19, 20 ……
Switching diodes, 21, 22 ... Transistors.

Claims (1)

[Claims] 1. A micro that outputs a pulse having a predetermined time width that occurs when the main power switch is turned on or off, and that disappears after a predetermined time from when the main power switch or the power switch is turned on. 2 of computer and flyback transformer with primary side and secondary side insulated
First means for rectifying and smoothing the voltage of the heater winding on the next side to output a rectified voltage within a predetermined time of a pulse having a predetermined time width output from the microcomputer; and a predetermined means generated from the microcomputer. Second means having a switching circuit to which an output pulse having a time width of 5 and a rectified voltage of the heater winding are applied in parallel, and a DC voltage is supplied to the second means at the same time when the main power switch is turned on. A protection device for a television receiver, comprising: a power supply voltage supply means; and an output of the second means connected in parallel to a horizontal oscillation circuit.