JPS6233412Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a high voltage protection circuit, and more particularly to a high voltage protection circuit that detects abnormal operation of a horizontal output circuit in a television receiver and prevents abnormally high voltage from being supplied to a cathode ray tube.

FIG. 1 is a diagram of a horizontal output circuit in a television receiver including a conventional flyback transformer. In Figure 1, 1 is a horizontal oscillation circuit, 2 is a horizontal drive transistor, 3 is a horizontal drive transformer, 4 is a power supply, 5 is a horizontal output transistor, 6
is a damper diode, 7 is a resonant capacitor, 8
1 is a deflection coil, 9 is an S correction capacitor, 10 is a flyback transformer, 11 is a high voltage rectifier diode, 12 is a high voltage varistor, 13 is a cathode ray tube, and 14 is a horizontal output circuit.

In the above configuration, if the capacitance value of the resonant capacitor 7 decreases for some reason, for example,
As is well known, the collector voltage of the horizontal output transistor 5 increases, and the high voltage supplied to the cathode ray tube 13 also increases. At this time, the high-pressure varistor 12 operates to prevent the pressure from rising above a certain certain value. However, in this circuit, although the high voltage applied to the cathode ray tube 13 is limited, the high voltage itself continues to be generated. Further, since high voltage is applied even during steady state, the withstand voltage and reliability of the high voltage varistor 12 pose problems. Further, if the horizontal output circuit 14 becomes abnormal, other circuits may be adversely affected, and the protection of the television receiver is insufficient.

Therefore, the main objective of this invention is to provide a high voltage protection circuit that can overcome the above-mentioned problems.

To summarize, this idea can be summarized as follows: In a television receiver, the resistor is
A reference voltage is generated by a Zener diode, a new tertiary winding is provided in the flyback transformer, the voltage generated in the tertiary winding is rectified, and this rectified voltage is compared with the reference voltage. A comparison circuit including a first transistor and a second transistor is provided, and when the horizontal output circuit malfunctions, the first transistor
A high voltage transistor is made non-conductive, a second transistor is made conductive, and a signal is derived from the second transistor to stop the operation of the horizontal output circuit, thereby stopping the high voltage supplied to the cathode ray tube. It is a protection circuit.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 2 is an electrical circuit diagram showing an embodiment of this invention. In FIG. 2, a new tertiary winding 24 is provided in the flyback transformer 10, and a diode 1
Connect to the anode of 5. The cathode of the diode 15 is connected to one end of each of the capacitor 16 and the resistors 17 and 18, and to the base of the transistor 19. The other ends of capacitor 16 and resistor 17 are connected to ground. This diode 1
5 acts as a rectifier, and a capacitor 16 acts as a smoother. The other end of the resistor 18 is connected to the positive electrode side of the power source 4. The collector of the transistor 19 is grounded via a resistor 20, and
Connected to the base of transistor 21. The emitter of transistor 19 is connected to the emitter of transistor 21, one end of resistor 22, and the cathode side of Zener diode 23. This resistance 22
The other end of the Zener diode 23 is connected to the positive electrode side of the power source 4, and the anode side of the Zener diode 23 is connected to the ground. That is, transistors 19 and 21 form a Schmitt circuit.

Here, the connection point between the Zener diode 23, the resistor 22, and the emitters of the transistors 19 and 21 becomes a reference voltage. The collector of the transistor 21 is connected to the base of the horizontal drive transistor 2, and the collector of the horizontal drive transistor 2 is connected to the primary side of the horizontal drive transformer 3. The horizontal output circuit connected to the secondary side of the horizontal drive transformer 3 is the same as that shown in FIG.

In operation, when the power supply 4 is first turned on during normal operation, base current begins to flow through the transistors 19 and 21. However, the collector of transistor 19 is grounded via resistor 20. On the other hand, the collector of the transistor 21 is grounded through the base of the horizontal drive transistor 2 at its emitter. In this way, transistor 1
Since the difference in the loads between transistors 9 and 21 is large, transistor 19 saturates quickly. Therefore, the base and emitter of the transistor 21 become non-conductive.
Collector output is not derived. Therefore, the horizontal drive transistor 2 is not affected. However, for example, when the capacitance value of the resonant capacitor 7 decreases for some reason, the pulse voltage generated in the secondary winding 25 of the flyback transformer 10 increases, as is well known. As a result, the high voltage applied to the cathode ray tube 13 increases. However, the pulse voltage generated in the tertiary winding 24 of the flyback transformer 10 also rises. This allows this pulse voltage to be applied to the diode 15 and capacitor 16.
rectify with. When this output voltage exceeds the aforementioned reference voltage (more precisely, the reference voltage - the base and emitter forward voltage drop of transistor 19), transistor 19 becomes non-conductive, and the voltage across resistor 20 connected to its collector decreases. do. Therefore, the base current of the transistor 21 flows from the collector of the transistor 21 to the horizontal drive transistor 2.
A base current is supplied to the base of the horizontal drive transistor 2 to make the horizontal drive transistor 2 conductive at all times. Therefore, the primary winding of the horizontal drive transformer 3 becomes the ground potential, and the output signal of the horizontal oscillation circuit 1 is no longer supplied to the horizontal drive transformer 3.
4 will stop the operation. Therefore, no high voltage is generated in the secondary winding 25 of the flyback transformer 10, and no high voltage is applied to the cathode ray tube 13. At this time, the pulse voltage generated in the tertiary winding 24 also ceases to occur, but since the bias voltage is applied to the base of the transistor 19 by the resistor 18, this state will remain until the abnormality in the circuit is removed. Hold.

This bias voltage is given by resistors 17 and 18, and the voltage value is between the emitter and the transistor 21.
Collector saturation voltage + horizontal drive transistor 2
It should be selected so that it is slightly higher than the base-emitter forward voltage of. Furthermore, the Zener diode 23 is selected so that this bias voltage does not affect the saturation of the transistor 19 during normal operation.

As described above, according to this embodiment, the abnormal voltage generated in the tertiary winding of the flyback transformer causes the first transistor to become non-conductive, thereby making the second transistor conductive, and furthermore, the horizontal drive transistor Since the load impedance of the tertiary winding of the flyback transformer increases, the first and second
The load on the comparison circuit made up of transistors is reduced, and a stable high-voltage protection circuit can be obtained. Further, no stress is applied to or damage to the horizontal output transistor.

As described above, according to this invention, a simple, inexpensive, and highly reliable high voltage protection circuit can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a horizontal output circuit in a television receiver including a conventional flyback transformer. FIG. 2 is an electrical circuit diagram as an embodiment of this invention. In the figure, 2 is a horizontal drive transistor;
4 is a power supply, 10 is a flyback transformer, 15 is a diode, 16 is a capacitor, 17, 18, 2
2 is a resistor, 19 and 21 are transistors, and 23 is a Zener diode.

Claims (1)

[Scope of utility model registration request] A horizontal drive transistor driven by a horizontal oscillation circuit, a horizontal drive transformer grounded via this horizontal drive transistor, a horizontal output transistor driven by this horizontal drive transformer, and a high voltage driven by this horizontal output transistor to the cathode ray tube. A flyback transformer to be supplied, a diode for rectifying pulses generated in the flyback transformer, a first transistor that is turned on when a reference voltage is applied and turned off when the output voltage of the diode exceeds the reference voltage; A high voltage protection circuit comprising a second transistor that is turned on when the first transistor is off, and forcibly turns on the horizontal drive transistor when the second transistor is on.