JPS63155958A - Horizontal drive circuit - Google Patents

Abstract

PURPOSE:To suppress an overcurrent of a horizontal drive transistor (TR) at application of power without increasing the core size of a transformer by supplying a bias voltage supplied to a base of the horizontal drive TR after a horizontal oscillation circuit starts stable operation. CONSTITUTION:A constant voltage diode 5 is connected to a collector of a drive TR 3 and connected further to a base of the horizontal drive TR 7 via a base resistor 6. The constant voltage diode 5 is conductive at a voltage level at a point (a) at a time t3. The potential at the point (a) rises at a time t1. A constant voltage diode 5 is turned on at the point of time and at a time t2 and the base voltage of the TR 7 is low at the time t2, then the TR 7 is not turned on and since the TR 7 is conductive after the constant voltage diode 5 is conductive at the time t3, no overcurrent flows to the TR 7 as its collector current 17. Thus, the overvoltage of the horizontal drive TR at power application is suppressed without increasing the core size of the transformer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a horizontal drive circuit for a television receiver.

The configuration of the horizontal oscillation, drive and drive circuits of a conventional television receiver is shown in FIG. 1 is a horizontal oscillation circuit, and 2 is a horizontal drive circuit. 3 is a drive transistor. 4,6
8 is a pace resistor that supplies a pace current to the horizontal drive transistor 7, and 8 is a horizontal drive transformer that supplies a base current from a secondary winding to a horizontal deflection output transistor (not shown).

Problems to be Solved by the Invention The horizontal oscillation circuit 1 and the horizontal drive circuit 2 are generally integrated circuits. When the power is turned on, the drive transistor 3 may sometimes start from an off state depending on the operating state of the internal circuit. FIG. 4 shows the waveforms of each part in this case. The voltage at a' rises to t5, and normal on/off operation occurs. On the other hand, the horizontal drive transistor 7 is t
It conducts from 2 and turns off at t, but from t2 to t5
Since the conduction period is long, the current peak in the primary winding of the transformer 8 increases, the transformer 8 becomes saturated, and the current increases further. As a result, when turned off at t5, a large back electromotive force v is generated. As a result, the withstand voltage exceeds the rated voltage of the transistor 7, and there is a risk of destruction.

Therefore, conventionally, the core size of the transformer 8 has been increased to prevent saturation due to excessive current when the power is turned on. This resulted in an increase in cost.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a circuit that can suppress excessive current in a horizontal drive transistor when power is turned on without increasing the core size of a transformer.

Means for Solving the Problems The present invention operates the horizontal drive circuit by configuring the bias voltage to be supplied to the base of the horizontal drive transistor after the horizontal oscillation circuit starts stable operation. It is.

According to the present invention, since the base bias of the horizontal drive circuit is applied after the horizontal oscillation circuit performs stable oscillation operation, it is possible to prevent the collector voltage from being applied to the horizontal drive transistor. It can prevent excessive current from flowing.

Embodiment FIG. 1 shows a horizontal drive circuit in an embodiment of the present invention. In FIG. 1, parts that are the same as those in FIG. 3 are given the same numbers and explanations will be omitted.

In the figure, a constant voltage diode 6 is connected to the collector of the drive transistor 3, and further connected to the base of a horizontal drive transistor 7 via a base resistor 6. This voltage regulator diode 6 is connected at time t in FIG.

conducts at the voltage level at point a at .

Next, its operation will be explained.

In FIG. 2, the potential at point a rises at time t. At this point and at the level of time t2, the constant voltage diode 6
is off, the base voltage of transistor 7 is low at t2 as shown in the figure, so it does not turn on, and tS
Since the transistor 7 becomes conductive only when the constant voltage diode 5 conducts, the collector current I
7, no excessive current will flow.

Effects of the Invention As described above, according to the present invention, excessive voltage at the time of power-on of the horizontal drive transistor can be suppressed without increasing the core size of the horizontal drive transformer.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the horizontal drive circuit of the present invention, FIG. 2 is a waveform diagram of voltage and current at each part in FIG. 1,
FIG. 3 is a circuit diagram of a conventional horizontal drive circuit, and FIG. 4 is a waveform diagram of voltages and currents at various parts in FIG. 1...--Horizontal oscillation circuit, 2...-Horizontal drive circuit, 3...--Horizontal drive transistor, 6...
... Constant voltage diode, 7 ... Horizontal drive transistor, 8 ... Horizontal drive transformer. Name of agent: Patent attorney Toshio Nakao and 1 other person5-
t voltage guide 7- Horizontal drive transistor 8- Horizontal drive transformer Fig. 1 Section 2 ↑ 1 Fig. 3

Claims (1)

[Claims] 1. A horizontal drive circuit comprising a horizontal oscillation circuit, a horizontal drive transistor, and an excessive collector voltage suppression circuit that supplies a base bias voltage of the horizontal drive transistor after the oscillation operation of the horizontal oscillation circuit is stabilized.