JPS6247031B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a horizontal excitation circuit for a television receiver.

FIG. 1 shows a conventional horizontal excitation circuit that does not use an excitation transformer, and FIG. 3 shows its operating voltage and current waveforms.

The oscillation output voltage a is applied to the base of the excitation transistor 1.
By applying , the base current b flows through the output transistor 2 and the collector current c is switched, thereby operating the horizontal output circuit. At this time, a retrace pulse d is generated at the collector of the output transistor 2.

Normally, a base current waveform shaping circuit including a capacitor 3 and a resistor 4 connected in parallel is connected to the base of the output transistor 2. This is achieved by making the forward base current (represented by I ₁ in Figure 3b) sufficiently large during the period (t ₁ to t ₂ ) in which the output transistor 2 is driven into a conductive state so as to reduce the saturation voltage of the output transistor 2. There is a base resistor 4 in order to reduce the storage _time ( A base capacitor 3 is provided in order to shorten time (t ₂ to _{t 3} ) and improve the cutoff characteristics, and to reverse bias the base-emitter of the output transistor 2 during the retrace pulse generation period.

However, the base resistor 4 must be made small in order to increase I ₁ , but it must be made large so that the base capacitor 3 is not discharged through the base resistor 4 in order to increase I ₂ .
In other words, the conditions required of the base resistor 4 to simultaneously increase I ₁ and I ₂ are contradictory.

Therefore, in the conventional circuit, it has been difficult to obtain stable performance in both the conduction state and the cutoff state for a high-output horizontal output circuit that requires sufficiently large I ₁ and I ₂ .

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a horizontal excitation circuit that reduces the collector-emitter saturation voltage of the output transistor, improves the cutoff characteristics, and operates the horizontal output circuit stably and with high reliability. It is on offer.

In the present invention, a switching element is placed in parallel with the base capacitor of the output transistor, and the switching element is made conductive when a forward base current is applied, and is cut off when a reverse base current is generated or when a retrace pulse is generated. As a result, both I _B1 and -I _B2 can be made large, and even in a high-output horizontal output circuit, the collector-emitter saturation voltage of the output transistor can be reduced and the cutoff characteristics can be improved.

FIG. 2 is a circuit diagram showing an embodiment of the horizontal excitation circuit according to the present invention.

In the figure, an excitation transistor 1, an output transistor 2, and a base capacitor 3 are similar to the conventional circuit shown in FIG.
A collector-emitter path of an NPN type base current control transistor 5 is connected in series with a resistor 4 which is connected in parallel with the resistor 4 . The emitter, collector, and base of this transistor 5 are respectively connected to the base of the output transistor 2, the emitter of the excitation transistor, and a circuit that generates a pulse having the same phase as the oscillation output pulse. The pulse applied to the base of the base current control transistor 5 is set so that the base current control transistor 5 is conductive during the period t ₁ to _{t 2} and cut off during the period t ₂ to _{t 4} .

With this arrangement, during the forward base current period (t ₁ to _{t 2} ) of the output transistor 2, the base current control transistor 5 becomes conductive, and if the base resistance 4 is made small, I ₁ can be made sufficiently large. In addition, the reverse current period and cutoff period (t ₂
~t ₄ ), the base current control transistor 5 is cut off, and the charge in the base capacitor 3 is transferred to the excitation transistor emitter resistor 6 and the output transistor 2.
discharge between the base and emitter of the Therefore,
In the conventional circuit shown in Fig. 1, the charge in the base capacitor 3 was mainly discharged through the base resistor 4, but in this circuit, I _B2 can be made large, and the output transistor is sufficiently discharged even during the retrace pulse generation period. It is possible to reverse bias between the base and emitter of the base capacitor 3 by the electric charge of the base capacitor 3.

In the above embodiment, the base current control transistor 5
Although an NPN type transistor was used as the oscillation output pulse, it is a PNP type transistor whose collector is connected to the base side of output transistor 2, its emitter is connected to the emitter side of excitation transistor 1, and its base is connected to a circuit that generates a pulse with the opposite phase to the oscillation output pulse. However, the operation is the same as in the above embodiment. Further, even if a switching element such as a thyristor is connected instead of a transistor, the same operation can be achieved.

In addition, the pulse that drives the switching element is
Even if it is not completely in phase with the oscillation output pulse or in opposite phase, as long as it drives the switching element from the conductive state to the cut-off state near the time (t ₂ ) when the output transistor 2 starts to be excited to the cut-off state. , almost the same effect can be expected.

The same applies even when there is no excitation transistor as in this embodiment and the output transistor is directly excited by the oscillation output.

According to the present invention, the collector-emitter saturation voltage of the output transistor 2 can be lowered and the cut-off characteristics can be improved, and the output transistor 2 can be sufficiently excited to the cut-off state during the retrace pulse generation period.

This makes it possible to stably and reliably excite the output transistor 2 even in a high-output horizontal output circuit using an inexpensive circuit without an excitation transformer.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional horizontal excitation circuit, Fig. 2 is a circuit diagram showing an embodiment of the horizontal excitation circuit according to the present invention, and Fig. 3 is an operating voltage and current of the main parts of the horizontal excitation circuit according to the present invention. It is a figure which shows a waveform. 2...Horizontal output transistor, 3...Capacitor, 4...Resistor, 5...Transistor.

Claims (1)

[Claims] 1 Consists of a horizontal output transistor, an excitation stage that generates an excitation signal to turn on and off the horizontal output transistor, a capacitor connected between the base of the horizontal output transistor and the excitation stage, a resistor, and a switching element. The switching element changes from a conductive state to a cut-off state when the horizontal output transistor starts to be excited to the cut-off state, and then becomes conductive again when the horizontal output transistor starts conducting. A horizontal excitation circuit characterized by being in a state.