JPS6025174Y2 - horizontal output circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to horizontal output circuits used in television receivers, etc., and in particular, the purpose of the invention is to turn off horizontal output transistors reliably and quickly in self-driven horizontal output circuits. shall be.

In current television receivers, the horizontal output transistor is generally driven by a drive circuit using a transformer, but the applicant aims to eliminate the transformer in such a drive circuit and reduce power consumption. We previously proposed that the horizontal output circuit be configured as a self-driven (self-excited) type as shown in FIG.

However, as in the circuit shown in Figure 1, by making the thyristor conductive, the base of the horizontal output transistor
Methods such as shorting the emitters and thereby turning off the horizontal output transistors require a relatively long period of time for the charge accumulated in the base region of the horizontal output transistors to discharge. The disadvantage is that it cannot be turned off.

Therefore, the present invention has been devised in consideration of these points, and the details thereof will be explained below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which 1 is a horizontal output transistor, 2 is a flyback transformer, 3 is a damper diode, 4 is a resonant capacitor, 5 is a horizontal deflection coil, and 6 is a sweep capacitor. In particular, it should be noted that a blocking oscillator is constructed using the transistor 1 and transformer 2 as main elements.

That is, the collector-emitter of the horizontal output transistor 1 and the primary winding 2a of the transformer 2 are connected in series to a DC power supply (10 B), and the pulse voltage generated in the feedback winding 2c of this transformer is connected to the coupling capacitor 7. This is a configuration in which positive feedback is provided to the base of the transistor 1 via the resistor 8 and the resistor 8.

Further, the pulse voltage generated in the low voltage winding 2a of the transformer 2 is rectified and smoothed by a diode 9 and a capacitor 10.
The DC low voltage (+12V) thus obtained is supplied as a power source to the horizontal output circuit 11.

Note that the high voltage winding of the flyback transformer 2 is omitted in the figure.

In the present invention, the self-driving type horizontal output circuit having such a configuration is particularly characterized by the following points.

That is, first, one end of the charge/discharge capacitor 13 is connected to the base of the horizontal output transistor 1, and the other end of this capacitor is connected to the DC low voltage (+12V) line 16 through the resistor 14 and diode 15. In addition, the connection point A between the capacitor 13 and the resistor 14 is grounded via a drive transistor 17 that is turned on by the output of the horizontal oscillator 11.

Next, a second resistor 19 is connected between the power supply (10B) and the connection point A, and a second resistor 20 is connected between the connection point A and the base of the horizontal output transistor 1. The starting current is supplied to the transistor 1 through the first and second resistors 19 and 20.

Note that the diode 21 and the resistor 22 are for clamping to prevent the base-emitter of the horizontal output transistor 1 from being reverse biased beyond a predetermined value.

Next, the operation of the horizontal output circuit will be explained with reference to the signal waveform diagram of FIG.

In Figure 3, the power switch (not shown) is turned on at time to.
When the power is applied (10B), the resistance becomes 19.20.
The base current it+(
Figure 3g) is played.

As a result, collector current tc (see figure b) begins to flow,
This current i.

Since the voltage (e in the figure) generated in the feedback winding 2c of the transformer 2 is positively fed back to the base, the horizontal output transistor 1 is quickly turned on.

Note that FIG. 3C shows the collector voltage waveform of transistor 1.

On the other hand, since charging of the sweep capacitor 6 is completed immediately after the power is turned on, the deflection current iy(
d) in the same figure flows, and this current iy therefore collector current j
c increases.

Then, when this collector current i increases to β times the base N current iB (β is the current amplification factor of the transistor) at time t1, the collector current can no longer continue to increase.

Therefore, the voltage generated in the feedback winding 2c of the flyback transformer becomes zero, and the values of the resistors 19 and 20.8 R19,
Since R20 and R8 are selected such that R19+R20>R8, the base potential of the transistor 1 becomes approximately zero, the base current iB is no longer supplied, and this transistor is turned off.

Then, a negative pulse voltage is generated in the feedback winding 2c as shown in FIG. 3e, and this negative voltage is applied to the base, so that the horizontal output transistor 1 is instantly turned off.

At the same time, a deflection current 1y flows from the sweep capacitor 6 through the deflection coil 5 in the direction of the resonance capacitor 4, and when it becomes zero at time t2, it reversely flows from the resonance capacitor 4 through the deflection coil 5 in the direction of the sweep capacitor 6. deflection current iy
flows.

Next, at time t3, when the deflection current '1y reaches a negative peak, the deflection current flows from the deflection coil 5 toward the damper diode 3.

When the retrace period (tl to t3) ends, a positive voltage is generated in the feedback winding (2c) of the transformer 2, and since this voltage is applied to the base of the transistor 1, the deflection current iy At the same time that becomes zero at time t4, transistor 1 returns to the on state, and thereafter the above-described operation is performed again.

Then, after the first blanking period has passed, a positive DC voltage is generated in the line 16 by the pulse voltage shown in FIG.
This voltage is applied as a power source to the horizontal oscillation circuit 11, and this oscillator becomes operational.

Therefore, if the oscillation frequency fO (period To) of the horizontal output circuit is set slightly lower than the horizontal oscillation frequency fH (period TH), for example, a little before the collector current iC of the horizontal output transistor 1 reaches its peak value (time At t5), a positive pulse (FIG. 3g) from the horizontal oscillation circuit 11 is applied to the base of the drive transistor 17, and this transistor 17 is turned on.

On the other hand, since the DC voltage of the line 16 is applied to the charging/discharging capacitor 13 via the diode 15 and the resistor 14, this capacitor is connected to the base of the horizontal output transistor 1.
It is charged to the polarity shown by the current flowing in the path between the emitters.

Therefore, when the drive transistor 17 is turned on, the voltage across the capacitor 13 is applied as a reverse bias between the base and emitter of the horizontal output transistor 1, and this transistor 1 momentarily Turn off soon.

At this time, since the point A is grounded when the drive transistor 17 is turned on, the base current (forward direction) is not supplied to the horizontal output transistor 1 through the resistor 19.20, and therefore the above turn-off is further reduced. It will definitely be done.

As a result, the oscillation frequency fO of the horizontal output circuit is locked to the horizontal oscillation frequency fH.

As explained above, according to the present invention, in a drive transformer-less horizontal output circuit, by applying a sufficient reverse bias between the base and emitter of the horizontal output transistor, this transistor can be turned off reliably and quickly. Moreover, since the circuit configuration is very simple, it is suitable for television receivers and the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a self-driven horizontal output circuit, FIG. 2 is a diagram showing an embodiment of the horizontal output circuit according to the present invention,
FIG. 3 is a signal waveform diagram of each part of FIG. 2. 1...Horizontal output transistor, 2...
Flyback transformer, 11...Horizontal oscillation circuit, 13...Charge/discharge capacitor, 17...
・Drive transistor, 19.20...1st
Second resistance.

Claims (3)

[Scope of utility model registration request] (1) In a horizontal output circuit constructed as a self-driving type by providing a feedback winding in a flyback transformer connected to a horizontal output transistor and feeding back the voltage generated in this winding to the base of the transistor, One end of the charging/discharging capacitor is connected to the base, and the other end of the capacitor is connected to a DC power supply via a resistor and grounded via a switching element that turns on and off in horizontal cycles, thereby controlling the voltage generated in the capacitor. A horizontal output circuit characterized in that when the switching element is conductive, a reverse bias voltage is applied between the base and emitter of the horizontal output transistor, thereby rapidly turning off the transistor. (2) The horizontal output circuit according to claim 1, wherein the DC power source is obtained by rectifying and smoothing pulses generated in the flyback transformer. (3) A first resistor is connected between the connection point on the switching element side of the capacitor and the power source of the horizontal output transistor, and a second resistor is connected between the connection point and the base, and 2. The horizontal output circuit according to claim 1, wherein the current flowing through the first and second resistors is supplied to the transistor as a starting current.