JPS5837175Y2 - Braun tube drive circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a drive circuit for a cathode ray tube in which one end of each of a heater and a cathode is connected.

Conventionally, it has become common knowledge that it is advantageous to apply a video signal to the cathode of a black-and-white television receiver.

On the other hand, in order to reduce the heater power, it becomes necessary to mechanically bring the cathode and the heater close to each other.

In that case, there is a cathode ray tube that connects the two for electrical safety.

Even in this case, it is common to apply a video signal to the cathode.

In this case, heater power is supplied from the secondary winding of the heater transformer, but its distributed capacitance becomes the distributed capacitance of the cathode circuit, leading to deterioration of the high frequency characteristics of the video output amplifier.

Therefore, the heater transformer must have a low distributed capacity, which increases cost.

This causes problems such as a decrease in efficiency, an increase in size, and an increase in leakage flux, and furthermore, the distributed capacity cannot be reduced to zero, resulting in a deterioration in performance.

Therefore, an object of this invention is to provide a drive circuit for a cathode ray tube that solves the above-mentioned problems.

FIG. 1 shows an embodiment of this invention.

In the figure, 1 is a VIF final stage coil, 2 and 3 are bias resistors, 4 is a detection diode, 5 is a detection load resistance, 6 is a video preamplifier transistor, 7 is a collector load, and 8
is the emitter resistance, 9 is the coupling resistance, 10 is the coupling capacitor, 11 is the coupling resistance, 12.13 is the bias resistance, 14
is a video output transistor, 15 is a load resistor, 16 is an emitter resistor, 17 is a gain adjustment resistor, 18 is a DC cut capacitor, 19 is a contrast volume, 20 is a coupling capacitor, 21 is a grid leak resistor, 22 is a voltage dividing resistor, 23 is the luminance paliohm, 24 is the cathode resistance, 2
5 is a cathode ray tube, 26 is a flyback transformer, 27 is a heater winding, ■8□, VB2 is a B power supply.

The detected output is applied to the base of the video preamplifier transistor 6 with positive polarity (meaning that the white level is in the positive direction and the synchronizing signal level is in the negative direction).

AGC and synchronous separation signals are taken out from the emitter.

Separately from these, a signal is taken out from the collector of the video output transistor 14.

A positive pulse vertical blanking signal (or a combined vertical and horizontal blanking signal) is applied to the base of the video output transistor 14.

A positive polarity signal is obtained at the collector of the output transistor 14 and is transmitted to the first grid G1 of the cathode ray tube 25.
Add to.

The cathode/heater terminal KH of the cathode ray tube 25 is connected to an AC fixed potential point, and a heater winding 27 is connected to an existing transformer, such as a flyback transformer 26, for the heater.

A feature of this configuration is the utilization of the first grid drive.

That is, firstly, by applying a video signal to the first grid G1, the cathode can be connected to a fixed potential point, and the influence of the distributed capacitance of the heater is reduced, so that the heater winding 27 is connected to the flyback transformer 26. can be provided.

Second, the vertical blanking signal utilizes a vertical retrace pulse, which becomes a positive pulse when the B voltage is positive.

The pulse application point has the least load effect at the base of the output transistor 14, etc., and the polarity of this configuration makes this possible.

By the way, when applying the pulse to the base of the output transistor 14, the pulse is also transmitted to the video preamplifier transistor 6 in the previous stage.

Therefore, if AGC, sync separation, and video signals are taken out from the same point, they cannot be applied to the base because it will adversely affect those circuits.

However, in the present invention, since these signals are separated, base application is possible.

In this way, the configuration of the first grid drive, the detection polarity, and the preamplifier makes it possible to eliminate the heater transformer and apply the positive blanking pulse to the base.

Note that due to the circuit configuration, transistor 6 and transistor 14
The coupling may be a DC coupling.

The coupling resistors 9 and 11 may not be used if the impedance of the connected circuit is high and no interference occurs.

Also, the cathode of the cathode ray tube 25 and the first grid G
1, a fixed bias other than ground may be applied, brightness adjustment may be performed on the first grid G1 side, and the value of the cathode resistor 24 may range from a normal cathode resistance value to a mere high-pressure discharge protection level. , can have a wide range of values depending on the distributed capacitance of the heater winding 27 and the operating conditions of the cathode ray tube 25.

FIG. 2 shows another embodiment.

In this circuit, a resistor 28 is connected between the collector of the transistor 6 and the capacitor 10.

This effect will be explained.

For effective use of the dynamic range of the video output stage,
There are cases where the signal from black to the tip of the synchronizing signal is output outside the linear region, and in FIG. 2, the output transistor 14 becomes saturated, the base and collector become conductive, and the human input impedance of the transistor 14 drops rapidly.

As a result, the equivalent load resistance of the preamplifier transistor 6 decreases rapidly, and the resistor 28 is used to reduce this effect.

As described above, this invention makes it possible to eliminate the heater transformer and apply positive pulses to the base of the video output stage, making it possible to reduce costs, reduce load effects, and improve video characteristics with a simple circuit configuration. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of this invention, and FIG. 2 is a circuit diagram of another embodiment. 6...Video preamplifier transistor, 14
...Video output transistor, 25...
... Braun tube, 26 ... Flyback transformer, 27 ... Heater winding.

Claims (2)

[Scope of utility model registration request] (1) Connect the base of the video preamplifier transistor to the anode of the detection diode, connect it to each input terminal of the video preamplifier and the synchronous separation circuit, and connect the collector of the video preamplifier transistor to the base of the video output transistor. connecting via a coupling circuit, connecting the collector of the video output transistor to a first grid of a cathode ray tube via a second coupling circuit, and connecting the heater of the cathode ray tube to a heater winding provided on a flyback transformer; A cathode ray tube drive circuit in which the base of the video output transistor is connected to a vertical output circuit that generates a positive pulse blanking signal. (2) The cathode ray tube drive circuit according to claim 1, wherein a resistor is connected in series between the video preamplifier transistor and the video output transistor.