JPS60143066A - Video output circuit - Google Patents

Abstract

PURPOSE:To prevent burning of fluorescent substance of a cathode ray tube by supplying a base bias power supply of a video output transistor (TR) from a separate power supply other than a video power supply so as to make the operation of a discharge spot killer complete. CONSTITUTION:When a video signal is inputted from a point A, the signal is amplified by a video drive TR3 and a video output TR4 and an output waveform is given to a cathode of a cathode ray tube 8 through a cathode resistor 11. A video power supply driving a video output circuit forms a pulse waveform outputted from a flyback transformer 12 by using a rectifier diode 13 and a smoothing capacitor 14. In this case, the video power current is decreased by supplying the base bias of the TR4 from a separate power supply other than the said video power supply, that is, a +B power supply so as to make the spot killer operation complete.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video output circuit such as a cathode ray positive display using a discharge type spot killer circuit.

The configuration of conventional examples and their problems In recent years, Yin@! There are two types of killer circuits: a containment type and a discharge type, but a discharge type is desired because it instantly eliminates the high voltage energy inside the cathode ray tube.

First, such a discharge type spot killer circuit will be explained.

A discharge type spot killer circuit releases the electron beam inside the cathode ray tube when the power is turned off, and after the energy has decreased, the remaining electron beam is contained to prevent burnout of the phosphor of the cathode ray tube. As shown in Figure 4, the circuit operation at this time is that when the power is turned off, the potential of the first grid is raised above that of the cathode to emit the entire electron beam as a forward bias, and then the first grid is lowered from the cathode and reverse biased. This is to confine the electron beam.

Generally, the time for this reverse bias is approximately 10 seconds or more, although it varies depending on the type of electrode wire of the cathode ray tube.

An example of a conventional video output circuit will be described below with reference to the drawings. FIG. 1 shows a conventional video output circuit using a discharge type spot killer circuit and its peripheral circuits. In the figure, 1 is the base resistance of the video drive transistor 3, 2 is the emitter resistance of the video drive transistor 3, 3 is the video drive transistor, 4 is the video output transistor, 6 and 6 are the bias resistances of the video output transistor 4, and 7 is the emitter resistance of the video drive transistor 3. The collector resistor of the video output transistor 4, 8 the cathode ray tube, 9 the emitter capacitor of the video drive transistor 3, 10 the base capacitor of the video output transistor 40, 11 the phantom cathode resistor, and 12 the flyback transformer (hereinafter referred to as FBT). ), 13 is a video power rectifier diode, 14 is a smoothing capacitor, and 19 is a discharge Jlt spot killer circuit.

The operation of the video output circuit configured as above will be described below. This video output circuit is generally called a grounded emitter/grounded base direct connection type video amplification circuit.
When a video signal is input from point A, the video signal is amplified by the video drive transistor 3 and the video output transistor 4, and an output waveform is applied to the cathode of the cathode ray tube 80 through the cathode resistor 511. In this case, the video power supply that drives the video output circuit outputs a DC voltage from the pulse waveform outputted by the FB 712 through the rectifying diode 13 and the smoothing capacitor 14.

The base bias voltage of the video output transistor 4 is supplied from the video power supply by dividing the bias resistor 6.6.

However, in the circuit configuration as described above, a spot was generated on the cathode ray tube 8 without performing the spot killer operation of the discharge. The operation will be explained using FIGS. 1 and 3. In FIG. 1, video output transistor 40
The current 1 flowing through the base bias resistor 6.6 always flows as a constant load. Collector current I2 changes depending on the magnitude of the video input signal. As shown in FIG. 3, when the power is turned off, the video power supply voltage drops rapidly because the video power supply current o (the sum of the bias current 1 and the collector current 12) is extracted from the smoothing capacitor 14. Similarly, the cathode and first group IJ voltages also drop rapidly. For this reason, the electron beam is not sufficiently emitted during the forward bias during the discharge jless spot killer operation described above, and '1. Cathode vs. 1st group when reverse biased
The cathode ray tube 8
However, there was a problem in that skipping occurred.

OBJECTS OF THE INVENTION The present invention solves all of the above-mentioned conventional problems, and aims to provide a video output circuit that perfectly performs the discharge type spot killer operation without impairing the original characteristics of the video output circuit. .

Structure of the Invention The video output circuit according to the present invention supplies a base bias voltage of a video output transistor whose emitter is gold-connected to the collector of a video drive transistor whose emitter is grounded through a resistor to a power source other than a power source which is connected to the collector resistor of the video output transistor. The circuit is configured so that the power is supplied from a separate power source, and by adopting this configuration, it is possible to perform all the reliable discharge type spot killer operations.

DESCRIPTION OF EMBODIMENT 1 Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows a video output circuit and its peripheral circuits in one embodiment of the present invention. In the drawings, parts having the same functions as those in FIG. 1 are designated by the same numbers and their explanations will be omitted. In FIG. 2, 15 is an input impedance adjustment resistor, 16 and 17 are collector peaking coils of the video output transistor 4, and 18 is a bypass capacitor for the video power supply.

The operation of the video output circuit configured as above will be described below. When a video signal is input from point A, it is amplified by the video drive transistor 3 and the video output transistor 4, and is configured to provide an output waveform to the cathode of the cathode line 8 through the cathode resistor 11. In this case, the video power supply that drives the video output circuit is I
A DC voltage (+e
oV)k is being created. Also, the base bias voltage of the video output transistor is 10B (-1) from the main power supply of this set.
-12V).

According to this embodiment, as described above, the base bias voltage of the video output transistor 4 is set to the base bias voltage of the video output transistor 4.
It was possible to reduce the video power supply current Io' by supplying it from a 10B power supply (+12V) other than the video power supply (-1-eoV'), that is, the power supply connected to the collector resistor of the video power supply (-1-eoV'). As shown in Figure 2, the video power supply current installation o?
There is only 2 collector currents, and 0 - 2. Due to this effect, the drop time of the video power supply when the power is cut off, that is, the drop time of the voltage, becomes extremely long compared to the conventional 1+1I.

This operation will be explained with reference to FIG. The solid line shows the voltage change at the cathode, and the broken line shows the voltage change when the first grid is powered off. Immediately after the power is turned off, the voltage of the first grid becomes higher than that of the cathode (forward bias) due to the discharge type spot killer circuit connected to the first grid, and an electron beam is emitted. after that,
The first grid potential is lower than the cathode potential (reverse biased) and confines the electron beam.

It can be seen that this has a much greater effect than the conventional chestnut shown in FIG. In addition, the syspot killer operation has been perfected, allowing the reverse bias to last for a long time (2 to 3 minutes).

In general, the video power source obtained from the FBT 12 has a relatively high voltage, and therefore has a small capacity and poor stability 1i. Further, the video output circuit of a cathode ray tube display is often attached to the neck of the cathode ray tube 8 in order to improve frequency characteristics as the band becomes wider, and high performance and miniaturization are required. By supplying the base bias voltage of the video output transistor 4 from the fully stable -1-B power supply (+12V), the stability of the base voltage is increased and the linearity of the video input voltage to the video output voltage is improved compared to the conventional case. Next, we will make the base bias resistor 6 lower power and smaller ('/2W →
1/4W) is now possible.

Effects of the Invention As described above, according to the present invention, by supplying the base bias power of the video output transistor from a separate power source other than the video power source, the operation of the discharge type spot killer is perfected, and the cathode ray tube's fluorescent light is improved. Light body burn can be prevented. In addition, if the separate power source is a stable low voltage power source, excellent effects can be obtained such as improving the linearity of the video output circuit and reducing the power consumption and size of the base bias resistor.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional 1-video output circuit and its surroundings.
Fig. 2 is a circuit diagram of the video output circuit and its surroundings in an embodiment of the present invention, Fig. 3 is a diagram of the operating characteristics of a spot killer in a conventional circuit, and Fig. 4 is a circuit diagram of an example of the present invention. FIG. 2 is an operational characteristic diagram of a spot killer in FIG. 2...Emitter resistance, 3...Video drive transistor, 4...Video output transistor, 6゜6...Bias resistance, 7-...Collector resistance, 12 ...Flyback transformer, 13
...Diode, 14 ...Capacitor, 18
...Bypass capacitor. Name of agent: Patent attorney Toshio Nakao and one other person
Figure WJ3 figure @4 figure

Claims (1)

[Claims] The base bias voltage of a video output transistor whose emitter is connected to the collector of a video drive transistor whose emitter is grounded through a resistor is supplied from a power source other than the power source connected to the collector resistor of the video output transistor. A transparent image output circuit characterized by the following.