JPH01282973A - spot killer circuit - Google Patents

Abstract

PURPOSE:To prevent spot burning without fail by loading blanking to an image output with a pulse, which is generated at the rising and falling time of a power source, and lowering a contrast control voltage. CONSTITUTION:By a pulse output port to be generated in a pulse generating circuit 1 at the rising and falling time of a power source voltage A, the base voltage of a transistor Tr1 in a switching circuit 13 rises up and this transistor Tr1 is turned on. Since a collector voltage falls down when the transistor Tr1 is turned on, a contrast control voltage E is lowered and contrast is narrowed down. The pulse output port of the pulse generating circuit 1 is inputted to a blanking input terminal 3 of an IC2 for signal processing and the blanking is loaded to the image output.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a spot burnout system that prevents spot burn by applying blanking to the video output when the power of a television receiver is turned on and off. It concerns the killer circuit.

[Prior Art] Fig. 3 shows a wiring diagram of a conventional spot killer circuit. and the rise of the base voltage (C) of this transistor (Tr).
A resistor (old) and a capacitor (Ct) that determine the time constants at the start and fall times, and the above transistor (T
Diode (Di) and capacitor (C2) that hold the emitter voltage (B) of r) at a predetermined voltage when falling
When the voltage (A) of the power supply (12) rises and falls, the collector output voltage (D) of the transistor (Tr) is made high and output. In other words, it generates a pulse.

(2) is a signal processing IC that converts a video signal (hereinafter referred to as Y signal) and a chroma signal (hereinafter referred to as C signal) into R,
It demodulates G and B signals, and has a Y signal input terminal (7), a C signal input terminal (8), and R, G, and H signal output terminals (14), (15), (16). , blanking input terminal (3), contrast control voltage input terminal (6)
) and a power supply voltage input terminal (5). (4)
is a blanking pulse output terminal from a flyback transformer (hereinafter referred to as FBT), not shown, and is connected to the blanking input terminal (C) of the signal processing IC (2).

(9) is a cathode ray tube (hereinafter referred to as CRT), (lO)
(11) is a contrast control voltage input terminal, and (11) is an ACL control voltage input terminal.

Next, the operation of the above configuration will be explained.

When the power supply (12) is turned on, its power supply voltage (A) rises as shown by the solid line in FIG. 4(a). At the same time, the emitter voltage (B) of the transistor (Tr) of the pulse generating circuit (1) rises as shown by the dotted line in FIG. 4(a), while the base voltage (C) of the transistor (Tr) rises.
slowly rises as shown by the dashed line in FIG. 4(a) due to the time constants of the resistor (R1) and capacitor (CI). Therefore, the transistor (Tr) continues to be turned on until the rise of its base voltage (C) is completed.
The collector output voltage (D) of the transistor (T') is the fourth
It becomes high as shown in figure (b).

In other words, a pulse is output, and this pulse is used for signal processing
It is input to the blanking input terminal (3) of C(2) and blanking is applied to the video output. This prevents spot burns because the Y signal is not input to the cathode of the CRT (9) until the deflection system circuit starts operating.

Further, when the power supply (12) is turned off and the power supply voltage (A) falls as shown by the solid line in FIG. 5(a), the base voltage of the transistor (Tr) of the pulse generation circuit (1) ( C) falls as shown by the dashed-dotted line in Fig. 5(a), whereas the emitter voltage (B
) is a diode (D
1) and the capacitor (C2) to maintain a predetermined voltage and keep the transistor (Tr) ON, and the collector output voltage (D) of the transistor (Tr) becomes as shown in FIG. 5(b). As a result, a high signal, that is, a pulse, is sent to the blanking input terminal (3), and before the operation of the deflection system circuit is stopped, the video output is blanked, thereby preventing spot burnout.

[Problem to be solved by the invention] The conventional spot killer circuit configured as follows:
Since the image output is only blanked when the power supply rises and falls, no current flows during the blanking sweep of the image output, so no ACL control operation is performed, and as a result, the contrast control voltage or full gain is applied. As shown by the dotted line in FIG. 2, there is a drawback that the contrast control voltage (E) rises above a predetermined voltage during steady operation. Therefore, when the power supply is turned off, the video output can be blanked until the deflection current disappears, but if even a small amount of signal remains, the video output becomes full gain, which can burn out the CRT. was there.

This invention was made to solve the above problems, and by lowering the contrast control voltage when the power is turned on and off, it is possible to reliably prevent spot burns. The purpose is to provide a spot killer circuit.

[Means for Solving the Problems] The spot killer circuit according to the present invention generates pulses when the power supply rises and falls, and uses these pulses to blank the video output and lower the contrast control voltage. Characterized by what has been done.

[Function] According to the present invention, a pulse is generated by detecting the power supply voltage when the power is turned on and off, and this pulse applies blanking to the video output, and the contrast control voltage is lowered to narrow down the contrast. If even a small amount of deflection current remains, signal transmission to the CRT can be stopped to reliably prevent spot burns.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a wiring diagram of a spot killer circuit according to an embodiment of the present invention. In the figure, (13) is a switching circuit, and this switching circuit (13) is a power supply (12).
), that is, when the power supply voltage (A) rises and falls, the contrast control voltage is lowered by the pulses generated by the pulse generation circuit (1), and its base is the pulse generation circuit (1). A switching transistor (Tri) is connected to the output side of the switching transistor (Tri), and a capacitor (C3) and a contrast control voltage input terminal (6) are connected to the collector side of this switching transistor (Tri).Other configurations are as follows. 3
Since it is the same as the conventional example shown in the figure, corresponding parts are given the same reference numerals and detailed explanation thereof will be omitted.

Next, the operation of the above configuration will be explained.

Power supply voltage (A) when turning on and off the power supply (12)
The operation of generating pulses at the rising edge and falling edge of , and the operation of blanking the video output using the generated pulses are exactly the same as in the conventional case, so their explanation will be omitted.

Here, the base voltage of the transistor (Tri) of the switching (13) increases due to the pulse output (D) generated by the pulse generating circuit (1) when the power supply voltage (A) rises and falls. , this transistor (Tri) is turned on. When the transistor (Tri) is turned on in this manner, its collector potential decreases, so the contrast control voltage (E) decreases and the contrast is reduced. This allows the power supply (12) to be turned on and off.
Even in the F mode, the input voltage (F) to the contrast control voltage input terminal (6) of the signal processing IC (2) is maintained at low level, thereby preventing spot burn on the CRT (9). .

[Effects of the Invention] As described above, according to the present invention, it is not necessary to blank the video output by the pulses generated at the rising and falling edges of the power supply, and by lowering the contrast control voltage, the spot Burns can be reliably prevented. Furthermore, since a simple switching circuit can be added to the conventional circuit, highly accurate countermeasures against spot burns can be realized at low cost.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram of a spot killer circuit according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the correlation between the contrast control voltage and the input voltage at the time of rising and falling of the power supply and during steady operation, and Fig. 3 is a wiring diagram of a conventional spot killer circuit, Fig. 4 is a voltage waveform diagram explaining the operation of the pulse generation circuit when the power is turned on, and Fig. 5 is a voltage waveform diagram explaining the operation of the pulse generation circuit when the power is turned off. It is. (1)...Pulse generation circuit, (2)...Signal processing IC1 (3)...Blanking input terminal, (6)...
・Contrast control voltage input terminal, (9)...CRT
, (11)...ACL control voltage input terminal, (13)...
...Switching circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A signal processing circuit that has a pulse generation circuit that generates pulses when the power supply rises and falls, and a blanking input terminal and contrast control voltage input terminal that blanks the video output using the generated pulses. and a switching circuit that lowers a contrast control voltage using the pulse.