JP2748695B2 - High-voltage generation circuit for television receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage generating circuit for a television receiver having a cathode ray tube.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a protection circuit in a conventional high voltage generating circuit for a television receiver. In FIG. 5, reference numeral 1 denotes an abnormal current detection resistor, which is connected to a + B (110 V) power supply and the secondary winding 172 of the flyback transformer 17, and has a transistor 2 connected to both ends thereof. The capacitor 3 and the Zener diode 4 are connected to the collector of the transistor 2, and the cathode of the Zener diode 4 is connected to the base of the transistor 5. Reference numeral 6 denotes a photocoupler, and the charged part A and the non-charged part B are insulated by the photocoupler 6.
Capacitors 7 and 8 are connected to the collector and the emitter of the phototransistor 601 in the photocoupler 6, respectively.
It is connected to a line protection terminal 901.

Next, the operation of the above configuration will be described. The voltage drop due to the normal current of the abnormal current detection resistor 1 connected to the + B power supply is small, and the transistor 2 is off. Secondary winding 1 of flyback transformer 17
72, the + B current increases, the voltage drop of the abnormal current detection resistor 1 increases, and the transistor 2
Is turned on, and the voltage of the capacitor 3 rises. As a result, the Zener diode 4 turns on, and the transistor 5 also turns on. Further, when the photocoupler 6 is turned on, that is, the phototransistor 601 is turned on, the charge stored in the capacitor 7 on the collector side is charged in the capacitor 8 on the emitter side, and the deflection I
The horizontal oscillation is stopped by driving the X-ray protection terminal 901 of C9, and the operation of the cathode ray tube of the television receiver is stopped.

[0004]

Since the conventional high-voltage generating circuit for a television receiver is constructed as described above, the operation of the protection circuit changes depending on the brightness of the screen of the cathode ray tube, and the safety is increased. Inadequate. To elaborate,
If the screen of the cathode ray tube is bright and the current is usually large,
The protection circuit works with a slight change in the current flowing through the + B power supply line. However, when the screen is dark and the current is normally small, +
If a large change does not appear in the current flowing through the B power supply line, the protection circuit does not operate, and therefore, when the small-scale discharge continues, the operation of the high-voltage generation circuit is not reliably stopped and sufficient safety is not provided. There was a problem that we could not expect. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a high-voltage generating circuit for a television receiver, which can be expected to ensure reliability regardless of the state of a screen of a cathode ray tube. The purpose is to:

[0005]

According to the present invention, there is provided a high-voltage generating circuit for a television receiver, comprising: a cathode- ray tube;
Current and the secondary current of the high- voltage transformer.
The circuit is configured to stop the circuit operation when the difference between the current and the current exceeds a predetermined value .

[0006]

According to the present invention, when an abnormality such as leakage occurs on the secondary side of the high-voltage transformer, the abnormality is determined by comparing the current flowing through the cathode of the cathode ray tube with the current flowing into the secondary winding of the high-voltage transformer. Is detected, and the operation of the high voltage generation circuit is stopped.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a high-voltage generating circuit for a television receiver according to an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a cathode ray tube, and 12, 13, and 14 denote cathodes corresponding to the three primary colors of R, G, and B. It is.

Reference numeral 15 denotes the cathode 12 of the cathode ray tube 11,
This is a current detection circuit for detecting an average current of three beams flowing through 13 and 14, and is connected to one input terminal of the comparator 16. Reference numeral 17 denotes a flyback transformer. A focus resistor 18 and an anode cap 19 are connected to the high voltage side of the secondary winding 172, and a resistor 20 is connected to the low voltage side.
An operation unit 21 as a high-voltage winding current detection circuit is connected to both ends of the resistor 20, and the output thereof is connected to the other input terminal of the comparator 16. Reference numeral 22 denotes a high-voltage generation stop circuit to which the output of the comparator 16 is connected. The flyback transformer 17 has a primary winding 171,
A tertiary winding 173 is incorporated in addition to the secondary winding 172.

Next, the operation of the above configuration will be described. The average of the currents flowing through the cathodes 12, 13, and 14 of the cathode ray tube 11 is I ₁ , and the current flowing through the resistor 20 is I _1
2 , the current flowing through the focus resistor 18 is I _2a , and the current flowing through the tertiary winding 173 of the flyback transformer 17 is I _2b.
Then I ₁ = I ₂ −I _2a −n ₁ · I
_2b (n ₁ : coefficient).

When the output voltage of the current detection circuit 15 is e ₁ , the output voltage of the computing unit 21 is e ₂ , and the voltage drop of the resistor 20 is e _R , e ₂ = n ₂ (e _R −e ₀ ). = E ₁
(N ₂ : coefficient, e ₀ : equivalent to the voltage drop due to I _2a and I _2b ), if the arithmetic unit 21 performs the operation, the equal voltage is input to the two inputs of the comparator 16 at normal times. Therefore, the output becomes LOW level.

Next, when an abnormality such as discharge occurs in the secondary winding 172 of the flyback transformer 17 or between the flyback transformer 17 and the anode cap 19, the current I2 flowing through the resistor 20 increases. Since the changes of I _2a , I _2b and I ₁ are slight with respect to the change of the current I _2, the current detection circuit 15 and the arithmetic unit 21
Relation between the voltage e _1, e ₂ respectively output from the e ₁ <
e ₂ becomes, from the comparator 16 outputs the High-level signal, a result, the discharge pressure generating stop circuit 22 is driven is stopped.

FIG. 2 is a diagram showing an example of the configuration of the current detection circuit 15. In FIG. 2, reference numeral 23 denotes an adder, which sends and adds the voltages generated at the cathodes 12, 13, and 14 of the cathode ray tube 11. And the sum of the voltage conversion values of the three beam currents is output. Reference numeral 24 denotes an integrating circuit, which averages by passing the output from the adder 23 and sends it to one input terminal of the comparator 16.

FIG. 3 is a diagram showing an example of the configuration of the high-voltage generation stop circuit 22. The output from the comparator 16 is connected to the gate of the thyristor 25, and a high-level signal at the time of abnormality turns on the thyristor 25. As a result, the transistor 26 is driven, whereby the relay 27 operates to turn off the main power supply.

FIG. 4 shows another configuration example of the high-voltage generation stop circuit 22. The difference from FIG.
Instead of using the microcomputer 28, the output signal of the comparator 16 activates the microcomputer 28 to drive the transistor 26, and the relay 27 operates to turn off the main power supply.

[0015]

As described above, according to the present invention, the operation of the high-voltage generating circuit can be reliably stopped at the time of abnormality such as discharge, regardless of the state of the screen of the cathode ray tube.
The safety of the high pressure section can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a high-voltage generation circuit for a television receiver according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a current detection circuit in FIG. 1;

FIG. 3 is a diagram illustrating a configuration example of a high-voltage generation stop circuit in FIG. 1;

FIG. 4 is a diagram illustrating another configuration example of the high-voltage generation stop circuit.

FIG. 5 is a configuration diagram showing a conventional high voltage generation circuit for a television receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Cathode ray tube 12, 13, 14 Cathode 15 Average current detection circuit of 3 beams 16 Comparator 17 Flyback transformer 21 Operation unit (high voltage winding current detection circuit) 22 High voltage generation stop circuit

Claims (1)

(57) [Claims] 1. A cathode ray tube for a television receiver.
Means for comparing the current and high anode voltage generating high voltage transformer of a high voltage winding current of said cathode ray tube through the cathode, when the current difference by the comparison means is equal to or greater than a predetermined value, means for stopping the circuit operation And a high-voltage generating circuit for a television receiver.