JPH0119795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a beam current suppression circuit for a television receiver in which the suppression level of a cathode ray tube beam current suppression circuit (ABL, ACL) can be arbitrarily varied.

FIG. 1 shows a circuit diagram of a conventional television receiver, and FIG. 2 shows an explanatory diagram of its operation. In FIG. 1, 1 is a flyback transformer, 2 is a cathode ray tube (cathode ray tube), D1 is a rectifier diode, and 3 is a beam current suppression circuit.
1 and E2 are the first and second voltage sources, TR1 is the first transistor, D2 is the first transistor TR1
, R1 is the first resistor,
C is a ripple removal capacitor.

In this circuit, when the first transistor TR1 is conductive and the beam current suppression circuit 3 operates, the beam current level I1 is (E1 - E2)/R1, and the DC voltage at the ground side terminal of the high voltage coil of the flyback transformer 1 is This beam current will be held constant even if fluctuations occur in the beam current, and moreover, this beam current is normally fixed. This is clear from FIG. In FIG. 2, the horizontal axis shows the beam current I1 when the beam current suppression circuit 3 is not provided, and the vertical axis shows the beam current I1 when the beam current suppression circuit 3 is provided.

By the way, when receiving general television signals with a cathode ray tube, the beam current level can be set at a set value, but if you connect a computer to the cathode ray tube,
When you want to display text on a cathode ray tube, that is, when receiving an RGB image on a cathode ray tube, passing too much beam current can make the text brighter, but there is a problem in that the focus becomes blurred and the text becomes blurred.

In order to solve this problem, the beam current level can be lowered depending on the use of the cathode ray tube, but since the conventional beam current suppression circuit was configured as described above, the beam current In order to change the suppression level, the voltage source voltage E1,
It is necessary to change either E2 or resistor R1, which is difficult in practice.

SUMMARY OF THE INVENTION An object of the present invention is to provide a beam current suppression circuit for a television receiver that can easily and arbitrarily vary the beam current suppression level.

FIG. 3 shows a circuit diagram of a beam current suppression circuit for a television receiver according to an embodiment of the present invention, and FIG. 4 shows an explanatory diagram of its operation.

In FIG. 3, the same reference numerals as in FIG. 1 indicate the same parts, and the difference from FIG. This is an added point. Here the second transistor TR
2 is for bypassing the beam current, and 4 is a third voltage source E3 and a resistor R2,
The variable voltage is connected to the second transistor TR consisting of R3.
This is a variable voltage supply circuit that supplies the base of 2.

Next, the operation will be explained.

In this circuit, the suppression current level I1 becomes I1=E1-E2/R1-I2 by flowing the current I2 through the transistor TR2, and the level can be varied by varying the current I2. Also, the current I2 is I2 = (R3/R2 + R3E3 - Vbe) / R4 (where Vbe is the base-emitter voltage), and a large variable range of the current I2 and thus the beam current I1 can be easily obtained by a small change in the voltage source voltage E3. Can be done. This can be easily understood by looking at FIG.

As described above, according to the present invention, a current bypass circuit whose current value can be easily changed by changing the set voltage is added to the beam current suppression circuit, so that the beam current suppression level can be easily switched. For example, when receiving a television broadcast, the above setting voltage can be set to zero and the suppression level can be increased.
When receiving an RGB image, the set voltage is set to a predetermined level and the suppression level is lowered to prevent blurring of characters.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the beam current suppression circuit of a conventional television receiver, Figure 2 is its operating waveform diagram,
FIG. 3 is a waveform diagram of a beam current suppression circuit of a television receiver according to an embodiment of the present invention, and FIG. 4 is an operational waveform diagram thereof. 1 is a flyback transformer, 2 is a cathode ray tube,
3 is a beam current suppression circuit, E1 and E2 are first and second voltage sources, TR1 and TR2 are first and second transistors, R1 is a first resistor, 4 is a variable voltage supply circuit, and R4 is a second voltage source. resistance.

Claims (1)

[Claims] 1. A first resistor connected between the ground side terminal of the high voltage coil of the flyback transformer and a first voltage source, a first transistor whose emitter is connected to a second voltage source, and the first transistor. and a diode connected between the base of the high-voltage coil and the ground terminal of the high-voltage coil, the circuit suppresses the beam current of the cathode ray tube according to DC voltage fluctuations of the ground terminal, the collector of which is connected to the ground terminal of the high-voltage coil. A television receiver comprising: a second transistor connected to each other and whose emitter is grounded via a second resistor; and a variable voltage supply circuit that supplies a variable voltage to the base of the second transistor. beam current suppression circuit.