JPS6150480A - Beam current switching circuit - Google Patents

Abstract

PURPOSE:To apply gamma correction except for a beam current measuring period by connecting a switching transistor (TR) between a beam current detection TR and a beam current measuring circuit. CONSTITUTION:Diodes 49, 50, 51 are added to a collector of current detection TRs 40, 41, 42, each cathode of the said diodes is connected in common and a switching TR52 is given to the common connecting point. A TR58 is used for pulse inversion. When the level of a pulse fed to a base of the TR58 is logical H, the TR58 is turned on and a TR52 is turned off. Thus, TRs 40-42 are inactivated, a beam current flows from the emitter to the base to attain gamma correction. On the other hand, when the level of the pulse is logical L, the TR52 is turned on, the TR40, 41, 42 are activated normally and the beam current is detected by a resistor 54.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a beam current switching circuit used in television receivers and the like.

Conventional configurations and their problems In general, cathode ray tubes for television receivers have a narrow dynamic range, which causes problems with focus characteristics such as blooming to obtain sufficient contrast. Therefore, in order to bring out the full performance of a cathode ray tube, it is common to perform a drive that suppresses the white part and reduces linearity. This improves problems such as blooming. This is called the gamma effect.

For example, the present invention allows comma correction to be performed by flowing the waste current for white balance control of a color television receiver with an automatic white balance adjustment function to a current measurement circuit only during the measurement period, and to the color signal output transistor during other periods. This relates to a beam current switching circuit.

FIG. 1 shows a current detection and measurement circuit for a conventional color television receiver with an automatic white balance adjustment function. In the figure, 19, 20, and 21 are current detection transistors,
The emitter of each transistor is connected to a resistor 22, 23 .
24 to the cathodes 25, 26, and 2 of the cathode ray tube.

Furthermore, there is a resistance of 1 between the emitter and the pace of this transistor.
6. ．． 17 and 18 are connected, and the bases are connected to the collectors of the color signal output transistors 4 and 6.6. The collectors of the three current detection transistors 19, 20 and 21 are grounded together through resistors 28 and 29. Then, the resistor 29 converts it into a voltage value ■s. The Zener diode 3o is for circuit protection.

Next, the operation of this circuit will be explained. The R, G, and B beam currents pass through resistors 22, 23, and 24 and enter the emitters of current detection transistors 19, 20, and 21. The current flowing from the emitter to the base and through the resistors 16, 17.18 is small, and most of the current flows from the emitter to the collector and flowing through the resistor 28.29.

Collector potential of color signal output transistors 4, 5.6 ■c
has no current detection transistor, and when the beam current 1b flows to the collector, the beam current 1b decreases compared to when it does not flow.

) Therefore, when the beam current is high, the drive is slightly reduced, which prevents too much brightness on the screen. That is, there is a gamma effect. However,
As in the circuit shown in Figure 1, the current detection transistor is 19°20
．． 21 enters and the beam current passes through the color signal output transistor 4.
, 5.6, gamma correction is not applied and problems such as blooming occur.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks and to configure a circuit that can perform current detection measurement for automatic white balance adjustment while applying gamma correction.

Structure of the Invention In the present invention, a transistor for beam current detection and a beam current measurement circuit are provided between the cathode of a cathode ray tube and a color signal output transistor, and a transistor for beam current detection and a beam current measurement circuit are provided. The collector of the switching transistor is connected between the beam current measurement circuit and the beam current measurement circuit, and the pulse signal is used to switch between the beam current measurement circuit and the gamma current measurement circuit. It is possible to perform corrections.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 31-48 and 63-66 are the same as the circuit in FIG. In the circuit of FIG. 2, diodes 49 and 50 are newly added to the collectors of the current detection transistors 40, 41, and 42.

51 is added, the cathodes of diodes 49, 50, and 51 are connected in common, and a switching transistor 52 is inserted at this common connection point. Another switching transistor 58 is used for Nogles inversion. A white-<lance pulse is created and applied to the base of the transistor 58, which is normally at a high level and changes to a low level only when measuring the white cross/s control current. 66.6
Complaint is resistance.

Next, the operation of this circuit will be explained. When the pulse applied to the base of switching transistor 58 is at a high level, transistor 58 is on. At this time, the collector potential of the transistor 68 becomes approximately Ov, so the transistor 62 is turned off. Therefore, when the pulse is at a high level, the collectors of the current detection transistors 40 to 42 are not connected to anything and do not function as PL transistors, and the beam current flows from the emitter to the base, making gamma correction possible. However, since the collector terminals of the three current detection transistors are connected, a diode is inserted in each to prevent current from flowing between them.

On the other hand, when the pulse becomes low level, the transistor 58 is turned off, the collector potential rises to 12V, and the transistor 62 is turned on.

When the transistor 52 is turned on, the current detection transistors 40, 41, and 42 start working normally, and the beam current flows out of the resistor 63, 54, so the resistor 54 converts it into a voltage value and detects it.

Effects of the Invention As described above, the present invention turns the switching transistor on and off, usually by disconnecting the collector of the current detection transistor, so that it cannot operate as a transistor and the beam current is changed. The signal is sent to the output transistor and gamma correction is performed.
Signal detection can be performed by making the current detection transistor conductive only during white balance adjustment.

[Brief explanation of drawings]

FIG. 1 is an electrical connection diagram of a conventional automatic white balance adjustment current detection and measurement circuit, and FIG. 2 is an electrical connection diagram of a beam current switching circuit in an embodiment of the present invention. 4.5.6...Color signal output transistor, 19~
21.40-42... Current detection transistor,
16-18, 37-39...Resistance, 22-24° 43-45...Resistance, 26-27.46-48.
... Cathode, 28.29.53.54 ... Resistor, 30.55 ... Zener diode, to 49 -
61... Diode, 52.58... Switching transistor, 66, 57... Resistor. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1 Figure 2

Claims (1)

[Claims] A beam current detection transistor and a beam current measurement circuit are provided between the cathode of the cathode ray tube and the color signal output transistor, and a switching transistor collector and emitter are provided between the beam current detection transistor and the beam current measurement circuit. and a beam current switching circuit configured to turn on and off the switching transistor in response to a pulse signal to switch whether the beam current flows through the color signal output transistor or the beam current measurement circuit.