JPS6145674Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a white balance adjustment circuit for a color television receiver.

When the heater is turned on, the first grid and cathode electrode of a color cathode ray tube expands and bends due to the heat, and as shown in Figure 1, the cathode current has a characteristic that initially flows in a large amount and then becomes constant after a while. . Therefore, when the heater is turned on, the cathode voltage
It is recognized that the static characteristics of Ek and cathode current Ik drift as shown in the steady state characteristics A to B.
In FIG. 2, Vc is the power supply voltage of the color output stage, and this level Vc is also the level of the vertical blanking signal. Although the characteristics in FIG. 1 are shown for a green electron gun, electron guns of other colors are also the same in that the initial drift as shown in FIG. 1 occurs, except that the bias is somewhat shallow. The black level _L1 of the video signal is adjusted to the steady state characteristic A.

Now, when the heater of the cathode ray tube is turned on, for the reason stated above, the steady state characteristic A changes to V ₂ as shown in Figure 2.
The characteristics of ro which drifted only appear. Therefore, a cathode current Ik ₁ flows in accordance with the vertical blanking signal component corresponding to the voltage difference V ₁ between the power supply voltage Vc of the color output stage and the black level.

To prevent this, the conventional white balance adjustment circuit inserts a resistor _R5 as shown in Figure 4 to adjust the cut-off voltage of the cathode ray tube when adjusting the white balance.
It was adjusted appropriately according to the above initial drift amount.

In FIG. 4, 1 is a video output stage, 2 is a vertical deflection circuit, Q ₁ is a blue output transistor whose base receives a B-Y color difference signal, whose emitter receives a video signal and whose combined signal is obtained from its collector. When the movable elements 4 and 5 are switched to the contacts a and b, the emitter is connected to the video output stage 1, and a power supply voltage V _B is applied to the vertical deflection circuit 2 to put it into operation;
The interlocking changeover switch VR _1b cuts off the coupling between the video output stage 1 and the emitter of the transistor _Q1 and puts the vertical deflection circuit 2 into an inactive state when switched to the contacts c and d. VR 2b is the first volume for adjusting the white balance on a bright screen when contacts A and B are switched, and VR _2b is for adjusting the white balance on a dark screen when interlocking changeover switch 3 is switched to contacts C and D. This is the second volume. Q ₂ is the red output transistor, Q ₃
is the green output transistor, and these transistors
Q ₂ and Q ₃ are related to the green output transistor Q ₃ and are the first
It has a similar circuit arrangement to the blue output transistor _Q1 , except that the volume is replaced by a fixed resistor _R4 .

The white balance adjustment circuit shown in Figure 4 inserts a resistor R ₅ when adjusting the white balance on a dark screen, and sets the second volume VR _2b to prevent a vertical blanking signal from being generated on the screen when the cathode ray tube heater is turned on. ，
VR _2r and VR _2g are adjusted, but since the first volume VR _1b and VR _1r are adjusted when adjusting the white balance on a bright screen, the emitter bias on a dark screen that was adjusted earlier will fluctuate, and the white balance on a bright screen will be adjusted. There is a drawback that the switch 3 must be repeatedly changed to make adjustments, such as readjustment on a bright screen and subsequent readjustment on a bright screen, which is not appropriate.

The present invention proposes a circuit that eliminates these drawbacks and allows easy adjustment of white balance.

In FIG. 5, in which the present invention is implemented, the same parts as in FIG. 4 are given the same number.

To explain the features of this invention using the blue circuit as a representative, in this invention, first, the first volume
VR _1b is inserted between the emitter of the blue output transistor Q ₁ and the interlocking changeover switch 3, a second volume VR _2b is inserted between the second electrode and the reference potential point, and the base is connected to the switch 3. When the switch 3 is switched to the contact a, b side, the connection with the vertical deflection circuit 2 is cut off and the emitter resistor _R9 of the vertical drive transistor _Q4 of the vertical deflection circuit 2 is connected to 1 volume
The video signal is guided to the emitter via VR _1b , and thereby the first volume VR _1b can adjust the white balance on a bright screen, and the switch 3
When switched to contacts c and d, one end of the first volume VR _1b floats in terms of the circuit, so that the first volume does not affect the emitter electrode side circuit and the emitter current is vertically driven via the switch 3. The vertical drive transistor _Q4 is cut off by the current flowing through the emitter resistor _R9 of the transistor _Q4 , and in this state, the second volume
The VR _2b makes it possible to adjust the white balance on dark screens. Note that _R10 is an emitter resistor, _C1 is a bypass capacitor, and _R6 is a resistor inserted in the line leading to the vertical drive transistor _Q4 .

The red circuit and green circuit have the same circuit configuration except that a fixed resistor _R4 is used instead of the first volume, and in some cases, a fixed resistor is used.
Naturally, R ₄ may be replaced with a volume.

Connections between these three color circuits and switch 3 are all made in common.

In Figure 5, to adjust the white balance,
First, switch the interlocking changeover switch 3 to contacts c and d and adjust the second volume VR _2g so that the static characteristic A' in steady state as shown in Fig. 3 moves to the right more than A in Fig. 1. The bias of the green output transistor _Q3 is changed to match the black level _L1 of the video signal to its characteristics. If you do this, V ₁ > V ₂ and the static characteristics will be affected when the cathode ray tube heater is turned on.
Even if the voltage is shifted to the left by _V2 , an undesired cathode current due to the vertical blanking signal will not flow and cause the dark screen to become unbalanced.

Regarding the blue circuit and red circuit, we consider the individual characteristics of the corresponding blue electron gun and red electron gun,
Perform bias settings in the same way. In this way,
After adjusting the white balance on a dark screen, switch switch 3 to contacts a and b to adjust the first volume.
You can adjust the white balance on bright screens using VR _1b and VR _1r .

As explained above, according to the present invention, white balance adjustment for dark screens and white balance adjustment for bright screens can be performed independently without affecting each other, making adjustments much easier than in the conventional case. effective.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining transient phenomena of a cathode ray tube, and FIGS. 2 and 3 are diagrams for explaining white balance adjustment on a dark screen of a color television receiver. FIG. 4 is a circuit diagram showing a conventional white balance adjustment circuit. FIG. 5 is a circuit diagram showing a white balance adjustment circuit implementing the present invention. 1... Video output stage, 2... Vertical deflection circuit, 3...
...Interlocking changeover switch, Q ₁ ...Blue output transistor, Q ₂ ...Red output transistor, Q ₃ ...
Green output transistor, Q ₄ ... Vertical drive transistor, VR _1b , VR _1r ... 1st volume,
VR _2b , VR _2r , VR _2g ...Second volume.

Claims (1)

[Claims for Utility Model Registration] (1) A color output transistor in which a color difference signal is applied to a first electrode, a video signal is applied to a second electrode, and the combined output is taken out from a third electrode; an interlocking changeover switch that connects the two electrodes and the video output stage and puts the vertical deflection circuit in an active state, and when switched to the other, cuts off the connection between the video output stage and the second electrode and puts the vertical deflection circuit in an inactive state; , a color television receiver comprising a first volume for adjusting white balance on a bright screen and a second volume for adjusting white balance on a dark screen, which are provided in the second electrode side circuit of the color output transistor. In the white balance adjustment circuit, the first volume is inserted between a second electrode of the color output transistor and the switch, the second volume is inserted between the second electrode and a reference potential point, and the first volume is inserted between the second electrode and the reference potential point. The two electrodes are connected to a resistor attached to a transistor of a vertical deflection circuit through the switch, and when the switch is switched to one of the two electrodes, the connection with the vertical deflection circuit is cut off and the resistor is connected to the transistor through the first volume. A video signal is guided to the second electrode, thereby causing the first
The white balance on a bright screen can be adjusted with the volume control, and when the switch is switched to the other side, one end of the first volume floats in terms of the circuit, so that the first volume does not affect the circuit on the second electrode side, and the second volume does not affect the circuit on the second electrode side. When the electrode current flows through the switch to the resistor of the transistor of the vertical deflection circuit, the transistor of the vertical deflection circuit is cut off, and in this state, the second volume adjusts the white balance on a dark screen. A white balance adjustment circuit for color television receivers featuring: (2) The white balance adjustment circuit for a color television receiver according to claim 1, wherein the transistor of the vertical deflection circuit is a vertical drive stage transistor. (3) The white balance adjustment circuit for a color television receiver according to claim 1, wherein the first electrode is a base, the second electrode is an emitter, and the third electrode is a collector.