JPH10210496A - Cut-off adjustment circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cut-off adjustment circuit, in which adjustment is conducted quickly with a simple and inexpensive configuration. SOLUTION: A cathode current detection circuit 16 that converts a cathode current into a voltage to output the voltage is connected in series between a cathode drive circuit 11 for each of primary colors and a cathode of a cathode-ray tube 12. In the case of adjusting a cut-off, the cathode current flows the cathode current detection circuit 16, and when the cut-off is not adjusted, the cathode current is switched to pass through the cathode current detection circuit 16, so as to flow to the cathode drive circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cut-off adjusting circuit used for a color television receiver, a color monitor, and the like.

[0002]

2. Description of the Related Art It is well known that in a video display device using a cathode ray tube (CRT) such as a color television receiver or a color monitor device, cutoff adjustment for determining a light emitting point of the CRT is performed. is there. An example of a conventional cutoff adjustment will be described with reference to FIGS.
FIG. 5 is a circuit diagram showing a general cathode drive circuit used in a video display device, FIG. 6 is a circuit diagram showing an example of a control circuit for performing cutoff adjustment, and FIGS. 7 and 8 are used in cutoff adjustment. It is a figure showing a CRT screen.

First, a general cathode drive circuit used in a video display device will be described with reference to FIG. FIG.
In, the R, G, and B primary color signals are input to the cathode drive circuit 11, and the cathode of the CRT 12 is driven.
Here, for simplification, one system of the cathode drive circuit 11
Only three systems are shown, but there are actually three systems. As shown, the cathode drive circuit 11 includes an NPN transistor T
R1 to TR3, PNP transistor TR4, resistor R1
R4, and diodes D1 and D2.
Connected to the cathode of RT12.

Further, a drive adjustment volume 13 and a cut-off volume adjustment volume 14 are provided in the transistor TR2.
Is connected. The drive adjustment volume 13
Are provided in the R and B cathode drive circuits 11, and the cutoff adjustment volume 14 is provided in all the R, G and B cathode drive circuits 11. A screen bias adjustment volume 15 is connected to a screen electrode of the CRT 12. In FIG. 5, Vcc is a power supply voltage,
6 to R9 are resistors, FBT is a flyback transformer, Ik
Is a cathode current flowing from the cathode of the CRT 12.

Now, a conventional cutoff adjustment will be described with reference to FIGS. In FIG. 6, a video output circuit 3 and a vertical output circuit 5 are connected to a service switch 1 via diodes 2 and 4. By switching the service switch 1 from the normal terminal a to the test terminal b, the video output DC level of the video output circuit 3 becomes 0 and the vertical output circuit 5 becomes inoperable.
The screen at T12 is forcibly set to one horizontal bright line 6 (so-called one horizontal screen) as shown in FIG.

[0006] Then, by setting the cut-off adjustment volumes 14 of the R, G, and B primary colors at substantially equal positions, and gradually increasing the screen bias adjustment volume 15, a primary color that shines first is found. As a result, a primary color having a light bias can be found. Next, in the two primary colors other than the primary light that illuminated first, FIG.
The cut-off adjustment is performed by adjusting the cut-off adjustment volume 14 so that one horizontal screen shown in FIG. After this,
The screen bias adjustment volume 15 is adjusted again so that one horizontal screen shown in FIG. 7 slightly shines.

Further, the low-luminance step-like pattern shown in FIG. 8 is supplied to the CRT 12, and the service switch 1 is switched to the normal terminal a. In the step-like pattern shown in FIG. 8, by checking whether or not the desired luminance portion is white, it is possible to roughly grasp the variation in the cutoff adjustment of each primary color. The low-luminance step-like pattern is, for example, -2, -1, 0, 1, 2, from the left side in the figure.
[IRE].

The above-described cutoff adjustment requires a complicated operation and an adjustment operation with a low-luminance dark screen. In this case, since the screen of the CRT 12 must be adjusted visually or using a sensor such as a television camera, the adjustment varies, and stable adjustment cannot be performed. In addition, when the coordinator performs the adjustment visually, a heavy burden is imposed on the coordinator.

As a means for solving such a problem,
There have been proposed various cutoff adjusting circuits for automatically performing cutoff adjustment. Examples thereof include JP-A-4-77082, JP-A-5-236501, and JP-A-8-126023. Each of the publications described in the publications includes a cathode current detection circuit and a feedback circuit that automatically performs cutoff adjustment based on a detection voltage detected by the cathode current detection circuit.

[0010]

However, in the conventional cut-off adjusting circuits described in these prior arts, the circuit configuration is complicated by using a comparator, and the circuit is not inexpensive. Because of the loop system using a circuit, there is a problem that a response delay occurs during the adjustment, and the adjustment takes a long time.

The present invention has been made in view of such a problem, and can be configured at a low cost with a simple configuration.
In addition, it is an object of the present invention to provide a cutoff adjustment circuit capable of performing adjustment quickly.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention adjusts a cathode current flowing from each primary color cathode of a cathode ray tube (12) to cut off the cathode ray tube. In a cutoff adjustment circuit for performing adjustment, a cathode current detection circuit (1) connected in series between a cathode drive circuit (11) for each primary color and the cathode, converts the cathode current into a voltage, and outputs the voltage.
6) and a switch (SW1) for switching the cathode current to flow through the cathode current detection circuit when the cutoff is not adjusted and the cathode current to flow through the cathode current detection circuit when the cutoff is not adjusted. , SW2) are provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a cutoff adjusting circuit according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of a cutoff adjusting circuit according to the present invention, and FIG.
3 is a circuit diagram showing one configuration example of the cathode current detection circuit 16 in FIG. 1, and FIGS. 3 and 4 are waveform diagrams for explaining a cutoff adjusting operation by the cutoff adjusting circuit of the present invention.

In FIG. 1, the primary color signals of R, G and B are
The signal is input to the cathode drive circuit 11, and the cathode of the CRT 12 is driven. Although only one cathode drive circuit 11 is shown here for simplification, there are actually three systems. The cathode drive circuit 11, as shown in FIG.
N transistors TR1 to TR3, PNP transistor T
R4, resistors R1 to R4, and diodes D1 and D2. The cathode drive circuit 11 is connected to the cathode of the CRT 12 via a cathode current detection circuit 16 and a resistor R5 provided according to the present invention. I have.

Further, the transistor TR2 has a drive adjustment volume 13 and a cut-off volume adjustment volume 14.
Is connected. The drive adjustment volume 13
Are provided in the R and B cathode drive circuits 11, and the cutoff adjustment volume 14 is provided in all the R, G and B cathode drive circuits 11. A screen bias adjustment volume 15 is connected to a screen electrode of the CRT 12. In FIG. 1, Vcc is a power supply voltage,
6 to R9 are resistors, FBT is a flyback transformer, Ik
Is a cathode current flowing from the cathode of the CRT 12.

Here, a configuration example of the cathode current detection circuit 16 will be described with reference to FIG. In FIG. 2, N
The collector of the PN transistor TR5 has the power supply voltage Vcc
Is connected to the resistor R10. The emitter of this transistor TR5 is connected to a PNP transistor TR6
And its collector is grounded via a resistor Rk. The base of the transistor TR6 is connected to the terminal b of the switch SW1, and the transistor TR5
Is connected to the terminal b of the switch SW2. The terminals a of these switches SW1 and SW2 are connected to each other.

In such a configuration, the cathode current I
k is input to the cathode current detection circuit 16 via the resistor R5. Switch SW in cathode current detection circuit 16
1 and SW2 are connected to the terminal b for cutoff adjustment, the cathode current Ik is
Amplified by Then, a voltage Vk proportional to the cathode current Ik can be taken out from the terminal 17 connected to the collector of the transistor TR6.

In the present invention, the cut-off adjustment is automatically performed using the voltage Vk extracted from the terminal 17. Although illustration is omitted, in the cutoff adjustment at the factory,
The voltage Vk obtained from the terminal 17 is input to an adjusting device for cutoff adjustment. As the adjusting device, a personal computer (personal computer) or the like can be used. The adjustment device performs A / D conversion of the voltage Vk and automatically performs cutoff adjustment as described below.

As in the prior art, one horizontal bright line 6 as shown in FIG.
Is projected. At this time, the switches SW1 and SW2 are connected to the terminal b. Then, the cutoff adjustment volumes 14 for the R, G, and B primary colors are set at substantially equal positions.
The screen bias adjustment volume 15 is set to the minimum. The cathode current Ik of R, G, B in this case
(R), Ik (G), and Ik (B) are all in the cutoff state (ie, 0) as shown in FIG.
When the screen bias adjustment volume 15 is gradually raised, as shown in FIG. 3B, for example, a cathode current Ik (G) of G flows, and first, the cathode current Ik
You can find the flowing primary colors. Thereafter, the screen bias adjustment volume 15 is returned to a position where the cathode current Ik becomes zero. The screen bias adjustment volume 15 is provided in the FBT. The rotation amount of the driver for adjusting the screen bias adjustment volume 15 can be automatically controlled by a personal computer (adjustment device).

Next, the low luminance step-like pattern shown in FIG. 8 is supplied to the CRT 12, and the service switch 1 in FIG. 6 is switched to the normal terminal a. At this time, as an example, the luminance of the step pattern is -2,
-1, 0, 1, 2 [IRE]. Note that 0 [IR
E] is a pedestal level. In this step-like pattern, the adjustment is performed so that the cutoff point of the cathode current Ik of the other two primary colors matches the primary color in which the cathode current Ik first flows. That is, as shown in FIG. 4A, the brightness of the step-like pattern is the cathode current I of R, G, B.
k (R), Ik (G) and Ik (B).
As shown in FIG. 4B, the cathode currents Ik (R) and Ik (R)
The cut-off adjustment volume 14 is adjusted so that k (B) matches the cathode current Ik (G) of G in which the cathode current Ik first flows. Cutoff adjustment volume 1
Since 4 is an electronic volume, this adjustment can be automatically performed by a personal computer (adjustment device).

In the present invention, the cathode drive circuit 11
The cathode current detection circuit 16 is connected in series between the CRT 12 and the cathode of the CRT 12, so that a slight smear occurs.
Therefore, during normal operation, that is, when the cutoff is not adjusted,
By connecting the switches SW1 and SW2 to the terminal a, switching is performed so that the cathode current Ik flows through the cathode current detection circuit 16 and flows to the cathode drive circuit 11. The switches SW1 and SW2 are switched by the adjusting device.

As can be understood from the above description, in the cutoff adjusting circuit of the present invention, the cathode current detecting circuit 1
6 is provided in series between the cathode drive circuit 11 and the cathode of the CRT 12, so that there is no delay in response during adjustment as in a loop system using a feedback circuit. Moreover, the cathode current detection circuit 1
6, the cathode current Ik is set to a voltage V proportional to the cathode current Ik.
Since it is sufficient to simply convert the signal to k and output it, an extremely simple circuit is sufficient as shown in FIG. 2 and the cost is low.

[0023]

As described above in detail, the cutoff adjusting circuit of the present invention is connected in series between the cathode drive circuit of each primary color and the cathode, and converts the cathode current into a voltage and outputs the voltage. A current detection circuit, and a switch that switches the cathode current to the cathode current detection circuit when the cutoff is adjusted and the cathode current to flow through the cathode current detection circuit when the cutoff is not adjusted. Therefore, a simple configuration can be used at a low cost, and the adjustment can be performed quickly.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a cathode current detection circuit 16 in FIG.

FIG. 3 is a waveform diagram for explaining a cutoff adjusting operation according to the present invention.

FIG. 4 is a waveform chart for explaining a cutoff adjusting operation according to the present invention.

FIG. 5 is a circuit diagram showing a general cathode drive circuit.

FIG. 6 is a circuit diagram illustrating an example of a control circuit for performing cutoff adjustment.

FIG. 7 is a diagram illustrating a CRT screen used for cutoff adjustment.

FIG. 8 is a diagram showing a CRT screen used for cutoff adjustment.

[Explanation of symbols]

 Reference Signs List 11 cathode drive circuit 12 cathode ray tube 13 drive adjustment volume 14 cut-off adjustment volume 15 screen bias adjustment volume 16 cathode current detection circuit 17 terminal SW1, SW2 switch

Claims (1)

[Claims] 1. A cutoff adjusting circuit for adjusting a cathode current flowing from a cathode of each primary color of a cathode ray tube to adjust cutoff of said cathode ray tube, wherein a cutoff adjusting circuit for each primary color and a cathode drive circuit are provided. A cathode current detection circuit that is connected in series and converts the cathode current into a voltage and outputs the voltage; and a cathode current that flows through the cathode current detection circuit when cutoff is adjusted and the cathode current when the cutoff is not adjusted. A cut-off adjustment circuit comprising: a switch for switching a detection circuit through so as to flow to the cathode drive circuit.