JPS6117438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brightness adjustment device for a color display device using a cathode ray tube.

Figure 1 shows the characteristics of the cathode/first grid tube voltage ( _VKG ) and light output of a color cathode ray tube (hereinafter abbreviated as CPT). The order of red R, blue B, and green G is not necessarily as shown in Figure 1, but mainly
Depending on the assembly precision of the CPT, the _VKG at which the R, B, and G optical outputs rise differ, as shown in FIG. 1. The voltage V _KG at which the optical output rises as shown in Figure 1, that is, V _G , V _B , _VR etc., is generally called the cut-off voltage. It is necessary to produce output. This is called cutoff voltage adjustment, and if this adjustment is incomplete, white reproducibility in dark areas of the screen will deteriorate.

The conventional cut-off voltage adjusting means will be explained below using a specific circuit.

Figure 2 is used in current color televisions.
This is an example of a CPT drive circuit. In Figure 2,
1 is CPT, 2R, 2G, 2B is load resistance, 3
R, 3G, 3B are drive transistors, 4R, 4
G, 4B are cut-off voltage adjustment resistors, 5R, 5
G, 5B are drive adjustment resistors, 6R, 6G, 6B
indicates a color difference signal, and 7 indicates a luminance signal.

In general, in recent inline CPT, R, G,
The first grid of each electron gun B is commonly set to ground potential. Therefore, the cut-off voltage adjustment described above is performed by independently changing the R, G, and B cathode terminal voltages. below,
This will be explained in detail using FIG.

The outputs of the color difference signal sources 6R, 6G, and 6B are set to zero,
Drive adjustment resistors 5R, 5G, and 5B are opened. At this time, drive transistors 3R, 3
Since a constant voltage E is applied to the bases of transistors G and 3B, the collector currents of drive transistors 3R, 3G and 3B are varied by changing the values of cut-off adjustment resistors 4R, 4G and 4B, respectively. As a result, the amount of voltage drop across the load resistors 2R, 2G, and 2B changes, so each cathode voltage also changes. This can be expressed as a formula as follows.

V _KG = V _CC -I _C R _L ......(1) where I _C : Collector current of drive transistors 3R, 3G, 3B R _L : Resistance value of load resistors 2R, 2G, 2B Also, I of equation (1) _C can be expressed by the following formula.

I _C ≒ I _E = E-V _BE /R _E ......(2) where V _BE : Base-emitter voltage of drive transistors 3R, 3G, 3B R _E : Voltage of cut-off adjustment resistors 4R, 4G, 4B Resistance value I _E : Emitter current of drive transistors 3R, 3G, 3B Therefore, from equations (1) and (2), V _KG = V _CC −R _L /R _E (E−V _BE ) ………(3) obtain. The resistors 4R, 4G, and 4B are adjusted so that V _KG expressed by equation (3) becomes the cut-off voltages V _R , V _G , and V _B of each electron gun in FIG. 1, respectively. White balance in dark areas of the screen can be maintained by setting the cathode potential to the cut-off voltage of each electron gun in CPT1.

Adjustment of the white balance in bright areas of the screen is performed by adjusting the resistance values of the drive adjustment resistors 5R, 5G, and 5B to adjust the amplification degrees of the drive transistors 3R, 3G, and 3B. Here, the color difference signals R-Y, G-Y, B-Y and the luminance signal Y are calculated by the driving transistors 3R, 3G, 3B, and the respective primary color signals R, G, B are obtained, and the cathode of CPT1 is driven. Ru. As shown in FIG. 1, the collector voltages of drive transistors 3R, 3G, and 3B vary between cut-off potential and zero potential depending on the input signal level. Therefore, if the cutoff voltage of CPT1 has large variations and the power supply voltage _Vcc is low, the possible amplitude range of the drive transistors 3R, 3G, and 3B becomes extremely narrow, and high output cannot be obtained. On the other hand, if the power supply voltage V _CC is increased in order to sufficiently absorb the variation in the cut-off voltage and widen the operating range of the drive transistors 3R, 3G, 3B, the load resistances 2R, 2G, 2B and the drive transistors 3R, 3G, 3B This increases losses and is not economical. Also, increase the power supply voltage V _CC and load resistance 2
By increasing R, 2G, and 2B, the operating current of the drive transistors 3R, 3G, and 3B can be reduced, and the output transistors 3R and 3B can be reduced without increasing loss.
When the operating range of 3G and 3B is expanded, the input capacitance of the cathode and the drive transistors 3R, 3G, 3B
The cut-off frequency of the drive circuit system, which is determined by the output capacitance and other stray capacitances such as wiring, and the load resistances 2R, 2G, and 2B, decreases, making it impossible to obtain a high-resolution screen.

A specific example of a CPT drive circuit that improves the above-mentioned drawbacks is shown in FIG. In Figure 3, 8R, 8G,
8B are input terminals for primary color signals R, G, and B, respectively;
9R, 9G, and 9B are amplifiers for amplifying the primary color signals R, G, and B; 10R, 10G, and 10B are DC regenerators; and 11 is a DC blocking capacitor. Amplifiers 9R, 9G, 9B each include an amplification transistor and its load resistance, and DC regenerators 10R, 10
G and 10B each have a transistor 13 that is turned on by the clamp pulse 12 generated during the black level period and turned off except for the clamp pulse period, and a clamp voltage adjustment that divides the voltage between the DC voltage 16 V _B1 and 17 V _B2 . The transistor 13 includes a variable resistor 14 and a diode 15 that protects the transistor 13 from reverse breakdown voltage.

Regarding the R primary color signal, the DC component of the R primary color signal amplified by the amplifier 8R is removed by the capacitor 11, and the DC component is regenerated by the DC regenerator 10R and supplied to the cathode of the CPT1. Since the DC component voltage of the primary color signal supplied to the cathode can be adjusted by adjusting the variable resistor 14, variations in the cutoff voltage of the electron gun are absorbed by this adjustment. That is, since variations in the cut-off voltage of the electron gun are adjusted by adjusting the DC regenerators 10R, 10G, and 10B, there is no need to absorb the variations in the amplifiers 9R, 9G, and 9B; There is no need to make the power supply voltage or load resistance value larger than necessary. Therefore, the third
The drive circuit shown in the figure can substantially eliminate the drawbacks of the drive circuit shown in FIG. 2 and achieve a wide band. However, regarding the brightness adjustment function, the drive circuit shown in FIG. 2 can be obtained by adjusting the DC voltage of the brightness signal Y, but in the drive circuit shown in _FIG. However, there are drawbacks as shown below.

The position of the slider of the variable resistor 14, that is, the power supply 16
and the voltage division ratio K of the variable power supply 17, the variable power supply 17
The transmission rate of the voltage V _B2 to the cathode is affected by this, and if the black level voltage at the cathode is V _K , then V _K = (V _B1 - V _B2 )K+V _B2 = K・V _B1 + (1-K) V _B2 ......(4) When K = 0, V _K = V _B2 When K = 1, V _K = V _B1 , and even for the same V _B1 , V _K differs depending on the value of K. As a result, due to variations in the voltage division ratio of the variable resistor 14 in cut-off adjustment for each color, even if the voltage V _B2 of the variable power supply 17 is adjusted for brightness adjustment, the transmission rate to the cathode is different, and each color is uniform. The brightness cannot be adjusted and the color changes, which is inconvenient. As described above, it is difficult to achieve a wide band with the drive circuit shown in FIG. 2, and with the circuit shown in FIG. 3, the color changes due to brightness adjustment, which is disadvantageous.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a color cathode ray tube drive circuit that has a wide band and does not cause color changes during brightness adjustment.

The present invention provides a cut-off adjustment variable resistor 1 in the broadband cathode ray tube drive device shown in FIG.
R, G, B, regardless of the adjustment position of 4.
The voltage of each cathode was adjusted equally by brightness adjustment so that the displayed color did not change.

That is, the present invention is characterized in that a constant voltage source is connected between fixed terminals of the variable resistor, and a variable voltage source is connected to one end of the variable resistor.

An embodiment of the present invention is shown in FIG. Components that are the same as in FIG. 3 are given the same numbers. 18 is a cut-off voltage power supply having the same function as the DC power supply 16 in FIG. 3, and 19 is a variable power supply for brightness adjustment. Power supply 1
8 has both ends connected to the variable resistor 14 and one end connected to the variable power supply 19. Therefore, if the voltage of the variable power supply 19 is V _C , the voltage of the power supply 18 is V _B , and the voltage division ratio of the variable resistor 14 is K, the cathode voltage V _K is V _K =K・V _B +V _C , and is variable. The voltage V _C appears as the cathode voltage V _K without being influenced by the voltage division ratio K. As a result, each color's variable resistor 1 is adjusted by adjusting the cutoff of each color.
Power supply 1 for brightness adjustment even if the voltage division ratio K of 4 varies.
By adjusting 9, the cathode voltage can be adjusted equally for each color, and the brightness can be adjusted without changing the color.

Another embodiment corresponding to the power source 18 and variable power source 19 in FIG. 4 is shown in FIG. 20 in Figure 5
21 is a rectifying diode, 22 is a smoothing capacitor, 23 is a variable voltage control transistor, 24 is a brightness adjustment variable resistor, and 25 is a DC power supply. The cut-off adjusting power supply 18 is obtained by rectifying a flyback pulse generated in the tertiary winding 26 of the flyback transformer with a diode 21 and smoothing it with a capacitor 22. The variable power supply 19 includes a transistor 23 whose collector is connected to the ground and whose power source is the DC power supply 25.
Emitter voltage is used. The voltage adjustment is obtained by adjusting the variable resistor 24. Furthermore, the same effect can be obtained even if the control transistor 23 uses a collector voltage whose emitter is grounded instead of whose collector is grounded. Furthermore, in the embodiment shown in FIG.
9 uses a positive power source, but the same effect can be obtained with a negative power source.

As described above, according to the present invention, it is possible to obtain a high-resolution screen using an economical low-power consumption wideband amplifier, and at the same time, it is possible to eliminate the drawback that the display color changes when adjusting the brightness.

[Brief explanation of the drawing]

Figure 1 shows the characteristics of a typical cathode ray tube.
Fig. 2 is a conventional cathode ray tube drive circuit diagram unsuitable for broadband expansion, Fig. 3 is a conventional cathode ray tube drive circuit diagram that is an improvement of Fig. 2, and Fig. 4 is a cathode ray tube drive circuit diagram according to an embodiment of the present invention. FIG. 5 is a circuit diagram showing another example of the power supply in the embodiment of FIG. 4. 1: Color cathode ray tube, 9R, 9G, 9B: Primary color signal amplifier, 10R, 10G, 10B: DC regenerator, 11: Capacitor, 14: Variable resistor, 1
7: Power supply, 18: Variable power supply.

Claims (1)

[Claims] 1 Three primary color signal amplifiers each supplying each primary color signal to each cathode of a color cathode ray tube having three electron guns via a capacitor, and a DC component of each primary color signal is connected to each connection point between the capacitor and the cathode. In a cathode ray tube drive device comprising three DC regenerators including variable resistors that reproduce independently of each other as components, a first one connected between fixed terminals of the variable resistors of the DC regenerator.
A cathode ray tube drive device comprising: a power source; and a second variable power source connected to one end of the variable resistor.