JPH05183835A - Luminance adjusting circuit - Google Patents

Abstract

PURPOSE:To inexpensively realize a luminance adjusting circuit which has the few number of circuit elements and high reliability for high voltage surge, is stable for temperature change and is capable of coping with a digital control, in a color display device. CONSTITUTION:The luminance adjusting circuit is composed by performing a cascade connection with an operational amplifier 6 and a grounded-emitter amplifier circuit from which high breakdown strength is easily obtained. A first input terminal 15 and the inversion input 7 of the operational amplifier 6 are connected in a first resistor 1, a second input terminal 16 and the noninverted input 8 of the operational amplifier 6 in a second resistor 2, the emitter of a grounded-emitter amplifier circuit 10 and the inversion input 7 of the operational amplifier 6 in a third resistor 3, and an output terminal 17 and the noninverted input 8 of the operational amplifier 6 in a fourth resistor 4, respectively. Thus, high voltage of about 100V can be controlled by the few number of elements and low voltage of 0 to 5V, temperature compentation by feedback can be performed and a rational luminance adjusting circuit can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a cathode ray tube (hereinafter CRT).
Abbreviated) and the like for a brightness adjustment circuit in a color display device.

[0002]

2. Description of the Related Art In recent years, color display devices have been required to have high brightness over a wide band due to higher performance as the range of use of computers has expanded. Conventionally, the cathode of the CRT is directly connected to the video signal amplifier circuit, and the brightness adjustment is performed by controlling the DC voltage of the video signal amplifier circuit. It is necessary to increase the power consumption, which increases power consumption. For this reason, from the direct connection type in the related art, a cathode clamp method in which a direct current component is cut off by a capacitor and a black level signal in a blanking period is clamped to a reference voltage to perform direct current regeneration has become mainstream.

A conventional brightness adjusting circuit will be described below. FIG. 3 is a block diagram showing a video output circuit portion of a color display device including a brightness adjusting circuit. In FIG. 3, 3
Reference numeral 1 is a video amplifier circuit, 32 is a CRT, 33 is a coupling capacitor, 34 is a clamp circuit, and 35 is a brightness adjustment circuit.
Since it is a color display device, there are three sets of the same circuit configuration for the three primary colors, but since the basic operation is exactly the same, only one set of circuits will be described below.

FIG. 4 is a circuit diagram of a conventional brightness adjusting circuit. This is the brightness adjustment circuit 35 in the block diagram of FIG.
Equivalent to. In FIG. 4, 41 is a first constant voltage circuit by a constant current IC, 42 is a first variable resistor, 43 is a second constant voltage circuit by a constant current IC, 44 is a third constant voltage by a constant current IC. A circuit, 45 is a second variable resistor, 46 is a power input terminal, and 47 is an output terminal. The first constant voltage circuit 41 and the first variable resistor 42 are common circuits for the three primary colors.

FIG. 5 is a diagram for explaining the operation of the constant current IC in FIG. In FIG. 6, 50 is a constant voltage IC, 51 is an input terminal, 52 is an output terminal, 53 is a control terminal, and 54 and 55.
Is resistance.

FIG. 6 is a diagram for explaining the operation of the constant voltage IC in FIG. In FIG. 6, 60 is a constant voltage IC, 61 is an input terminal, 62 is an output terminal, 63 is a control terminal, 64 and 65.
Is resistance.

The operation of the conventional brightness adjusting circuit configured as described above will be described below.

First, the principle of brightness adjustment will be described with reference to FIG. The video signal amplified by the video amplifier circuit 31 is CRT3.
Although it has a sufficient signal amplitude to drive 2, the DC component is determined only by the dynamic range of the video amplifier circuit 31 regardless of the characteristics of the CRT 32. Therefore, the DC component is once cut off by the coupling capacitor 33. From the brightness adjustment circuit 35 to the clamp circuit 34, 3 of the CRT 32
A DC voltage is supplied so that the primary color is just at the black level, and the clamp circuit 34 operates to give the DC voltage of the signal line when the video signal becomes a black signal during the blanking period.
This voltage is held in the coupling capacitor 33, and the CRT 32
A desired image is displayed on. When the user of the display device changes the brightness, the brightness adjustment circuit 35 to the clamp circuit 34 are arranged so that the balance of the three primary colors of the CRT 32 is not lost.
The three direct current voltages applied to the CRT 32 simultaneously rise and fall, while the three direct current voltages must be individually raised and lowered in order to correct the variation between the three primary colors of the CRT 32 during the production of the display device.

Next, the operation of the constant current IC will be described with reference to FIG. Here, in order to make the explanation easy to understand, the input terminal 51
Of the constant current IC 50 from the input terminal 51 to the output terminal 52 of the constant current IC 50 is Ia and the resistance of the resistor 5 is 5.
The current flowing through the resistor 4 and the resistor 55 is Ib. The current at the control terminal 53 is small enough to be ignored.

As a characteristic of the constant current IC 50, Vb has a reference voltage (for example, 2.5 V) inside the constant current IC 50.
If Vb is lower than the reference voltage, Ia is increased, and if Vb is lower than the reference voltage, Ia is increased. Examples of commercially available ICs include the 431 type. On the other hand V
a and Vb are determined by Ib and the resistance values of the resistors 54 and 55. Current flowing from the outside, ie Ia + I
If b is constant, if Ib increases, Vb increases and becomes higher than the reference voltage, so that Ia also increases and, as a result, Ib decreases. Conversely, if Ib decreases, V
Since b decreases and becomes lower than the reference voltage, Ia also decreases, and as a result, Ib increases. Due to this action, Ib maintains a constant value even when the current flowing from the outside fluctuates, and therefore Va has a constant value, so that a constant voltage circuit is configured as a whole.

Next, the operation of the constant voltage IC using FIG. 6 will be described. Here, the output terminal 6 is used to make the explanation easy to understand.
2 is Vc for the control terminal 63, Vd is the voltage for the control terminal 63 with respect to ground, and the input terminal 6 of the constant voltage IC 60 is
The current flowing from 1 to the output terminal 62 is Ic, and the current flowing through the resistors 64 and 65 is Id. Control terminal 6
The current at 3 is almost negligible.

The characteristic of the constant voltage IC 60 is that Vc is a reference voltage (for example, 24 V) inside the constant voltage IC 60.
When it is higher, Ic is decreased. On the contrary, when Vc is lower than the reference voltage, Ic is increased. Examples of commercially available ICs include the 7824 type. On the other hand, Vc
Is determined by Id and the resistance value of the resistor 64. If the current flowing out to the outside, that is, Ic-Id is constant, I
When d increases, Vc increases and becomes higher than the reference voltage, so Ic decreases, and as a result, Id decreases and Vc decreases. Conversely, if Id decreases, Vc decreases and becomes lower than the reference voltage, so Ic increases, and as a result, Id increases and Vc increases. By this action, Vc and Id
Keeps a constant value. Here, since Vd is determined by Id and the resistance value of the resistor 65, it also becomes a constant value, and a constant voltage circuit is configured as a whole.

Next, the operation of the conventional brightness adjusting circuit will be described with reference to FIG. First, the first constant voltage circuit 41 and the second constant voltage circuit 43 perform the constant voltage operation as described in FIG. 5, and the voltages are set to V31 and V32, respectively. Similarly, the third constant voltage circuit 44 performs a constant voltage operation as described in FIG. 6, and sets this voltage to V33. By the way, the first variable resistor 32 is connected to the first constant voltage circuit 31, and therefore V31 is the first variable resistor 3
It can be varied within a certain range by the change of 2. Similarly third
The second variable resistor 35 is connected to the constant voltage circuit 34, and V33 is varied within a certain range by the change of the second variable resistor 35. With these, the output terminal 37
The voltage, that is, V31 + V32 + V33 can be varied within a certain range by the first variable resistor 32 and the second variable resistor 35. Generally, the first variable resistor 32 is a variable resistor for brightness adjustment common to the three primary colors operated by the user of the display device, and the second variable resistor 35 is the variation among the three primary colors due to CRT during the production of the display device. Used to correct the.

[0014]

However, in the above configuration, the voltage required for brightness adjustment in the cathode voltage of the CRT is about 100 V, whereas the commonly available constant voltage IC or constant voltage IC. Current IC
Since the withstand voltage is as low as about 30 to 40 V, it is necessary to use these ICs in series by stacking several stages. Also generally CR
Although a high voltage surge is generated in the cathode of T due to the discharge in the tube, the above-mentioned IC is relatively weak to the high voltage surge, and there is a problem in reliability.

Further, in order to cope with the recently increasing digitized control system, the variable resistor cannot be directly controlled by the direct current output of 0 to 5 V in the D / A converter, so that the circuit structure must be devised. It is necessary and requires additional circuitry such as a voltage shift circuit to control the high voltage.

As described above, in the conventional brightness adjusting circuit,
There were problems such as an increase in the number of circuit elements and a decrease in reliability.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a highly reliable brightness adjusting circuit having a small number of circuit elements.

[0018]

In order to achieve this object, a brightness adjusting circuit of the present invention is a circuit having two input terminals and one output terminal, and has an inverting input and a non-inverting input, And an operational amplifier having an output and a grounded-emitter amplifier circuit having a series feedback resistor in the emitter are connected in series, and a first resistor is provided between the first input terminal and the inverting input of the operational amplifier. A second resistor is provided between the second input terminal and the inverting input of the operational amplifier, and a third resistor is provided between the inverting input of the operational amplifier and the emitter of the grounded-emitter amplifier circuit. A fourth resistor is provided between the non-inverting input of the operational amplifier and the output terminal, and a fifth resistor is provided between the non-inverting input of the operational amplifier and the ground.

[0019]

With this configuration, first, the transistors used in the grounded-emitter amplifier circuit and the emitter-follower circuit are
In general, a device having a withstand voltage of 100 V or more is easily available, so that it is not necessary to stack elements to guarantee the withstand voltage of the circuit. Further, the transistor is more resistant to high voltage surge than the IC, while the operational amplifier, which is relatively weak to high voltage surge, is located far from the CRT cathode, which is the source of high voltage surge, and therefore has high reliability against breakdown.

Moreover, a direct current voltage of 0 to 5 V obtained from a general D / A converter is directly input to both the first input terminal and the second input terminal to control a voltage of about 100 V at the output terminal. Therefore, it is possible to easily cope with the digitization control.

By the way, in general, it is necessary for the transistor to perform temperature compensation, but a third resistor is provided between the inverting input of the operational amplifier and the emitter of the grounded-emitter amplifier circuit, and further, the non-inverting input of the operational amplifier and the emitter follower circuit. Since the fourth resistor is provided between the grounded emitter amplifier circuit and the emitter follower circuit in the feedback loop of the operational amplifier, the respective resistors are temperature-compensated and are very stable.

As a result, it is possible to provide a highly reliable brightness adjusting circuit with a small number of circuit elements.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a circuit diagram of a brightness adjusting circuit according to a first embodiment of the present invention. This corresponds to the brightness adjusting circuit 35 in the block diagram of FIG. 3 which has already been described in the conventional example. In FIG. 1, 1 is a first resistor, 2 is a second resistor, 3 is a third resistor, 4 is a fourth resistor, 5 is a fifth resistor, 6 is an operational amplifier, and 7 is an operational amplifier 6. An inverting input, 8 is a non-inverting input of the operational amplifier 6, and 9 is an output of the operational amplifier. Reference numeral 10 is an NPN type transistor, 11 is an emitter resistance, and 12 is a collector resistance, and the above three elements constitute a grounded-emitter amplifier circuit. Reference numeral 13 is a PNP type transistor, and 14 is a load resistance, and the above two elements form an emitter follower circuit. Reference numeral 15 is a first input terminal, 16 is a second input terminal, 17 is an output terminal, and 18 is a power supply terminal.

The operation of the brightness adjusting circuit configured as described above will be described below with reference to the drawings. In FIG. 1, the voltage of the first input terminal 15 is V1, the voltage of the second input terminal 16 is V2, the emitter voltage of the NPN transistor 10 is V3, the output terminal 17 voltage is V4, and the inverting input 7 of the operational amplifier 6 is used. Is VO, the voltage of the non-inverting input 8 of the operational amplifier 6 is VN, the voltage of the power supply terminal 18 is VCC, PN
The base-emitter voltage of the P-type transistor 13 is set to VB.
E, the resistance value of the first resistor 1 is R1, the resistance value of the second resistor 2 is R2, the resistance value of the third resistor 3 is R3, and the fourth resistor 4
R4, the resistance value of the fifth resistance 5 is R5, the resistance value of the emitter resistance 11 is R6, the resistance value of the collector resistance 12 is R7, the current flowing through the first resistance 1 is I1, and the second resistance is The current flowing through 2 is I2, and the current flowing through the third resistor 3 is I
3, the current flowing through the fourth resistor 4 is I4, the current flowing through the fifth resistor 5 is I5, and the base ground current amplification factor of the NPN transistor 10 is A.

Since the voltage amplification factor of the operational amplifier 6 is very large,

[0027]

[Equation 1]

[0028]

[Equation 2]

[0029]

[Equation 3]

Is satisfied.

First, regarding the inverting input 7, from (Equation 2),

[0032]

[Equation 4]

Therefore, the emitter voltage of the NPN transistor 10 is

[0034]

[Equation 5]

As described above, it is completely independent of the base-emitter voltage of the NPN transistor 10.

Next, considering the non-inverting input 8,

[0037]

[Equation 6]

Substituting (Equation 6) into (Equation 5),

[0039]

[Equation 7]

It becomes like this.

On the other hand, focusing on the grounded emitter amplifier circuit and the emitter follower circuit,

[0042]

[Equation 8]

It becomes Substituting (Equation 8) into (Equation 7) here,

[0044]

[Equation 9]

Summarizing V4 from (Equation 9),

[0046]

[Equation 10]

That is, the voltage V4 of the output terminal 17 can be linearly controlled by the voltage V1 of the first input terminal 15 and the voltage V2 of the second input terminal 16.

As can be seen from (Equation 10), in the brightness control circuit of this embodiment, the base of the NPN transistor 10 to
The emitter-to-emitter voltage is completely irrelevant. Also, the denominator of (Equation 10) is larger than 1, which means that feedback is applied by the fourth resistor 4 and the influence of fluctuations in the power supply terminal voltage VCC and the base-emitter voltage VBE of the PNP transistor 13 is reduced. Is shown.

As described above, according to this embodiment, a circuit having two input terminals and one output terminal, which has an inverting input, a non-inverting input, and an output, and an emitter. A grounded-emitter amplifier circuit having a series feedback resistor is connected in cascade, a first resistor is provided between the first input terminal and the inverting input of the operational amplifier, and the second input terminal is connected to the above. A second resistor is provided between the inverting input of the operational amplifier and a third resistor between the inverting input of the operational amplifier and the emitter of the grounded-emitter amplifier circuit. By providing the fourth resistor between the output terminal and the fifth resistor between the non-inverting input of the operational amplifier and the ground, the number of semiconductor elements is smaller than that of the conventional brightness adjusting circuit. Resistant to high voltage surges,
It is possible to realize a brightness adjustment circuit that can directly support digitalization control and that is stable even with temperature changes.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram of a brightness adjusting circuit according to the second embodiment of the present invention. In FIG. 2, portions surrounded by dotted lines, ie, 21, 22, and 23 are the same as the three groups of the brightness adjusting circuit in the first embodiment of the present invention described in FIG. 1 in order to correspond to the three primary colors of the color display device. It is used, 21 is a brightness adjusting circuit for red image, 22
Is a brightness adjusting circuit for green image, and 23 is a brightness adjusting circuit for blue image.

Reference numeral 24 is a red image D / A converter, 25 is a green image D / A converter, and 26 is a blue image D / A converter. The red image brightness adjusting circuit 21 and the green image brightness are provided. It is connected to the first input terminals of the adjustment circuit 22 and the blue image brightness adjustment circuit 23, respectively. Reference numeral 27 is a D / A converter for simultaneous adjustment of three primary colors, which is commonly connected to the second input terminals of the red image brightness adjusting circuit 21, the green image brightness adjusting circuit 22, and the blue image brightness adjusting circuit 23. ..

28 is an output terminal for red image, 29 is an output terminal for green image, and 30 is an output terminal for blue image.

Next, the operation will be described. The basic operations of the red image brightness adjusting circuit 21, the green image brightness adjusting circuit 22, and the blue image brightness adjusting circuit 23 have already been described with reference to FIG.

In FIG. 2, the brightness adjusting circuit 2 for red image is shown.
1. Since the second input terminals of the green image luminance adjusting circuit 22 and the blue image luminance adjusting circuit 23 are commonly connected, the red image output terminal 28, the green image output terminal 29,
D / A for simultaneous adjustment of three primary colors for the voltage of the blue video output terminal 30
The converter 27 can simultaneously control linearly. This allows the brightness of the three primary colors of the color display device to be changed at the same time.

Further, in FIG. 2, the first input terminals of the red image brightness adjusting circuit 21, the green image brightness adjusting circuit 22, and the blue image brightness adjusting circuit 23 are independently connected, and therefore, for the red image. Set the voltage of the output terminal 28 to D / A for red video.
In the converter 24, connect the green video output terminal 29 to the green video D / A.
In the converter 25, the voltage of the blue video output terminal 30 can be linearly controlled individually in the blue video D / A converter 26. This allows the brightness of the three primary colors of the color display device to be changed individually.

As described above, according to this embodiment, the three brightness adjusting circuits described in the first embodiment are used, and the respective first input terminals are individually connected to the three D / A converters. However, by connecting each of the second input terminals to one D / A converter in common, in addition to the features of the first embodiment, the variation among the three primary colors due to the CRT is produced at the time of producing the color display device. Adjustment for each of the three primary colors necessary for correction,
It is possible to digitally control the adjustments common to the three primary colors operated by the user of the color display device.

In the second embodiment, since four commercially available operational amplifiers are integrated in one package, one package is sufficient for mounting the circuit, and the remaining one circuit is the other one. It has the advantage that it can be used for applications.

In the second embodiment, when the control voltage is applied by the variable resistor without using the D / A converter,
Although it is not digitalized control, there is no problem in other operations.

In both the first and second embodiments, the output terminal is connected from the emitter of the emitter follower circuit, but in principle it is connected from the collector of the grounded emitter circuit and the emitter follower circuit is omitted. Is also good. However, in the actual brightness adjustment circuit, the transient current when the DC voltage of the black signal is applied by the clamp circuit is large, so if the emitter follower circuit is omitted, the voltage of the output terminal does not fluctuate. The current needs to be quite large. This increases the power consumption of the grounded-emitter circuit and is not suitable for practical use.

Further, in the present invention, a capacitor is connected between the output terminal and the ground in order to further reduce the voltage fluctuation of the output terminal due to the transient current when the DC voltage of the black signal is applied by the clamp circuit. Needless to say, is effective.

[0062]

As described above, the present invention is a circuit having two input terminals and one output terminal, and an operational amplifier having an inverting input, a non-inverting input, and an output, and an emitter connected in series. A grounded-emitter amplifier circuit having a feedback resistor is connected in cascade, a first resistor is provided between the first input terminal and the inverting input of the operational amplifier, and the second input terminal and the operational amplifier are provided. A second resistor is provided between the inverting input of the amplifier and a third resistor between the inverting input of the operational amplifier and the emitter of the grounded-emitter amplifier circuit, and the non-inverting input and output terminal of the operational amplifier are provided. A fourth resistor is provided between the operational amplifier and the non-inverting input of the operational amplifier, and the fifth resistor is provided between the ground and the circuit. Therefore, the number of circuit elements is small, the reliability against a high voltage surge is high, and the temperature is high. Stable against changes and compatible with digital control In which it is excellent can be realized at low cost ability brightness adjustment circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a brightness adjusting circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a brightness adjusting circuit according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a video output circuit portion of a color display device including a brightness adjustment circuit.

FIG. 4 is a circuit diagram of a conventional brightness adjustment circuit.

FIG. 5 is an operation explanatory diagram of a constant current IC.

FIG. 6 is an operation explanatory diagram of a constant voltage IC.

[Explanation of symbols]

 6 operational amplifier 10 NPN type transistor 13 PNP type transistor 15 first input terminal 16 second input terminal

Claims (2)

[Claims] 1. A circuit having two input terminals and one output terminal, an operational amplifier having an inverting input, a non-inverting input, and an output, and a grounded-emitter amplifier circuit having a series feedback resistor in the emitter. And are connected in cascade, the first
A first resistor is provided between the input terminal of the operational amplifier and the inverting input of the operational amplifier, and a second resistor is provided between the second input terminal and the inverting input of the operational amplifier. A third resistor is provided between the non-inverting input of the operational amplifier and the output terminal, and a fourth resistor is provided between the non-inverting input of the operational amplifier and the output terminal. A brightness adjusting circuit, wherein a fifth resistor is provided between and. 2. A brightness adjusting circuit comprising three brightness adjusting circuits according to claim 1, wherein each of the second input terminals is commonly connected.