JPH05313611A - Liquid crystal display device and electronic equipment - Google Patents

Abstract

PURPOSE:To improve display unevenness by controlling the base current of a transistor, which outputs liquid crystal driving voltages, in accordance with the difference between the detected and reference voltages. CONSTITUTION:A first resistance 40 and a constant voltage diode 80 are serially connected and a reference voltage source is configured by applying a liquid crystal driving voltage. Moreover, the reference voltage is supplied to the emitter of a transistor 20 and a detected voltage is supplied to the base. When a liquid crystal driving voltage is slightly increased, the detected voltage becomes higher in proportion thereto and the difference from the reference voltage becomes larger. Then, the equivalent resistance of the transistor 20 becomes smaller. Thus, the base voltage of a transistor 10 becomes smaller than the emitter voltage of the transistor 10, i.e., the voltage driving voltage, thereby the base of the transistor 10 is restricted within small one and furthermore, the corrector current of the transistor 10 is restricted within little one. Therefore, the liquid crystal driving voltage is kept constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a power supply circuit for a liquid crystal display device.

[0002]

2. Description of the Related Art Generally, a voltage required to drive a liquid crystal panel of a liquid crystal display device (hereinafter referred to as a liquid crystal drive voltage) needs to be changed according to a viewing angle and an ambient temperature. The power supply circuit has a circuit for adjusting this voltage. Here, FIG. 2 shows the configuration of a circuit for adjusting the voltage of a power supply circuit according to the related art. In the figure, 10 is a transistor, 250 is a fixed resistor, 260 is a variable resistor, 270 is a variable resistor, 271 is a slider of the variable resistor 270, terminal T1 is an input terminal for inputting a voltage from an external power source, and terminal T2 is a liquid crystal drive. It is an output terminal that outputs a voltage. With the above structure, the collector electrode of the transistor 10 has a terminal T
A voltage is applied from an external power supply via 1 and a voltage output from the emitter electrode is output as a liquid crystal drive voltage via a terminal T2. The fixed resistor 250, the variable resistor 270, and the fixed resistor 260 are connected in series to form a voltage dividing circuit. The voltage dividing circuit has a configuration in which a voltage obtained by reducing the voltage supplied from the outside to an arbitrary fraction is applied to the base electrode of the transistor 10 to control the current flowing through the base. That is, it was composed of a so-called emitter-follower circuit.

[0003]

Here, depending on the size of the liquid crystal panel, a large liquid crystal panel is a capacitive load having a capacity of about several hundreds nF, so that it transiently ranges from several tens to several hundreds of milliamperes. A large current flows. However, in the conventional power supply circuit, when the output impedance of the external power supply is not sufficiently small, the voltage of the external power supply fluctuates due to this transient current. As a result, the voltage output from the voltage division circuit fluctuates, and the liquid crystal drive voltage also fluctuates accordingly. Further, since the DC amplification factor of the transistor 10 is not infinity but at most about several hundreds, the current flowing through the base of the transistor changes by the transient current in the order of several hundreds μm to several milliamperes. The current flowing through this base flows through the resistors that make up the voltage divider circuit,
As a result, the voltage of the base is changed, which also changes the liquid crystal drive voltage. This fluctuation can be reduced by sufficiently reducing the resistance value of the resistor that constitutes the voltage division circuit, but this is not realistic because it consumes unnecessary current. As a result of investigations by the authors, this variation depends on the configuration of the power supply circuit and the size of the liquid crystal panel.
When the liquid crystal drive voltage was about 30 V, this voltage fluctuation sometimes reached a peak of 2 to 3 volts.

As described above, there has been a problem that the display of the liquid crystal panel becomes uneven due to the fluctuation of the voltage.

The present invention has been made in view of the above problem, and controls the liquid crystal drive voltage output from the transistor by the difference between the reference voltage and the arbitrary fraction of the liquid crystal drive voltage. To reduce fluctuations,
It is therefore an object of the present invention to provide a high-quality electronic device equipped with a display device that is compact and lightweight and has no display unevenness and a high-quality display device.

[0006]

The liquid crystal display device according to the first aspect of the present invention comprises a transistor and a current control circuit for controlling the current flowing through the base electrode of the transistor, and a voltage is externally applied to the collector electrode of the transistor. In addition, in a liquid crystal display device including a power supply circuit that uses the voltage output from the emitter electrode of the transistor as a liquid crystal drive voltage and controls the current flowing to the base electrode of the transistor by a current control circuit to change the liquid crystal drive voltage. A voltage dividing circuit for outputting a liquid crystal driving voltage, which is a fractional one of the liquid crystal driving voltage, as a detection voltage, the current control circuit connecting a plurality of resistors including a variable resistor in series, and a reference voltage. And a means for controlling the current flowing to the base electrode of the transistor by the difference between the detected voltage and the voltage generated by the reference voltage source. Characterized in that it Bei.

A second aspect of the present invention is characterized in that the first display device is provided with the display device.

[0008]

【Example】

[Embodiment 1] The driving method of the present invention will be described in more detail with reference to an embodiment. Here, the case where the liquid crystal drive voltage is positive will be described. FIG. 1 is a diagram showing a configuration of a voltage adjusting circuit of a power supply circuit of the present invention. In the figure, 10 and 20 are NPN transistors, 30, 40, 50 and 60 are fixed resistors, 70 is a variable resistor, 71 is a slider of the variable resistor 70, and 80 is a constant voltage diode. T1 is an input terminal for supplying a voltage of an external power source, and T2 is an output terminal for outputting a liquid crystal driving voltage.
Here, the fixed resistor 50, the variable resistor 70, and the fixed resistor 60 are connected in series to form a voltage dividing circuit. This voltage division circuit includes fixed resistors 50 and 60 and a variable resistor 7.
A voltage Vd (hereinafter, this voltage is referred to as a detection voltage) obtained by making the liquid crystal drive voltage 1 / arbitrary by setting the resistance value of 0 to an appropriate value is output from the slider 71 of the variable resistor 7.

A fixed resistor 40 and a constant voltage diode 80 are connected in series, and a liquid crystal driving voltage is applied to form a reference voltage source. That is, the constant voltage diode 80 generates a constant voltage even if the liquid crystal drive voltage fluctuates. (Hereinafter, this voltage is referred to as reference voltage VR.) The reference voltage Vr is supplied to the emitter of the transistor 20,
The detection voltage Vd is supplied to the base. Therefore, when the difference between the reference voltage Vr and the detection voltage Vd becomes large,
It tries to flow a large collector current. In other words, when the transistor 20 is considered to be equivalent to resistance, this resistance becomes smaller.

With the fixed resistor 30 and the transistor 20,
The base voltage of the transistor 10 is generated. That is, the base voltage of the transistor 10 is determined by the equivalent resistance of the fixed resistor 30 and the transistor 20.

With the above configuration, when the liquid crystal drive voltage is slightly increased, the detection voltage Vd is proportionally increased.
Becomes higher and the difference from the reference voltage Vr becomes larger. Then, the equivalent resistance of the transistor 20 decreases. As a result, the base voltage of the transistor 10 becomes
Since it is smaller than the voltage of the emitter of, that is, the voltage drive voltage, the base of the transistor 10 is limited to a small
Further, the collector current of the transistor 10 is also limited to a small value. In other words, the equivalent resistance of the transistor 10 increases, so that the liquid crystal drive voltage decreases. By feedback-controlling the voltage fluctuation of the liquid crystal drive voltage in this way, the liquid crystal drive voltage is kept constant.

As described above, since the mechanism for keeping the liquid crystal driving voltage constant is the mechanism for controlling only by the difference between the detected voltage obtained from the liquid crystal driving voltage and the reference voltage, it is not affected by the voltage fluctuation of the external power source. Absent. Further, the change in the base current of the transistor 20 with respect to the change in the detection voltage is extremely small, and the influence on the detection voltage is extremely small in the order of μ ampere. For example, if the resistance values of the fixed resistor 50, the variable resistor 70, and the fixed resistor 60 forming the voltage dividing circuit are on the order of 10 KΩ, the influence on the detection voltage is about several tens of mV.

By using the circuit having the above-mentioned configuration for the voltage adjusting circuit of the power supply circuit of the liquid crystal display device, even if a liquid crystal panel having a large capacity is actually driven, the voltage fluctuation of the liquid crystal drive voltage is reduced to 0. It could be suppressed to about 1V. As a result, the display unevenness is remarkably improved. Although the liquid crystal drive voltage is a positive voltage here, this can be easily realized even if the liquid crystal drive voltage is a negative voltage.
It is sufficient to replace 0 and 20 with PNP type transistors and reverse the direction of the constant voltage diode.

[Embodiment 2] By mounting the liquid crystal display device of Embodiment 1 on an electronic device which requires a display, it is possible to provide an electronic device having a good display quality and thus a high quality.

[0015]

As described above, the fluctuation of the liquid crystal drive voltage is detected as the detection voltage, and the base current of the transistor that outputs the liquid crystal drive voltage is controlled by the difference between this voltage and the reference voltage, thereby changing the voltage. It was possible to output a liquid crystal drive voltage with less discharge, and this could significantly improve display unevenness. As a result, it was possible to provide a high-quality liquid crystal display device and a high-quality electronic device.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a voltage adjustment circuit of a power supply circuit according to a first embodiment.

FIG. 2 is a diagram showing a configuration of a voltage adjustment circuit of a power supply circuit according to a conventional technique.

[Explanation of symbols]

 10 and 20 are NPN type transistors 30, 40, 50 and 60 are fixed resistors 70 are variable resistors 71 are sliders of variable resistors 70 are constant voltage diodes T1 are input terminals for inputting voltage from an external power source T2 is an output terminal for outputting a liquid crystal drive voltage

Claims (2)

[Claims] 1. A liquid crystal panel comprising a transistor and a current control circuit for controlling a current flowing through the base electrode of the transistor, wherein a voltage is externally applied to a collector electrode of the transistor to output a voltage output from an emitter electrode of the transistor. In the liquid crystal display device including a power supply circuit for changing the liquid crystal drive voltage by controlling the current applied to the base electrode of the transistor by the current control circuit, the current control circuit comprises: The liquid crystal drive voltage is obtained by connecting a plurality of resistors including a variable resistor in series, and an arbitrary fraction of the liquid crystal drive voltage.
A voltage dividing circuit for outputting the voltage as a detection voltage, a reference voltage source, and means for controlling a current flowing through the base electrode of the transistor by a difference between the detection voltage and the voltage generated by the reference voltage source. Liquid crystal display device. 2. An electronic device comprising the display device according to claim 1.