JPH0545624A - Liquid crystal panel heater driving circuit - Google Patents

Abstract

PURPOSE:To eliminate the restrictions of an operating temperature range by making a panel heater generate heat up to proper temperature and improving the response and reliability of a liquid crystal panel. CONSTITUTION:A thermistor R1 and a Zener diode D1 are connected in parallel to the feedback part of a switching regulator type power circuit 1 and when the thermistor increases in resistance value at low temperature to raise a panel heater driving voltage Vo, the Zener diode D1 turns ON to clamp the voltage to a specific potential.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal panel heater driving circuit used in a liquid crystal television receiver.

[0002]

2. Description of the Related Art In recent years, design considerations for reliability such as operating temperature and storage temperature of a liquid crystal panel in a portable television receiver have been emphasized.

An example of the above-mentioned conventional liquid crystal panel heater driving circuit will be described below with reference to the drawings.

The liquid crystal panel heater operates so as to increase the amount of heat generated by the panel heater by increasing the panel heater driving voltage Vo when the temperature is low and to improve the response speed of the liquid crystal panel.

The heat generation amount of the panel heater is proportional to the panel heater driving voltage Vo.

FIG. 3 is a circuit diagram showing the structure of a conventional liquid crystal panel heater drive circuit. In the figure, 1 is a power supply circuit, 2 is a power supply circuit composed of an IC, and 3 is a liquid crystal panel heater.

As shown in FIG. 3, a predetermined voltage is applied from a cross point of a thermistor R1 connected in series between the output terminal of the power supply circuit 1 and the ground and a bias resistor R2 via a current control resistor R3. By feeding back to the feedback terminal of the power supply circuit 2, a predetermined stabilized panel heater driving voltage Vo is obtained.

FIG. 4 shows the temperature change of the thermistor R1 shown in FIG.
The change in resistance value (vertical axis) with respect to the horizontal axis is shown. Figure 3
Feedback voltage Vr in the feedback section of
Is in a state equal to the reference voltage (for example, 0.5 V) of the operational amplifier 2-1 inside the power supply circuit 2, and when the power supply is shut down, the panel heater driving voltage Vo changes greatly, and the current control resistor R3 adjusts it. When the feedback voltage Vr becomes 0.5 V or more and becomes less than 0.5 V, the power supply is shut down.

FIG. 5 is a graph showing the relationship between the ambient temperature (horizontal axis) and the panel heater driving voltage Vo (vertical axis) in the conventional example.

[0010]

However, in the above-mentioned structure, at the time of low temperature, as shown in FIG.
As the resistance value of 1 increases, the panel heater driving voltage Vo increases as shown in FIG.
1 is saturated, that is, the panel heater driving voltage Vo rises to, for example, about 11.8 V, and as a result, the divided voltage between the thermistor R1 and the bias resistor R2 changes, so the feedback voltage Vr is changed and the power supply is shut down. Has a problem that the operating temperature range is limited because the panel heater driving voltage Vo is stopped.

An object of the present invention is to solve such problems and to always control the liquid crystal panel heater at an appropriate temperature.

[0012]

According to the present invention, in a feedback portion of a power supply circuit, a thermistor R1 and a Zener diode D having a temperature characteristic sufficiently smaller than that of the thermistor R1 are provided.
1 is connected in parallel.

[0013]

According to the present invention, when the temperature is low, the resistance value of the thermistor R1 increases and the panel heater driving voltage Vo rises, but the Zener diode D1 clamps the voltage to a predetermined voltage, so that the power supply shutdown is activated. The operating temperature range is no longer limited.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal panel heater drive circuit according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of a liquid crystal panel heater driving circuit according to an embodiment of the present invention.

In the present invention, a parallel circuit of a thermistor R1 and a Zener diode D1 and a bias resistor R2 are connected in series between the output terminal of the power supply circuit 1 and the ground, as in the conventional example, and the thermistor R1 and Zener are connected in series. A predetermined output voltage is obtained by feeding back a predetermined voltage from the intersection of the parallel circuit of the diode D1 and the bias resistor R2 to the feedback terminal of the power supply circuit 2 via the current control resistor R3. .

For example, the resistance value of the thermistor R1 increases at a low temperature and the panel heater driving voltage Vo increases, but when the voltage across the thermistor R1 exceeds a certain voltage, the Zener diode D1 connected in parallel to the thermistor R1 turns on. However, the panel heater driving voltage Vo is clamped at a predetermined voltage (for example, 9.6V), and the power supply shutdown does not operate.

FIG. 2 is a graph showing the relationship between the ambient temperature (horizontal axis) and the panel heater driving voltage Vo (vertical axis) in the embodiment of FIG. 1 described above. It is clamped at 9.6 V) and it can be seen that the power shutdown does not work. When the temperature is high, it is not necessary to use the liquid crystal panel heater 3, so that the power supply circuit 1 can be turned off by a separate circuit, so that there is no problem.

[0019]

As described above, in the liquid crystal panel heater drive circuit of the present invention, the operating temperature range is limited by the configuration in which the thermistor R1 and the Zener diode D1 are connected in parallel to the feedback portion of the switching regulator type power supply circuit 1. A liquid crystal panel heater drive circuit that is not operated can be easily realized, and the operating temperature of the liquid crystal panel can be
Problems with reliability such as storage temperature are also solved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a liquid crystal panel heater driving circuit according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an ambient temperature and a panel heater driving voltage Vo according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a liquid crystal panel heater drive circuit in a conventional example.

FIG. 4 is a graph showing changes in resistance value of the thermistor R1 with respect to changes in temperature.

FIG. 5 is a graph showing the relationship between ambient temperature and panel heater driving voltage Vo in a conventional example.

[Explanation of symbols]

1, 2 ... Power supply circuit, 1-1 ... Transistor, 2-1 ... Operational amplifier, 3 ... Liquid crystal panel heater, D1 ... Zener diode, R2 ... Bias resistor, R3 ... Current control resistor.

Claims (1)

[Claims] 1. A liquid crystal panel heater drive circuit, wherein a thermistor and a Zener diode are connected in parallel to a feedback section of a switching regulator type power supply circuit.