Power supply circuit, LCD driver IC, LCD driver circuit, and liquid crystal display device

Abstract

A power supply circuit is provided with a temperature gradient variable circuit that produces a gradient voltage whose voltage level varies with a temperature gradient commensurate with the ambient temperature and a temperature gradient setting circuit that produces an output voltage (and hence a drive voltage of an LCD panel) by adjusting the temperature gradient and the voltage level of the gradient voltage. With this configuration, it is possible to supply the optimal drive voltage despite variations in the ambient temperature or variations in characteristics of LCD panels.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of a cellular phone terminal according to the present invention;

FIG. 2 is a timing chart showing an example of scanning signals and data signals;

FIG. 3 is a circuit block diagram showing an example of the configuration of a power supply circuit 31; and

FIGS. 4A to 4D are diagrams illustrating the operation for producing internal voltages VH and VL.

Claims

1. A power supply circuit, comprising: a temperature gradient variable circuit that produces a gradient voltage whose voltage level varies with a temperature gradient commensurate with an ambient temperature; anda temperature gradient setting circuit that produces a first drive voltage of a load by adjusting the temperature gradient and/or the voltage level of the gradient voltage.

2. The power supply circuit of claim 1, further comprising: a drive voltage clamping circuit that setting an upper limit and/or a lower limit for the first drive voltage.

3. The power supply circuit of claim 2, further comprising: a polarity inverting circuit that produces a second drive voltage of the load by inverting a polarity of the first drive voltage.

4. The power supply circuit of claim 1, wherein the temperature gradient variable circuit includes a diode having an anode from which a reference gradient voltage is extracted, the anode being connected to an internal voltage application terminal via a first resistor,a first amplifier that produces a first gradient voltage by amplifying the reference gradient voltage by a first gain,a second amplifier that produces a second gradient voltage by amplifying the reference gradient voltage by a second gain that is greater than the first gain,a first DC voltage source that produces a first reference voltage,a third amplifier that outputs a difference between the second gradient voltage and the first reference voltage as a third gradient voltage, anda selector that selects, as the gradient voltage, one of the first gradient voltage and the third gradient voltage, depending on which has a higher voltage.

5. The power supply circuit of claim 1, wherein the temperature gradient setting circuit includes an operational amplifier,a second resistor that is connected, at one end thereof, to an output terminal of the temperature gradient variable circuit and is connected, at the other end thereof, to an inverting input terminal of the operational amplifier,a second DC voltage source that produces a second reference voltage and applies the second reference voltage thus produced to a non-inverting input terminal of the operational amplifier, anda third resistor that is connected, at one end thereof, to the inverting input terminal of the operational amplifier and is connected, at the other end thereof, to an output terminal of the operational amplifier,the temperature gradient variable circuit is an inverting amplifier circuit that outputs an output voltage of the operational amplifier as the first drive voltage of the load, andaccording to a given control signal, the second DC voltage source can adjust a voltage level of the second reference voltage and/or the third resistor can adjust a resistance value thereof.

6. An LCD driver IC, comprising: a power supply circuit that produces a drive voltage of a liquid crystal display panel, whereinthe power supply circuit includes a temperature gradient variable circuit that produces a gradient voltage whose voltage level varies with a temperature gradient commensurate with an ambient temperature, anda temperature gradient setting circuit that produces a first drive voltage of a load by adjusting the temperature gradient and/or the voltage level of the gradient voltage.

7. A liquid crystal display device, comprising: a liquid crystal display panel; andan LCD driver IC that drives and controls the liquid crystal display panel, whereinthe LCD driver IC includes a power supply circuit that produces a drive voltage of the liquid crystal display panel, andthe power supply circuit includes a temperature gradient variable circuit that produces a gradient voltage whose voltage level varies with a temperature gradient commensurate with an ambient temperature, anda temperature gradient setting circuit that produces a first drive voltage of a load by adjusting the temperature gradient and/or the voltage level of the gradient voltage.

8. The liquid crystal display device of claim 7, wherein the liquid crystal display panel includes a thin-film diode as an active element that drives a liquid crystal cell.

9. A power supply circuit that produces an output voltage, wherein the power supply circuit is provided with first, second, and third set temperatures (the first set temperature the second set temperature the third set temperature), anda temperature gradient of the output voltage between the first set temperature and the second set temperature is greater than a temperature gradient of the output voltage between the second set temperature and the third set temperature.

10. An LCD driver circuit that drives and controls a liquid crystal display panel, wherein an output voltage of the LCD driver circuit gradually decreases as an ambient temperature of the LCD driver circuit increases.