JP2002260897A - Circuit for adjusting brightness of backlight - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of parts in a circuit for adjusting a brightness of backlight for an LCD display. SOLUTION: Output current of an inverter circuit 12 driving a cold cathode fluorescent tube 14 is controlled by a burst signal of a burst signal generating circuit 13. A burst signal controlling part 13a is equipped with a voltage detecting feature of a power source battery and a feature to control duty ratio of a burst signal, the output current of an inverter circuit 12 and brightness of the cold cathode fluorescent tube 14 are controlled at a constant value by changing the duty in response to a power source voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight brightness adjusting circuit used for an LCD display, and more particularly to a backlight brightness adjusting circuit for reducing the number of components.

[0002]

2. Description of the Related Art LC such as a notebook personal computer
A conventional backlight luminance adjustment circuit used for a D display will be described with reference to the drawings. In FIG. 4, 1 is a power battery, 2 is a DC-DC converter circuit, 3 is an inverter circuit, 4 is a burst signal generation circuit, 4a is a burst signal control unit, and 5 is a cold cathode fluorescent tube.

FIG. 5 is an operation timing chart of the above-described brightness adjustment circuit. The DC-DC converter circuit 2 transforms the voltage to a predetermined voltage and supplies power to the inverter circuit 3 regardless of the fluctuation of the voltage of the power supply battery 1. I do. Burst signal generation circuit 4
Outputs a rectangular wave burst signal of a predetermined duty ratio to the drive element of the inverter circuit 3 under the control of the burst signal control unit 4a, and the inverter circuit 3 performs an intermittent switching operation according to the burst signal to output a set current. Then, the cold cathode fluorescent tube 5 is turned on at a predetermined luminance.

When a manual adjusting means such as a variable resistor for adjusting the duty ratio of the burst signal generating circuit 4 is provided, the brightness of the cold cathode fluorescent tube 5 is adjusted by changing the duty ratio of the burst signal. can do.

Although illustration is omitted, a burst signal
There is also known a brightness adjustment circuit configured to switch the output of the DC-DC converter circuit 2 so as to operate similarly to the above-described circuit.

[0006]

The inverter circuit used for the brightness adjustment circuit of the LCD display is composed of a self-excited resonance type loyer circuit using transistors and a switching transformer, and the output current of the loyer circuit depends on the input voltage. . For this reason, in a battery-operated notebook personal computer or the like having a large fluctuation range of the power supply voltage, a DC-DC converter circuit is configured to keep the input voltage of the inverter circuit constant, and the inverter is controlled by a burst signal having a predetermined duty ratio. A predetermined current is output from the circuit to control the brightness of the cold cathode fluorescent tube to be constant. Therefore, the number of parts is large and the shape tends to be large.

Therefore, there arises a technical problem to be solved in order to provide a backlight luminance adjusting circuit which can be reduced in size by reducing the number of components, and the present invention aims to solve the above problem. And

[0008]

SUMMARY OF THE INVENTION The present invention proposes to achieve the above object, and switches an inverter circuit by a burst signal to control the brightness of a cold cathode fluorescent tube or the like driven by the inverter circuit. A brightness adjustment circuit for a backlight, comprising: means for detecting an input voltage or an output current of an inverter circuit; and controlling a duty ratio of a burst signal of a burst signal generation circuit according to a detected value of the input voltage or an output current. A means for setting the output current of the inverter circuit to a set value regardless of the input voltage is provided,
An object of the present invention is to provide a backlight luminance adjustment circuit for controlling the luminance of a cold cathode fluorescent tube or the like.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail. FIG. 1 shows a luminance adjustment circuit of a backlight for an LCD display, 11 is a power supply battery, 12 is an inverter circuit, 13 is a burst signal generation circuit, 13a is a burst signal control unit, and 14 is a cold cathode fluorescent tube. The circuit configuration is such that the DC-DC converter circuit in the brightness adjustment circuit is eliminated.

The burst signal control section 13a controls the output current of the inverter circuit 12 (the brightness of the cold cathode fluorescent lamp 14) by controlling the voltage detection function of the power supply battery 11 and the on / off duty ratio of the burst signal according to the power supply voltage. It has a function of controlling to a predetermined value, may use a microprocessor, or may have an analog discrete configuration, and is not particularly limited.

FIG. 2 is an operation timing chart of the above-mentioned luminance adjustment circuit, in which the time axis is compressed and the change in operation is exaggerated. As shown, the burst signal control unit 13a responds to a change in the voltage of the battery 11 by
The duty ratio of 3 is controlled, and when the power supply voltage decreases, the on-duty of the burst signal is increased. As a result, the on-duty of the output of the inverter circuit 12 increases to offset the current decrease due to the voltage drop, the output current of the inverter circuit 12 is controlled to be constant irrespective of the change in the battery voltage, and the brightness of the cold cathode fluorescent tube 14 It will be constant.

FIG. 3 shows another embodiment of the luminance adjusting circuit. A burst signal control section 13a detects an output current of the inverter circuit 12 and feeds back a duty ratio of the burst signal so as to have a constant output current value. It is configured to control and performs the same operation as the circuit of FIG.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible within the technical scope of the present invention, and it goes without saying that the present invention extends to those modified embodiments. is there.

[0014]

As described above, the backlight luminance adjusting circuit of the present invention controls the output current of the inverter circuit for driving the backlight by changing the duty ratio of the burst signal, and controls the output of the inverter circuit. Since the current is configured to be constant, there is no need for a DC-DC converter circuit that compensates for battery voltage changes, eliminating power loss and heat generation by the DC-DC converter circuit, and reducing costs and reducing size. To play.

[Brief description of the drawings]

FIG. 1 is a block diagram of a luminance adjustment circuit according to the present invention.

FIG. 2 is a timing chart showing the operation of the brightness adjustment circuit of the present invention.

FIG. 3 is a block diagram showing another embodiment of a brightness adjustment circuit.

FIG. 4 is a block diagram of a conventional luminance adjustment circuit.

FIG. 5 is a timing chart showing the operation of a conventional luminance adjustment circuit.

[Explanation of symbols]

 11 Power battery 12 Inverter circuit 3 Burst signal generation circuit 13a Burst signal control unit 14 Cold cathode fluorescent tube

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasunobu Fushihara 1049 Oita, Oita, Oaza, Iizuka-shi, Fukuoka Inside Kyushu Mitsumi Co., Ltd. F-term in Mitsumi Oshima Co., Ltd. (reference) 3K098 CC40 DD01 DD22 DD35 EE17 EE32 FF03 FF04 5H007 BB03 DA05 DB01 DC02 DC05

Claims (1)

[Claims] 1. A backlight luminance adjusting circuit for controlling the luminance of a cold cathode fluorescent tube or the like driven by an inverter circuit by switching an inverter circuit by a burst signal, wherein an input voltage or an output current of the inverter circuit is detected. Means for controlling the duty ratio of the burst signal of the burst signal generation circuit in accordance with the detected value of the input voltage or the output current, and setting the output current of the inverter circuit to the set value regardless of the input voltage. A backlight luminance adjustment circuit that controls the luminance of cathode fluorescent tubes and the like.