KR20080053844A - Backlight driving circuit for liquid crystal display device - Google Patents

Abstract

A back light driving circuit of an LCD(Liquid Crystal Display) is provided to control the brightness of the back light as several types freely, thereby implementing the optimum brightness. An LED(Light Emitting Diode) array(22) has M column * M row of LEDs and provides light source of an LCD panel. A line current switch member(23) switches the current by lines relating to the LEDs on the LED array. A back light driving member(24) controls the voltage supplied to the LED array and also controls the brightness by the LED lines through the line current switch member. The line current switch member includes the number M of switching devices for connecting the M row of LEDs to the enable terminals of the back light driving member selectively. The switching transistor is a MOS(Metal Oxide Semiconductor) transistor.

Description

BACKLIGHT DRIVING CIRCUIT FOR LIQUID CRYSTAL DISPLAY DEVICE}

1 is a block diagram of a backlight driving circuit of a liquid crystal display device according to the prior art.

2 is a block diagram of a backlight driving circuit of the liquid crystal display device according to the present invention;

*** Description of the symbols for the main parts of the drawings ***

21: power supply 22: LED array

23: line current interruption unit 24: backlight driving unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight driving technology of a liquid crystal display device, and more particularly, to a backlight driving circuit of a liquid crystal display device which can freely adjust the brightness of a backlight implemented by a light emitting diode.

In general, a liquid crystal display device is a display device in which image information is individually supplied to pixels arranged in a matrix, and a desired image is displayed by adjusting light transmittance of the pixels. Accordingly, the liquid crystal display includes a liquid crystal panel in which pixels, which are the smallest unit for implementing an image, are arranged in an active matrix form, and a driving unit for driving the liquid crystal panel. Since the LCD does not emit light by itself, a backlight unit is provided to supply light to the LCD.

These backlight units are in a trend of miniaturization, thinness, and light weight, and according to these trends, light emitting diodes, which are advantageous in power consumption, weight, and brightness, are used instead of cold cathode lamps (CCFL) used in backlight units. (Hereinafter referred to as 'LED') has been proposed.

1 is a circuit diagram of a LED backlight unit according to the prior art, as shown therein, a power supply unit 11 for supplying driving power to the LED array 12; An LED array 12 arranged in LEDs of N rows * M columns and used as a light source of a TFT LCD; The backlight driver 13 controls the voltage supplied from the power supply unit 11 to the LED array 12 to control the overall brightness of the LED array 12. The operation thereof will be described as follows.

The driving power output from the power supply unit 11 is supplied to the LED array 12 arranged as the LEDs of the N rows * M columns through the coil L and the diode D. However, the driving power flows to the feedback terminals FB1 to FB6 of the backlight driver 13 through the LEDs of the M columns on the LED array 12, respectively. Therefore, the LEDs of the N rows * M columns emit light of the same brightness.

When the backlight driver 13 receives the backlight brightness control signal PWM from the system, the backlight driver 13 adjusts the voltage supplied to the LED array 12 using the MOS transistor M. FIG. Accordingly, the brightness of all the LEDs (LEDs) in the N rows * M columns on the LED array 12 is equally controlled.

In other words, the backlight driver 13 adjusts the voltage supplied to the LED array 12 through the MOS transistor M in accordance with the requested brightness control signal PWM, whereby the LED array 12 The driving voltages of all the LEDs in row N * column M of the phase are equally adjusted. As a result, the brightness of all LEDs (LEDs) in N rows * M columns on the LED array 12 is uniformly adjusted.

As described above, in the backlight driving circuit of the LCD according to the related art, only the overall brightness can be adjusted when adjusting the brightness of the LED array, so that the brightness of the backlight cannot be freely controlled, thereby consuming unnecessary power. There was a problem such as.

Accordingly, it is an object of the present invention to divide the LEDs on the LED array into circuits so that it is possible to freely control the on / off of the divided LEDs.

The present invention for achieving the above object, the LED array having an N row * M column of LEDs to provide a light source of the liquid crystal panel; A line current interrupter for interrupting current per line with respect to the LEDs on the LED array; In addition to controlling the voltage supplied to the LED array, characterized in that it comprises a backlight driver for controlling the brightness for each LED line through the line current interruption.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram showing an embodiment of a backlight driving circuit of the liquid crystal display according to the present invention. As shown in FIG. 2, the power supply unit 21 supplies driving power to the LED array 22; An LED array 22 in which N rows * M columns of LEDs are arranged and used as a light source of the TFT LCD; A line current interrupter 23 for interrupting current per line with respect to the LEDs on the LED array 22; By controlling the voltage supplied from the power supply unit 21 to the LED array 22, the overall brightness of the LED array 22 is controlled, and the brightness of each LED line is controlled through the line current interrupter 23. It will be described in detail with reference to Figure 6 attached to the operation of the present invention configured as described above, which is configured as a backlight driver 24 as follows.

The driving power output from the power supply 21 is supplied to the LED array 22 arranged as the LEDs of the N rows * M columns through the coil L and the diode D. However, after the driving power supplies the LEDs of the M columns on the LED array 22, the feedback terminals FB1 of the backlight driver 24 are again passed through the MOS transistors (N-channel MOS transistors) M1-M6. -FB6). Therefore, the LEDs of the N rows * M columns on the LED array 22 emit light of the same brightness.

When the backlight brightness control signal PWM is input from the system, the backlight driver 24 adjusts the voltage supplied to the LED array 22 using the MOS transistor M. FIG. Accordingly, the brightness of all LEDs (LEDs) in N rows * M columns on the LED array 22 is equally controlled.

In other words, the backlight driver 24 adjusts the voltage supplied to the LED array 22 through the MOS transistor M according to the requested brightness control signal PWM, and thereby the LED array 22. The driving voltages of all the LEDs in row N * column M of the phase are equally adjusted. As a result, the brightness of all the LEDs (LEDs) in N rows * M columns on the LED array 22 is equally adjusted.

Meanwhile, as described above, the driving power output from the power supply unit 21 passes through the LEDs of the M columns on the LED array 22, and then again through the MOS transistors M1-M6, respectively. Since the current flows through the feedback terminals FB1-FB6, the current flowing through the MOS transistors M1-M6 can be interrupted to control brightness by line (column).

For example, when the LEDs in the odd rows of the LEDs of the M columns on the LED array 22 are turned on and the LEDs in the even rows are turned off, the backlight driver 24 has its own enable terminal EN1. It outputs 'high' voltage at, EN3, EN5) and 'low' voltage at the remaining enable terminals (EN2, EN4, EN6).

Accordingly, among the MOS transistors M1-M6, the MOS transistors M1, M3, and M5 are turned on, and the remaining MOS transistors M2, M4, and M6 are turned off. As a result, the LEDs in the odd rows are turned on and the LEDs in the even rows are turned off among the LEDs in the M rows on the LED array 22.

As another example, when the minimum brightness is to be maintained, the backlight driver 24 outputs a 'high' voltage to any enable terminal (eg, EN3) among the enable terminals EN1 to EN6 and the remaining enable parts. Outputs a low voltage to the terminals EN1, EN2 and EN4-EN6.

Accordingly, one of the MOS transistors M1 to M6 is turned on, and the remaining MOS transistors M1, M2 and M4-M6 are turned off. As a result, the LEDs of the third column among the LEDs (LEDs) of the M column on the LED array 22 are turned on, and the LEDs of the remaining columns are turned off.

In this manner, the backlight driver 24 turns on any MOS transistors among the MOS transistors M1-M6 to selectively select only LEDs of a desired column among M LEDs on the LED array 22. Can be turned on.

In the above description, an LED array 22 in which eight LEDs are connected to one column and six columns are arranged is taken as an example. However, in order to guarantee precise and various control of brightness (luminance) on the LED array 22, the number of unit LEDs (LEDs) in each column is reduced, the number of columns is increased, and the driving thereof is controlled in the above manner. Just do it.

As described in detail above, the present invention can divide the LEDs on the LED array into circuits and freely control their on / off, thereby achieving an optimum brightness brightness.

In addition, since the brightness of the LED array can be appropriately controlled, the brightness is unnecessarily high, and there is an effect of preventing waste of power.

Claims (4)

An LED array having LEDs in N rows * M columns to provide a light source of the liquid crystal panel; A line current interrupter for interrupting current per line with respect to the LEDs on the LED array; And a backlight driver for controlling the voltage supplied to the LED array and controlling the brightness for each LED line through the line current interruption unit. The backlight driving circuit of claim 1, wherein the line current control unit comprises M switching elements for selectively connecting the LEDs of the M columns to the enable terminal of the backlight driving unit. 3. The backlight driving circuit of claim 2, wherein the switching element is a MOS transistor. The method of claim 3, wherein the drain of the MOS transistor is connected to the cathode of the LED of the column M, the source is connected to the feedback terminal of the backlight driver, respectively, the gate is connected to the enable terminal of the backlight driver, respectively. A backlight driving circuit of a liquid crystal display device.

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