KR100711218B1 - Driving circuit for Back light of LCD - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight driving circuit of a liquid crystal display device that enables multiple lamps to be lit in a state where a transformer is removed. The circuit includes an electrostatic source for supplying an alternating voltage of a predetermined magnitude; A control unit configured to receive a switching control signal and to selectively output the AC voltage while the switching control signal is in an enabled state; an output unit configured to receive and charge an output voltage of the control unit and to charge and charge the load means; The controller controls the magnitude of the voltage charged in the output unit by varying the frequency of application of the AC voltage.

Description

Backlit driving circuit for liquid crystal display device {Driving circuit for Back light of LCD}

1 and 2 show a backlight driving circuit according to the prior art.

3 shows a backlight driving circuit for a liquid crystal display device according to the present invention;

4 is an operational waveform diagram of a backlight driving circuit according to the present invention;

5 shows an equivalent circuit of an output unit.

6 is a waveform diagram of voltage characteristics of a load;

7 is a waveform diagram showing an output voltage and an output current of a backlight driving circuit according to the present invention;

8 is a waveform diagram showing an output power of a backlight driving circuit according to the present invention;

9 illustrates a backlight driving circuit according to the present invention applied to an external electrode fluorescent lamp (EEFL).

* Names of symbols for main parts of the drawings

110: electrostatic source 120: filter unit

130: switching unit 140: DC blocking unit

150: output unit 160: external electrode

170: fluorescent electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight driving circuit of a liquid crystal display device, and more particularly, to a backlight driving circuit of a liquid crystal display device which enables multiple lamps to be lit while a transformer is removed.

The liquid crystal display device applies an electric field to the liquid crystal interposed between the two substrates, and adjusts the intensity of the electric field to adjust the amount of light transmitted through the substrate to obtain an image signal desired by the user. Unlike the CRT, the liquid crystal display device is not a display device that emits light by itself, and thus has a separate light source for visually representing an image on the back of the liquid crystal panel. Therefore, the liquid crystal display is used by a backlight having a fluorescent lamp as a light source, and has a backlight driving circuit for applying a driving voltage to the backlight.

Representative, a conventional liquid crystal display device is a backlight drive circuit of the Royer type shown in Fig. 1 and the full bridge type shown in Fig. 2 to typically supply a driving voltage to the backlight. Was used. The conventional backlight driving circuit as described above has a circuit configuration including transformers 100 and 101 therein. Here, the transformer (100, 101) is a passive element mainly used in the output terminal of the power supply circuit for the amplification of the voltage, the component having a lot of variables in the design, as the most difficult of the analog circuit elements and require the core technology to be.

As described above, the transformers 100 and 101 directly affect power loss, noise, and noise generation in circuit design, and are expensive and have a large obstacle to design of the substrate due to their large size. In particular, the transformer (100, 101) generates a lot of heat, there is a disadvantage that must limit the output voltage and switching frequency.

Conventionally, in order to solve the problems of the conventional backlight driving circuit using the transformer as described above, various solutions in terms of control have been proposed, but the conventional backlight as described above unless the transformer is removed. There is a limit to eliminate the problem of the driving circuit.

Accordingly, the present invention was created to solve the problems inherent in the prior art as described above, and an object of the present invention is to remove a transformer provided in a backlight driving circuit and to apply a simple circuit configuration to a back of a liquid crystal display device. The present invention provides a light driving circuit.

In order to achieve the above object, according to one aspect of the present invention, there is provided a backlight driving circuit of a liquid crystal display device, comprising: an electrostatic source for supplying an alternating voltage of a predetermined magnitude; A control unit for receiving a switching control signal and selectively outputting the AC voltage during an enable state of the switching control signal; And an output unit configured to receive the output voltage of the controller, charge and charge the battery, and apply a constant voltage to the load means, wherein the controller adjusts the magnitude of the voltage charged to the output unit by varying an application frequency of the AC voltage. It is done.

In the above configuration, the control unit varies the frequency of the AC voltage in accordance with the enable period of the switching control signal.

In the above configuration, the output unit includes: an inductor means connected in series with the output voltage of the control unit; And capacitor means connected in parallel with the output voltage of the controller, and charges and discharges the output voltage transmitted from the controller through the inductor means and the capacitor means.

In the above configuration, the output unit controls the magnitude of the voltage charged and discharged by adjusting the sizes of the inductor means and the capacitor means.

In the configuration, the control unit, the filter unit for receiving the AC voltage transmitted from the electrostatic source; A switching unit configured to receive a switching control signal and selectively output an AC voltage transmitted from the filter unit; And a DC blocking unit which cuts off a DC component of an AC voltage transmitted from the switching unit and transmits the DC component to the output unit.

In the above configuration, the switching unit is composed of a MOS switch.

(Example)

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

3 shows a backlight driving circuit for a liquid crystal display according to the present invention.

The backlight driving circuit of the liquid crystal display according to the present invention includes a plurality of electrostatic sources 110, a filter unit 120, a switching unit 130, a direct current (DC) blocking unit 140, and a plurality of parallel connection units of the direct current blocking unit. The output unit 150 is provided.

The electrostatic source 110 refers to an AC voltage source for supplying an AC voltage Vs having a predetermined size to a circuit. The filter unit 120 includes an inductor L _f connected in series to the electrostatic source 110 and a capacitor C _f connected in parallel to the electrostatic source 110, and is connected to an input power source provided from the electrostatic source 110. Eliminates noise and harmonics included. Here, the inductor L ₁ shown in the drawing is for making a constant current.

The switching unit 130 includes a MOS switch 131 having a reverse diode D therein, and is configured to enable the switching control signal V _gain input to the gate terminal of the MOS switch 131. Accordingly, the input power (Vs) transmitted from the filter unit 120 is selectively transmitted to the DC blocking unit 140.

DC blocking unit 140 is composed of a blocking capacitor (C _b ) connected in series with the output node of the switching unit 130, DC (DC) component of the input power (Vsw) transferred from the switching unit 130 Remove it. Here, the capacitor C _P shown in the figure represents an anti-parallel capacitor for stabilizing power supply.

Each of the output units 150 includes an inductor L _r connected in series to the DC blocking unit 140 and a capacitor C _r connected in parallel, respectively, and input power transmitted from the DC blocking unit 140. Charge and discharge, supplying a load (R) connected to each output node, that is, a voltage greater than the input power (Vs) to the fluorescent lamp.

In the backlight driving circuit according to the present invention as described above, the input voltage Vs input to the output unit 16 according to the enable period of the switching control signal V _gain input to the switching unit 130. The core technology is to apply the boosted voltage (Vsw) to the load (R) by varying the frequency of the voltage, and thereby adjusting the magnitude of the voltage charged in the output unit (16).

In this regard, Fig. 4 shows an operational waveform diagram of the backlight driving circuit according to the present invention.

As shown, the switching unit 130 maintains the off state until the time point 't0' and starts operation at the time point 't1' when the switching control signal V _gain is enabled. Then, the internal diode of the MOS switch 131 is operated between the 't1' and 't2' time, it is fully operating at the 't2' time. Thereafter, the switching current Isw input to the switching unit 130 rises up to a time point 't3', and at this time, the output unit 140 is input power Vs applied through the switching unit 130. Is charged to the inductor L _r and the capacitor C _f . Thereafter, the MOS switch 131 is turned off at the time 't3' when the switching control signal V _gain is disabled. Thereafter, the output unit 140 supplies the load R with the voltage Vsw in which the predetermined voltage charged in the input power source Vs, the inductor L _r , and the capacitor C _f is added. Therefore, the voltage Vsw supplied to the load R has a voltage level boosted by the predetermined voltage charged in the inductor L _r and the capacitor C _{f in the} input power source Vs (relative to the input power source). Q times the voltage gain).

Referring to FIG. 5, the operation of the output unit 140 will be described. 5 is a diagram illustrating an equivalent circuit of the output unit. The output unit 140 is charging energy according to a simple combination of the inductor jωL and the capacitor 1 / jωC, and outputs the output voltage Vsw required for the load R. I can make it. This can be seen through the formula attached below.

Here, 'Z' represents the equivalent impedance of the output unit 140, 'f' represents the switching frequency. As can be seen from the above equation, the switching frequency f and the charge capacity of the inductor L and the capacitor C have an inverse relationship. That is, as the switching frequency f of the variable input power Vs increases as the on / off operation of the switching unit 130 increases, the charge capacity of the inductor L and the capacitor C decreases. If the switching frequency f has a fixed value, the magnitude of the voltage Vsw applied to the load R may be adjusted by adjusting the sizes of the inductor L and the capacitor C itself.

Next, the voltage characteristics of the circuit of the present invention having the above operating characteristics will be described with reference to FIGS. 6 to 8.

First, referring to FIG. 6, it can be seen that the backlight driving circuit according to the present invention increases the voltage Vsw input to the load R in proportion to 1 to 5 times with respect to the input power source Vs. have. That is, as can be seen through Figure 7, the backlight driving circuit according to the present invention can obtain an output voltage of up to 1000V and an output current of 10mA, thus, as shown in Figure 8, to obtain an output power of 40W Can be. Therefore, the backlight driving circuit according to the present invention includes a plurality of output units 150, thereby simultaneously driving a plurality of cold cathode fluorescent lamps (CCFLs) having a multi-lighting method, that is, electrodes located therein. can do.

In addition, the present invention can be applied to an external electrode fluorescent lamp (EEFL).

Referring to FIG. 9, the backlight driving circuit applied to the external electrode fluorescent lamp has the same configuration as that of FIG. 3. However, since the external electrode fluorescent lamp 170 has an electrode formed outside, a plurality of external electrode fluorescent lamps 170 are connected to one external electrode 160 in parallel. Therefore, the backlight driving circuit applied to the external electrode fluorescent lamp efficiently configures the plurality of external electrode fluorescent lamps 170 connected in parallel to one external electrode 160 by configuring a plurality of output units 150 connected in parallel. Can be driven.

According to the above-described configuration of the present invention, the backlight driving circuit for the liquid crystal display device according to the present invention can generate a high output capable of lighting multiple lights through a simple circuit configuration including a switching unit and an output unit, and eliminates the transformer. Accordingly, the size, weight and price of the circuit system can be reduced.

While the invention has been shown and described with reference to certain preferred embodiments, the invention is not so limited, and the invention is not limited to the spirit and scope of the present invention, which is provided by the following claims. It will be readily apparent to those skilled in the art that these various modifications and variations can be made.

Claims (6)

In the backlight driving circuit of the liquid crystal display device, An electrostatic source for supplying an AC voltage of a predetermined magnitude; A control unit which receives a switching control signal and selectively outputs the AC voltage while the switching control signal is in an enabled state; An output unit configured to receive and charge / discharge the output voltage of the controller to apply a constant voltage to the load means; And the control unit controls the magnitude of the voltage charged in the output unit by varying the frequency of application of the AC voltage. The method of claim 1, The control unit, And a frequency of the AC voltage is varied in accordance with an enable period of the switching control signal. The method of claim 1, The output unit, Inductor means connected in series with the output voltage of the controller; And Capacitor means connected in parallel to the output voltage of the control unit, And a charging and discharging of an output voltage transmitted from a control unit through the inductor means and the capacitor means. The method of claim 3, wherein The output unit, And a size of the voltage charged and discharged by adjusting the sizes of the inductor means and the capacitor means. The method of claim 1, The control unit, A filter unit to receive the AC voltage transferred from the electrostatic source; A switching unit configured to receive a switching control signal and selectively output an AC voltage transmitted from the filter unit while the switching control signal is in an enabled state; And And a DC blocking unit which blocks a DC component of the AC voltage transmitted from the switching unit and delivers the DC component to the output unit. The method of claim 5, The switching unit, A backlight drive circuit comprising a MOS switch.

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