KR20050000175A - Apparatus for driving lamp of liquid crystal display device - Google Patents

Abstract

The present invention relates to a lamp driving device of a liquid crystal display device which can stably supply current supplied to a lamp by preventing mutual interference between a plurality of lamps.

The lamp driving apparatus of the liquid crystal display according to an exemplary embodiment of the present invention may include a plurality of lamps, a lamp housing disposed side by side so that two lamps among the plurality of lamps form a pair, and a pair of lamps. It is characterized in that it comprises an inverter unit having a plurality of inverters for supplying the lamp driving current having a different phase and the lamp driving current having the same phase to adjacent lamps of a pair of lamps.

This, the present invention can minimize the leakage current due to lamp mutual interference and can drive the lamps stably.

Description

Lamp driving device for liquid crystal display device {APPARATUS FOR DRIVING LAMP OF LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a lamp driving device of a liquid crystal display device, and more particularly, to a lamp driving device of a liquid crystal display device which can stably supply current supplied to a lamp by preventing mutual interference between a plurality of lamps.

In general, liquid crystal displays (hereinafter referred to as "LCDs") have tended to be gradually widened due to their light weight, thinness, and low power consumption. According to this trend, LCDs are used for office automation equipment, audio / video equipment, and the like. On the other hand, the LCD is controlled to display the desired image on the screen by adjusting the transmission amount of the light beam according to the image signal applied to the plurality of control switches arranged in a matrix form.

Since the LCD is not a self-luminous display device, a light source such as a back light is required. As a light source used for the backlight, a cold cathode tube (hereinafter referred to as "CCFL") is used.

CCFL is a light source tube using the cold emission (electron emission caused by the strong electric field applied to the surface of the cathode), low heat, high brightness, long life, full color is easy. These CCFLs include a light guide type, a direct type type, a reflecting plate type, and the like, and a light source tube suitable for the type of LCD is adopted.

The CCFL uses an inverter circuit for obtaining a high voltage power from a low voltage DC power supply.

1 and 2, the lamp driving apparatus of the LCD according to the related art has a lamp housing 10 accommodating a plurality of lamps and a plurality of inverters for supplying a lamp driving voltage to each of the plurality of lamps. A current detector 30 having a inverter unit 20, a first printed circuit board 12 on which the inverter unit 20 is mounted, a plurality of current detectors for detecting tube currents of each of a plurality of inverters, and a current detector unit A second printed circuit board 32 on which 30 is mounted is connected between the current detector 30 and the inverter unit 20 to supply the feedback signal from the current detector 30 to the inverter unit 20. A feedback line 36 is provided.

The lamp housing 10 is provided with an accommodating space for accommodating a plurality of lamps and is stacked on the support main 2.

Each of the plurality of lamps receives a lamp driving voltage from the inverter unit 20 to irradiate a liquid crystal panel (not shown) with visible light.

The first printed circuit board 12 is disposed on one side of the support main 2 to be folded to the rear surface of the support main 2.

The second printed circuit board 32 is disposed on one side of the support main 2 to be folded to the rear surface of the support main 2. At this time, a protection chassis 34 for protecting the second printed circuit board 32 is provided between the second printed circuit board 32 and the support main 2.

The feedback line 36 is connected between the first and second printed circuit boards 12 and 32 folded on the rear surface of the support main 2 to electrically connect the current detector 30 and the inverter unit 20. In the feedback line 36, a plurality of signal wires are formed.

Each of the plurality of inverters 21 constituting the inverter unit 20 includes a switching circuit 24 for switching a voltage from the voltage source Vin in response to a switching control signal, and a switching circuit 24 as shown in FIG. 3. Transformer 22 for converting the voltage supplied by the switching of the signal into a lamp driving voltage, and a pulse width modulation circuit for switching the switching circuit 24 in response to the feedback signal FB from the current detector 30 26).

The switching circuit 24 includes at least one switch element for switching the voltage from the voltage source Vin to the transformer 22 in response to the switching control signal from the pulse width modulation circuit 26.

The transformer 22 consists of a primary winding connected to the switching circuit 24 and a secondary winding connected to the lamp 40. Both ends of the primary winding are connected to the switching circuit 24, one side of the secondary winding is connected to the first electrode terminal of the lamp 40 and the other end is connected to the ground voltage source GND. The transformer 22 converts the voltage supplied to the primary winding by the turns ratio of the primary and secondary windings, and induces the secondary winding. The voltage induced in the secondary winding is supplied to the lamp 40 through the first electrode terminal of the lamp 40 to turn on the lamp 40.

The pulse width modulation circuit 26 controls the switching cycle of the switching circuit 24 in response to the feedback signal FB from the current detector 30. That is, the pulse width modulation circuit 26 controls the switching period of the switching elements constituting the switching circuit 24 in response to the feedback signal FB to control the voltage supplied to the transformer 22.

Each of the plurality of current detectors 31 constituting the current detector 30 is connected between the second electrode terminal of the lamp 40 and the ground voltage source GND as shown in FIG. 3 to detect from the lamp 40. The feedback signal FB corresponding to the obtained tube current value is supplied to the pulse width modulation circuit 26. To this end, each of the current detectors 30 includes a first resistor R1 connected between the second electrode terminal of the lamp 40 and the ground voltage source GND, and between the first resistor R1 and the ground voltage source GND. A first diode connected between the variable resistor RB connected to the first node N1 and the pulse width modulation circuit 26 between the variable electrode RB connected to the second electrode terminal of the lamp 40 and the first resistor R1 ( D1) and a second diode D2 connected between the second node N2 and the base voltage source GND, which are between the first node N1 and the first diode D1.

The first resistor and the variable resistor R1 and RB detect the current value of the second electrode terminal of the lamp 40 by the divided resistance value and display the current value on the first node N1. The feedback signal FB, which is the detected detection signal on the first node N1, is supplied to the pulse width modulation circuit 26 via the first diode D1. The second diode D2 blocks the impulse of the negative potential to maintain the lowest potential of the feedback signal FB at zero potential.

The lamp driving apparatus of the LCD according to the related art is a transformer 22 by switching of the switching circuit 24 in which the voltage from the voltage source Vin is controlled by the pulse width modulation circuit 26 of the inverter 20. Is supplied to the primary side of the winding. The voltage supplied to the primary winding of the transformer 22 is converted by the primary and secondary winding ratios of the transformer 22 and is induced in the secondary winding. The current induced in the secondary winding of the transformer 22 is supplied to the lamp 40 so that the lamp 40 is turned on. When the lamp 40 is turned on, the current detector 30 detects the tube current of the lamp 40 and supplies a feedback signal FB corresponding to the detected detection signal to the pulse width modulation circuit 26. Accordingly, the pulse width modulation circuit 26 converts the switching period of the switching circuit 24 in response to the feedback signal FB to control the voltage supplied to the primary winding of the transformer 22.

As described above, in the lamp driving apparatus of the LCD according to the related art, lamp driving voltages supplied to a plurality of lamps have the same phase. Accordingly, the leakage current increases in each of the plurality of lamps, thereby increasing the power consumption. In detail, the phase of the driving current supplied to the plurality of lamps is the same, so that the leakage current increases because the impedance of each lamp increases. In addition, leakage current increases due to an increase in impedance due to current / phase coupling between adjacent lamps. Therefore, the driving of the lamps becomes unstable due to the leakage current of each of the plurality of lamps.

Accordingly, an object of the present invention is to provide a lamp driving apparatus of a liquid crystal display device which can stably supply current supplied to a lamp by preventing mutual interference between a plurality of lamps.

1 is a plan view showing a lamp driving device of a conventional liquid crystal display device.

2 is a rear view showing a lamp driving device of the conventional liquid crystal display device.

FIG. 3 is a circuit diagram schematically illustrating a lamp driving device of the liquid crystal display shown in FIGS. 1 and 2.

4 is a diagram showing the phase of a current supplied to each of the plurality of lamps shown in FIG.

5 is a plan view showing a lamp driving apparatus of the liquid crystal display according to an embodiment of the present invention.

6 is a rear view illustrating a lamp driving device of the liquid crystal display according to the exemplary embodiment of the present invention.

FIG. 7 is a circuit diagram schematically illustrating a lamp driving device of the liquid crystal display shown in FIGS. 5 and 6.

FIG. 8 is a diagram showing a phase of a current supplied to each of the plurality of lamps shown in FIG. 5. FIG.

<Description of Symbols for Main Parts of Drawings>

2, 102: support main 10, 110: lamp housing

12, 32, 112: printed circuit board 20, 120: inverter

21, 121: inverter 22, 122: transformer

24, 124: switching circuit 26, 126: pulse width modulation circuit

30, 130: current detector 31, 131: current detector

34: protection chassis 36: feedback line

40, 140, 140a to 140n: lamp 136: base voltage line

In order to achieve the above object, the lamp driving apparatus of the liquid crystal display according to the embodiment of the present invention is a lamp housing which is arranged side by side to a pair of a plurality of lamps, two of the plurality of lamps, And an inverter unit having a plurality of inverters for supplying lamp driving currents having different phases to the pair of lamps and supplying lamp driving currents having the same phase to adjacent lamps of the pair of lamps. It is done.

The lamp driving apparatus of the liquid crystal display device may further include a current detector for detecting the lamp driving current supplied to each of the plurality of lamps in the inverter.

The lamp driving apparatus of the liquid crystal display device may further include a printed circuit board mounted with the inverter unit and the current detection unit and folded to a rear surface of the liquid crystal display device.

The lamp driving apparatus of the liquid crystal display may further include a common line commonly connected to the second electrode terminals of the plurality of lamps, and a base voltage line for connecting the common line to a base voltage source.

In the lamp driving apparatus of the liquid crystal display device, each of the inverters converts a voltage from a voltage source into the lamp driving current and supplies the first electrode terminal of each of the plurality of lamps to switch the voltage to the transformer. And a control unit for controlling the switching circuit based on a feedback signal from the current detection unit.

In the lamp driving device of the liquid crystal display device, the inverter is supplied with a current in a positive phase to the first of the pair of lamps, and a current in a reverse phase to the second lamp at the same time. .

In the lamp driving device of the liquid crystal display device, at the same time, a first phase of the other pair of lamps adjacent to the pair of lamps is supplied with an antiphase current, and a second lamp is supplied with a positive phase current. It is characterized by.

In the lamp driving device of the liquid crystal display device, the current detector is connected to the secondary winding of the transformer.

In the lamp driving device of the liquid crystal display, the current detector includes a resistor connected between the secondary winding of the transformer and a base voltage source, a first node connected between the secondary winding of the transformer and the resistor and the first node. And a variable resistor connected between the diode, the node between the first diode and the control unit, and the base voltage source, and a capacitor connected in parallel with the variable resistor.

In the lamp driving device of the liquid crystal display device, the current detector further comprises a second diode connected between the node between the first node and the first diode and the base voltage source.

Other objects and features of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 5 to 8.

Referring to FIG. 5, the driving apparatus of the liquid crystal display according to the exemplary embodiment of the present invention may include a lamp housing 110 accommodating a plurality of lamps and a driving voltage of a positive phase and an antiphase lamp according to positions of each of the plurality of lamps. A printed circuit board 112 mounted with an inverter unit 120 having a plurality of inverters for supplying a current and a current detector 130 having a plurality of current detectors for detecting a tube current supplied to each of the plurality of inverters; A base voltage line 136 for connecting each of the lamps to a base voltage source GND.

The lamp housing 110 is provided with an accommodating space for accommodating a plurality of lamps and is stacked on the support main 102.

Each of the plurality of lamps receives a lamp driving voltage from the inverter unit 120 to irradiate visible light to a liquid crystal panel (not shown). The first electrode terminal of each of the plurality of lamps is connected to the inverter unit 120 and the second electrode terminal is connected to the ground voltage source GND.

The printed circuit board 112 is disposed at one side of the support main 102 to be folded to the rear surface of the support main 102.

The base voltage line 136 electrically connects each of the plurality of lamps to the printed circuit board 112 folded on the back side of the support main 102. At least one signal line is formed on the base voltage line 136.

Each of the plurality of inverters 121 constituting the inverter unit 120 includes a switching circuit 124 and a switching circuit 124 for switching the voltage from the voltage source Vin in response to the switching control signal as shown in FIG. 7. For switching the switching circuit 124 in response to the feedback signal FB from the transformer 122 and the transformer 122 for converting the voltage supplied by the switching of the voltage into the positive or reverse phase lamp driving voltage. The pulse width modulation circuit 126 is provided.

The switching circuit 124 includes at least one switch element for switching the voltage from the voltage source Vin to the transformer 122 in response to the switching control signal from the pulse width modulation circuit 126. Capacitors (not shown) may be connected to the output terminal of the switching circuit 124 in series or in parallel according to the circuit driving method.

Each of the plurality of current detectors 131 constituting the current detector 130 is supplied to the lamp 140 on the secondary winding of the transformer 122 or to the secondary winding of the transformer 122 as shown in FIG. 7. The feedback signal FB corresponding to the induced current value is supplied to the pulse width modulation circuit 126. To this end, each of the current detectors 131 includes a first resistor R1 connected between the secondary winding of the transformer 122 and the ground voltage source GND, and the secondary winding and the first resistor R1 of the transformer 122. The first diode D1 connected between the first node N1 and the pulse width modulation circuit 126 between the first node N1 and the second node N2 between the first node N1 and the first diode D1. And a second diode D2 connected between the base voltage source GND and a third node N3 and the base voltage source GND connected between the first diode D1 and the pulse width modulation circuit 126. A variable resistor RB and a second capacitor C2 connected in parallel to the variable resistor RB are provided.

The first resistor R1 detects the current value of the secondary winding of the transformer 122 by the resistance value and causes the first resistor R1 to appear on the first node N1. The feedback signal FB, which is the detected detection signal on the first node N1, is supplied to the pulse width modulation circuit 126 via the first diode D1. The second diode D2 interrupts the impulse of the negative potential to maintain the lowest potential of the feedback signal FB at zero potential. The variable resistor RB and the second capacitor C2 allow the potential of the feedback signal FB via the first diode D1 to be converted into a DC level to be supplied to the pulse width modulation circuit 126.

The transformer 122 is composed of a primary winding connected to the switching circuit 124 and a secondary winding connected to the lamp 140. Both ends of the primary winding are connected to the switching circuit 124, one side of the secondary winding is connected to the first electrode terminal of the lamp 140, and the other end is connected to the current detector 130. The transformer 122 converts the voltage supplied to the primary winding by the turns ratio of the primary and secondary windings, and induces the secondary winding. The voltage induced in the secondary winding is supplied to the lamp 140 through the first electrode terminal of the lamp 140 to turn on the lamp 140.

As such, the transformer 122 supplies current having a different phase at the same time to each of the odd (first) and even (odd) lamps among the plurality of lamps, as well as the previous even (odd) The odd-numbered (good) lamps adjacent to the lamps are supplied with current having the same phase at the same time. To this end, the secondary winding of the transformer 122 outputting a current having a positive phase at the same time point is wound in the same direction as the direction of the primary winding, while the secondary of the transformer 122 outputting a current having a reverse phase is present. The side winding is wound in the direction opposite to the winding direction of the primary winding.

Accordingly, at the same time, as shown in FIG. 8, the transformer 122 supplies a current in a positive phase to the first lamp 140a and a current in a reverse phase to the second lamp 140b as shown in FIG. 8. The third lamp 140c is supplied with an antiphase current; The phase current is supplied to the N-th lamp 140n-2, the phase current is supplied to the N-1 lamp 140n-1, and the reverse phase current is supplied to the N-th lamp 140n. . Accordingly, the first lamp 140a and the second lamp 140b, ..., the N-1 lamp 140n-1 and the N-th lamp 140n, the first and second lamps 140a and 140b. The leakage current is minimized by reducing the impedance by the current / phase coupling between them. Therefore, the driving of the lamps becomes unstable due to the leakage current of each of the plurality of lamps 140a to 140n. Meanwhile, the phase of the current supplied to the odd-numbered lamps 140a, 140c, ..., 140n-1 is equal to the phase of the current supplied to the previous even-numbered lamps 140b, 140d, ..., 140n. In this way, the lamp mutual interference due to the output noise of the transformer can be blocked at the source, thereby stably driving the lamp.

Meanwhile, a first capacitor C1 is connected between the secondary winding of the transformer 122 and the first electrode terminal of each of the plurality of lamps, and the first capacitor C1 may be selectively used according to a circuit driving method. have.

The pulse width modulation circuit 126 controls the switching cycle of the switching circuit 124 in response to the feedback signal FB from the current detector 130. That is, the pulse width modulation circuit 126 controls the switching period of the switching element constituting the switching circuit 124 in response to the feedback signal FB to control the voltage supplied to the transformer 122.

As described above, the lamp driving apparatus of the liquid crystal display according to the exemplary embodiment of the present invention is adapted to the switching of the switching circuit 124 in which the voltage from the voltage source Vin is controlled by the pulse width modulation circuit 126 of the inverter 120. Is supplied to the primary winding of transformer 122. The voltage supplied to the primary winding of the transformer 122 is converted by the primary and secondary winding ratios of the transformer 122 and induced in the secondary winding. The current induced in the secondary winding of the transformer 122 is supplied to the lamp 140 to light the lamp 140. When the lamp 140 is turned on, the current detector 130 detects a current induced in the secondary winding of the transformer 122 or supplied to the first electrode terminal of the lamp 140 and a feedback signal corresponding to the detected detection signal. (FB) is supplied to the pulse width modulation circuit 126. Accordingly, the pulse width modulation circuit 126 converts the switching period of the switching circuit 124 in response to the feedback signal FB to control the voltage supplied to the primary winding of the transformer 122.

As described above, in the lamp driving apparatus of the liquid crystal display according to the exemplary embodiment of the present invention, as shown in FIG. 8, the lamp driving voltage supplied to the plurality of lamps is inverse between the adjacent lamps 140a, 140b,. It has a phase. Accordingly, the leakage current becomes zero in each of the plurality of lamps 140a, 140b, ..., so that the power consumption is reduced. In detail, the driving currents supplied to the adjacent lamps 140a, 140b,... Of the plurality of lamps 140a, 140b,..., 140n have reversed phases, respectively. Is canceled by the current overlap of ..., and the leakage current becomes zero (0). In addition, the leakage current becomes zero because the increase in impedance due to current / phase coupling between adjacent lamps 140a, 140b, ... becomes zero due to current overlap.

In addition, in the lamp driving apparatus of the liquid crystal display according to the exemplary embodiment of the present invention, as shown in FIG. 8, an odd number of currents having a positive phase among the plurality of lamps 140a, 140b,..., 140n is supplied. A pair of lamps (140a, 140b) including lamps 140a, 140c, ..., 140n-1 and even-numbered lamps 140b, 140d, ..., 140n to which a current having an antiphase is supplied. ), (140c, 140d), ..., (140n-1, 140n), the even-numbered lamp (140b, 140d, ..., 140n-2) and the odd-numbered lamp (140c, 140e, ..., 140n-1), i.e., adjacent currents due to the output noise of the transformer 122 by supplying the current supplied to the 2M + 1 (0 is a positive integer) lamps and the 2M lamps in phase The mutual interference between the transformers 122 is prevented. Accordingly, the present invention can supply a stable current to the lamps.

On the other hand, the lamp driving device of the liquid crystal display according to the embodiment of the present invention, as shown in Figure 7 because the current detection unit 130 is connected to the secondary winding of the transformer 122 to mount the current detection unit as in the prior art There is no need for a separate printed circuit board and protective chassis. Thus, the structure of the present invention is simplified.

As described above, the lamp driving apparatus of the liquid crystal display according to the exemplary embodiment of the present invention supplies the phases of the currents supplied between adjacent lamps differently, and the phases of the currents supplied to the 2M + 1 lamps and the 2M lamps. Supply the same. Accordingly, the present invention can minimize leakage current due to lamp mutual interference and can stably drive lamps.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (10)

Multiple lamps, A lamp housing disposed side by side so that two of the plurality of lamps are paired; And an inverter unit having a plurality of inverters for supplying lamp driving currents having different phases to the pair of lamps and supplying lamp driving currents having the same phase to adjacent lamps of the pair of lamps. A lamp drive device for a liquid crystal display device. The method of claim 1, And a current detector for detecting the lamp driving current supplied to each of the plurality of lamps in the inverter. The method of claim 2, And a printed circuit board mounted on the inverter unit and the current detection unit and folded to the rear surface of the liquid crystal display device. The method of claim 1, A common line commonly connected to the second electrode terminals of the plurality of lamps; And a base voltage line for connecting the common line to a base voltage source. The method of claim 2, Each of the inverters, A transformer for converting a voltage from a voltage source into the lamp driving current and supplying the lamp to a first electrode terminal of each of the plurality of lamps; A switching circuit for switching the voltage to the transformer; And a control unit for controlling the switching circuit based on a feedback signal from the current detection unit. The method of claim 1, The inverter, And at the same time, the first phase of the pair of lamps is supplied with a positive phase current, and the second lamp is supplied with a reverse phase current. The method of claim 6, The lamp of the liquid crystal display device, characterized in that the first phase of the other pair of lamps adjacent to the pair of lamps at the same time is supplied with a reverse phase current, the second lamp is supplied with a positive phase current Drive system. The method of claim 5, wherein The current detector, And a lamp driving device connected to the transformer secondary winding. The method of claim 5, wherein The current detector, A resistor connected between the secondary winding of the transformer and the base voltage source, A first diode connected between the control unit and a first node between the secondary winding of the transformer and the resistor; A variable resistor connected between the node between the first diode and the control unit and the base voltage source; And a capacitor connected in parallel to said variable resistor. The method of claim 9, And the current detector further comprises a second diode connected between the node between the first node and the first diode and the base voltage source.