KR100449913B1 - An apparatus for lighting a multi-lamp in back light device of a LCD display - Google Patents

Abstract

The present invention provides a multi-lamp lighting device for a backlight of a liquid crystal display which can drive the multi-lamp with high efficiency with low power consumption while minimizing the size of the device.

To this end, the present invention is a backlight multi-lamp lighting device having a plurality of lamps that are illuminated as a backlight light source of a large-screen liquid crystal display by applying a DC voltage, which is operated by a gate signal to convert the DC voltage into a pulse wave AC voltage. AC conversion means for converting, series resonance means for converting an AC voltage in the form of a pulse wave from the AC conversion means into an AC voltage of a sine wave in accordance with a resonance operation, and driven by a sine wave AC voltage from the series resonance means. And lighting means for lighting each lamp, and control means for generating a gate signal for controlling the AC voltage converting operation of the AC converting means.

Description

{An apparatus for lighting a multi-lamp in back light device of a LCD display}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilamp lighting device for backlight of a liquid crystal display, and more particularly, to a multilamp lighting device for a backlight of a liquid crystal display for stably driving a multilamp applied for a backlight as the size of the liquid crystal display increases. It is about.

In general, a liquid crystal display applied to a monitor of a personal computer or a display screen of a notebook computer does not have its own light emitting function, and thus requires a backlight device as a separate light emitting device.

The backlight device is attached to the rear or bottom of the liquid crystal display to illuminate the display screen image displayed on the liquid crystal display device. As a light source applied to the backlight device, a cold cathode discharge lamp (Cold Cathode Fluorescent Lamp) is mainly used. Conventional backlight lamp lighting apparatus for lighting the cold cathode discharge lamp is used as shown in FIG.

1 is a view showing a circuit configuration of a backlight lamp lighting device of a conventional liquid crystal display. As shown in FIG. 1, the conventional lamp lighting device for a backlight includes a DC power supply (Vdc) and the DC power supply. Buck converter BC consisting of switching element Q1 connected to (Vdc), diode D1 and inductor I1, winding type transformer T1, and iron core of this winding type transformer T1. Self-contained switching means (SS) consisting of a pair of switching elements (Q2, Q3) connected to the auxiliary winding (W1) and the capacitor (C1) and connected to both ends of the input winding of the winding transformer (T1), respectively. Cold cathode discharge lamp (CCFL) connected to the output winding of the winding transformer (T1) and element protection resistor (R1), diode (D2) for bypassing the voltage of the output winding of the winding transformer (T1), the winding type Voltage of the winding of the output side of transformer T1 and reference voltage Vr Comparator CP1 for comparing a gate signal to the switching element Q1 of the buck converter BC by comparing ef, and the controller CON1 for adjusting the reference voltage Vref input to the comparator CP1. It is composed.

In the operation of the conventional backlight lamp lighting device configured as described above, if a reference voltage Vref of a predetermined level is generated from the control unit CON1 and input to the comparator CP1, the comparator CP1 has a winding-type transformer. The gate signal according to the result of comparing the output voltage of T1 and the reference voltage Vref is output.

In the buck converter BC, the switching element Q1 operates according to the gate signal generated from the comparator CP1, and the DC voltage output from the DC power supply Vdc is converted into an AC voltage having a triangular wave shape, thereby winding the transformer T1. Is applied to the input winding of

At this time, in the pair of switching means Q2 and Q3 of the self-switching switch SS, the winding type transformer T1 uses an AC voltage induced from the iron core of the winding type transformer T1 to the auxiliary winding W1 as a gate signal. By alternately switching both ends of the winding of the input side of the winding, an alternating voltage in the form of a sine wave is generated in the winding of the output side of the winding transformer T1.

When an AC voltage is generated at the input winding of the wound transformer T1 by the switching operation of the self-switching means SS, the cold cathode discharge lamp CCFL is turned on by the AC voltage.

On the other hand, recently, in the case of a monitor of a laptop computer or a personal computer employing a liquid crystal display, the actual visible screen is continuously slimmed and enlarged, and according to such a trend of enlargement, the discharge for backlight of the liquid crystal display is increased. Since a lamp has a limited brightness with a single lamp, a multi-type lamp is used in which a plurality of lamps are connected in parallel according to the size of the liquid crystal display monitor.

However, as described above, when the conventional lamp discharge lamp lighting device is provided with a plurality of lamps in proportion to the increase in size of the liquid crystal display, a plurality of backlight lamp discharge driving device is required to drive such lamps. Therefore, not only the overall volume of the backlight device is increased, but also the power consumption is excessively increased.

Accordingly, the present invention has been made to solve the conventional problems as described above, the object of the multi-lamp for backlight of the liquid crystal display to drive the multi-lamp with high power consumption by low power consumption while minimizing the size of the device It is to provide a lighting device.

1 is a view showing the circuit configuration of a backlight lamp lighting device of a conventional general liquid crystal display,

2 is a view showing the circuit configuration of the multi-lamp lighting device for backlight of the liquid crystal display according to the present invention,

3 is a circuit configuration diagram illustrating an operation state of a section in which an AC voltage of a positive period is input in an upward curve in a backlight multilamp lighting apparatus of a liquid crystal display according to the present invention;

4 is a circuit diagram illustrating an operation state of a section in which an AC voltage of a positive period is input in a falling curve in a backlight multilamp lighting apparatus of a liquid crystal display according to the present invention;

5 is a circuit diagram illustrating an operation state of a section in which an AC voltage of a negative period is input in a falling curve in a backlight multilamp lighting apparatus of a liquid crystal display according to the present invention;

6A and 6B are graphs showing input current characteristics and output current characteristics during an inverter operation of a multilamp lighting apparatus according to a preferred embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10, 20, 30, 40: switching element, 11, 21, 31, 41, 102, 103: diode,

50,70,80,81: capacitor, 60: wound transformer,

90, 91: discharge lamp, 100: lamp current detection unit,

110: control unit.

In order to achieve the above object, according to the present invention, in the multi-lamp lighting device for backlight having a plurality of lamps that are illuminated as a backlight light source of a large-screen liquid crystal display is applied by a gate signal, operating by a gate signal to AC converting means for converting to an AC voltage in the form of a pulse wave, series resonating means for converting an AC voltage in the form of a pulse wave from the AC converting means into an AC voltage of a sine wave in accordance with a resonance operation, and sinusoidal ac from the series resonating means. Lighting of the multi-lamp for the backlight of the liquid crystal display, characterized by consisting of a lighting drive means for driving a plurality of lamps respectively driven by a voltage, and a control means for generating a gate signal for controlling the AC voltage conversion operation of the AC conversion means. Provide the device.

Hereinafter, the present invention configured as described above will be described in detail with reference to the accompanying drawings.

That is, FIG. 2 is a diagram showing a circuit configuration of a backlight multilamp lighting device of a liquid crystal display according to the present invention.

As shown in FIG. 2, the multi-lamp lighting apparatus for backlight of the liquid crystal display according to the present invention includes the first to fourth switching elements 10, 20, 30, and 40, and a capacitor 50 constituting a series resonant circuit. , A boosting transformer 60, a parallel capacitor 70, a series capacitor 80 and 81 connected to the secondary side of the transformer 60, a plurality of cold cathode discharge lamps 90 and 91, and a lamp current detection unit 100. And a control unit 110.

The plurality of switching elements 10, 20, 30, and 40 are switched by the gate signals S1 to S4 generated by the control unit 110 to convert the DC voltage Vcc into an AC voltage in the form of a pulse wave. In order to apply to both input terminals (61, 62) of the step-up transformer 60, it is preferably made of a MOS field effect transistor (MOS FET).

Here, the first switching device 10 and the second switching device 20 are connected in series between the DC voltage (Vcc) terminal and the ground terminal of one side, respectively, the third switching device 30 and the fourth switching device 40 is connected in series between the DC voltage Vcc terminal and the ground terminal of the other side, respectively.

Also, a dead time in which all of the switching elements 10, 20, 30, and 40 are turned off between the drains and the source terminals of the first to fourth switching elements 10, 20, 30, and 40. The bypass diodes 11, 21, 31, 41 for canceling the current remaining in the input terminals 61, 62 and the line of the boosting transformer 60 are connected in parallel, respectively.

One end of the capacitor 50 is connected between the connecting end of the first switching element 10 and the second switching element 20, and the other end thereof is connected in series with one input terminal 61 of the boosting transformer 60. On the other hand, the boosting transformer 60 has the one input terminal 61 is connected in series with the capacitor 50, the other input terminal 62 is the third switching device 30 and the fourth switching device ( Between the connection ends of 40).

Here, both input terminals 61 and 62 of the capacitor 50 and the boosting transformer 60 constitute an LC series resonant circuit in a state in which the input terminals 61 and 62 are respectively connected in series, which is the first to fourth switching elements 10. In addition to converting an AC voltage in the form of a pulse wave generated at, 20, 30, and 40 into an AC voltage in the form of a sine wave, it is generated when switching the corresponding first to fourth switching elements 10, 20, 30, and 40. This is to maximize the efficiency of energy transfer and loss due to cut-off voltage.

The lamp current detection circuit 100 converts an AC current flowing through the cold cathode discharge lamps 90 and 91 into a DC voltage in order to return a current value for adjusting the brightness of the cold cathode discharge lamp 90.91. As input to the control unit 110, it is composed of a current detection resistor 101 and a pair of bypass diodes (102, 103).

The control unit 110 receives the current detection voltage IL from the lamp current detection circuit 100, and operates a function key from an external device or a separate sensor (for example, a sensor for detecting a power operation of the liquid crystal display monitor). The cold cathode discharge lamps 90 and 91 are turned on by applying the gate signals S1 to S4 to the respective switching elements 10, 20, 30, and 40 according to the input signal input from the control signal or the built-in control algorithm. It is to make it possible.

Here, the gate signals S1 to S4 output from the controller 110 may be set to match the resonant frequency of the LC series resonant circuit including the capacitor 50 and the boosting transformer 60.

On the other hand, the controller 110 detects current values flowing through the cold cathode discharge lamps 90 and 91 by the current detection voltage IL input from the lamp current detection circuit 100 to determine the current brightness. When the difference occurs between the determined luminance value and the predetermined target luminance, or when the luminance is changed by a function key operation from the outside, the cold cathode discharge lamps 90 and 91 are adjusted by adjusting the pulse widths of the gate signals S1 to S4. Allows the current value to be added or decreased.

Here, the parallel capacitor 70 of the secondary side of the transformer 60 is initially connected in parallel to the secondary terminals 63 and 64 of the transformer when the cold cathode discharge lamps 90 and 91 are driven, and thus the LC parallel resonance circuit is used. The driving voltage of the cold cathode discharge lamps 90 and 91 is generated, and the power factor after the lighting of the cold cathode discharge lamps 90 and 91 is turned on.

The series capacitors (80, 81) on the secondary side of the transformer (60) operate to allow equal current distribution between the lamps. The cold cathode discharge lamps (90, 91) have a main voltage when they are turned on, and the lamps are turned on. Afterwards, since the current is important, the impedance component of each lamp (90,91) is a few mega ohms when the light is turned on by the series capacitor (80,81), which is very large compared to the corresponding capacitor (80,81). Since the voltage is applied to all of the cold cathode discharge lamps 90 and 91, and after lighting, the impedance of the corresponding lamps 90 and 91 becomes several kilo ohms and is relatively higher than that of the series capacitors 80 and 81. By having a very small value, the magnitude of the input current is almost equal.

Here, the cold cathode discharge lamps 90 and 91 have negative resistance characteristics that are lowered from several mega ohms before lighting to several kilo ohms after lighting.

Next, the operation of the present invention made as described above will be described in detail with reference to the operation state diagram of Figs.

First, as shown in FIG. 3, the control to turn on the plurality of cold cathode discharge lamps 90 and 91 in the initial state according to a function key operation from the outside, an input signal of a separate sensor, or a control algorithm built therein. When the condition is satisfied, the gate signal is output from the controller 110 to each of the switching elements 10, 20, 30, and 40.

Here, the controller 110 applies an ON gate signal to the first switching device 10 and the fourth switching device 40, and the second switching device 20 and the third switching device 30. The furnace applies an OFF gate signal.

The first switching device 10 and the fourth switching device 40 are turned on by receiving an ON gate signal from the controller 110, and the second switching device 20 and the third switching device 30 are turned on. As the OFF gate signal is applied to maintain the turn-off state, the DC voltage Vcc applied from a predetermined DC power supply means made of a battery or the like is transmitted from the first switching element 10 to the fourth capacitor 50 through the capacitor 50. It is applied to both input terminals 61 and 62 of the boosting transformer 60 via a path to the switching element 40.

In this case, an induced voltage corresponding to an input voltage is generated at both output terminals 63 and 64 of the boosting transformer 60, and voltages generated at both output terminals 63 and 64 of the boosting transformer 60 are generated. It is energized from the output terminal 63 to the cold cathode discharge lamps 90 and 91 and applied to the lamp current detection unit 100.

As shown in FIG. 3, an AC voltage of a positive (+) period is a section in which a rising curve is input to the boosting transformer 60, and the DC voltage Vcc is a capacitor 50 and a boosting transformer ( The resonance curve is drawn by the resonance action of the LC series resonant circuit composed of its own inductance component, which is converted into an alternating voltage in which the rising curve is drawn during the positive (+) period, and is input to the boosting transformer 60. do.

Accordingly, the AC voltages having the same waveform as the input side are delayed by a predetermined phase difference at both output terminals 63 and 64 of the boosting transformer 60, and a rising curve is generated during the AC voltage of the positive period. The AC voltage is applied and energized.

In this state, the lamp current detection unit 100 converts the current values flowing through the cold cathode discharge lamps 90 and 91 into voltage values and inputs them to the controller 110 as the current detection voltage IL.

The control unit 110 detects a current value flowing through the cold cathode discharge lamps 90 and 91 by the current detection voltage IL from the lamp current detection unit 100 and accordingly to the current cold cathode discharge lamp 90 according to the detected current value. , The luminance of (91) is determined.

Next, with reference to the circuit diagram of Figure 4 will be described the operating state of the section in which the positive voltage of the positive period is input in the falling curve in the backlight multi-lamp lighting device of the liquid crystal display according to the present invention. .

As shown in FIG. 4, the control unit 110 applies an off gate signal to all of the first to fourth switching elements 10, 20, 30, and 40, and the first switching element 10 and the fourth switching element. As the switching device 40 is turned on in the turned on state (see FIG. 3), each of the switching devices 10, 20, 30, and 40 is turned off.

In this state, a positive (+) period of the AC voltage is a falling curve is input to the step-up transformer 60, the first switching device 10 and the fourth switching device 40 is switched off state The positive polarity voltage, which was applied before the voltage, gradually decreases in a resonance curve due to the resonance of the LC series resonant circuit constituted by the capacitor 50 and the boosting transformer 60. The AC voltage that draws the falling curve during the cycle is input to the transformer 60.

Accordingly, the AC voltages having the same waveform as the input side are delayed by a predetermined phase difference at both output terminals 63 and 64 of the boosting transformer 60, and a falling curve is generated during the positive period of the AC voltage. The AC voltage is applied to the cold cathode discharge lamps 90 and 91 and is energized.

In this case, the current value flowing through the cold cathode discharge lamps 90 and 91 is converted into a voltage value by the lamp current detector 100 and input to the controller 110, and the controller 110 receives the lamp current from the lamp current detector 100. The current value flowing through the cold cathode discharge lamps 90 and 91 is detected by the voltage level of the current detection voltage IL applied, and the brightness of the current lamps 90 and 91 is determined by the detected current value.

Next, an operation state of a section in which an AC voltage of a negative period is input in a falling curve in the backlight multilamp lighting apparatus of the liquid crystal display according to the present invention will be described with reference to the circuit diagram of FIG. 5. .

As shown in FIG. 5, the controller 110 applies an on-gate signal to the second switching device 20 and the third switching device 30, while the first switching device 10 and the fourth switching device 30 are applied. The off gate signal is applied to the switching device 40.

Accordingly, the second switching device 20 and the third switching device 30 are turned on by the on gate signal, and the first switching device 10 and the fourth switching device 40 remain turned off. Accordingly, the DC voltage Vcc is input to both input terminals 61 of the boosting transformer 60 through an energization path from the third switching element 30 to the second switching element 20 via the capacitor 50. 62).

At this time, an induced voltage corresponding to an input voltage is generated at both output terminals 63 and 64 of the boosting transformer 60, and voltages generated at both output terminals 63 and 64 of the boosting transformer 60 are generated. The lamp current detection circuit 100 is energized from the ground terminal to which the lamp current detection circuit 100 is connected to the cold cathode discharge lamps 90 and 91 and applied to the input terminal 63 of the boosting transformer 60.

As shown in FIG. 5, an AC voltage having a negative period is a falling curve and is input to the boosting transformer 60, and the DC voltage Vcc is a capacitor 50 and a boosting transformer ( The resonance curve is drawn by the resonance action of the LC series resonant circuit constituted by 60). The resonance curve is changed into an AC voltage which draws a falling curve during the negative period and is input to the boosting transformer 60.

Accordingly, the AC voltages having the same waveform as the input side are delayed by a predetermined phase difference at both output terminals 63 and 64 of the boosting transformer 60, and a falling curve is generated during the negative period of the AC voltage. The AC voltage is applied to the cold cathode discharge lamps 90 and 91 and is energized.

In this case, the current value flowing through the cold cathode discharge lamps 90 and 91 is converted into a voltage value by the lamp current detector 100 and input to the controller 110, and the controller 110 detects the lamp current detector 100. The current value flowing through the cold cathode discharge lamps 90 and 91 is detected based on the voltage level of the current detection voltage IL applied from the device, and the luminance of the current cold cathode discharge lamps 90 and 91 is determined based on the detected current value. do.

Next, as shown in FIG. 4, the controller 110 applies an off gate signal to all of the first to fourth switching devices 10, 20, 30, and 40, and the second switching device ( 20 and the third switching element 30 are switched from the turn on state to the turn off state.

This operating state is a period in which the negative voltage of the negative period is inputted to the boosting transformer 60 while drawing a rising curve, and the second switching device 20 and the third switching device 30 are turned off. The negative period voltage, which was applied before switching, gradually decreases while drawing a resonance curve by the resonance action of the LC series resonant circuit composed of the capacitor 50 and the boosting transformer 60. The AC voltage drawing the rising curve is input to the boosting transformer 60.

Accordingly, the AC voltages having the same waveform as the input side are delayed by a predetermined phase difference at both output terminals 63 and 64 of the boosting transformer 60 to draw a rising curve during the negative period of the AC voltage. An AC voltage is applied to the cold cathode discharge lamps 90 and 91 so as to be energized.

At this time, the current value flowing through the cold cathode discharge lamp (90,91) is converted into a voltage value by the lamp current detection unit 100 is input to the control unit 110, the control unit 110 from the lamp current detection unit 100 The current value flowing through the cold cathode discharge lamps 90 and 91 is detected by the voltage level of the current detection voltage IL applied, and the luminance of the current cold cathode discharge lamps 90 and 91 is determined based on the detected current value. .

As described above, the controller 110 repeats the process of selectively switching the respective switching elements 10, 20, 30, and 40 in a predetermined order, thereby converting the DC voltage Vcc into a pulse wave form. The voltage can be converted to a voltage, and the AC voltage in the form of a pulse wave converted by the switching operation of each switching element 10, 20, 30, 40 as described above is composed of a capacitor 50 and a boost transformer 60. It is converted into an sine wave AC voltage by the resonance action of the series circuit.

As described above, the sine wave AC voltage generated by the switching operation of each switching element 10, 20, 30, 40 and the LC series resonant circuit constituted by the capacitor 50 and the boosting transformer 60 is performed. Is supplied to the cold cathode discharge lamps 90 and 91 while being input to the boosting transformer 60 and boosted by a predetermined level, the cold cathode discharge is caused by the AC voltage of the sine wave output from the boosting transformer 60. Lamps 90 and 91 light up.

At this time, the control unit 110 is the cold cathode discharge lamp (90,91) by the current detection voltage (IL) from the lamp current detection unit 100 for detecting the current value of the cold cathode discharge lamp (90,91) The cold cathode discharge lamp is determined by adjusting the pulse width of the gate signal when the current brightness of the LED is determined and there is a difference between the current brightness and the preset target brightness or when the brightness is to be changed by an external function key input by the user. Voltage and current values applied to (90,91) are added and subtracted.

As shown in FIGS. 6A and 6B, the input and output current characteristics of the lighting device that functions as an inverter as a result of the operation as described above are illustrated.

As shown in FIG. 6A, when driving frequency bands of each cold cathode discharge lamp are set to 50 kHZ to 60 kHz and allowable input voltage is set to 15 V to 20 V while driving a total of six cold cathode discharge lamps. The change of the input current with respect to the regulated voltage appears linearly with luminance.

As shown in FIG. 6B, when the output currents of the three cold cathode discharge lamps for each channel are summed by measuring the output of the lighting device by dividing the channel 1 and the channel 2, the output current of 9 mA per discharge lamp. As 27mA is measured for each channel, the current deviation between both channels appears to be small. Therefore, since the linearity of the input / output current according to the luminance control voltage is possible, stable output and free control of the luminance are possible.

It is a matter of course that the present invention having the above-described embodiments can be variously modified and implemented without departing from the technical gist of the present invention without departing from the embodiments.

As described above, according to the present invention, by reducing the number of lighting devices for turning on the backlight multilamp of a large-screen liquid crystal display into a single unit, it is possible not only to reduce power consumption but also to reduce the overall size of the apparatus. In addition, the multi-lamp lighting output is made evenly, and the electromagnetic interference can be greatly reduced.

In addition, in the present invention, by controlling the pulse width of the gate signal applied to the switching element of the lighting device to adjust the current value applied to the lamp, there is an advantage that the brightness of the lamp can be freely adjusted from 0 to 100%. .

Claims (6)

In the backlight multi-lamp lighting device having a plurality of lamps that are applied as a backlight light source of a large-screen liquid crystal display by applying a DC voltage, AC conversion means operated by a gate signal to convert the DC voltage into an AC voltage in the form of a pulse wave; A series resonance means for converting an AC voltage in the form of a pulse wave from the AC conversion means into an AC voltage of a sine wave in accordance with a resonance operation; Lighting driving means driven by a sine wave AC voltage from said series resonating means to light each of said plurality of lamps; And a control means for generating a gate signal for controlling the AC voltage conversion operation of the AC conversion means. According to claim 1, wherein the AC conversion means are connected in series between the DC voltage terminal and the ground terminal of one side and operated by a gate signal, respectively, and between the DC voltage terminal and the ground terminal of the other side And a third switching element and a fourth switching element each connected in series and operated by a gate signal. 3. The method of claim 2, wherein the series resonator means includes a capacitor connected between a series connection end of the first and second switching elements, one end of which is connected in series with the capacitor, and the other end of which is connected in series with the third and fourth switching elements. Multi-lamp lighting device for the backlight of the liquid crystal display, characterized in that it comprises an input terminal of the boosting transformer connected between the connection stage. [4] The liquid crystal display of claim 3, wherein the lighting driving means has both ends connected in parallel with the plurality of lamps, respectively, and an output terminal of a boosting transformer for boosting an AC voltage of a sine wave to apply to the plurality of lamps. Multilamp lighting device for backlight. 2. The apparatus of claim 1, further comprising a lamp current detector for detecting a current value applied to the plurality of lamps to generate a current detection voltage; And the control means is configured to determine the brightness of the lamp by the current detection voltage from the lamp current detection unit. 6. The liquid crystal display of claim 5, wherein the control means is configured to adjust and control the pulse width of the gate signal for adjusting the luminance based on the lamp luminance value determined from the current detection voltage of the lamp current detection unit. Multi lamp lighting device for backlight.