Apparatus and method of driving lamp of liquid crystal display device

A lamp driving apparatus of a liquid crystal display device includes m lamp groups in which a plurality of lamps generating light are disposed; n (n<m) inverter parts to generate an AC voltage for driving the lamps; an inverter controller to control the inverter parts; and a multiplexer to selectively supply the AC voltage generated at the n inverter parts to the n lamp groups among the m lamp groups. In each frame, a clock signal is divided into n divided signals. Different sets of lamp groups are driven during each of the divided signals.

This application claims the benefit of the Korean Patent Application No. P2004-101552 filed on Dec. 4, 2004, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a lamp driving apparatus of a liquid crystal display device, and more particularly to a lamp driving apparatus and method of a liquid crystal display device that is adaptive for reducing cost.

DESCRIPTION OF THE RELATED ART

Generally, a liquid crystal display device s being used in an increasing number of applications as it is light, thin, and has low driving power consumption. These applications include office automation equipment, audio/video equipment and so on. The liquid crystal display device controls the transmitted amount of light in accordance with a video signal applied to a plurality of control switches which are arranged in a matrix, thereby displaying a desired picture on a screen.

In this way, the liquid crystal display device is not a self luminous display device, thus it requires a light source such as a backlight. A cold cathode fluorescent tube (hereinafter, referred to as “CCFT”) is used as the light source in the backlight.

The CCFL is a light source tube that generates light through cold emission-electron emission generated because a strong electric field is applied to a cathode surface—so that it has low heat generation, high brightness, long life span, full color and so on. Different types of CCFLs include a light guide type, a direct light type and a reflector type. An appropriate type of light source tube is selected dependent on the requirements of the liquid crystal display device.

In this way, the CCFL uses an inverter circuit for obtaining a high voltage power source from a DC power source of low voltage.

FIG. 1is a diagram representing a lamp driving apparatus of a liquid crystal display device of the prior art.FIG. 2is a diagram representing an inverter part shown inFIG. 1.

Referring toFIGS. 1 and 2, a lamp driving apparatus of the liquid crystal display device according to the prior art includes a plurality of lamp groups7formed with a plurality of lamps6which generate light; a plurality of inverter parts4to drive the lamps6by supplying an AC voltage of high voltage to the lamps6; and an inverter controller2to control the inverter part4.

Each of the lamp groups7is composed of at least two lamps6, and each of the lamps6receives a lamp output voltage from the inverter8to produce visible light. Each of the lamps6is composed of a glass tube and an inert gas inside the glass tube, wherein the inert gas is charged in the glass tube and phosphorus is spread over the inner wall of the glass tube.

Each of the inverter parts4is connected to each lamp of the associated lamp group7, is driven by an enable signal ENA supplied from the inverter controller2, drives the lamp6using of a clock signal CLK and a drive power source VCC supplied from the inverter controller2, and transmits to the inverter controller2a state signal ACK that is generated when a problem exists in the lamp6. Accordingly, if the state signal ACK is supplied to the inverter controller2, the inverter controller2stops the drive of the inverter part4when something is wrong in the lamp6. Each of the inverter parts4includes a transformer18for supplying a high voltage to the lamp6, a switch device part16for supplying a DC power source VDD supplied from the outside to the transformer18in accordance with the output value of the inverter8.

The transformer18includes a primary winding Ti1connected to the switch device part16and a secondary winding T2connected to the lamp6. Both ends of the primary winding T1are connected to the switch device part16. One end of the secondary winding T2is connected to one side of the lamp6, and the other end is connected to a feedback circuit14. The voltage supplied from the switch device part16is converted into an AC voltage of high voltage by a winding ratio between the primary winding T1and the secondary winding T2of the transformer18.

The inverter8generates drive signals PDR1, NDR1, PDR2, NDR2to drive the switch device part16by use of the clock signal CLK and the drive power source VCC supplied from the inverter controller2. The inverter8includes a drive signal generator10to drive the switch device part16, a feedback circuit14connected to the transformer18to detect the output voltage of the transformer18, and a switch controller12to generate a control signal SCS for controlling the switch device part16on the basis of the feedback signal FB from the feedback circuit14.

The feedback circuit14generates the feedback signal FB corresponding to the AC voltage of high voltage supplied from the other end of the secondary winding T2of the transformer18to supply it to the switch controller12.

The switch controller12generates a switching control signal SCS controlling the switching of the switch device part16in accordance with the feedback signal FB from the feedback signal14.

The drive signal generator10generates the drive signal PDR1, NDR1, PDR2, NDR2for driving the switch device part16in accordance with the drive power source VCC supplied from the inverter controller2and the switching control signal SCS supplied from the switch controller12, to supply them to the switch device part16.

The switch device part16is driven in accordance with the drive signals PDR1, NDR1, PDR2, PDR2supplied from the drive signal generator10to supply the DC voltage VDD supplied from the outside to the primary winding T1of the transformer18. The switch device part16includes a first switch device part16A for supplying a positive (+) DC voltage to the primary winding T1of the transformer18and a second switch device part16B for supplying a negative (−) DC voltage to the primary winding T1of the transformer18.

The first switch device part16A supplies the positive (+) DC voltage VDD to both ends (between A and B) of the primary winding1of the transformer18. The first switch device part16A includes a first switch device Q1installed at one side of the primary winding T1of the transformer18and the DC power source VDD to be driven by the first drive signal PDR1supplied from the drive signal generator10; and a second switch device Q2installed between a ground voltage source GND and one side of the primary winding T1of the transformer18to be driven by the second drive signal NDR1supplied from the drive signal generator10. The first switch device Q1is a P type transistor (MOSFET or BJT) and the second switch device Q2is an N type transistor (MOSFET or BJT).

The second switch device part16B supplies the negative (−) DC voltage VDD to both ends (between A and B) of the primary winding T1of the transformer18. The second switch device part16B includes a third switch device Q3installed at the other side of the primary winding T1of the transformer18and the DC power source VDD to be driven by the third drive signal PDR2supplied from the drive signal generator10; and a fourth switch device Q4installed between a ground voltage source GND and the other side of the primary winding T1of the transformer18to be driven by the fourth drive signal NDR2supplied from the drive signal generator10. The third switch device Q3is a P type transistor (MOSFET or BJT) and the second switch device Q4is an N type transistor (MOSFET or BJT).

The inverter controller2receives a polarity control signal POL for controlling the polarity of a dimming signal and an inverter selection signal SEL from a system (not shown) and supplies to the inverter part4the dimming signal L1to Lm for controlling the brightness of light generated from the lamp6, an enable signal ENA for driving the inverter part4, and a clock signal CLK and the drive power source VCC for generating the drive signal PDR1, NDR1, PDR2, NDR2. The inverter controller2intercepts the drive of the inverter part4when something is wrong in the lamp6when the state signal ACK is supplied from the inverter part4.

However, the lamp driving apparatus of the liquid crystal display device of the prior art has m (m is an integer) lamp groups7each connected to m of the inverter parts4and each driven by the AC voltage of high voltage supplied from the m inverter parts4. The large number of the inverter parts4increases the cost of the liquid crystal display device.

SUMMARY OF THE INVENTION

By way of introduction only, in one embodiment, a lamp driving apparatus of a liquid crystal display device, comprises: m (m is an integer of at least 2) lamp groups each having a plurality of lamps; n (n is an integer smaller than m) inverter parts to generate an AC voltage of high voltage for driving the lamps; an inverter controller to control the inverter parts; and a multiplexer to selectively supply the AC voltage of high voltage generated at the n inverter parts to the n lamp groups among the m lamp groups.

In another embodiment, a method for driving a lamp a display device having m (m is an integer of at least 2) lamp groups in each of which at least two lamps are disposed and n (n is an integer smaller than m) inverter parts to generate a drive voltage for driving the lamps is presented. The method comprises: generating n drive voltages for driving the lamps; dividing a clock signal into m divided signals; and selectively supplying the n drive voltages to n lamp groups for one frame using the m divided signals.

In another embodiment, a lamp driving apparatus comprises: m (m>1) lamp groups each containing a plurality of lamps; n inverter parts (1≦n<m) that each generate an AC voltage sufficient to drive the lamps of at least one of the lamp groups, fewer inverter parts being disposed in the lamp driving apparatus than lamp groups; an inverter controller that controls the inverter parts; and a multiplexer that selects different sets of lamp groups to be driven such that all of the lamp groups are driven for at least a portion of each frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the preferred embodiments of the present invention will be described in detail with reference toFIGS. 3 to 15.

FIG. 3is a diagram representing a lamp driving apparatus of a liquid crystal display device according to an embodiment of the present invention.

Referring toFIG. 3, the liquid crystal display device according to an embodiment of the present invention includes a plurality of lamp groups57where a plurality of lamps that generate light are formed; a plurality of inverter parts54to generate an AC voltage of high voltage which is required for driving the lamps; an inverter controller52to control the inverter parts54; and a high voltage multiplexer80for supplying the AC voltage of high voltage generated in the inverter parts54to the lamp groups57which are driven among the lamp groups.

The lamp group57, as shown inFIG. 2, is composed of at least two lamps6, each of which irradiates a liquid crystal display panel (not shown) with visible light using the AC voltage of high voltage supplied through the high voltage multiplexer80. Each of the lamps6includes a glass tube and invert gas inside the glass tube, and the inert gas is charged into the glass tube and phosphorus is spread over the inner wall of the glass tube. Each of the lamps6has electrons emitted to collide with the inert gas within the glass tube to increase the amount of electrons in geometrical progression when the AC voltage of high voltage generated in the inverter part54is supplied to a high voltage electrode by the high voltage multiplexer80. The increased electrons make an electric current flow in the inside of the glass tube, thus the inert gas Ar, Ne becomes excited by the electrons to generate energy and the generated energy excites mercury to emit ultraviolet radiation. The ultraviolet radiation collides with the luminous phosphorus spread over the inner wall of the glass tube, thereby emitting visible radiation.

Each of the inverter parts54, as shown inFIG. 2, is driven by an enable signal ENA supplied from the inverter controller52, and generates an AC voltage of high voltage required for driving the lamp by use of a drive power source VCC and a clock signal CLK supplied from the inverter controller52and transmits a state signal ACK to the inverter controller52in accordance with the presence or absence of a problem with the lamp6. Accordingly, the inverter controller controls the drive of the inverter part54in accordance with the state of the lamp6when the state signal ACK is supplied to the inverter controller52. Each of the inverter parts54includes a transformer18to generate an AC voltage of high voltage which drives the lamp6, a switch device part16to supply a DC power source VDD to the transformer18in accordance with the output signal of the inverter8, and an inverter8for driving the switch device part16.

The transformer18includes a primary winding T1connected to the switch device part16and a secondary winding T2connected to the high voltage multiplexer80. Both ends of the primary winding T1are connected to the switch device part16, and one end of the secondary winding T2is connected to the high voltage multiplexer80and the other end is connected to a feedback circuit14. The voltage supplied from the switch device part16is converted into the AC voltage of high voltage by the winding ratio between the primary winding T1and the secondary winding T2and induced to the secondary winding T2of the transformer18. At this moment, the AC voltage of high voltage induced to the secondary winding T2of the transformer18is supplied to the high voltage multiplexer80and the high voltage multiplexer80supplies the AC voltage of high voltage in accordance with a clock signal CLK supplied from the inverter controller52, to n (n is an integer smaller than m) lamp groups571to57namong m lamps571to57m.

The inverter8generates drive signals PDR1, NDR1, PDR2, NDR2for driving a switch device part16by use of the drive power source VCC and the clock signal CLK supplied from the inverter controller52. The inverter8includes a drive signal generator10for driving a switch device part16, a feedback circuit14connected to the transformer18to detect the output voltage of the transformer18, and a switch controller12to generate a control signal SCS for controlling the drive of the switch device part16on the basis of a feedback signal FB from the feedback circuit14.

The feedback circuit14generates the feedback signal FB corresponding to the AC voltage of high voltage supplied from the other end of the secondary winding T2of the transformer18to supply it to the switch controller12.

The switch controller12generates a switching control signal SCS in accordance with the feedback signal FB from the feedback circuit14. The generated switching control signal SCS is supplied to the drive signal generator10

The drive signal generator10generates the drive signal PDR1, NDR1, PDR2, NDR2for driving the switch device part16in accordance with the switching control signal SCS supplied from the switch control part12and the drive power source VCC supplied from the inverter controller52, to supply it to the switch device part16. The drive signal PDR1, NDR1, PDR2, NDR2supplied from the drive signal generator10to the switch device part16is the same as shown inFIG. 5.

The switch device part16is driven in accordance with the drive signal PDR1, NDR1, PDR2, NDR2supplied to the drive signal generator10to supply the DC power source VDD to the primary winding T1of the transformer18. The switch device part16includes a first switch device part16A for supplying a positive (+) DC voltage to the primary winding T1of the transformer18and a second switch device part16B for supplying a negative (−) DC voltage to the primary winding T1of the transformer18.

The first switch device part16A supplies the positive (+) DC voltage VDD to both ends (between A and B) of the primary winding T1of the transformer18. The first switch device part16A includes a first switch device Q1installed at one side of the primary winding T1of the transformer18and the DC power source VDD to be driven by the first drive signal PDR1supplied from the drive signal generator10; and a second switch device Q2installed between a ground voltage source GND and one side of the primary winding T1of the transformer18to be driven by the second drive signal NDR1supplied from the drive signal generator10. The first switch device Q1is a P type transistor (MOSFET or BJT) and the second switch device Q2is an N type transistor (MOSFET or BJT). The first and second switch devices Q1, Q2, if the first and second drive signal PDR1, NDR1shown inFIG. 4are supplied, supplies the DC voltage VDD to one side of the primary winding T1of the transformer18if the first and second drive signal PDR1, NDR1are in a low state. Accordingly, a first DC voltage VoutH is supplied to one side of the primary winding T1of the transformer18as shown inFIG. 5(a). However, the voltage is not supplied to the one side of the primary winding T1of the transformer18if the first and second drive signal PDR1, NDR1are in a high state.

The second switch device part16B supplies the negative (−) DC voltage VDD to both ends (between A and B) of the primary winding T1of the transformer18. The second switch device part16B includes a third switch device Q3installed at the other side of the primary winding T1of the transformer18and the DC power source VDD to be driven by the third drive signal PDR2supplied from the drive signal generator10; and a fourth switch device Q4installed between a ground voltage source GND and the other side of the primary winding T1of the transformer18to be driven by the fourth drive signal NDR2supplied from the drive signal generator10. At this moment, the third switch device Q3is a P type transistor (MOSFET or BJT) and the second switch device Q4is an N type transistor (MOSFET or BJT). The third and fourth switch devices Q3, Q4, if the third and fourth drive signal PDR2, NDR2shown inFIG. 4are supplied, supplies the DC voltage VDD to the other side of the primary winding T1of the transformer18if the third and fourth drive signal PDR2, NDR2are in a low state. Accordingly, a second DC voltage VoutL is supplied to the other side of the primary winding T1of the transformer18as shown inFIG. 5(b). However, the voltage is not supplied to the other side of the primary winding T1of the transformer18if the third and fourth drive signal PDR2, NDR2are in a high state.

A tank voltage as ofFIG. 5(c) is generated at both ends (between a and b) of the first winding T1of the transformer18by the drive of the first and second switch drivers16A and16B. Because of this, the pyramidal wave current is induced to the primary winding T1of the transformer18as shown inFIG. 4.

The inverter controller52receives a polarity control signal POL for controlling the polarity of a dimming signal and an inverter selection signal SEL from a system (not shown) and supplies to the inverter part54the dimming signal L1to Lm for controlling the brightness of light generated from the lamp6, an enable signal ENA for driving the inverter part54, and a clock signal CLK and the drive power source VCC for generating the drive signal PDR1, NDR1, PDR2, NDR2. The inverter controller52intercepts the drive of the inverter part54when something is wrong in the lamp6when the state signal ACK is supplied from the inverter part54.

The high voltage multiplexer80supplies the AC voltage of high voltage generated at the inverter part54in accordance with the clock signal supplied from the inverter controller52, to n (n is an integer smaller than m) lamp groups571to57namong m (m is an integer of 2 or above) lamp groups57. High voltage multiplexer80, as shown inFIG. 6, includes a frequency divider82to divide the clock signal CLK supplied from the inverter controller52; and a switch part86to supply the AC voltage of high voltage generated at the n inverters54in accordance with a division signal CP from the frequency divider82the control signal CS1to CSn to the n (n is an integer smaller than m) lamp groups571to57namong the m lamp groups571to57m.

The frequency divider82divides the clock signal CLK supplied from the inverter controller52into m division signals to supply the division signal to the switch part86. For example, if the lamp driving apparatus of the liquid crystal display device of the present invention has five inverter parts541to545and eight lamp groups571to578, as shown inFIG. 7, the frequency divider82divides into eight the clock signal CLK inputted from the inverter controller52. The division signal CP from the frequency divider82is used as the clock signal of the switch part86.

The switch part86supplies the AC voltage of high voltage generated at the n inverters54by being switched by the switching control signals CS1to CSn supplied from the switch part86, to the n (n is an integer smaller than m) the lamp groups571to57namong the m lamp groups571to57m.The switch part86, as shown inFIG. 8, includes the n switch array parts861to86nso that the AC voltage of high voltage generated at the n inverter part54is supplied to the n (n is an integer smaller than m) lamp groups571to57namong the m lamp groups571to57min accordance with the switching control signals CS1to CSn supplied from the switch part86. In other words, the liquid crystal display device of the present invention includes five inverter parts541to545, the switch part86includes five switch array parts861to865. Each of the switch array parts861to86n,as shown inFIG. 9, has m switches Q1to Qm each connect any one among the first to nthinverter parts541to54nwith m nodes N1to Nm between the first to mthlamp groups571to57m.Each of the m switches Q1to Qm is turned on or off in accordance with the state value S1to Sm of each switching control signal CS1to CSn. Because of this, each of the switch array parts861to86nselectively supplies the AC voltage of high voltage generated in any one of the first to nth inverter parts541to54nto any one of the first to mthlamp group571to57min accordance with the switching control signal CS1to CSn. Each of the switches Q1to Qm is a semiconductor switching device, e.g., a MOSFET, IGBT, SCR or BJT.

The lamp driving method of the liquid crystal display device according to the embodiment of the present invention, is described as follows. Herein, it will be described assuming that the liquid crystal display device of the present invention has the five inverter parts541to545and the eight lamp groups571to578, and the AC voltages of high voltage generated at the first to fifth inverter parts541to545are each supplied to the first to fifth lamp groups571to575in T1period of the division signal CP shown inFIG. 7.

By the division signal CP from the frequency divider82and the control signal CS1to CSn from the inverter controller52, ‘10000000’ is stored at the first switch array part861, ‘01000000’ is stored at the second switch array part862and ‘00100000’ is stored at the third switch array part863. Further, ‘00010000’ is stored at the fourth switch array part864and ‘00001000’ is stored at the fifth switch array part865. Herein, in case that the liquid crystal display device is driven at 60 Hz, one frame is 1/60 second (16.7 ms), thus one period of the division signal CP is set to be about 2.08 ms for driving eight lamp groups571to578for one frame period. Accordingly, the division signal CP of the T1period shown inFIG. 7is supplied to the switch part86, i.e., the switching control signals CS1to CS5, are supplied to the first to eighth switches Q1to Q8of each of the first to fifth switch array parts861to865. In the first switch array part861, only the first switch Q1is turned on by the first switching control signal CS1to supply the AC voltage of high voltage V1generated at the first inverter part541to the first lamp group571. The second to eighth switches Q2to Q8of the first switch array part861remain in the off state. Further, in the second switch array part862, only the second switch Q2is turned on by the second switching control signal CS2to supply the AC voltage of high voltage V2generated at the second inverter part542to the second lamp group572. The first switch Q1and the third to eighth switches Q3to Q8of the second switch array part862remain in the off state. And, in the third to fifth switch array parts863to865, only the third to fifth switches Q3to Q5are turned on by the third to fifth switching control signals CS3to CS5to supply the AC voltage of high voltage generated at the third to fifth inverter parts543to545to the third to fifth lamp groups573to575. The rest of the switches of the third to fifth switch array parts863to865remain in the off state. Accordingly, if the division signal CP of T1period is supplied to the switch part86, as shown inFIG. 10, only the first to fifth lamp groups571to575are turned on among the eight lamp groups571to578.

The division signal CP of T2period and the switching control signal CS1to CS5are thus supplied to the first to eighth switches Q1to Q8of the first to fifth switch array parts861to865.

Accordingly, in the first switch array part861, the first switch Q1is turned off, the second switch Q2is turned on and the rest of the switches Q3to Q8remain in the previous off state. Further, in the second switch array part862, the second switch Q2is turned off, the third switch Q3is turned on and the rest of the switches Q1and Q4to Q8remain in the previous off state. And, in the third to fifth switch array parts863to865, the third to fifth switches Q3to Q5, which were turned on in the T1period, are turned off, the fourth to sixth switches Q4to Q6are turned on and the rest of the switches remain in the previous off state. Accordingly, in the T2period, the AC voltage of high voltage V1to V5generated at the first to fifth inverter parts541to545are each supplied to the second to sixth lamp groups571to575. Because of this, the second to sixth lamp groups571to575are turned on in the T2period of the division signal CP. And then, in the driving method of the T3to T8periods, as described in the T1and T2, the switches Q1to Q8of the first to fifth switch array parts861to865in accordance with the division signal CP and the switching control signal CS1to CS5, sequentially turned on to supply the AC voltage of high voltage generated at the first to fifth inverter parts541to545to the five lamp groups among the eight lamp groups571to578. In other words, in the T3period of the division signal CP, the AC voltage of high voltage generated at the first to fifth inverter parts541to545is supplied to each of the third to seventh lamp groups573to577. In the T4period of the division signal CP, the AC voltage of high voltage generated at the first to fifth inverter parts541to545is supplied to each of the fourth to eighth lamp groups574to578. In the T5period of the division signal CP, the AC voltage of high voltage generated at the first to fifth inverter parts541to545is supplied to each of the fifth to eighth lamp groups575to578and the first lamp groups571. In the T6period of the division signal CP, the AC voltage of high voltage generated at the first to fifth inverter parts541to545is supplied to each of the sixth to eighth lamp groups576to578and the first to second lamp groups571,572. In the T7period of the division signal CP, the AC voltage of high voltage generated at the first to fifth inverter parts541to545is supplied to each of the seventh to eighth lamp groups577to578and the first to third lamp groups571to573. In the T8period of the division signal CP, the AC voltage of high voltage generated at the first to fifth inverter parts541to545is supplied to each of the eighth lamp groups578and the first to fourth lamp groups571to574. Because of this, eight lamp groups571to578are turned on for one frame in the order shown inFIG. 14. After this, the drive from the T1period to the T8period repeats.

Only the driving method of the five inverter parts541to545and the eight lamp groups571to578are explained in the above, but the number of the inverter parts54and the lamp groups57can be changed as desired. That is, if the size of the liquid crystal display device becomes bigger, and the number of lamps to transmit light to the liquid crystal display panel (not shown) increases, the number of lamp groups57can be changed and/or the number of lamps included in the lamp group57can be changed. Accordingly, the number of the inverter part54, which generates the AC voltage of high voltage used in driving the lamps, can also be changed.

In this way, the lamp driving apparatus of the liquid crystal display device according to the embodiment of the present invention selectively supplies the AC voltage of high voltage generated at the n (n is an integer) inverters541to54nto the n (n is an integer smaller than m) lamp groups571to57namong the m (m is an integer bigger than n) lamp groups571to57mfor one frame by use of the multiplexer80, thereby driving the lamp formed at the lamp group57. Because of this, the number of inverter parts54, which generate the AC voltage of high voltage required for driving the lamp, become reduced, thereby reducing the cost of the liquid crystal display device.

As described above, the lamp driving apparatus of the liquid crystal display according to the embodiment of the present invention selectively supplies the AC voltage of high voltage generated at the n (n is an integer) inverters to the n (n is an integer smaller than m) lamp groups among the m (m is an integer bigger than n) lamp groups for one frame by use of the multiplexer, thereby driving the lamp formed at the lamp group57. Because of this, the number of inverter parts, which generate the AC voltage of high voltage used for driving the lamp, is reduced, thus the cost of the liquid crystal display device can be reduced.