HK1119013A - Drive circuit and driving method for a plurality of lamps - Google Patents

Description

Driving circuit and method for multiple lamp tubes

Technical Field

The present invention relates to a driving circuit, and more particularly, to a circuit and method for driving a lamp.

Background

Liquid Crystal Display (LCD) panels are suitable for various applications ranging from portable electronic devices to pointing devices, such as portable computers, video cameras, mobile phones, PDAs, game machines, medical instruments, car navigation systems, and industrial machinery. In LCD applications, it is often desirable to use a backlight to illuminate the panel. Typically, LCD backlights should have high brightness, long life, and good uniformity characteristics. There are currently various types of LCD backlight sources such as an electron light emitting tube (EL), a Light Emitting Diode (LED), a Cold Cathode Fluorescent Lamp (CCFL), a Flat Fluorescent Lamp (FFL), an External Electrode Fluorescent Lamp (EEFL), a Hot Cathode Fluorescent Lamp (HCFL), and a Carbon Nanotube (CNT).

CCFL backlights are commonly used for graphics and color displays and are widely used in large or medium sized LCD panels. Also, the CCFL is composed of a phosphor-coated glass cylinder having cathodes at both ends, and can be used as a light emitting source of the LCD panel. In addition, as LCD panels continue to increase in size, for example, for LCD televisions or large LCD displays, backlighting systems may operate with multiple lamps to provide sufficient illumination.

A high voltage direct current/alternating current (DC/AC) converter, referred to as an inverter, is typically required to drive the CCFL. Most CCFL DC/AC converters can be designed as an adjustable switching circuit for generating an output AC power source with a specific voltage and frequency. A typical CCFL inverter requires an AC waveform output at a frequency of about 20-80khz with an operating voltage having a Root Mean Square (RMS) value of about 400-800V. Also, with the advent of large LCD panels, multi-lamp driving is required due to the use of a plurality of CCFLs therein. For the multiple lamp case, a DC/AC converter (inverter) drives multiple CCFLs, typically connected in parallel. For example, fig. 1 illustrates a conventional driver circuit 100. The driving circuit 100 is used to drive four CCFLs 142, 144, 146 and 148, and includes a switching circuit 110 and 2 transformers 114 and 116. Transformers 114 and 116 have a primary winding and a secondary winding, respectively. The switching circuit 110 is used to convert an external DC power from a DC power source 112 to a first AC power and deliver the first AC power to the primary windings of the transformers 114 and 116. The secondary windings of transformers 114 and 116 are coupled to CCFLs 142 and 144 and CCFLs 146 and 148, respectively, for energizing CCFLs 142, 144, 146 and 148. Here, the transformers 114 and 116 are used to boost the first AC power having a relatively low level to a second AC power having a high level, thereby satisfying the need to drive the CCFLs 142, 144, 146 and 148. Capacitors 118 and 120 are also coupled to the secondary windings of transformers 114 and 116, respectively.

Fig. 2 illustrates another conventional driver circuit 200. The driving circuit 200 is used to drive a plurality of CCFLs 242, 244 and 246, and includes a switching circuit 210 and a plurality of transformers 214, 216 and 218. Transformers 214, 216 and 218 have primary and secondary windings, respectively. The switching circuit 210 is coupled to the primary windings of the transformers 214, 216 and 218. The switching circuit 210 is used to convert an external DC power from the DC power source 212 to a first AC power and deliver the first AC power to the primary windings of the transformers 214, 216 and 218. The secondary windings of the transformers 214, 216 and 218 are coupled to the CCFLs 242, 244 and 246, respectively, for energizing the CCFLs 242, 244 and 246. Capacitors 222, 224, 226 are also coupled to the secondary windings of transformers 214, 216 and 218, respectively.

These structures have a well-known problem in that the CCFL current may be in an unbalanced state due to variations in lamp voltage and load characteristics of the CCFL, and variations in resistance and temperature of the CCFL. The imbalance of the CCFL current may cause a reduction in the service life of the CCFL and non-uniformity of the brightness.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a circuit and a method for driving a plurality of backlight lamps, which have the characteristics of current balance, low cost and high efficiency and have a current monitoring function.

To solve the above technical problems, the present invention provides a circuit for driving a plurality of lamps, such as Cold Cathode Fluorescent Lamps (CCFLs). Pairs of lamps are formed by coupling pairs of lamps. Each pair of the multiple pairs of lamps is composed of two lamps which are mutually coupled in series. Pairs of lamps are coupled in parallel. The circuit includes a switching circuit, a transformer, and a plurality of balanced chokes. The switching circuit is used for converting a DC power source into a first AC power source. The transformer has a primary coil and a secondary coil. The primary winding of the transformer is coupled to the switching circuit to receive the first AC power and to energize the secondary winding to generate a second AC power from the secondary winding to energize the plurality of lamps. Each balanced choke has a primary coil and a secondary coil. The primary and secondary windings of each balanced choke are coupled to two of the pairs of lamps, respectively, to equalize the currents flowing through the two pairs of lamps.

Drawings

The features and advantages of embodiments of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:

fig. 1 is a circuit diagram showing a driving circuit for driving four CCFLs in the related art.

Fig. 2 is a circuit diagram of a driving circuit for driving a plurality of CCFLs in the related art.

Fig. 3 is a circuit diagram illustrating a driving circuit for driving four CCFLs according to one embodiment of the present invention.

Fig. 4 is a circuit diagram illustrating a driving circuit for driving six CCFLs according to one embodiment of the present invention.

Fig. 5 is a circuit diagram illustrating a driving circuit for driving a plurality of CCFLs according to one embodiment of the present invention.

Fig. 6 is a flowchart illustrating a method for driving a plurality of CCFLs, in accordance with one embodiment of the present invention.

Detailed Description

Hereinafter, a detailed description will be given of embodiments of the present invention. While the invention will be described in conjunction with the embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.

Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known schemes, procedures, components and circuits have not been described in detail so as not to obscure the present invention.

As shown in fig. 3, a driver circuit 300 according to one embodiment of the invention is illustrated. The driving circuit 300 is used to drive 4 Cold Cathode Fluorescent Lamps (CCFLs) 342, 344, 346 and 348. The driver circuit 300 includes a switching circuit 310 coupled to an external Direct Current (DC) power source, such as a battery 312. The switching circuit 310 acts as a DC/AC converter or an inverter to convert DC power from the battery 312 to a first Alternating Current (AC) power source. The first AC power is transferred to the primary winding 315 of the transformer 314, thereby exciting the secondary winding 316 of the transformer 314 to output a second AC power.

The switching circuit 310 includes a plurality of switches, such as MOSFETs or other transistor types, and may constitute various circuits, such as a Royer, full bridge, half bridge, or push-pull inverter circuit configuration.

For example, according to one embodiment of the present invention, the switching circuit 310 includes 2 pairs of MOSFETs (not shown) forming a full bridge inverter circuit. Each pair of MOSFETs includes two MOSFETs coupled in series with each other. Moreover, the two pairs of MOSFETs are coupled in parallel with each other. In this embodiment, both ends of the primary coil 315 of the transformer 314 are coupled to the two pairs of MOSFETs, respectively, so as to receive the first AC power from the switching circuit 310.

In another embodiment, switching circuit 310 forms a half-bridge inverter circuit. In this embodiment, the switching circuit 310 includes two MOSFETs coupled in series with each other. The primary winding 315 of the transformer 314 is coupled to two MOSFETs and ground at both ends, respectively, to receive the first AC power from the switching circuit 310.

Further, according to an embodiment of the present invention, the switching circuit 310 may form a Royer inverter circuit. The switching circuit 310 includes two transistors. It will be appreciated by those skilled in the art that in this embodiment, the primary winding 315 of the transformer 314 includes three input terminals, not shown in fig. 3. Wherein, two ends of the primary coil 315 are coupled to the transistor. In addition, the other end of the primary coil 315 is coupled to a DC power source 312 for delivering DC power to the middle of the primary coil 315.

In another embodiment, the switching circuit 310 forms a push-pull inverter circuit. The switching circuit 310 includes two MOSFETs. It will be appreciated by those skilled in the art that in this embodiment, the primary winding 315 of the transformer 314 includes three input terminals, not shown in fig. 3. Wherein both ends of the primary coil 315 are coupled to the MOSFET. In addition, the other end of the primary coil 315 is coupled to a DC power source 312 for delivering DC power to the middle of the primary coil 315.

In order to drive the CCFLs 342, 344, 346 and 348, a proper AC power having a high voltage and a high frequency is supplied. For example, the root mean square value of the starting voltage for igniting the CCFLs 342, 344, 346, and 348 should be greater than 1000 volts, the operating voltage will typically be between about 400 and 800 volts, and the operating frequency will typically be about 20-80 kHz.

According to an embodiment of the present invention, the first AC power outputted by the switching circuit 310 has a relatively low level. The transformer 314 serves to boost the first AC power and output a second AC power having a high level, which is used to drive the CCFLs 342, 344, 346 and 348. It will be apparent to those skilled in the art that the ratio of the voltages across secondary winding 316 to primary winding 315 and the turns ratio of secondary winding 316 to primary winding 315 are directly proportional. In other words, the second AC power having a high level is generated according to a high turn ratio of the transformer. The secondary winding 316 of the transformer 314 is coupled to the CCFLs 342, 344, 346 and 348 to provide power thereto.

As shown in fig. 3, a capacitor 318 is coupled in parallel with the secondary winding 316 of the transformer 314 for filtering noise from the CCFLs 342, 344, 346 and 348. Four capacitors 322, 324, 326 and 328, for example 15 picofarads to 39 picofarads, are coupled in series with the CCFLs 342, 344, 346 and 348, respectively. In the driver circuit 300, the current in the transition period from the start-up voltage to the operating voltage is realized or established by the capacitors 322, 324, 326 and 328. Capacitors 322, 324, 326 and 328 act as ballasts to provide impedance. The capacitance values of the capacitors 322, 324, 326 and 328 are converted to a relatively high impedance during the switching period, thereby continuously powering the CCFLs 342, 344, 346 and 348.

As shown in FIG. 3, CCFLs 342 and 346, coupled in series with each other, form a first branch 352. In addition, CCFLs 344 and 348 are both coupled to ground and are coupled in series with each other to form a second branch circuit 354. The balanced choke 360 includes a primary winding 362 coupled in series with the first branch circuit 352 and a secondary winding 364 coupled in series with the second branch circuit 354 to balance the current flowing through the first branch circuit 352 and through the second branch circuit 354. In particular, for example, in the second branch circuit 354, current flows from the secondary winding 316 of the transformer 314 to ground through the CCFL344 and the secondary winding 364 of the balanced choke 360, and from ground to the secondary winding 316 of the transformer 314 through the CCFL 348. In the first branch circuit 352, current flows from one end of the secondary winding 316 of the transformer 314 back to the other end of the secondary winding 316 of the transformer 314 through the CCFLs 342 and 346. The balanced choke 360 includes a primary winding 362 and a secondary winding 364 operable to balance the current flowing through the first branch circuit 352 and the current flowing through the second branch circuit 354.

According to an embodiment of the present invention, the primary winding 362 and the secondary winding 364 of the balanced choke 360 have the same number of turns and are wound on the same core. Thus, the current flowing through the primary winding 362 and the current flowing through the secondary winding 364 are essentially equal. Since the CCFL342 is coupled in series with the primary winding 362 of the balanced choke 360 and the CCFL344 is coupled in series with the secondary winding 364 of the balanced choke 360, the current flowing through the CCFL342 and the current flowing through the CCFL344 are essentially equal. Similarly, the current flowing through the CCFL 346 is substantially equal to the current flowing through the CCFL 348. In other words, the currents flowing through the four CCFLs 342, 344, 346 and 348 are substantially equal to each other, and the brightness of the four CCFLs 342, 344, 346 and 348 can be kept uniform.

According to an embodiment of the present invention, the driving circuit 300 includes a protection circuit 370. The protection circuit 370 is coupled to the second branch circuit 354 for generating a current feedback signal 382. The current feedback signal 382 is transmitted to a controller 380. The current feedback signal 382 corresponds to the current flowing through the secondary winding 364 of the balanced choke 360. Since the current flowing through the secondary winding 364 of the balanced choke 360 is substantially equal to the current flowing through the CCFLs 342, 344, 346 and 348, the current feedback signal 382 may serve as a current signal corresponding to the current flowing through the CCFLs 342, 344, 346 and 348.

As shown in fig. 3, the protection circuit 370 includes a first diode 372, a second diode 374, a resistor 376 and a capacitor 378 according to an embodiment of the present invention. The two diodes 372 and 374 are coupled in parallel and in reverse with each other and serve to ground the secondary 364 of the balanced choke 360. Capacitor 378 and resistor 376 are coupled in parallel with each other and are used to ground first diode 372. The CCFL348 is also grounded. Therefore, when current flows from the CCFL344 in the forward direction to the protection circuit 370, current will flow through the first diode 372, the capacitor 378 and the resistor 376 to ground. When current flows in the negative direction from the CCFL348 to ground, current will flow through the second diode 374 to the CCFL 344. Resistor 376 generates a voltage signal representative of the current flowing through secondary coil 364, thereby forming current feedback signal 382.

A controller 380 coupled to the switching circuit 310 is used to control the output power or voltage of the switching circuit 310 to a predetermined value. The controller 380 is used to receive the current feedback signal 382 generated by the protection circuit 370 to control the switching circuit 310, and then the current flowing through the CCFL348 can be controlled to a predetermined value.

According to one embodiment of the present invention, a Pulse Width Modulation (PWM) signal is used to control the current flowing through the CCFLs 342, 344, 346, and 348. The controller 380 generates a set of PWM signals to control switches in the switching circuit 310, which is not shown in the figure. The duty cycle of the PWM signal can regulate the current flowing through the CCFLs 342, 344, 346 and 348, thereby adjusting the brightness of the CCFLs 342, 344, 346 and 348.

Alternatively, according to another embodiment of the present invention, the DC voltage from the power supply 312 may be regulated to regulate the current flowing through the CCFLs 342, 344, 346, and 348.

In the driving circuit 300, only one transformer and one balance choke are used, so that the current balance among the four CCFLs can be realized. Furthermore, the number of transformers, MOSFETs and other R/C components used can be reduced compared to the prior art topologies shown in fig. 1 and 2. The cost and size of the printed circuit board (PC board) can be reduced.

Fig. 4 shows a driving circuit 400 according to another embodiment of the invention. In fig. 4, the driving circuit 400 is used to drive six CCFLs 442, 444, 446, 448, 450 and 452. The driver circuit 400 includes a switching circuit 410 coupled to a DC power source, such as a battery 412. The driving circuit 400 in fig. 4 is similar to the driving circuit 300 in fig. 3. For simplicity, elements in the driving circuit 400 labeled the same as those in the driving circuit 300 have similar functions, and will not be described in detail here.

The switching circuit 410 includes 2 transformers 414 and 416. The switching circuit 410 is coupled to the primary windings 492 and 496 of the transformers 414 and 416 to deliver AC power to the transformers 414 and 416. The secondary coils 494 and 498 of transformers 414 and 416 are coupled to the six CCFLs 442, 444, 446, 448, 450 and 452 to energize the CCFLs 442, 444, 446, 448, 450 and 452. CCFLs 442 and 452 are coupled in series with each other and the current flowing through CCFLs 442 and 452 is substantially equal. The CCFLs 444 and 450 are coupled in series with each other and the current flowing through the CCFLs 444 and 450 is substantially equal. The CCFLs 446 and 448 are grounded, respectively, and thus the currents flowing through the CCFLs 446 and 448 are substantially equal. The balanced choke 460 includes a primary coil 482 and a secondary coil 484 that are coupled in series with the CCFLs 442 and 452 and the CCFLs 444 and 450, respectively. Thus, the current flowing through the CCFL442 is substantially equal to the current flowing through the CCFL 444. Similarly, the balanced choke 462 includes a primary coil 486 and a secondary coil 488 coupled in series with the CCFLs 444 and 450 and the CCFLs 446 and 448, respectively. The current flowing through the CCFL444 is substantially equal to the current flowing through the CCFL 446. Therefore, the current flowing through the six CCFLs 442, 444, 446, 448, 450 and 452 is substantially equal, and the brightness of the six CCFLs 442, 444, 446, 448, 450 and 452 will remain uniform.

In the driver circuit 400, the number of turns of the primary windings 492 and 496 of the two transformers 414 and 416 is the same, and the number of turns of their secondary windings 494 and 498 is also the same. The primary windings 492 and 496 of the transformers 414 and 416 are coupled in parallel with each other. The switching circuit 410 is coupled to both primary windings 492 and 496 of the transformers 414 and 416. Accordingly, the transformers 414 and 416 receive AC power having the same energy from the switching circuit 410. In addition, the secondary windings 494 and 498 of the transformers 414 and 416 are opposite to each other. Transformers 414 and 416 each provide half the energy of the total energy required by the six CCFLs 442, 444, 446, 448, 450 and 452. Thus, the maximum current and voltage values of the transformers 414 and 416 may be reduced, while the temperature of the transformers 414 and 416 may be reduced.

Fig. 5 shows a circuit 500 for driving multiple CCFLs, in accordance with one embodiment of the invention. In fig. 5, a driving circuit 500 is used to drive 2N CCFLs 542, 544, 546, 548, 550 and 552, where N is an integer. The driver circuit 500 includes a switching circuit 510 coupled to a DC power source, such as a battery 512. The driving circuit 500 shown in fig. 5 is similar to the driving circuit 300 shown in fig. 3. For simplicity, elements of the driving circuit 500 that are labeled the same as the driving circuit 300 have similar functions and will not be described in detail here.

In one embodiment, the CCFLs shown in FIG. 5 include a first CCFL542, a second CCFL 544, a (2N-1) th CCFL550 and a 2N CCFL 552. N pairs of CCFLs 541, 543,.. and 545 are formed by coupling 2N CCFLs 542, 544.., 550 and 552 in pairs. Each of the N pairs of CCFLs 541, 543,. and 545 has 2 CCFLs coupled in series with each other. In other words, two lamps adjacent in sequence among the 2N CCFLs 542, 544, including the first CCFL542 and the second CCFL 544, are coupled in series with each other. Thus, N CCFL pairs 541, 543,.. and 545 of CCFLs 542, 544.., 550 and 552 are formed. For example, a first CCFL542 and a second CCFL 544 are coupled in series with each other to form a first CCFL pair 541, a third CCFL546 and a fourth CCFL548 are coupled in series with each other to form a second CCFL pair 543, and a (2N-1) th CCFL550 and a 2N CCFL552 are coupled in series with each other to form a ground N CCFL pair 545. The N CCFL pairs 541, 543,. and 545 are coupled in parallel with each other. The second AC power generated by the secondary winding 516 of the transformer 514 powers N CCFL pairs 541, 543,. and 545 in parallel. N-1 balanced chokes 560, 562,. . . And 564 are used to balance the current flowing through the N CCFL pairs 541, 543. For example, the primary coil 582 of the first balanced choke 560 is coupled in series with a first pair 541 of CCFLs comprising 542 and 544, and the secondary coil 584 of the first balanced choke 560 is coupled in series with a second pair 543 of CCFLs 546 and 548. The currents flowing through the first and second CCFL pairs 541, 543 are substantially equal to each other. In other words, N-1 balanced chokes 560, 562,. . . Each of the balance chokes 564 is used to balance the current flowing through 2 of the N CCFL pairs 541, 543. The primary coil of the kth balanced choke is coupled in series with the (2 x K-1) th and (2 x K) th CCFLs, and the secondary coil of the kth balanced choke is coupled in series with the (2 x K +2) th and (2 x K +1) th CCFLs. Thus, the currents flowing through the 2N CCFLs 542, 544, 550 and 552 are substantially equal to each other. Thus, the brightness of the 2N CCFLs 542, 544, 550 and 552 will remain consistent.

In addition, the circuit for driving the CCFL according to the exemplary embodiment of the present invention may be equally applied to other lamps, such as External Electrode Fluorescent Lamps (EEFLs).

Fig. 6 is a flow chart 600 of a method for driving a plurality of Cold Cathode Fluorescent Lamps (CCFLs) in an electronic device, such as a Liquid Crystal Display (LCD) panel, in accordance with one embodiment of the present invention. In step 602, an external DC power source is converted to a first AC power source by means of a switching circuit, such as a Royer, full bridge, half bridge, or push-pull inverter circuit configuration.

In step 604, the first AC power source is boosted to a second AC power source. The voltage of the second AC power is higher than that of the first AC power, and is suitable for lighting the CCFL. In one embodiment, the rms voltage of the second AC power source is greater than 1,000 volts during the lighting of the CCFL, and is about 400 to 800 volts after the CCFL is lit. A transformer may be used to step up the first AC power source to the second AC power source.

In step 606, a second AC power is provided to the plurality of CCFLs, including from the first CCFL to the 2N CCFL.

In step 608, the CCFL pairs are coupled to form N pairs of CCFLs from the first pair to the nth pair. Each pair of CCFLs has two CCFLs coupled in series with each other. In other words, the (2 × K-1) th CCFL and the (2 × K) th CCFL are coupled in series with each other to form a K-th pair of CCFLs, where K is 1, 2. Thereafter, a second AC power is supplied to the N pairs of CCFLs connected in parallel.

In step 610, the current flowing through the coupled pair of CCFLs is balanced. The plurality of balanced chokes includes first to N-1 th balanced chokes each having a primary coil and a secondary coil for balancing currents flowing through each pair of CCFLs. In one embodiment, the primary and secondary coils of each balanced choke have the same number of turns, so that the currents flowing through the primary and secondary coils are essentially equal. The primary coil of the kth balanced choke is coupled in series with the kth pair of CCFLs and the secondary coil of the kth balanced choke is coupled in series with the K +1 th pair of CCFLs, so that the currents flowing through the kth and K +1 th pairs of CCFLs are essentially equal, where K is 1, 2. Thus, the currents flowing through all the CCFLs are essentially equal to each other.

In step 612, a current feedback signal is generated by sensing the current flowing through a CCFL. Since the currents flowing through all of the CCFLs are essentially equal, a current feedback signal indicative of the current flowing through a certain CCFL may be used to indicate the current flowing through all of the CCFLs. According to one embodiment of the present invention, a protection circuit including a resistor and two diodes may be used to sense current and generate a current feedback signal.

In step 614, the current flowing through the CCFL is controlled to a predetermined value by controlling the first AC power source in response to a current feedback signal. A controller is used to receive and respond to the current feedback signal to control the first AC power source at a predetermined value so that the current flowing through the CCFL can be controlled at a predetermined value. Thus, the brightness of the CCFL can be controlled, dimmed or stabilized at a predetermined level.

Although the foregoing description and drawings represent embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the present principles as defined in the accompanying claims. It will be appreciated by those skilled in the art that the present invention may be varied in form, structure, arrangement, proportions, materials, elements, components and otherwise, used in the practice of the invention, depending upon specific environments and operating requirements, without departing from the principles of the present invention. Accordingly, the presently disclosed embodiments are meant to be illustrative only and not limiting, the scope of the invention being indicated by the appended claims and their legal equivalents, rather than by the foregoing description.

Claims (21)

1. A circuit for driving a plurality of lamps including first through 2 nth lamps, comprising:

switching circuitry for converting an external DC power source to a first AC power source;

a first transformer having a primary winding and a secondary winding, wherein the primary winding is coupled to the switching circuit for receiving the first AC power and energizing the secondary winding such that a second AC power is generated from the secondary winding for powering the plurality of lamps; and

a plurality of balanced chokes including first through N-1 th balanced chokes and each having a primary coil and a secondary coil, wherein the plurality of lamps are coupled in pairs to form a plurality of pairs of lamps, each pair of lamps in the plurality of pairs of lamps including two lamps coupled in series with each other, and the primary coil and the secondary coil of each balanced choke in the plurality of balanced chokes are coupled in series with two pairs of lamps in the plurality of pairs of lamps, respectively, to balance currents flowing through the plurality of lamps.

2. The circuit of claim 1, comprising:

the protection circuit is coupled to one of the lamps and used for detecting the current flowing through the lamp.

3. The circuit of claim 2, comprising:

a controller for adjusting said current flowing through said one of said plurality of lamps to a predetermined level by controlling said switching circuit in response to said detected current flowing through said one of said plurality of lamps.

4. The circuit of claim 1, wherein the switching circuit is a full bridge circuit.

5. The circuit of claim 1, wherein the switching circuit is a half bridge circuit.

6. The circuit of claim 1, wherein the switching circuit is a push-pull circuit.

7. The circuit of claim 1, wherein the switching circuit is a Royer circuit.

8. The circuit of claim 1, including a second transformer having a primary winding and a secondary winding, wherein said primary winding of said second transformer is coupled in parallel with said primary winding of said first transformer and said secondary winding of said second transformer is coupled in series with said secondary winding of said first transformer, said second transformer receiving said first AC power in common with said first transformer to power said plurality of lamps.

9. The circuit of claim 1, wherein a primary coil of a kth balanced choke of the plurality of balanced chokes is coupled in series with a (2K-1) th lamp and a 2 x K-th lamp, and the secondary coil of the kth balanced choke is coupled in series with a (2K +2) th lamp and a (2K +1) th lamp, wherein K is 1, 2, … N-1.

10. The circuit of claim 9 wherein said primary and said secondary of each balanced choke have the same number of turns, such that said current flowing through each of said lamps is equal.

11. The circuit of claim 2, wherein the protection circuit comprises:

a first diode for grounding said one of said plurality of lamps;

a second diode coupled in anti-parallel with the first diode; and

a resistor coupled in series with the first diode, a voltage across the resistor being representative of the current flowing through the one of the plurality of lamps.

12. The circuit of claim 1, wherein the plurality of lamps comprises a plurality of Cold Cathode Fluorescent Lamps (CCFLs).

13. A method for driving a plurality of lamps including first through 2 nth lamps, comprising:

converting an external DC power supply into a first AC power supply;

step up the first AC power source to a second AC power source;

providing the second alternating current power supply to the plurality of lamps;

pairing the plurality of lamps to form a plurality of pairs of lamps, and two lamps of each pair of lamps in the plurality of pairs of lamps being coupled in series with each other; and

the currents flowing through the pairs of lamps are balanced.

14. The method of claim 13, wherein balancing the currents flowing through the plurality of pairs of lamps comprises:

coupling one of the plurality of pairs of lamps with a primary coil of a balanced choke; and

coupling another of the plurality of pairs of lamps with a secondary of the balanced choke to balance the current flowing through the plurality of pairs of lamps.

15. The method of claim 14, wherein the primary coil and the secondary coil of the balanced choke have the same number of turns.

16. The method of claim 13, comprising:

the current flowing through one of the lamps is detected to generate a current feedback signal.

17. The method of claim 16, further comprising:

controlling the current flowing through the one of the plurality of lamps in response to the current feedback signal.

18. The method of claim 13, wherein the multiple lamps are multiple cold cathode fluorescent lamps.

19. A display system, comprising:

a Liquid Crystal Display (LCD) panel;

a plurality of lamps for illuminating the LCD panel;

a switching circuit for converting an external DC power supply into a first AC power supply;

a transformer having a primary winding and a secondary winding, wherein the primary winding is coupled to the switching circuit for receiving the first ac power and supplying power to the secondary winding, such that a second ac power is generated by the secondary winding for supplying power to the plurality of lamps; and

a plurality of balanced chokes including first through N-1 th balanced chokes, each balanced choke having a primary coil and a secondary coil, wherein the plurality of lamps are paired to form a plurality of pairs of lamps, each pair of the plurality of pairs of lamps including two lamps coupled in series with each other, and the primary coil and the secondary coil of each balanced choke of the plurality of balanced chokes are coupled in series with two pairs of the plurality of pairs of lamps, respectively, to balance currents flowing through the plurality of lamps.

20. The display system of claim 19, comprising:

and the protection circuit is coupled with one lamp tube in the multiple lamp tubes and is used for detecting the current flowing through the lamp tube in the multiple lamp tubes.

21. The display system of claim 20, comprising:

a controller responsive to the detected current flowing through the one of the plurality of lamps to control the switching circuit to adjust the current flowing through the one of the plurality of lamps to a predetermined value.