Driver system and method with cyclic configuration for multiple cold-cathode fluorescent lamps and/or external-electrode fluorescent lamps

System and method for driving a plurality of cold-cathode fluorescent lamps. The system includes a subsystem configured to receive at least a DC voltage and generate a first AC voltage in response to at least the DC voltage, a power converter configured to receive the first AC voltage and convert the first AC voltage to at least a second AC voltage, and a plurality of current balancing devices. Each of the plurality of current balancing devices is configured to receive two currents and balance the two currents. The power converter and the plurality of current balancing devices are capable of being directly or indirectly coupled to a plurality of cold-cathode fluorescent lamps.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 200610027052.3, filed May 26, 2006, titled “Driver System and Method with Cyclic Configuration for Multiple Cod-Cathode Fluorescent Lamps and/or External-Electrode Fluorescent Lamps,” by inventors Lieyi Fang, Changshan Zhang, Zhiliang Chen, and Shifeng Zhao, commonly assigned, incorporated by reference herein for all purposes.

Not Applicable

Not Applicable

BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. More particularly, the invention provides a system and method with cyclic configuration. Merely by way of example, the invention has been applied to driving multiple cold-cathode fluorescent lamps, and/or external-electrode fluorescent lamps. But it would be recognized that the invention has a much broader range of applicability.

The cold-cathode fluorescent lamp (CCFL) and external-electrode fluorescent lamp (EEFL) have been widely used to provide backlight for a liquid crystal display (LCD) module. The CCFL and EEFL often each require a high alternate current (AC) voltage such as 2 kV for ignition and normal operation. Such a high AC voltage can be provided by a CCFL driver system or an EEFL driver system. The CCFL driver system and the EEFL driver system each receive a low direct current (DC) voltage and convert the low DC voltage to the high AC voltage.

FIG. 1is a simplified conventional driver system for CCFL and/or EEFL. The driver system100includes a control subsystem110and an AC power supply subsystem120. The control subsystem110receives a power supply voltage VDDAand certain control signals. The control signals include an enabling (ENA) signal and a dimming (DIM) signal. In response, the control subsystem110outputs gate drive signals to the AC power supply subsystem120. The AC power supply subsystem120includes one or more MOSFET transistors and one or more power transformers, and receives a low DC voltage VIN. The MOSFET transistors convert the low DC voltage VINto a low AC voltage in response to the gate drive signals. The low AC voltage is boosted to a high AC voltage VOUTby the power transformers, and the high AC voltage VOUTis sent to drive a system190. The system190includes one or more CCFLs and/or one or more EEFLs. The system190provides a current and voltage feedback to the control subsystem110.

As shown inFIG. 1, the system190includes one or more CCFLs and/or one or more EEFLs. These lamps can be used to provide backlight for an LCD panel. For a large LCD panel, a single-lamp backlight module often cannot provide sufficient backlighting. Consequently, a multi-lamp backlight module often is needed. For example, an LCD panel may require 20 to 40 lamps in order to provide high-intensity illumination for displaying full motion videos. From these lamps, the individual currents need to be balanced in order to maintain the display uniformity. For example, the current difference between different lamps should be maintained within a reasonable tolerance.

To balance lamp currents, some conventional techniques have been developed. For example, the conventional techniques use impedance matching schemes to build a balance controller for equalizing lamp currents. In another example, the conventional techniques use one or more common-mode chokes, which can balance the lamp currents. But these conventional systems can have various weaknesses in terms of flexibility, stability, and/or simplicity.

Hence it is highly desirable to improve techniques for multi-lamp driver system for CCFLs and/or EEFLs.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. More particularly, the invention provides a system and method with cyclic configuration. Merely by way of example, the invention has been applied to driving multiple cold-cathode fluorescent lamps, and/or external-electrode fluorescent lamps. But it would be recognized that the invention has a much broader range of applicability.

According to one embodiment of the present invention, a system for driving a plurality of cold-cathode fluorescent lamps includes a subsystem configured to receive at least a DC voltage and generate a first AC voltage in response to at least the DC voltage, a power converter configured to receive the first AC voltage and convert the first AC voltage to at least a second AC voltage, and a plurality of current balancing devices. Each of the plurality of current balancing devices is configured to receive two currents and balance the two currents. The power converter and the plurality of current balancing devices are capable of being directly or indirectly coupled to a plurality of cold-cathode fluorescent lamps. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps. The first lamp and the second lamp are associated with a first current and a second current respectively. Additionally, a first current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current and the first current and to balance the lamp current and the first current, and a second current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current and the second current and to balance the lamp current and the first current.

According to another embodiment of the present invention, a system for driving a plurality of cold-cathode fluorescent lamps includes a subsystem configured to receive at least a DC voltage and generate a first AC voltage in response to at least the DC voltage, a power converter configured to receive the first AC voltage and convert the first AC voltage to at least a second AC voltage, and a plurality of current balancing devices. Each of the plurality of current balancing devices is configured to receive two currents and balance the two currents. The power converter and the plurality of current balancing devices are capable of being directly or indirectly coupled to a first plurality of cold-cathode fluorescent lamps. The first plurality of cold-cathode fluorescent lamps includes a second plurality of cold-cathode fluorescent lamps and a third lamp, and the third cold-cathode fluorescent lamp is associated with a first current. For each of the second plurality of cold-cathode fluorescent lamps, each of the second plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the second plurality of cold-cathode fluorescent lamps includes at least a fourth lamp. The fourth lamp is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a second current. Additionally, a first current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current and the second current and to balance the lamp current and the second current. Moreover, if the second plurality of cold-cathode fluorescent lamps further includes a fifth lamp which is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a third current, a second current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current, and the first current or the third current, and is further configured to balance the lamp current, and first current or the third current.

According to yet another embodiment of the present invention, a system for driving a plurality of cold-cathode fluorescent lamps includes a subsystem configured to receive at least a DC voltage and generate a first AC voltage in response to at least the DC voltage, a power converter configured to receive the first AC voltage and convert the first AC voltage to at least a second AC voltage, and a plurality of current balancing devices. Each of the plurality of current balancing devices is configured to receive two currents and balance the two currents. The power converter and the plurality of current balancing devices are capable of being directly or indirectly coupled to a plurality of cold-cathode fluorescent lamps. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a first lamp current and a second lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps. The first lamp and the second lamp are associated with a third lamp current and a fourth lamp current respectively. Additionally, a first current balancing device selected from the plurality of current balancing devices is configured to receive the first lamp current and the third lamp current and to balance the first lamp current and the third lamp current, and a second current balancing device selected from the plurality of current balancing devices is configured to receive the second lamp current and the fourth lamp current and to balance the second lamp current and the fourth lamp current.

According to yet another embodiment, a method for driving a plurality of cold-cathode fluorescent lamps includes receiving at least a DC voltage, generating a first AC voltage in response to at least the DC voltage, receiving the first AC voltage, converting the first AC voltage to at least a second AC voltage, and driving a plurality of cold-cathode fluorescent lamps with at least the second AC voltage. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps, and the first lamp and the second lamp are associated with a first current and a second current respectively. Additionally, for the each of the plurality of cold-cathode fluorescent lamps, the method includes receiving the lamp current and the first current, balancing the lamp current and the first current, receiving the lamp current and the second current, and balancing the lamp current and the first current.

According to yet another embodiment, a method for driving a plurality of cold-cathode fluorescent lamps includes receiving at least a DC voltage, generating a first AC voltage in response to at least the DC voltage, receiving the first AC voltage, converting the first AC voltage to at least a second AC voltage, and driving a first plurality of cold-cathode fluorescent lamps with at least the second AC voltage. The first plurality of cold-cathode fluorescent lamps includes a second plurality of cold-cathode fluorescent lamps and a third lamp, and the third cold-cathode fluorescent lamp is associated with a first current. For each of the second plurality of cold-cathode fluorescent lamps, each of the second plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the second plurality of cold-cathode fluorescent lamps includes at least a fourth lamp, which is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a second current. Additionally, for the each of the second plurality of cold-cathode fluorescent lamps, the method includes receiving the lamp current and the second current, and balancing the lamp current and the second current. Moreover, if the second plurality of cold-cathode fluorescent lamps further includes a fifth lamp, which is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a third current, the method includes receiving the lamp current, and the first current or the third current, and balancing the lamp current, and first current or the third current.

According to yet another embodiment, a method for driving a plurality of cold-cathode fluorescent lamps includes receiving at least a DC voltage, generating a first AC voltage in response to at least the DC voltage, receiving the first AC voltage, converting the first AC voltage to at least a second AC voltage, and driving a plurality of cold-cathode fluorescent lamps with at least the second AC voltage. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a first lamp current and a second lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps, and the first lamp and the second lamp are associated with a third lamp current and a fourth lamp current respectively. Additionally, for the each of the plurality of cold-cathode fluorescent lamps, the method includes receiving the first lamp current and the third lamp current, balancing the first lamp current and the third lamp current, receiving the second lamp current and the fourth lamp current, and balancing the second lamp current and the fourth lamp current.

Many benefits are achieved by way of the present invention over conventional techniques. For example, some embodiments of the present invention provide a driver system that can balance currents between or among any number of lamps. Certain embodiments of the present invention provide a configuration in which only one or two inductive windings are in series with each lamp between the secondary winding of the transformer and the ground voltage. For example, the one or two inductive windings belong to one or two current balance chokes respectively. In another example, the currents flowing through at least majority of the lamps go through same types of circuit components. Some embodiments of the present invention provide great flexibility to the design and manufacturing of multi-lamp driver system. Certain embodiments of the present invention can improve stability and reliability of a multi-lamp driver system. Some embodiments of the present invention can simplify processes and lower costs for making a multi-lamp driver system. Certain embodiments of the present invention can balance both the currents flowing into some lamps and the currents flowing out of certain lamps. Some embodiments of the present invention can improve current balancing of a multi-lamp driver system by eliminating or reducing adverse effects by stray conductance or parasitic capacitance of the lamps. Certain embodiments of the present invention can provide current balancing to lamps driven by different transformers using cyclic current balance schemes. Some embodiments of the present invention can improve brightness uniformity on an LCD screen lit by a plurality of lamps that are driven by one or more transformers. Depending upon the embodiment, one or more of these benefits may be achieved. These and other benefits will be described in more detail throughout the present specification and more particularly below.

Various additional objects, features and advantages of the present invention can be more fully appreciated with reference to the detailed description and the accompanying drawings that follow.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. More particularly, the invention provides a system and method with cyclic configuration. Merely by way of example, the invention has been applied to driving multiple cold-cathode fluorescent lamps, and/or external-electrode fluorescent lamps. But it would be recognized that the invention has a much broader range of applicability.

For multiple cold-cathode fluorescent lamps and/or external-electrode fluorescent lamps, current balancing often is needed in order to provide uniform brightness over a LCD panel. But the current balancing can be difficult to achieve. For example, the negative operating impedance and positive current-temperature characteristics of a lamp can accelerate current imbalance and eventually drive the multi-lamp backlight module into a runaway situation. The multi-lamp backlight module includes a plurality of lamps parallel to the same driving source. In another example, unmatched parasitic parameters of the lamps, especially the parasitic capacitance, can exacerbate the current imbalance. In yet another example, cross-coupling between lamps may also contribute to the current imbalance.

As discussed above, there are conventional techniques for balancing lamp currents, but these conventional techniques have various weaknesses. For example, some conventional techniques can work for only two lamps driven by the same power transformer. In another example, certain conventional technique use a pyramid topology for stacking common-mode chokes as the number of lamps increases. The pyramid structure can make the multi-lamp driver system unstable and can complicate the layout of printed circuit board (PCB).

In yet another example, certain conventional techniques use an increasing number of inductors as the number of lamps increases. These inductors are parts of the balance chokes, and are in series with each other. To achieve current balance, the inductance of each balance choke should equal to its mutual inductance because the voltage across the series of the inductors needs to equal zero. These constraints on the balance chokes may limit applications of the corresponding conventional techniques.

FIG. 2is a simplified driver system according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The driver system200includes a power and control subsystem210, a power converter220, the plurality of capacitors230, one or more current balance chokes240, one or more current balance chokes250, a current sensing feedback component260, and a voltage supply270. Although the above has been shown using a selected group of components for the system200, there can be many alternatives, modifications, and variations. For example, some of the components may be expanded and/or combined. Other components may be inserted to those noted above. Depending upon the embodiment, the arrangement of components may be interchanged with others replaced. For example, the system200is used to regulate a plurality of cold-cathode fluorescent lamps and/or external-electrode fluorescent lamps, such as a plurality of lamps290. Further details of these components are found throughout the present specification and more particularly below.

The power and control subsystem210receives a voltage272from the voltage supply270. For example, the voltage272is a DC voltage. In another example, the voltage272is equal to 5 volts. In response, the power and control subsystem210generates and provides an AC voltage212to the power converter220.

According to an embodiment, the power and control subsystem210also receives certain control signals. For example, the control signals include an enabling (ENA) signal and a dimming (DIM) signal. In response, the power and control subsystem210generates one or more gate drive signals. Additionally, the power and control subsystem210includes one or more MOSFET transistors. These MOSFET transistors convert the voltage272to the AC voltage212in response to the one or more gate drive signals. According to another embodiment, the voltage supply270can use various types of configurations, such as Royer, push-pull, half-bridge, and/or full bridge.

The power converter220receives the AC voltage212and outputs an AC voltage222to the plurality of capacitors230. According to one embodiment, the power converter220is a transformer. For example, the transformer includes a primary winding and a secondary winding. The primary winding receives the AC voltage212from the power and control subsystem210, and the secondary winding outputs the AC voltage222to the one or more capacitors230. For example, the secondary winding of the transformer has a much larger number of turns than the primary winding. According to another embodiment, the peak-to-peak amplitude of the AC voltage222is larger than the peak-to-peak amplitude of the AC voltage212.

The plurality of capacitors230includes capacitors C230, 2×1−1, C230, 2×1, . . . , C230, 2×m−1, C230, 2×m, . . . , C230, 2×n−1, C230, 2×n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. In one embodiment, each capacitor includes two capacitor plates. One of these two capacitor plates receives the AC voltage222, and the other of these two capacitor plates is coupled to the one or more current balance chokes240.

The one or more current balance chokes240include current balance chokes B240, 1, B240, 2, . . . , B240, m, . . . , B240, n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. For example, each current balance choke is a common-mode choke. In another example, each current balance choke is a balun choke. In yet another example, each current balance choke includes a magnetic core and two windings. Each of these two windings are wound on the magnetic core. According to an embodiment, one of these two windings is coupled to a capacitor plate of a capacitor, and the other of these two windings is coupled to a capacitor plate of another capacitor. For example, the current balance choke B240, mis coupled to capacitors C230, 2×m−1and C230, 2×m.

The one or more current balance chokes250include current balance chokes B250, 1, B250, 2, . . . , B250, m, . . . , B250, n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. For example, each current balance choke is a common-mode choke. In another example, each current balance choke is a balun choke. In yet another example, each current balance choke includes a magnetic core and two windings. Each of these two windings are wound on the magnetic core. According to an embodiment, one winding for the current balance choke B250, 1is coupled to the current sensing feedback component260, and the other winding for the current balance choke B250, 1is coupled to a predetermined voltage level, such as the ground voltage. According to another embodiment, both windings for the current balance choke B250, mother than B250, 1are coupled to a predetermined voltage level, such as the ground voltage.

The current sensing feedback component260provides a current sensing signal262to the power and control subsystem210. For example, the power and control subsystem210uses the current sensing signal262to regulate the current flowing into and/or out of each of the plurality of lamps290. In another example, the power and control subsystem210includes a PWM controller whose output pulse width is adjusted in accordance with the current sensing signal262.

As discussed above, the system200is used to regulate the plurality of lamps290according to an embodiment of the present invention. For example, the plurality of lamps290includes one or more cold-cathode fluorescent lamps, and/or one or more external-electrode fluorescent lamps. In another example, the plurality of lamps290includes lamps L290, 2×1−1, L290, 2×1, . . . , L290, 2×m−1, L290, 2×m, . . . , L290, 2×n−1, L290, 2×n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n.

In one embodiment, each lamp includes two terminals. For example, one of the two terminals, e.g., a high-voltage terminal, is coupled to one winding of one of the one or more current balance chokes240, and the other of the two terminals, e.g., a low-voltage terminal, is coupled to one winding of one of the one or more current balance chokes250. In one embodiment, one winding of the current balance choke B240, mis coupled to one terminal of Lamp L290, 2×m−1, and the other winding of the current balance choke B240, mis coupled to one terminal of Lamp L290, 2×m. In another embodiment, if m is larger than 1, one winding of the current balance choke B250, mis coupled to one terminal of Lamp L290, 2×(m−1), and the other winding of the current balance choke B250, mis coupled to one terminal of Lamp L290, 2×m−1. In yet another embodiment, one winding of the current balance choke B250, 1is coupled to one terminal of Lamp L290, 2×n, and the other winding of the current balance choke B250, 1is coupled to one terminal of Lamp L290, 2×1−1.

In another embodiment, the connections between the plurality of lamps290and the current balance chokes240and250are arranged in a cyclic configuration. For example, the high-voltage terminal of Lamp L290, 2×m−1and the high-voltage terminal for Lamp L290, 2×mare connected to the same current balance choke B240, m. The current balance choke B240, mcan make the currents flowing into the high voltage terminals of the Lamps L290, 2×m−1and L290, 2×mto be the same. In another example, if m is larger than 1, the low-voltage terminal of Lamp L290, 2×(m−1)and the low-voltage terminal of Lamp L290, 2×m−1are connected to the same current balance choke B250, m. The current balance choke B250, mcan make the currents flowing out of the low voltage terminals of the Lamps L290, 2×(m−1)and L290, 2×m−1to be the same. In yet another example, the low-voltage terminal of Lamp L290, 2×n, and the low-voltage terminal of Lamp L290, 2×1−1are coupled to the same current balance choke B250, 1. The current balance choke B250, 1can make the currents flowing out of the low voltage terminals of the Lamps L290, 2×nand L290, 2×1−1to be the same. In yet another embodiment, the system200can make currents flowing through the plurality of lamps290the same if a current flowing into a high-terminal of a lamp is substantially the same as another current flowing out of a low-voltage terminal of the same lamp.

As discussed above and further emphasized here,FIG. 2is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. In one embodiment, the power and control subsystem210receives a voltage sensing signal, in addition to or instead of the current sensing signal262. In another embodiment, the current sensing signal262represents the current from any single lamp selected from the plurality of lamps290. In yet another embodiment, the current sensing signal262represents the total current of some or all of the plurality of lamps290, and the total current can be regulated by the power and control subsystem210.

According to another embodiment, the system200is used to regulate a plurality of lamps290including an odd number of lamps. For example, the plurality of lamps290includes lamps L290, 2×1−1, L290, 2×1, . . . , L290, 2×m−1, L290, 2×m, . . . , and L290, 2×n−1. Additionally, the plurality of capacitors230includes capacitors C230, 2×1−1, C230, 2×1, . . . , C230, 2×m−1, C230, 2×m, C230, 2×n−1. Moreover, the one or more current balance chokes240include current balance chokes B240, 1, B240, 2, . . . , B240, m, . . . , B240, n−1. Also, the one or more current balance chokes250include current balance chokes B250, 1, B250, 2, . . . , B250, m, . . . , B250, n. n is an integer larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. In one embodiment, the high-voltage terminal of Lamp L290, 2×n−1is coupled to a capacitor plate of the capacitor C230, 2×n−1. In another embodiment, the low-voltage terminal of Lamp L290, 2×n−1, and the low-voltage terminal of Lamp L290, 2×1−1are coupled to the same current balance choke B250, 1. The current balance choke B250, 1can make the currents flowing out of the low voltage terminals of the Lamps L290, 2×n−1and L290, 2×1−1to be the same. In yet another embodiment, the current balance choke B250, 1and the low-voltage terminal of Lamp L290, 2×(n−1)are coupled to the current balance choke B250, n. The current balance choke B250, 1can make the currents flowing out of the low voltage terminals of the Lamps L290, 2×n−1and L290, 2×1−1to be the same. For example, the current from Lamp L290, 2×n−1flows through one winding of the current balance choke B250, 1and then flow through one winding of the current balance choke B250, n. Accordingly, the current balance choke B250, ncan make the currents flowing out of the low voltage terminals of the Lamps L290, 2×(n−1)and L290, 2×n−1to be the same.

FIG. 3is a simplified driver system according to another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The driver system300includes a power and control subsystem310, a power converter320, the plurality of capacitors330, one or more current balance chokes340, one or more current balance chokes350, a current sensing feedback component360, and a voltage supply370. Although the above has been shown using a selected group of components for the system300, there can be many alternatives, modifications, and variations. For example, some of the components may be expanded and/or combined. Other components may be inserted to those noted above. Depending upon the embodiment, the arrangement of components may be interchanged with others replaced. For example, the system300is used to regulate a plurality of cold-cathode fluorescent lamps and/or external-electrode fluorescent lamps, such as a plurality of lamps390. Further details of these components are found throughout the present specification and more particularly below.

The power and control subsystem310receives a voltage372from the voltage supply370. For example, the voltage372is a DC voltage. In another example, the voltage372is equal to 5 volts. In response, the power and control subsystem310generates and provides an AC voltage312to the power converter320.

According to an embodiment, the power and control subsystem310also receives certain control signals. For example, the control signals include an enabling (ENA) signal and a dimming (DIM) signal. In response, the power and control subsystem310generates one or more gate drive signals. Additionally, the power and control subsystem310includes one or more MOSFET transistors. These MOSFET transistors convert the voltage372to the AC voltage312in response to the one or more gate drive signals. According to another embodiment, the voltage supply370can use various types of configurations, such as Royer, push-pull, half-bridge, and/or full bridge.

The power converter320receives the AC voltage312and outputs an AC voltage322to the plurality of capacitors330. According to one embodiment, the power converter320is a transformer. For example, the transformer includes a primary winding and a secondary winding. The primary winding receives the AC voltage312from the power and control subsystem310, and the secondary winding outputs the AC voltage322to the one or more capacitors330. For example, the secondary winding of the transformer has a much larger number of turns than the primary winding. According to another embodiment, the peak-to-peak amplitude of the AC voltage322is larger than the peak-to-peak amplitude of the AC voltage312.

The plurality of capacitors330includes capacitors C330, 2×1−1, C330, 2×1, . . . , C330, 2×m−1, C330, 2×m, . . . , C330, 2×n−1, C330, 2×n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. In one embodiment, each capacitor includes two capacitor plates. One of these two capacitor plates receives the AC voltage322.

The one or more current balance chokes340include current balance chokes B340, 1, B340, 2, . . . , B340, m, . . . , B340, n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. For example, each current balance choke is a common-mode choke. In another example, each current balance choke is a balun choke. In yet another example, each current balance choke includes a magnetic core and two windings. Each of these two windings are wound on the magnetic core.

The one or more current balance chokes350include current balance chokes B350, 1, B350, 2, . . . , B350, m, . . . , B350, n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. For example, each current balance choke is a common-mode choke. In another example, each current balance choke is a balun choke. In yet another example, each current balance choke includes a magnetic core and two windings. Each of these two windings are wound on the magnetic core. According to an embodiment, one winding for the current balance choke B350, 1is coupled to the current sensing feedback component360, and the other winding for the current balance choke B350, 1is coupled to a predetermined voltage level, such as the ground voltage. According to another embodiment, both windings for the current balance choke B250, mother than B250, 1are coupled to a predetermined voltage level, such as the ground voltage.

According to an embodiment, if m is larger than 1, one winding of the current balance choke B350, mis coupled to one winding of the current balance choke B340, m−1, and the other winding of the current balance choke B350, mis coupled to one winding of the current balance choke B340, m. According to another embodiment, one winding of the current balance choke B350, 1is coupled to one winding of the current balance choke B340, n, and the other winding of the current balance choke B350, 1is coupled to one winding of the current balance choke B340, 1.

The current sensing feedback component360provides a current sensing signal362to the power and control subsystem310. For example, the power and control subsystem310uses the current sensing signal362to regulate the current flowing into and/or out of each of the plurality of lamps390. In another example, the power and control subsystem310includes a PWM controller whose output pulse width is adjusted in accordance with the current sensing signal362.

As discussed above, the system300is used to regulate the plurality of lamps390according to an embodiment of the present invention. For example, the plurality of lamps390includes one or more cold-cathode fluorescent lamps, and/or one or more external-electrode fluorescent lamps. In another example, the plurality of lamps390includes lamps L390, 2×1−1, L390, 2×1, . . . , L390, 2×m−1, L390, 2×m, . . . , L390, 2×n−1, L390, 2×n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n.

In one embodiment, each lamp includes two terminals. For example, one of the two terminals, e.g., a high-voltage terminal, is coupled to one capacitor plate of one of the plurality of capacitors330, and the other of the two terminals, e.g., a low-voltage terminal, is coupled to one winding of one of the one or more current balance chokes340. In another example, the high-voltage terminal of Lamp L390, 2×m−1is coupled to the capacitor C330, 2×m−1, and the high-voltage terminal of Lamp L390, 2×mis coupled to the capacitor C330, 2×m. Additionally, the low-voltage terminals of Lamps L390, 2×m−1and L390, 2×mare coupled to the current balance choke B340, m.

In another embodiment, the connections among the plurality of lamps390, the current balance chokes340, and the current balance chokes350are arranged in a cyclic configuration. For example, the current from low-voltage terminal of Lamp L390, 2×m−1flows through one winding of the current balance choke B340, m, and one winding of the current balance choke B350, m. In another example, if m is smaller than n, the current from low-voltage terminal of Lamp L390, 2×mflows through one winding of the current balance choke B340, m, and one winding of the current balance choke B350, m+1. In yet another example, if m is equal to n, the current from low-voltage terminal of Lamp L390, 2×nflows through one winding of the current balance choke B340, m, and one winding of the current balance choke B350, 1. In yet another embodiment, the system300can make currents flowing from the plurality of lamps390the same as shown inFIG. 3.

As discussed above and further emphasized here,FIG. 3is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. In one embodiment, the power and control subsystem310receives a voltage sensing signal, in addition to or instead of the current sensing signal362. In another embodiment, the current sensing signal362represents the current from any single lamp selected from the plurality of lamps390. In yet another embodiment, the current sensing signal362represents the total current of some or all of the plurality of lamps390, and the total current can be regulated by the power and control subsystem310.

According to another embodiment, the system300is used to regulate a plurality of lamps390including an odd number of lamps. For example, the plurality of lamps390includes lamps L390, 2×1−1, L390, 2×1, . . . , L390, 2×m−1, L390, 2×m, . . . , and L390, 2×n−1. Additionally, the plurality of capacitors330includes capacitors C330, 2×1−1, C330, 2×1, . . . , C330, 2×m−1, C330, 2×m, . . . , C330, 2×n−1. Moreover, the one or more current balance chokes340include current balance chokes B340, 1, B340, 2, . . . , B340, m, . . . , B340, n−1. Also, the one or more current balance chokes350include current balance chokes B350, 1, B350, 2, . . . , B350, m, . . . , B350, n. n is an integer larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. For example, if m is smaller than n, the current from low-voltage terminal of Lamp L390, 2×m−1flows through one winding of the current balance choke B340, m, and one winding of the current balance choke B350, m. Additionally, the current from the low-voltage terminal of Lamp L390, 2×n−1flows through one winding of the current balance choke B350, 1, and the current from the low-voltage terminal of Lamp L390, 1flows through one winding of the current balance choke B340, 1and one winding of the current balance choke B350, 1. Accordingly, the current balance choke B350, 1can make currents from the low-voltage terminal of Lamp L390, 2×n−1and the low-voltage terminal of Lamp L390, 1the same.

In another example, the current from the low-voltage terminal of Lamp L390, 2×(n−1)flows through one winding of the current balance choke B340, n−1and one winding of the current balance choke B350, n. Additionally, the current balance choke B350, 1and the current balance choke B340, n−1are coupled to the current balance choke B350, n. Accordingly, the current balance choke B350, ncan make the currents flowing out of the low voltage terminals of the Lamps L390, 2×(n−1)and L390, 2×n−1to be the same.

FIG. 4is a simplified driver system300according to yet another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. As shown inFIG. 4, the driver system300is used to regulate a plurality of lamps390including three lamps. For example, the plurality of lamps390includes lamps L390, 2×1−1, L390, 2×1, and L390, 2×2−1. Additionally, the plurality of capacitors330includes capacitors C330, 2×1−1, C330, 2×1, and C330, 2×2−1. Moreover, the one or more current balance chokes340include the current balance choke B340, 1. Also, the one or more current balance chokes350include current balance chokes B350, 1and B350, 2. For example, the current from low-voltage terminal of Lamp L390, 2×1−1flows through one winding of the current balance choke B340, 1, and one winding of the current balance choke B350, 1. Additionally, the current from the low-voltage terminal of Lamp L390, 2×2−1flows through one winding of the current balance choke B350, 1, and the current from the low-voltage terminal of Lamp L390, 1flows through one winding of the current balance choke B340, 1and one winding of the current balance choke B350, 1. Accordingly, the current balance choke B350, 1can make currents from the low-voltage terminal of Lamp L390, 2×2−1and the low-voltage terminal of Lamp L390, 1the same. In another example, the current from the low-voltage terminal of Lamp L390, 2flows through one winding of the current balance choke B340, 1and one winding of the current balance choke B350, 2. Additionally, the current balance choke B350, 1and the current balance choke B340, 1are coupled to the current balance choke B350, 2. Accordingly, the current balance choke B350, 2can make the currents flowing out of the low voltage terminals of the Lamps L390, 2and L390, 3to be the same.

FIG. 5is a simplified driver system according to yet another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The driver system500includes a power and control subsystem510, a power converter520, the plurality of capacitors530, one or more current balance chokes540, one or more current balance chokes550, a current sensing feedback component560, and a voltage supply570. Although the above has been shown using a selected group of components for the system500, there can be many alternatives, modifications, and variations. For example, some of the components may be expanded and/or combined. Other components may be inserted to those noted above. Depending upon the embodiment, the arrangement of components may be interchanged with others replaced. For example, the system500is used to regulate a plurality of cold-cathode fluorescent lamps and/or external-electrode fluorescent lamps, such as a plurality of lamps590. Further details of these components are found throughout the present specification and more particularly below.

The power and control subsystem510receives a voltage572from the voltage supply570. For example, the voltage572is a DC voltage. In another example, the voltage572is equal to 5 volts. In response, the power and control subsystem510generates and provides an AC voltage512to the power converter520.

According to an embodiment, the power and control subsystem510also receives certain control signals. For example, the control signals include an enabling (ENA) signal and a dimming (DIM) signal. In response, the power and control subsystem510generates one or more gate drive signals. Additionally, the power and control subsystem510includes one or more MOSFET transistors. These MOSFET transistors convert the voltage572to the AC voltage512in response to the one or more gate drive signals. According to another embodiment, the voltage supply570can use various types of configurations, such as Royer, push-pull, half-bridge, and/or full bridge.

The power converter520receives the AC voltage512and outputs an AC voltage522to the plurality of capacitors530. According to one embodiment, the power converter520is a transformer. For example, the transformer includes a primary winding and a secondary winding. The primary winding receives the AC voltage512from the power and control subsystem510, and the secondary winding outputs the AC voltage522to the one or more capacitors530. For example, the secondary winding of the transformer has a much larger number of turns than the primary winding. According to another embodiment, the peak-to-peak amplitude of the AC voltage522is larger than the peak-to-peak amplitude of the AC voltage512.

The plurality of capacitors530includes capacitors C530, 2×1−1, C530, 2×1, . . . , C530, 2×m−1, C530, 2×m, . . . , C530, 2×n−1, C530, 2×n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. In one embodiment, each capacitor includes two capacitor plates. One of these two capacitor plates receives the AC voltage522, and the other of these two capacitor plates is coupled to the one or more current balance chokes540.

The one or more current balance chokes540include current balance chokes B540, 1, B540, 2, . . . , B540, m, . . . , B540, n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. For example, each current balance choke is a common-mode choke. In another example, each current balance choke is a balun choke. In yet another example, each current balance choke includes a magnetic core and two windings. Each of these two windings are wound on the magnetic core. According to an embodiment, one of these two windings is coupled to a capacitor plate of a capacitor, and the other of these two windings is coupled to a capacitor plate of another capacitor. For example, the current balance choke B540, mis coupled to capacitors C530, 2×m−1and C530, 2×m.

The one or more current balance chokes550include current balance chokes B550, 1, B550, 2, . . . , B550, m, . . . , B550, n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n. For example, each current balance choke is a common-mode choke. In another example, each current balance choke is a balun choke. In yet another example, each current balance choke includes a magnetic core and two windings. Each of these two windings are wound on the magnetic core.

According to an embodiment, if m is larger than 1, one winding of the current balance choke B550, mis coupled to one winding of the current balance choke B540, m−1, and the other winding of the current balance choke B550, mis coupled to one winding of the current balance choke B540, m. According to another embodiment, one winding of the current balance choke B550, 1is coupled to one winding of the current balance choke B540, n, and the other winding of the current balance choke B550, 1is coupled to one winding of the current balance choke B540, 1.

The current sensing feedback component560provides a current sensing signal562to the power and control subsystem510. For example, the power and control subsystem510uses the current sensing signal562to regulate the current flowing into and/or out of each of the plurality of lamps590. In another example, the power and control subsystem510includes a PWM controller whose output pulse width is adjusted in accordance with the current sensing signal562.

As discussed above, the system500is used to regulate the plurality of lamps590according to an embodiment of the present invention. For example, the plurality of lamps590includes one or more cold-cathode fluorescent lamps, and/or one or more external-electrode fluorescent lamps. In another example, the plurality of lamps590includes lamps L590, 2×1−1, L590, 2×1, . . . , L590, 2×m−1, L590, 2×m, . . . , L590, 2×n−1, L590, 2×n. n is an integer equal to or larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n.

In one embodiment, each lamp includes two terminals. For example, one of the two terminals, e.g., a high-voltage terminal, is coupled to one winding of the one or more current balance chokes550. In another example, the low-voltage terminal of Lamp L590, 2×mis coupled to coupled to a predetermined voltage level, such as the ground voltage. In yet another example, if m is larger than 1, the low-voltage terminal of Lamp L590, 2×m−1is coupled to a predetermined voltage level, such as the ground voltage. In yet another example, the low-voltage terminal of Lamp L390, 2×1−1is coupled to the current sensing feedback component560.

In another embodiment, the connections among the plurality of lamps590, the current balance chokes540, and the current balance chokes550are arranged in a cyclic configuration. For example, the current flowing into high-voltage terminal of Lamp L590, 2×mflows through one winding of the current balance choke B540, m, and one winding of the current balance choke B550, m. In another example, if m is larger than 1, the current flowing into high-voltage terminal of Lamp L590, 2×m−1flows through one winding of the current balance choke B540, m−1, and one winding of the current balance choke B550, m. In yet another example, if m is equal to 1, the current flowing into high-voltage terminal of Lamp L390, 2×1−1flows through one winding of the current balance choke B540, 1, and one winding of the current balance choke B550, m. In yet another embodiment, the system500can make currents flowing into the plurality of lamps590the same as shown inFIG. 5.

As discussed above and further emphasized here,FIG. 5is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. In one embodiment, the power and control subsystem510receives a voltage sensing signal, in addition to or instead of the current sensing signal562. In another embodiment, the current sensing signal562represents the current from any single lamp selected from the plurality of lamps590. In yet another embodiment, the current sensing signal562represents the total current of some or all of the plurality of lamps590, and the total current can be regulated by the power and control subsystem510.

According to another embodiment, the system300is used to regulate the plurality of lamps590including an odd number of lamps. For example, the plurality of lamps590includes lamps L590, 2×1−1, L590, 2×1, . . . , L590, 2×m−1, L590, 2×m, . . . , and L590, 2×n−1. n is an integer larger than 1, and m is an integer equal to or larger than 1, and is equal to or smaller than n.

FIGS. 2,3,4, and5are merely examples, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, the plurality of capacitors230,330, or530are coupled to a plurality of transformers. In another example, the plurality of transformers are used to regulate the plurality of cold-cathode fluorescent lamps and/or external-electrode fluorescent lamps, such as a plurality of lamps290,390, or590.

FIG. 6is a simplified driver system200according to yet another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The driver system200includes a power and control subsystem, a power converter, the plurality of capacitors, one or more current balance chokes, one or more current balance chokes, a current sensing feedback component, and a voltage supply. For example, the power converter includes a plurality of transformers, whose primary windings are coupled to the power and control subsystem and whose secondary windings are coupled to different capacitors selected from the plurality of capacitors.

FIG. 7is a simplified driver system300according to yet another embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. The driver system300includes a power and control subsystem, a power converter, the plurality of capacitors, one or more current balance chokes, one or more current balance chokes, a current sensing feedback component, and a voltage supply. For example, the power converter includes a plurality of transformers, whose primary windings are coupled to the power and control subsystem and whose secondary windings are coupled to different capacitors selected from the plurality of capacitors.

According to another embodiment of the present invention, a system for driving a plurality of cold-cathode fluorescent lamps includes a subsystem configured to receive at least a DC voltage and generate a first AC voltage in response to at least the DC voltage, a power converter configured to receive the first AC voltage and convert the first AC voltage to at least a second AC voltage, and a plurality of current balancing devices. Each of the plurality of current balancing devices is configured to receive two currents and balance the two currents. The power converter and the plurality of current balancing devices are capable of being directly or indirectly coupled to a plurality of cold-cathode fluorescent lamps. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps. The first lamp and the second lamp are associated with a first current and a second current respectively. Additionally, a first current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current and the first current and to balance the lamp current and the first current, and a second current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current and the second current and to balance the lamp current and the first current. For example, the system is implemented according toFIG. 3,FIG. 5, and/orFIG. 7.

According to yet another embodiment of the present invention, a system for driving a plurality of cold-cathode fluorescent lamps includes a subsystem configured to receive at least a DC voltage and generate a first AC voltage in response to at least the DC voltage, a power converter configured to receive the first AC voltage and convert the first AC voltage to at least a second AC voltage, and a plurality of current balancing devices. Each of the plurality of current balancing devices is configured to receive two currents and balance the two currents. The power converter and the plurality of current balancing devices are capable of being directly or indirectly coupled to a first plurality of cold-cathode fluorescent lamps. The first plurality of cold-cathode fluorescent lamps includes a second plurality of cold-cathode fluorescent lamps and a third lamp, and the third cold-cathode fluorescent lamp is associated with a first current. For each of the second plurality of cold-cathode fluorescent lamps, each of the second plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the second plurality of cold-cathode fluorescent lamps includes at least a fourth lamp. The fourth lamp is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a second current. Additionally, a first current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current and the second current and to balance the lamp current and the second current. Moreover, if the second plurality of cold-cathode fluorescent lamps further includes a fifth lamp which is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a third current, a second current balancing device selected from the plurality of current balancing devices is configured to receive the lamp current, and the first current or the third current, and is further configured to balance the lamp current, and first current or the third current. For example, the system is implemented according toFIG. 4.

According to yet another embodiment of the present invention, a system for driving a plurality of cold-cathode fluorescent lamps includes a subsystem configured to receive at least a DC voltage and generate a first AC voltage in response to at least the DC voltage, a power converter configured to receive the first AC voltage and convert the first AC voltage to at least a second AC voltage, and a plurality of current balancing devices. Each of the plurality of current balancing devices is configured to receive two currents and balance the two currents. The power converter and the plurality of current balancing devices are capable of being directly or indirectly coupled to a plurality of cold-cathode fluorescent lamps. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a first lamp current and a second lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps. The first lamp and the second lamp are associated with a third lamp current and a fourth lamp current respectively. Additionally, a first current balancing device selected from the plurality of current balancing devices is configured to receive the first lamp current and the third lamp current and to balance the first lamp current and the third lamp current, and a second current balancing device selected from the plurality of current balancing devices is configured to receive the second lamp current and the fourth lamp current and to balance the second lamp current and the fourth lamp current. For example, the system is implemented according toFIG. 2and/orFIG. 6.

According to yet another embodiment, a method for driving a plurality of cold-cathode fluorescent lamps includes receiving at least a DC voltage, generating a first AC voltage in response to at least the DC voltage, receiving the first AC voltage, converting the first AC voltage to at least a second AC voltage, and driving a plurality of cold-cathode fluorescent lamps with at least the second AC voltage. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps, and the first lamp and the second lamp are associated with a first current and a second current respectively. Additionally, for the each of the plurality of cold-cathode fluorescent lamps, the method includes receiving the lamp current and the first current, balancing the lamp current and the first current, receiving the lamp current and the second current, and balancing the lamp current and the first current. For example, the method is performed according toFIG. 3,FIG. 5, and/orFIG. 7.

According to yet another embodiment, a method for driving a plurality of cold-cathode fluorescent lamps includes receiving at least a DC voltage, generating a first AC voltage in response to at least the DC voltage, receiving the first AC voltage, converting the first AC voltage to at least a second AC voltage, and driving a first plurality of cold-cathode fluorescent lamps with at least the second AC voltage. The first plurality of cold-cathode fluorescent lamps includes a second plurality of cold-cathode fluorescent lamps and a third lamp, and the third cold-cathode fluorescent lamp is associated with a first current. For each of the second plurality of cold-cathode fluorescent lamps, each of the second plurality of cold-cathode fluorescent lamps is associated with a lamp current, and the second plurality of cold-cathode fluorescent lamps includes at least a fourth lamp, which is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a second current. Additionally, for the each of the second plurality of cold-cathode fluorescent lamps, the method includes receiving the lamp current and the second current, and balancing the lamp current and the second current. Moreover, if the second plurality of cold-cathode fluorescent lamps further includes a fifth lamp, which is different from the each of the second plurality of cold-cathode fluorescent lamps and is associated with a third current, the method includes receiving the lamp current, and the first current or the third current, and balancing the lamp current, and first current or the third current. For example, the method is performed according toFIG. 4.

According to yet another embodiment, a method for driving a plurality of cold-cathode fluorescent lamps includes receiving at least a DC voltage, generating a first AC voltage in response to at least the DC voltage, receiving the first AC voltage, converting the first AC voltage to at least a second AC voltage, and driving a plurality of cold-cathode fluorescent lamps with at least the second AC voltage. For each of the plurality of cold-cathode fluorescent lamps, each of the plurality of cold-cathode fluorescent lamps is associated with a first lamp current and a second lamp current, and the plurality of cold-cathode fluorescent lamps includes at least a first lamp and a second lamp. Both the first lamp and the second lamp are different from the each of the plurality of cold-cathode fluorescent lamps, and the first lamp and the second lamp are associated with a third lamp current and a fourth lamp current respectively. Additionally, for the each of the plurality of cold-cathode fluorescent lamps, the method includes receiving the first lamp current and the third lamp current, balancing the first lamp current and the third lamp current, receiving the second lamp current and the fourth lamp current, and balancing the second lamp current and the fourth lamp current. For example, the method is performed according toFIG. 2and/orFIG. 6.

The present invention has various advantages. Some embodiments of the present invention provide a driver system that can balance currents between or among any number of lamps. Certain embodiments of the present invention provide a configuration in which only one or two inductive windings are in series with each lamp between the secondary winding of the transformer and the ground voltage. For example, the one or two inductive windings belong to one or two current balance chokes respectively. In another example, the currents flowing through at least majority of the lamps go through same types of circuit components. Some embodiments of the present invention provide great flexibility to the design and manufacturing of multi-lamp driver system. Certain embodiments of the present invention can improve stability and reliability of a multi-lamp driver system. Some embodiments of the present invention can simplify processes and lower costs for making a multi-lamp driver system. Certain embodiments of the present invention can balance both the currents flowing into some lamps and the currents flowing out of certain lamps. Some embodiments of the present invention can improve current balancing of a multi-lamp driver system by eliminating or reducing adverse effects by stray conductance or parasitic capacitance of the lamps. Certain embodiments of the present invention can provide current balancing to lamps driven by different transformers using cyclic current balance schemes. Some embodiments of the present invention can improve brightness uniformity on an LCD screen lit by a plurality of lamps that are driven by one or more transformers.