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. 1 is a simplified conventional driver system for CCFL and/or EEFL. The driver system 100 includes a control subsystem 110 and an AC power supply subsystem 120. The control subsystem 110 receives a power supply voltage VDDA and certain control signals. The control signals include an enabling (ENA) signal and a dimming (DIM) signal. In response, the control subsystem 110 outputs gate drive signals to the AC power supply subsystem 120. The AC power supply subsystem 120 includes 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 VIN to a low AC voltage in response to the gate drive signals. The low AC voltage is boosted to a high AC voltage VOUT by the power transformers, and the high AC voltage VOUT is sent to drive a system 190. The system 190 includes one or more CCFLs and/or one or more EEFLs. The system 190 provides a current and voltage feedback to the control subsystem 110.
As shown in FIG. 1, the system 190 includes 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.