Low-cost, single-channel CCFL controller reduces BOM cost for LCD backlighting
(Product News, 03 Apr 2008 )
Maxim Integrated Products introduces the DS3991 low-cost, single-channel controller for CCFLs that are used to backlight liquid-crystal displays (LCDs). Supporting both push-pull and half-bridge drive schemes, this device converts a DC voltage (5V to 24V) to the high-voltage (300Vrms to 1400Vrms) AC waveform that is required to power CCFLs. These drive schemes use only a minimal number of external components, thus reducing component and assembly cost and making the design easy to implement. Additionally, the push-pull drive scheme provides an efficient DC-to-AC conversion and produces near-sinusoidal waveforms. Supporting both single- and multiple-lamp configurations, the DS3991 is ideal for backlighting LCD PC monitors and TVs.
The DS3991 drives two logic-level, n-channel MOSFETs that are tied between a step-up transformer and a ground. The transformer has a center tap on the primary side that is connected to the DC supply. The DS3991 alternately turns on the two MOSFETs to create the high-voltage AC waveform on the secondary side. By varying the duration of the MOSFET turn-on times, the controller is able to accurately control the amount of current flowing through the CCFL lamp.
