Dallas introduces the DS3992/DS3994 dual/quad cold cathode fluorescent lamp controller for backlighting applications in LCD and PC LCDs. The DS3992 supports an architecture that drives one lamp per channel with completely independent lamp control; while the DS3994 supports an architecture that drives one to four lamps per channel while allowing multiple DS3994 controllers to be cascaded. The DS3992/DS3994 uses a push-pull drive architecture to convert DC voltage (5V to 24V) to the high voltage (600VRMS to 1200VRMS and 300VRMS to 1400VRMS, respectively) AC waveforms required for CCFL power. The push-pull drive architecture requires very few external components, reducing component and assembly costs and simplifying PCB design. The push-pull drive architecture also enables efficient DC-to-AC conversion and produces an approximately sinusoidal waveform. Each channel of the DS3992/DS3994 drives two logic-level n-channel MOSFETs, which are connected between the two terminals of the step-up transformer and ground. The primary side of the transformer has a center tap and the center tap is connected to a DC power supply. The DS3992/DS3994 alternately turn on two MOSFETs to create a high-voltage AC waveform on the secondary side. By changing the duty cycle of the MOSFET turn-on, the controller can accurately control the current flowing through the CCFL lamp. The series resistor on the low side of the CCFL is used to sense current. The voltage across the resistor is fed to the lamp current monitor (LCM) input of each device. The DS3992/DS3994 then compares the measured voltage across the resistor to the internal reference voltage to determine the duty cycle of the MOSFET gate turn-on. Each CCFL lamp can be independently controlled to achieve balanced control of all lamp brightness and maximize lamp life and brightness.
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Tisineo (Hi-Tech) Technology Co. Ltd , http://www.tisineosafe.com