General Description

The HT9921 are pulse width modulated (PWM) high-efficiency LED driver control ICs. They allow efficient operation of LED strings from voltage sources ranging up to 400VDC. The HT9921 include an internal high-voltage switching MOSFET controlled with fixed off-time TOFF of approximately 10μs. The LED string is driven at constant current, thus providing constant light output and enhanced reliability. The output current is internally fixed at 20mA for HT9921.The peak current control scheme provides good regulation of the output current throughout the universal AC line voltage range of 85 to 264VAC or DC input voltage of 20 to 400V.