P-52: A New Dynamic Headroom Controller using Storage Delay Time of BJT for Low Power Consumption of LED Backlight

A new dynamic headroom control circuit for PWM LED drivers was proposed. Unlike conventional headroom control circuits, the proposed circuit uses storage delay time of BJTs. During off periods of the PWM driver, the proposed circuit senses the storage delay time from the base of BJT and minimizes the error between the sensed time and a reference delay time by adjusting the converter output voltage consecutively. A reverse recovery time of KTC4380 that determined by storage delay time and rising time was measured for different values of the VCE. Based on the measurement results, a reference pulse width was determined. By applying the reference determined, the proposed circuit was simulated by LTspice for verification and the simulation results showed that the proposed circuit well controlled the headroom voltage of the current source. Hence, the low power consumption could be achieved.