Patent ID: 8493001

Claim:
A controller applied in a light emitting diode (LED) driver for selectively controlling a level of a reference voltage signal, the LED driver comprising a boost converter for driving a LED circuit according to the reference voltage signal and a dim signal, the controller comprising: a counter counting a counting parameter, which indicates a duty cycle length of the dim signal, in response to a front edge of the dim signal, the counting parameter comprising n bits, wherein n is an integer greater than 1; a sample circuit, sampling a most significant bit (MSB) of the n bits to obtain a first sample signal in response to a rear edge of the dim signal to obtain a first sample signal, wherein when the first sample signal corresponds to an end value, it is indicated that the duty cycle length is greater than or equal to a first threshold, and when the first sample signal corresponds to an initial value, it is indicated that the duty cycle length is smaller than the first threshold; and a source circuit, providing the reference voltage signal corresponding to a first voltage level in response to the end value of the first sample signal and providing the reference signal corresponding to a second voltage level in response to the initial value of the first sample signal, wherein, the first voltage level is lower than the second voltage level.