Patent ID: 8917029

Claim:
A light-emitting diode (LED) driver, providing a drive voltage for driving an LED circuit according to an input voltage in response to a pulse width modulation (PWM) dimming signal, the LED driver comprising: a current regulator, enabled in a first PWM period in response to the PWM dimming signal to control a drive current passing through the LED circuit, and disabled outside the first PWM period to cut off the drive current and to correspondingly disable the LED circuit; a dimming signal generator, for generating a prolonged PWM dimming signal according to the PWM dimming signal, the prolonged PWM dimming signal having a second PWM period, the first PWM period and the second PWM period substantially overlapped, the second PWM period having a prolonged PWM period compared to the first PWM period, a length of the prolonged PWM period associated with a level of the input voltage, wherein the dimming signal generator further comprises: a voltage-controlled delay unit, for determining the prolonged PWM period in response to the level of the input voltage, and delaying the PWM dimming signal by the prolonged PWM period to output a delayed PWM dimming signal, wherein the voltage-controlled delay unit comprises: a bias unit, for determining a bias current according to the input voltage, a size of the bias current associated with the level of the input voltage; and a delay unit, having an operating delay time for determining the prolonged PWM period, for determining the operating delay time in response to the size of the bias current, and delaying the PWM dimming signal by the operating delay time to output the delayed PWM dimming signal; a first logic operational unit, for providing a leading edge sampling signal indicative of a leading edge of the PWM dimming signal according to the PWM dimming signal; a second logic operational unit, for providing a trailing edge sampling signal indicative of a trailing edge of the delayed PWM dimming signal according to the delayed PWM dimming signal; and a flip-flop, for triggering a leading edge of the prolonged PWM dimming signal in response to the leading edge sampling signal, and triggering a trailing edge of the prolonged PWM dimming signal in response to the trailing edge sampling signal; and a boost converter, enabled in the second PWM period in response to the prolonged PWM dimming signal to maintain a level of the drive voltage according to the input voltage.