Full-Range LED Dimming Driver With Ultrahigh Frequency PWM Shunt Dimming Control

Abstract

This paper explores an ultrahigh dimming frequency Light-Emitting Diode (LED) pulse width modulation (PWM) shunt dimming driver that achieves the full-range dimming. Firstly, the dimming frequency is improved to 20kHz for avoiding flicker and audible noise in high dimming requirements application, such as film and television shooting. Secondly, this paper reduces dimming ratio loss at ultrahigh dimming frequency by removing output capacitor. As a result, given 1% dimming ratio is achieved. Subsequently, for improving LED current square waveform at ultrahigh dimming frequency, it is necessary to suppress parasitic oscillation at the falling edge in LED current. Therefore, this paper proposes a method which connects a fast recovery diode with LED in series. In such way, parasitic oscillation at the falling edge in LED current is suppressed. Meanwhile, linear dimming performance is improved such as dimming linearity of low ratio and circuit reliability. Finally, a 120 W experimental prototype is built to drive an LED array comprising 9 LEDs in parallel and 15 LEDs in series. The switching frequency and dimming frequency of prototype are 500 kHz and 20 kHz, respectively. In addition, it achieves full dimming range of 1% to 99.99%.

Keywords

• Output capacitance
• PWM shunt dimming
• ultrahigh dimming frequency
• full-range dimming
• parasitic parameters