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

Yifeng Wang,Yuqi Hou,Yan Liang,Xiaochen Wu,Pengyu Cheng,Lei Li

doi:10.1109/access.2020.2990400

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%.

Highlights

The light-emitting diodes (LEDs) have attracted much attention due to its advantages, such as long lifespan, high luminous efficacy (250 lm/W), small size, and zero pollution [1]–[3]
For achieving the full-range dimming and obtaining better LED current square waveform at ultrahigh dimming frequency, the following studies are carried out: 1) Builds the mathematical model consisting of parasitic parameters
This paper considers three main parasitic parameters, including LED junction capacitance CJ, Q3 drain-source capacitance CDS, and long wires parasitic inductance Lg

Summary

INTRODUCTION

The light-emitting diodes (LEDs) have attracted much attention due to its advantages, such as long lifespan (approximately 25,000 to 50,000 hours), high luminous efficacy (250 lm/W), small size, and zero pollution [1]–[3]. Study [5] performs discontinuous conduction mode (DCM) control on a buck converter without an output capacitor using DC driving technology It controls LED illuminance by adjusting the number of current pulses in the dimming period. In order to eliminate audible noise and avoid flicker, the dimming frequency is improved as high as 20 kHz in this paper Both the full-range dimming and better LED current square waveform at ultrahigh dimming frequency should be achieved. For achieving the full-range dimming and obtaining better LED current square waveform at ultrahigh dimming frequency, the following studies are carried out: 1) Builds the mathematical model consisting of parasitic parameters. For analyzing the effect of parasitic parameters on system stability and performance of output port, high frequency LED dynamic equivalent circuit (in case of high frequency LED current and ULED > VD) need to be built. The high frequency LED dynamic equivalent circuit which is shown in Fig. is obtained by parallel connection of 1/k and CJ

STABILITY ANALYSIS WITH CONSIDERATION OF PARASITIC PARAMETERS

EFFECT OF PARASITIC PARAMETERS ON LED CURRENT SQUARE WAVEFORM

EXPERIMENTAL RESULTS AND DISCUSSIONS

CONCLUSION