LLC LED Driver with Current-Sharing Capacitor Having Low Voltage Stress

Wen-Zhuang Jiang,Jenn-Jong Shieh,Kuo-Ing Hwu

doi:10.3390/en14010112

Wen-Zhuang Jiang, Jenn-Jong Shieh + Show 1 more

Open Access

https://doi.org/10.3390/en14010112

Copy DOI

Journal: Energies	Publication Date: Dec 28, 2020
Citations: 2	License type: CC BY 4.0

Affiliation: Powertech Technology (Taiwan), Feng Chia University

Abstract

In this paper, an LLC light-emitting diode (LLC LED) driver based on the current-sharing capacitor is presented. In the proposed LED driver, the LLC resonant converter is used to step down the high input voltage, to provide galvanic isolation, to offer a constant current for LEDs. Moreover, the current-sharing capacitor connected to the central-tapped point of the secondary-side winding is used to balance the currents in two LED strings. By doing so, the voltage stress on this capacitor is quite low. Above all, the equivalent forward voltages of the two LED strings are generally influenced by the temperature and the LED current, and this does not affect the current-sharing performance, as will be demonstrated by experiment on the difference in number of LEDs between the two LED strings. In addition, only the current in one LED string is sensed and controlled by negative feedback control, while the current in the other LED string is determined by the current-sharing capacitor. Moreover, this makes the current control so easy. Afterwards, the basic operating principles and analyses are given, particularly for how to derive the effective resistive load from the LED string. Eventually, some experimental results are provided to validate the effectiveness of the proposed LED driver.

Highlights

As compared with the traditional lighting sources, like the incandescent lights, fluorescent lights, and halogen lights, etc., the high-brightness lighting-emitting diodes (LEDs) have become promising due to their long life, compact size, and eco-friendly characteristics [1]
The LEDs can be connected in series and parallel, depending on the output voltage and current of the LED driver
Multiple LEDs are connected in series to form an LED string, and the LED strings are connected in parallel with each other

Summary

Introduction

As compared with the traditional lighting sources, like the incandescent lights, fluorescent lights, and halogen lights, etc., the high-brightness lighting-emitting diodes (LEDs) have become promising due to their long life, compact size, and eco-friendly characteristics [1]. S1 keeps OFF, but S2 is turned ON with zero voltage switching (ZVS) due to iLr flowing through Db2 During this state, iLr is smaller than iLm. the current -ip is reflected from the secondary side to the primary side, thereby making D2 forward biased and providing energy to Co2 and LS2. S2 keeps OFF, but S1 is turned ON with ZVS due to iLr flowing through Db1 During this state, −iLr is smaller than −iLm. the current ip is transferred from the primary side to the secondary side, making D1 forward biased and providing energy to Co1 and LS1. The voltage nVo1 is across Lm, causing iLm to be increased linearly This state ends when iLr reaches zero at t = t0 + Ts

LED Modeling

Effect of Variations in Equivalent forward Voltage on Current Sharing

Selection of LED String

Determination of Transformer Turns Ratio

Findings

20 V vgs2