Very-High-Frequency Resonant Dual-Channel LED Driver With Capacitive Current Balance and Low Voltage Stress on Diodes

By combining the existing very-high-frequency (VHF) dc/dc converter and resonant switched capacitor (SC) techniques, this article proposes a VHF dual-channel light-emitting diode (LED) driver with capacitive current balance. Unlike the conventional capacitive current-balancing LED drivers, the proposed one has higher power density, and no current spike occurred at the switching moment. Due to the problem of higher voltage stress on the diode in resonant operation for the existing VHF LED drivers, the proposed one makes both diodes that are alternately turned on clamp to each other by extending one more LED channel without adding any resonant components. As a result, the voltage stress on diode can be reduced to the total dc output voltage, which is beneficial for selecting switching components. In addition, the parasitic capacitance of both diodes can be a part of the required capacitor regardless of their inconsistency, which means that they can be absorbed by one discrete capacitor and further promote power density. The analysis and design consideration of the proposed LED driver are studied in detail. With the on–off control strategy, the feasibility and theoretical analysis are experimentally verified with a rated output power of 12 W dual-channel prototype.

I. Introduction

With the advantages of long lifespan, high luminous efficacy, and small size, high-brightness light-emitting diodes (LEDs) are gradually replacing high-intensity discharge, incandescent and fluorescent lamps in various applications, such as residential lighting, automobiles, and backlighting [1], [2], [3]. Due to the limited brightness of a single LED, multiple LEDs usually operate together for the requirement of brightness. In fact, the inherited features of negative temperature coefficient and manufacturing tolerance, as well as nonlinear volt-ampere characteristics, have a substantial impact on whether the brightness of LEDs can be balanced. The simplest solution is to connect all the LEDs in a series manner. However, the sharp increase in output terminal voltage may exceed the safety limit and affect the reliability of the LEDs [4]. To address this problem, it is necessary to use a current-balancing technique on the parallel LED structure to balance their brightness.