LED 장수명화를 위한 전해커패시터를 사용하지 않는 LED 구동용 AC/DC 컨버터

Abstract

LED devices offer more than twice the luminous efficacy of fluorescent lamps and are environmentally friendly as they do not contain mercury. However, the lifespan of an LED lighting fixture is determined not by the LED chip itself, but by the electrolytic capacitors within the LED driver. While typical electrolytic capacitors last only 2,000 to 5,000 hours, modern LED packages can last in excess of 50,000 hours, significantly shortening the lifespan of the lighting fixture. Furthermore, high temperature and humidity accelerate the evaporation of the electrolyte and the ESR increase, further shortening the lifespan. Furthermore, IEC61000-3-2 limits the harmonic current as a percentage of the input current at fundamental frequency and requires a power factor of at least 0.9, while IEEE1789-2015 strictly limits 100/120 Hz ripple current to prevent flickering, which can cause discomfort to the human body and cameras. Therefore, LED drivers must simultaneously meet the requirements of long life, high power quality, and flicker suppression. To achieve long life, the use of electrolytic capacitors must first be limited. This paper proposes a novel topology that eliminates electrolytic capacitors, adds small film capacitors and auxiliary MOSFETs for active power decoupling, and utilizes software-based peak-flat PWM to optimize power factor, flicker, efficiency, and long life. Based on a flyback converter, the proposed topology adds small auxiliary circuit to maintain continuous LED current even when the input voltage is near zero. Peak-flat PWM reduces 120 Hz ripple by nearly half without compromising power factor. Eliminating electrolytic capacitors and replacing them with small film capacitors reduces the size of the LED driver, increases mechanical design freedom, and extends the replacement cycle to more than five years, significantly reducing maintenance costs. The proposed circuit topology was applied to an LED driving circuit with a rated output of 100 W and 24 V, and the validity of the proposed method was verified through computer simulations and hardware experiments.