Current-fed isolated PFC pre-regulator for multiple LED lamps with extended lifetime

Abstract

To emit high-quality LED light, one or a bin of LED lamp(s) is normally driven by a PWM-controlled constant current source to minimize device variation and achieve accurate brightness control. Powered from offline AC mains, the front-end power converters should provide a relatively low DC voltage bus for the inputs of post-end LED current regulators. To match the long lifetime of LEDs, the whole LED driver (ballast) should work as durably as the LEDs. However, the lifetime of the driver is usually limited by the high-voltage electrolytic charge storage capacitors used in conventional PFC pre-regulators. In this paper, our previously proposed resonant current-fed isolated PFC pre-regulator is extended to operate in discontinuous conduction mode (DCM). It allows the use of the low-voltage storage capacitors on the transformer secondary, and therefore extends the overall lifetime of the LED lighting system. A detailed procedure for finding the expected lifetime of the low-voltage electrolytic capacitor is given. As before, the high-voltage stress on the main switches, which is typical in current-fed isolated converters, is reduced substantially by taking advantage of the transformer leakage inductance necessary for resonance. Additionally, high efficiency is ensured by the use of dual non-cascading structures. Steady-state state-space averaging analysis is performed for designing the converter in DCM operation. A prototype converter is built to verify performance of the proposed PFC LED pre-regulator. Copyright © 2011 John Wiley & Sons, Ltd.