A simple PWM method for improving lamp current crest factor of valley-filled electronic ballast

In this paper, a PWM method to improve the lamp current crest factor (CCF) of the valley-tilled electronic ballast (VFEB) is presented. The VFEB has merits of high power factor, simple structure, and low cost. However, it results in an excessive CCF, which will shorten the lifetime of low-pressure discharge lamp. The proposed method controls switching duty ratio by feeding forward the dc-link voltage waveform of VFEB. It decreased the duty ratio with rising of dc-link voltage. Therefore, the proposed method could restrain the lamp peak current and improve the lamp CCF. The control block diagram and basic theory are introduced to improve the CCF. The computer simulations verify the proposed method and derive a minimum lamp CCF. The experimental results demonstrate that the lamp CCF was reduced from 1.9 to 1.58, the ac line power factor is 96%, and the input current THD is 29.3%. The fixed switching frequency operation gains a satisfactory power quality. Copyright (C) 2008 John Wiley & Sons, Ltd.