AC-DC Power-Factor-Corrected Switching Converter Based on Air-Gap Transformer and Pulse Position Modulator for Lighting Applications

In this paper an AC-DC power-factor-corrected switching converter based on pulse position modulator (PPM) is realized and applied to drive LED array. The PPM is realized using a Timer, which consists of a comparator and one RS flip-flop. The Timer is connected as an oscillator of lowfrequency around 5 kHz. The pulse position varies with the input rectified-voltage as modulating signal. AC-DC powerfactor- corrected switching converter with regulation of line voltage range (100 - 140Vac) is achieved by a certain value of primary inductance of the proposed air-gap transformer. The operating principles of the converter are described and also the approach used to achieve the power factor correction (PFC) through a control circuit based on PPM. Experimental results taken from the laboratory prototype are included.