Three-switch LLC resonant converter for high efficiency TV power supply with universal input voltage

Abstract

General power supply over 75W consists of two stages, PFC stage to meet the PF re-striction and DC/DC stage to regulate constant output voltage. In universal line application such as TV power supply, efficiency of power supply at low line is lower compared to high line. To solve this problem, a new three-switch LLC resonant converter for high efficiency at low line is proposed in this paper. The proposed converter changes transformer turns-ratio by changing gate driving according to input voltage, low line or high line. At high line, proposed converter has series connected transformer which is normal operation. At low line, proposed converter has parallel connected transformer which has two times voltage gain compared to high line. Since proposed converter increases voltage gain changing mode according to input line, it can be designed to obtain high efficiency in universal line. To confirm the validity of this paper, the prototype of TV power supply with universal line input, $90~264V_{rms}$, and 19V/200W dc output is tested