Frequency-controlled series-resonant converter with synchronous rectifier

This paper presents an analysis and experimental results for a frequency-controlled series-resonant de-de converter that consists of a Class-D zero-voltage-switching (ZVS) series-resonant inverter and a center-tapped synchronous rectifier. If the dr output voltage is low, the efficiency of the converter is dominated by the efficiency of the rectifier. Low on-resistance metal-oxide-semiconductor field-effect transistors (MOSFETs) are used in the rectifier instead of diodes because the forward voltage drop across the rectifying device is low, resulting in a high efficiency. The do output voltage is regulated against variations in the load resistance and the de input voltage by varying the operating frequency. Experimental results are presented for a converter with a do input voltage of 150 V, an output voltage of 5 V, and a dc load resistance ranging from 0.5 to 5.5 Omega. The measured efficiency was 86% for a 50 W output and 89% for a 25 W output. The theoretical results were in good agreement with the measured results.