Controlled resonant converters with switching frequency fixed

This paper presents a method to regulate the output voltage of resonant DC-DC converter without changing switching frequency. It is based on the concept of changing resonant frequency by using either a variable inductance circuit or a variable capacitance, which is controlled auxiliary switches. The switching loss of the auxiliary switch is minimized due to no intersection between the voltage and the current. A 1-MHz, 50W breadboard regulator of Class-E converter has been built which shows high efficiency of 93.7%.