High-Speed (MHz) Series Resonant Converter (SRC) Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer

In this paper, design and analysis of an isolated low-profile, series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) power transformer was presented. For obtaining the stringent height switch mode power supplies, a multilayered coreless PCB power transformer of approximately 4:1 turn´s ratio was designed in a four-layered PCB laminate that can be operated in megahertz switching frequency. The outermost radius of the transformer is 10 mm with achieved power density of 16 W/cm². The energy efficiency of the power transformer is found to be in the range of 87-96% with the output power level of 0.1-50 W operated at a frequency of 2.6 MHz. This designed step-down transformer was utilized in the SRC and evaluated. The supply voltage of the converter is varied from 60-120 VDC with a nominal input voltage of 90 V and has been tested up to the power level of 34.5 W. The energy efficiency of the converter under zero-voltage switching condition is found to be in the range of 80-86.5% with the switching frequency range of 2.4-2.75 MHz. By using a constant off-time frequency modulation technique, the converter was regulated to 20 VDC for different load conditions. Thermal profile with converter loss at nominal voltage is presented.