High speed series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) step-down power transformer

In this paper, simulation and experimental results of an isolated low profile, series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) step-down power transformer are described. The designed converter prototype was operated in MHz switching frequency region. For obtaining the stringent height switch mode power supplies (SMPS), a new multilayered coreless PCB power transformer of approximately 4:1 turn's ratio was designed in a four layered PCB laminate. The outermost radius of the step-down power transformer is 10mm with achieved power density of 16W/cm². The energy efficiency of the power transformer is found to be in the range of approximately 87-96% with the output power level of 0.1-50W in the frequency range of 1.5-4MHz. This designed step-down power transformer was utilized in SRC and evaluated. The supply voltage of converter is varied from 60-120V DC with a nominal input voltage of 90V. The SRC has been tested successfully upto the output power level of 34.5W. The energy efficiency from the converter prototype under Zero Voltage Switching (ZVS) condition is found to be in the range of 80 86.5% with the switching frequency range of 2.4-2.75MHz. By using constant off-time frequency modulation technique the output voltage of converter is regulated to 20V DC for different load conditions. Thermal profile and the loss estimation of SRC at nominal voltage are also presented.