Optimised power stages for high frequency 380/440 VAC medium power switch mode supplies

The authors present the elements necessary to make the optimum choice of power semiconductors (for the transistors and secondary diodes) and the power stage configurations for medium power SMPS (between 1 to 15 kVA). The power stage realized comprises of an asymmetrical bridge forward converter. An optimised power switch combining bipolar and MOSFET technologies is developed. It is capable of switching in excess of 50 A at 25 kHz on the 380/440 VAC rectified three phase mains. Secondary diode choice depends largely on the transformer ratio and the desired output DC voltage. Conduction losses at 25 kHz govern the choice of secondary diodes