200°C operation of a 500 W DC-DC converter utilizing power MOSFETs

This paper presents results from the operation of the power stage of a 500 W DC-DC converter at an ambient temperature of 200°C. This converter is designed to provide an output voltage of 42 V DC from a 28 V DC input. It utilizes an H-bridge configuration composed of 8 International Rectifier Power MOSFETs (parallel connections of 2 MOSFETs) and 4 Motorola diodes to convert the DC input voltage to high frequency square wave which can then be stepped up with a transformer. The transformer output voltage is then rectified and filtered to produce the DC output voltage. A phase-shifted PWM switching scheme is utilized to control the MOSFETs in the H-bridge. This scheme allows zero-voltage turn-on of the MOSFETs to improve the efficiency. The efficiency of this converter when operated on the laboratory bench was measured to be 89%. The H-bridge and transformer were then placed in an oven and operated over an ambient temperature range of 20-200°C. The efficiency varied from 86% to 85.4% over this temperature range. The long feedthroughs for oven operation caused the efficiency to decrease from 89% to 86.1%