200/spl deg/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/spl deg/C. This converter is designed to provide an output voltage of 12-Vdc from a 28-Vdc input. It utilizes an H-bridge configuration composed of eight International Rectifier power MOSFETs (parallel connections of two MOSFETs) and four Motorola diodes to convert the DC input voltage to a 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 pulse-width modulation (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/spl deg/C-200/spl deg/C. The efficiency varied from 86.1% to 85.4% over this temperature range. The long feedthroughs for oven operation caused the efficiency to decrease from 89% to 86.1%.