Paralleling of semiconductors including temperature feedback, using spreadsheet or simulation tool, to calculate current and temperature differences

Paralleling of semiconductors like IGBTs and diodes is complicated due to the usually negative temperature coefficient of forward voltage drop, and positive temperature coefficient of switching losses. The authors state which component knowledge is necessary as data input and then present two efficient tools for calculating the current and temperature differences of the paralleled semiconductor chips. When using either of the two tools, a spreadsheet or circuit simulation program, the feedback from the temperature is included through iterations. It is shown that for instance a 20% imbalance in voltage drop and switching loss may demand a derating down to 32% in a typical chopper application at 20 kHz. With a sinusoidal current, as in a motor inverter, with 20% imbalance, a derating down to 69% is sufficient. Large switching versus conduction losses are very bad when paralleling typical bipolar semiconductors. When parallelling, it is optimal with a faster semiconductor, or a lower frequency, compared to when using a single switch. The authors also give measured data for various IGBTs, and illustrations of measured current sharing between paralleled IGBTs