Abstract
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. This paper states which components knowledge is necessary as input and then presents 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 simulations programme, 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 paralleling, it is optimal with a faster semiconductor, or a lower frequency, compared to when using one single switch. This paper also gives measured data for various IGBTs, and pictures of measured current sharing between parallel IGBTs.
