Precise Evaluation of Input, Output, and Reverse Transfer Capacitances of Power Devices
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Increasing Importance of Capacitance Measurement
The switching frequency in power conversion circuits is increasing. This primarily reduces the size of passive components, such as smoothing capacitors and reactors. Accurate characterizing device parameters affecting switching performance becomes more important as higher switching frequencies increase power circuit switching losses.
Rg and Crss dictate switching speed while Ciss determines driving condition. Power loss due to charging and discharging Coss is the primary component of switching loss in the case of a resonant converter. Crss and Coss have voltage dependency in the nano-farad range due to the power device’s depletion region modulating with applied varying operational voltages.
These capacitances are conventionally measured by an LCR meter. However, the maximum voltage of an integrated LCR voltage source is limited to around ±40 V. Therefore, most device data sheets do not include capacitance measurement data with more than ±40 V bias.