Measurement of Large-Signal COSS and COSS Losses of Transistors Based on Nonlinear Resonance

In this letter, we present a new measurement technique to evaluate the large-signal output capacitance (COSS) of transistors as well as the COSS energy dissipation (EDISS), based on the nonlinear resonance between a known inductor and the output capacitance of the device under test. The method is simple and robust, and only requires a single voltage measurement to extract the large-signal COSS both in charging and discharging transients. By changing the circuit parameters, it is possible to tune the resonance frequency (even above 40 MHz) and the voltage swing (even above 1 kV) with dv/dt exceeding 100 V/ns, even though the method relies only on a low-voltage dc source, without the need for high-voltage RF amplifiers. The single-pulse operation of the method enables measuring COSS and EDISS at very high frequency and dv/dt values without any thermal runaway. Using the proposed method, we extracted large-signal COSS and EDISS of power transistors based on different semiconductor technologies. The obtained results were verified by Sawyer-Tower method and data reported in the literature. In particular, dv/dt-independent COSS losses were measured in cascode GaN transistors. The precise characterization of large-signal COSS of transistors presented in this letter is essential for the design of power converters, especially those operating at high switching frequencies.