Coaxial Current Transformer for Test and Characterization of High-Power Semiconductor Devices Under Hard and Soft Switching

The use of a coaxial current transformer (CCT) is an interesting choice for pulsed measurement of current through power devices during switching transients. The CCT is used to reflect current for convenient external measurement with minimal insertion impedance in the critical power circuit. This paper analyzes the characteristics of the CCT and explains how it can be integrated into test setups for both press-pack and module packages. Finite-element techniques are applied to the study of the CCT to obtain detailed electrical and magnetic characteristics. Current distribution in the primary and secondary circuits, flux densities, and insertion inductance and resistance are among the design information that can be obtained through finite-element analysis. Analytical and numerical results are obtained for the proposed CCT that is integrated in test setups for MOS turn-off thyristors (press-pack) and high-voltage insulated gate bipolar transistors (module) characterization. Index Terms--Coaxial current transformer, current measurement, semiconductor device characterization.