A Resonant Approach to Transformer Loss Characterization

While a transformer's inductance matrix is reason-ably constant with respect to drive and frequency (up until self-resonance) and can be measured using a network analyzer, its losses are nonlinear functions of frequency and therefore difficult to characterize, especially at MHz frequencies and above. This paper presents a resonant approach to measuring a transformer's losses, including the coupled effects of both windings, at a specific operating point. We further show that, to an acceptable error, the results can be extrapolated to different operating points. The method is experimentally validated by the characterization of several transformers whose losses are confirmed by hand calculation, finite element analysis simulation, and calorimetric measurement. This work enables accurate and full characterization of transformer losses in the high frequency regime.