Improved L-C resonant decay technique for Q measurement of quasilinear power inductors: New results for MPP and ferrite powdered cores

The L-C resonant decay technique for measuring circuit Q or losses is improved by eliminating the switch from the inductor-capacitor loop. A MOSFET switch is used instead to momentarily connect the resonant circuit to an exciting voltage source, which itself is gated off during the decay transient. Very reproducible low duty cycle data could be taken this way over a dynamic voltage range of at least 10:1. Circuit Q is computed from a polynomial fit to the sequence of the decaying voltage maxima. This method was applied to measure the losses at 60 kHz in inductors having loose powder cores of moly permalloy (MPP) and a Mn-Zn power ferrite. After the copper and capacitor losses are separated, the resulting specific core loss is shown to be roughly as expected for the MPP powder, but anomalously high for the ferrite powder. Possible causes are mentioned.