A 125 kHz Self-Oscillating Inverter for Inductive Power Transfer Applications With Power MOSFET In-Circuit Self-Test

Low-frequency, self-oscillating inverters are widely used in Inductive Power Transfer (IPT) applications such as induction heating, household appliances, and electric vehicles. Due to cost constraints, transistors are often operated close to their absolute maximum ratings, which has a significant impact on the system reliability. The gate charge required to turn on a MOS transistor is closely related to oxide damage and can therefore be used as an indicator of device stress and aging. This paper proposes a novel approach to measure the turn-on gate charge that does not require the drain/source terminals to be disconnected from the high-current path, making it possible to monitor a power MOSFET under real conditions. For the first time, the idea is applied to an IPT system based on a self-oscillating inverter. The inverter schematic is modified to allow automated In-Circuit Self-Test (ICST), and experimental results are obtained. The turn-on gate charge and plateau gate voltage measured in-circuit are consistent with those obtained for the isolated MOSFETs (i.e., with an off-circuit test fixture). Although preliminary, these results demonstrate that ICST is a promising method for reliability assessment and predictive maintenance of WPT and IPT systems.