A new optically-isolated power converter for 12 V gate drive power supplies applied to high voltage and high speed switching devices

We present a new design for an isolated power converter using optical power transducer (OPT) technology. The converter transmits optical power from a laser diode (LD) to a phototransducer (PT) across an air gap. The PT device consists of 12 GaAs pn junctions, each current-matched to achieve a record optical-to-electrical power conversion efficiency of ≥ 66% with an open-circuit voltage of 14.5 V. Using a LD with 840 nm wavelength, the OPT can output more than 3.2 W of electrical power with 25% electrical-to-optical-to-electrical conversion efficiency, a value twice as efficient as a similar OPT built using previous generation PT technology. This new prototype successfully provides the driving power to the gate driver for 75 kV/μs fast switching of a SiC-MOSFET, made possible by a low stray input-to-output capacitance of ≤ 1 pF. We measure a 70% reduction in conducted electromagnetic interference (EMI) compared to a conventional transformer-based isolated power supply.