Wide Bandgap Photoconductive Switches Driven by Laser Diodes as a High-Voltage Mosfet Replacement for Bioelectrics and Accelerator Applications

The Optical Transconductance Varistor (OTV) represents a new class of photonically controlled, high-voltage power electronic device. It takes advantage of the bulk photonic properties of wide bandgap (WBG) materials, eliminating the traditional semiconductor control junction. Without drift region limitations, carrier excitation occurs on the order of picoseconds and in the bulk of the crystal; decay of the carriers is dependent on doping. Conductivity is therefore proportional to optical intensity so the device exhibits a transconductance-like property, in contrast to conventional photoconductive semiconductor switches (PCSS). The device is bidirectional and inherent optical isolation provides scalability in voltage and current capability. Recent testing demonstrated switching for bioelectric applications of kilovolt levels at 1 MHz repetition rate with a 10 ns rise time. A second device with a 50% duty cycle demonstrated operation at 20 kV and 2.5 A at over 125 kHz switching frequency. The OTV has use in pulsed power applications such as electroporation and accelerators and also in higher duty cycle cases such as power conversion for the electrical grid. Device background, present status and future development are set forth.