Advances in Photon Triggered Thyristors for High Current Applications

Thyristors are a semiconductor closing switch with inherent low forward voltage drop and high voltage blocking capability. Typically, these devices are turned on with a current pulse to a gate electrode or by a localized light pulse. Both of these methods limit the rate-of-rise of current (dl/dt), especially for high voltage devices. Increasing the gate area results in an increased dl/dt but at the expense of a reduction in the current carrying area. With the advance of light triggering using "leaky" fibers, quasi-uniform illumination of a thyristor can now be realized resulting in high dl/dt for high voltage (>10 kV) devices. The large area illumination is accomplished using fiber-coupled diode laser bars. Examples of test circuits and their corresponding current waveforms are shown using large area illumination thyristors (~100 kA, ~lMA²-sec).