Phototransistor switch for breaker applications

An effort to develop a directly light-driven transistor with a view toward installing it in parallel with the mechanical breaker to relieve the stresses inherent in opening a mechanical circuit is described. This development divides into 3 main areas: first, the development of process suitable for fabricating high voltage transistors; second, a comprehensive set of calculations covering the most important aspects of design, fabrication, and operation of the device; and third, experimental measurements on prototype devices fabricated using the process developed. The calculations indicate that although it is possible to fabricate a high voltage-high current phototransistor, such a device is inherently incapable of operating efficiently under those conditions. This was verified on prototype devices which did achieve 1200V breakdown voltage, and did operate at up to 230 A-cm(2), but whose gain, even after amplification in a Darlington configuration, reached only about 40 before falling off again at high currents.