Fast high current switch for higher power switching power supplies

In a high power switched mode supply (SMPS) there is a need for a high power switching device. Generally three types of semiconductor switching devices are used in this type of application, thyristors, bipolar junction transistor (BJTs) and field effect transistors (FETs). Thyristors can handle very high power, but suffer from relatively slow switching times, and are generally used at frequencies below 10 kHz. BJTs with high power handling capabilities are also slow, particularly high current devices, and maximum switching frequencies are typically under 50 kHz. FETs can be switched on and off very fast and can operate at frequencies above 100 kHz. However, their power handling at high voltages is not as good as thyristors or BJTs. The authors present a technique for paralleling two low cost, medium power BJTs driven by a single low voltage, high current FET to form a high voltage, high power, high speed switching module