The Rating and Application of SCRs Designed for Power Switching at High Frequencies

Inverter, chopper, and other pulse applications, operating at repetition rates up to 25 000 pps (pulses per second), are very demanding for the silicon controlled rectifier because of the high rates of rise of anode current (di/dt) which are imposed. The di/dt rating of the SCR is important since high di/dt of anode current produces excessive heating in the device and, if this is not controlled, device destruction will result. This necessitates an SCR specifically designed for such applications and, also, a family of performance curves to enable the circuit designer to determine its capability reliably in his particular application. These performance curves consider the combined effect of the important SCR dynamic parameters, di/dt, dv/dt, and turn-off time. As a result, the high-frequency SCR is adaptable to many applications which previously imposed dynamic conditions too severe for SCRs to withstand because of excessive switching losses. The use of these curves is demonstrated through actual circuit application examples. The rating methods used for high-frequency SCRs are discussed and compared to methods normally used for conventional SCRs which do not include the effects of switching losses and high di/dt.