5SHY4045L0006

The key to success was in the GTO itself. More precisely, the only thing wrong with it was an enormous control problem. Because of the demand for high turn-off amplification, the GTO passes through a region during the transition from the conducting (thyristor) to the non-conducting (transistor) states when both anode voltage and cathode current are impressed (red background). As with a mechanical switch, however, a four-layer device can only assume one of two stable states — on and off. The transition tends to instability and has to be got through as quickly as possible and be supported by snubber

The rate-of-change of the drive is critical for the operation of the GCT. The cathode current has to be turned off in less than 1 µs, otherwise the device moves into the unstable part of the characteristic. This corresponds to dIG/dt ≥ 3000 A/µs for a 3 kA GCT and proportionally more or less for other types. The voltage needed results for a given inductance of the gate circuit, respectively the inductance for a given gate voltage.
On the other hand, a simple, reliable and cost-effective drive unit is only possible at low voltages. An ideal voltage is –20 V, because the gate can withstand this voltage after turn-off. The permissible leakage inductance for interrupting 3 kA is 6 nH or less which is only 1/50 of the usual value for a GTO. It was possible to achieve this value by adopting a coaxial configuration of the device connection and a multi-layer connection to the power output of the drive