Equivalent‐circuit model analyses of the dv/dt characteristics of a complex pnpn switch circuit

This paper describes a complex pnpn switch (thyristor) circuit which offers high noise-immunity and high gate-sensitivity at the same time. The circuit has a protection transistor which short-circuits the gate and cathode of the thyristor instantaneously when a noise enters. This has a critical slew rate of about 1000 V/μs (= 200 V/0.2 μs) at a gate-trigger current of 0.1 mA. However, it is found that the thyristor makes a false turn-on when the storage time of the protection transistor is shorter than the gate recovery time of the thyristor. This phenomenon is designated “a turn-off time racing false ignition.” To analyze this phenomenon, an equivalent circuit of the complex pnpn switch circuit is proposed. It is found that no false turn-on occurs when the anodecathode voltage of the thyristor is lower than the dynamic blocking voltage VF.