A design tradeoff relationship between thyristor ratings

Designers of high-power circuits have not previously been able to quantitatively estimate the design tradeoffs which are available between the blocking voltage, current density, and turn-off time of a thyristor. In this paper, a new tradeoff relationship is derived by combining simple relationships from well-known device theory. The constants in this relationship are empirically adjusted to correlate with present commercial thyristors. The relationship shows that for a given turnoff time there is a corresponding blocking voltage which allows a given thyristor size to control the maximum load power. It also shows the penalties involved for other choices of these ratings. Generalized plots will help the circuit designer to more fully understand the interaction of device tradeoffs and circuit tradeoffs. The relationship emphasizes the thermal basis for current ratings, and also provides an objective means for comparing various thyristors.