In addition to diodes, thyristors are also used for transient suppression
(Figure 5.13). They are typically four-layer (pnpn) semiconductor devices for unidirectional
and five-layer devices for single-chip bidirectional use. Thyristors are
turned to the on state by a voltage trigger as shown in Figure 5.10. In the turn on
state, the voltage drops across the device is only a few volts, allowing large surge
current conduction through it. Operating voltages range from 20 V up to 250 V
with current ratings of 50 to 200 A for 10/100 ms.