How SCRs Function

Unlike transistors, which may show an exponentially varying output current pattern, equivalent to the applied input switching current, SCRs have specific triggering levels below which they may not conduct properly. However, once the trigger level crosses the optimal value, an SCR may swing into full conduction.
Another typical property associated with SCRs is their “latching” behavior with DC operated loads, where the anode to cathode conduction through the load latches or “holds-on” even after the gate trigger is inhibited. However, with AC operated loads the above drawback, or rather benefit, is not available and the load is switched ON or OFF exactly in response to the switching of the SCR’s gate triggers.
The following few simple SCR circuits are based on the above properties of the device. Let’s learn how the discussed features can be exploited for some useful applications.