Editing Silicon controlled rectifier (section)

== Thyristor turn-on methods ==

# forward-voltage triggering
# gate triggering
# ''dv''/''dt'' triggering
#thermal triggering
# light triggering

Forward-voltage triggering occurs when the anode–cathode forward voltage is increased with the gate circuit opened. This is known as avalanche breakdown, during which junction J2 will break down. At sufficient voltages, the thyristor changes to its on state with low voltage drop and large forward current. In this case, J1 and J3 are already forward-[[Biasing|biased]].

In order for gate triggering to occur, the thyristor should be in the forward blocking state where the applied voltage is less than the breakdown voltage, otherwise forward-voltage triggering may occur. A single small positive voltage pulse can then be applied between the gate and the cathode. This supplies a single gate current pulse that turns the thyristor onto its on state. In practice, this is the most common method used to trigger a thyristor.

Temperature triggering occurs when the width of depletion region decreases as the temperature is increased. When the SCR is near VPO a very small increase in temperature causes junction J2 to be removed which triggers the device.