Triggering methods of SCR

What is Triggering?

The process of turning ON the SCR is called Triggering.

Various Triggering Methods of SCR

The following methods are generally used to turn on the SCR.

• Voltage Triggering
• Gate Triggering
• dv/dt Triggering
• Light Triggering

a. Voltage Triggering of SCR

If the forward voltage applied is equal to or exceeds the forward break-over voltage, the SCR turns on without any gate voltage. This method is not used because the SCR may be damaged.

b. Gate Triggering of SCR

When the SCR is in the forward blocking state, a positive gate voltage applied between the gate and the cathode can turn the SCR ON.

If the gate current is increased the forward blocking voltage is reduced. Due to gate current, charges are injected into the P-Layer. If the Gate current is higher, more charges are injected and lower is the forward breakover voltage. When gate current flows, the reversed biased junction breaks down and the SCR turns ON.

The Gate signal is not at all required after turn ON.

c. dv/dt Triggering of SCR

A reverse biased SCR is like a capacitor. If the applied forward voltage changes very rapidly, a charging current flows through the SCR and SCR turns ON. This method is not suitable because the SCR may be damaged.

d. Light Triggering if SCR

Light energy is used to hit the reverse-biased junction and free electrons are released. This cause the SCR to turn ON. This type of triggering is used in LASCR (Light Activated Silicon Controlled Rectifier).

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