Trigerring Methods

• • Thermal Triggering: Increase in temperature decrease the width of depletion layer of a semiconductor. If applied voltage is near the breakdown voltage, the increase in temperature triggers the SCR.
• • Radiation Triggering: SCR can be triggered by bombarding photons which results electron-hole pairs. Such SCR are called Light Activated SCR (LASCR).
• • Voltage Triggering: Increase in forward biased voltage causes electrons and holes to concentrate in the reverse biased junction. This increases the blocking current and the SCR is triggered.
• • Differential Triggering: If the rate of rise of voltage exceeds the critical rate of rise of voltage SCR is triggered.
• • Gate Triggering: This is most easy and useful method to turn ON SCR. While designing the gate circuit following points must be considered: Appropriate gate to cathode voltage must be applied when SCR is forward biased. Gate signal should be removed after SCR is turned ON. When SCR is reversed biased, no gate signal should be applied. When SCR is in the OFF state, negative voltage should be applied between the gate and cathode.