Thyristor turn-on methods on one card

Lesson notes

Key points

• Gate triggering: A positive gate current pulse with forward bias: the normal, controlled method.
• Forward voltage: Exceed forward breakover voltage and it turns on, usually unwanted and risky.
• dv/dt triggering: A fast-rising anode voltage charges junction capacitance and falsely triggers it.
• Thermal triggering: High temperature raises leakage current until the device turns on itself.
• Light triggering: Light on the junction creates carriers; used in LASCRs for HVDC valves.
• Snubber circuit: An RC across the thyristor limits dv/dt to stop false triggering.

Takeaway: Only gate triggering is wanted; the rest you design against.