Industrial electronics
Explainer
Why SCRs fire when you didn't ask
An SCR can switch on with zero gate current. Here's the exam trap.
Quick check · tap an answer to continue
Lesson notes
Key points
- A rapid rise of anode voltage, dv/dt, charges the junction capacitance and the charging current can act like gate current.
- A snubber, a resistor and capacitor in series across the SCR, slows dv/dt and prevents this false triggering.
- Other turn-on routes are exceeding the forward breakover voltage, high temperature and light on the junction.
- Do not confuse protections: snubbers limit dv/dt, while a series inductor limits di/dt at turn-on.
Takeaway: Snubbers tame dv/dt; series inductors tame di/dt.
Quick check: Which component limits dv/dt across an SCR?
- Series inductor
- Parallel RC snubber
- Gate resistor
dv/dt triggeringRC snubberTurn-on methodsdv/dt vs di/dt
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