Industrial electronics
Explainer
The SCR: a switch that latches on
One tiny gate pulse can switch on thousands of amps and keep them flowing.
Quick check · tap an answer to continue
Lesson notes
Key points
- A silicon controlled rectifier, or SCR, is a four-layer PNPN device with three terminals: anode, cathode and gate.
- With forward anode voltage, a short gate current pulse triggers the device into conduction.
- Once anode current exceeds the latching current, the SCR stays on even after the gate signal is removed.
- It only turns off when anode current falls below the holding current, for example at an AC zero crossing.
Definitions
- Latching current
- Minimum anode current needed right after triggering for the SCR to stay on without gate drive.
Takeaway: The gate turns an SCR on; low anode current turns it off.
Quick check: Once latched, how does an SCR normally turn off?
- Remove the gate signal
- Current below holding value
- Apply more gate current
SCRTriggeringLatching currentHolding current
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