# 5. SCR Turn-On Structure

## PNPN Stack

P+ – N-well – P-sub – N+

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## Regenerative Condition

\[
\beta_{NPN} \times \beta_{PNP} > 1
\]

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## Turn-On Sequence

1. Trigger event
2. NPN turns on
3. PNP turns on
4. Positive feedback loop
5. Latch-on