# 3. Snapback Physics

## Negative Differential Resistance

\[
\frac{dV}{dI} < 0
\]

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## Characteristic Points

- \( V_{t1} \): Trigger voltage
- \( V_h \): Holding voltage
- On-state resistance

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## Mechanism

1. Avalanche breakdown
2. Carrier injection
3. BJT activation
4. Voltage collapse