A Schmitt trigger is a comparator with hysteresis: it has two switching thresholds instead of one — an upper trip point V₊ and a lower one V₋. The output goes high only when the input rises above V₊, and goes low only when the input falls below V₋. The gap (V₊ − V₋) is the hysteresis band.
Why use it
- Noise immunity: a noisy signal hovering near a single threshold makes a plain comparator chatter; the hysteresis band absorbs the noise.
- Clean edges from slow signals: a slowly rising/falling input (e.g. an RC ramp) is converted into a single, fast, well-defined output transition.
- Debouncing mechanical switch inputs.
Common uses
- Undervoltage lockout (UVLO) and power-on enable logic — see inrush current.
- Squaring up slow or noisy signals into clean logic levels.
- Simple RC relaxation oscillators.
Often available as a logic gate variant (e.g. 74HC14 inverter) or built from an op-amp / comparator with positive feedback.