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Schmitt trigger

Op-amps and analog ICs · Intermediate · about 15 minutes · part of Zen’s Electronics Design Mastery

Positive feedback from the output to IN+ makes two thresholds: the output flips low when the input rises past the upper one and only flips back when it falls below the lower one. That hysteresis ignores noise on a slow signal.

Schmitt trigger: the circuit on the simulator's bench

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How it works

Feedback fraction β = R1/(R1+R2) = 0.175

Output swings to about ±10.5 V, so the thresholds are ±β·Vsat = ±1.842 V, a hysteresis band of 3.684 V.

Try it on the bench

  1. Lower R2 to 22 kΩ: the band widens. If it grows past the input peaks the output stops switching.
  2. Remove R2: with no feedback it becomes a plain comparator, flipping at 0 V.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “Op-Amps & Analog ICs”.

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