LM393 Working Principle & Circuit Explanation

LM393 working principle: illustrated functional stages, basic circuit and connections — Select the diagram to read it at full resolution.

How it works

3 stages · Explore one step at a time

Step 1 / 3

Compare the two inputs

The differential input stage responds to IN+ minus IN−. No analog-to-digital converter or firmware is needed.

Step 2 / 3

Sink current or release the node

A negative input difference turns the output transistor on. A positive difference turns it off. The external pull-up supplies the HIGH level.

Step 3 / 3

Make a stable decision

Keep inputs in their common-mode range. Add positive-feedback hysteresis when a slowly changing or noisy signal would chatter around the threshold.

Find the switching threshold

Adjust VIN and the reference. Remove the pull-up to see why it matters.

5 V · DC explorer

Signal input IN+ · V Reference IN− · V Connect 10 kΩ pull-up to 5 V

IN+ − IN−—

Output state—

Pull-up current—

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Violet: offset-sensitive transition · Amber: input outside the recommended range.

DC teaching model for channel A. The ±9 mV band uses the maximum input-offset magnitude over 0–70°C; it is uncertainty, not hysteresis. LOW uses a 0.13 V illustrative estimate. Propagation delay, input bias, leakage and noise are omitted.

LM393 Working Principle

LM393 at a glance