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Comparator Threshold Calculator

Work out comparator threshold instantly with clear inputs, formula shown and shareable results.

About Comparator Threshold Calculator

The comparator threshold is set by a resistor divider from the reference. Adding positive feedback through a large resistor shifts the threshold depending on the output state, creating hysteresis that prevents chatter when a slow or noisy input crosses the threshold.

Formula

Comparator with hysteresis

Vth = V x R2/(R1+R2); hysteresis window = V x (R1||R2) / ((R1||R2) + Rhyst)

Worked example

With the default values below, Comparator Threshold Calculator returns Nominal threshold of 2.5000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Reference supply
5 V
Upper divider resistor
10,000 Ω
Lower divider resistor
10,000 Ω
Hysteresis feedback resistor
1,000,000 Ω

Results

Nominal threshold
2.5000 V
Upper trip point
2.5124 V
Lower trip point
2.4876 V
Hysteresis window
24.88 mV

Step by step

  1. 1Values used
  2. 2Comparator with hysteresis
  3. 3Nominal threshold= 2.5000 V
  4. 4Upper trip point= 2.5124 V
  5. 5Lower trip point= 2.4876 V
  6. 6Hysteresis window= 24.88 mV

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Why is hysteresis necessary?

Without it, noise on a slowly changing input causes multiple transitions at the crossing point. Hysteresis makes the threshold move away after each switch.

How much hysteresis should I use?

At least a few times the peak-to-peak input noise. Too much delays detection and shifts the effective trip level.

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