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RC Time Constant Calculator — Solve τ, R or C + Cutoff & Timing

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Solve for Resistance Resistance unit Capacitance Capacitance unit Charge target (%) Must be greater than 0 and below 100.Remaining charge during discharge (%) Must be greater than 0 and below 100.

Calculated result

τ = 1 s

Solved RC set: 10 kΩ · 100 µF · τ 1 s

5τ settling reference: 5 s · ideal charge ≈ 99.326%

First-order cutoff: 0.159155 Hz

Time to 90% charge: 2.302585 s

Time to 10% remaining on discharge: 2.302585 s

Charge reference: 1τ 63.212% · 3τ 95.021% · 5τ 99.326%

Show the working

1. τ = 10 kΩ × 100 µF = 1 s.
2. fc = 1 ÷ (2π × 1 s) = 0.159154943 Hz.
3. Charge target time = −τ ln(1 − 0.9) = 2.302585093 s.
4. Discharge target time = −τ ln(0.1) = 2.302585093 s.

Ideal first-order RC model. Component tolerance, leakage, ESR, source impedance and connected load can shift real timing.

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