Calculate
Formula and method
τ = R × C, with R in ohms and C in farads. Charging toward Vf: V(t) = Vf + (V0 − Vf)e−t/τ. Discharging toward zero: V(t) = V0e−t/τ. Transition fraction is 1 − e−t/τ.
Worked example
10 kΩ and 100 µF give τ = 1 second. Charging from 0 to 5 V yields about 3.1606 V at 1 second; discharging from 5 V yields about 1.8394 V.
Limits and safety
At 1τ, approximately 63.2% of a transition is complete; at 5τ, approximately 99.3%. Neither is exactly fully charged or discharged. Ideal R/C behavior does not model leakage, tolerance, ESR, or source limits.
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