What is an RC Time Constant?
The RC time constant describes how quickly a capacitor charges or discharges through a resistor.
The symbol for the time constant is τ, pronounced "tau".
RC Time Constant Formula
τ = R × C
What Happens During Charging?
After one time constant, the capacitor reaches approximately 63.2% of its final voltage.
After five time constants, the capacitor reaches approximately 99.3% of its final voltage.
Common RC Timing Points
- 1τ = 63.2%
- 2τ = 86.5%
- 3τ = 95.0%
- 4τ = 98.2%
- 5τ = 99.3%
Capacitor Charging Formula
Vc = Vs × (1 - e-t/RC)
This formula calculates the capacitor voltage during charging.