The RC time constant (τ) is the time required to charge a capacitor through a resistor to approximately 63.2% of the supply voltage. It is given by the product of resistance (R) and capacitance (C). This calculator computes the time constant, cutoff frequency, and voltage at specific time intervals. Essential for filter design, timing circuits, and pulse shaping.
📐 RC Circuit Formulas
Time Constant: τ = R × C (seconds) Cutoff Frequency: f_c = 1 / (2π × τ) (Hz) Charging Voltage: Vc(t) = Vf × (1 - e^(-t/τ)) Discharging Voltage: Vc(t) = Vi × e^(-t/τ)
📊 RC Time Constant Reference
RC Combination
τ (seconds)
f_c (Hz)
Application
100Ω / 100µF
0.010
15.9
Power supply filtering
1kΩ / 100µF
0.100
1.59
Audio filtering
10kΩ / 10µF
0.100
1.59
Timing circuits
100kΩ / 1µF
0.100
1.59
Low frequency filters
1MΩ / 0.1µF
0.100
1.59
Long timing
10kΩ / 100nF
0.001
159
High pass filter
📌 Charge/Discharge Percentages
1τ (63.2%): Charged to 63.2% of final voltage
2τ (86.5%): Charged to 86.5% of final voltage
3τ (95.0%): Charged to 95.0% of final voltage
4τ (98.2%): Charged to 98.2% of final voltage
5τ (99.3%): Considered fully charged
💡 Applications of RC Circuits
Low-Pass Filters: Pass low frequencies, block high frequencies
High-Pass Filters: Pass high frequencies, block low frequencies