RC Time Constant Calculator
RC Time Constant (τ)
Calculate τ = R × C
Voltage at Time t
Calculate capacitor voltage during charging: V(t) = Vs × (1 - e^(-t/τ))
Formula
τ = R × C | V(t) = Vs × (1 - e^(-t/τ)) [charging] | V(t) = V₀ × e^(-t/τ) [discharging] | fc = 1 / (2πRC)
Frequently Asked Questions
What is an RC time constant?
The RC time constant (τ = R × C) is the time it takes for a capacitor to charge to approximately 63.2% of the supply voltage, or discharge to 36.8% of its initial voltage. After 5τ, the capacitor is considered fully charged (99.3%).
What are RC circuits used for?
RC circuits are used in timing circuits, filters (low-pass and high-pass), signal coupling and decoupling, power supply smoothing, debouncing switches, and wave-shaping circuits. The cutoff frequency of an RC filter is fc = 1/(2πRC).
How long does it take to fully charge a capacitor?
Theoretically, a capacitor never fully charges in an RC circuit. In practice, after 5 time constants (5τ), the capacitor reaches 99.3% of the supply voltage, which is considered fully charged for most applications.
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