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RC Delay Calculator

Calculate RC Time Constant & Charge/Discharge Delay

Resistance R (Ω)
Capacitance C (F)
Supply Voltage V₀ (V)
Target Voltage Vt (V)

RC Charge/Discharge Formulas

Time Constant: τ = R × C
Charge: V(t) = V₀ × (1 - e^(-t/τ))
Discharge: V(t) = V₀ × e^(-t/τ)
Time: t = -τ × ln(1 - V(t)/V₀)

τ determines charge/discharge speed. 1τ = 63.2%, 3τ = 95%, 5τ = 99.3%.

⚠ Units: R=Ω, C=F, τ=seconds. Common values: pF(10⁻¹²), nF(10⁻⁹), μF(10⁻⁶), mF(10⁻³). Target voltage < supply voltage.

What is RC Charge/Discharge?

An RC circuit is a series resistor-capacitor network. When voltage is applied, the capacitor charges exponentially. When disconnected, it discharges. τ=R×C defines the speed.

Time Constant

τ=RC (seconds). Larger τ = slower. 1τ=63.2%, 3τ=95%, 5τ=steady state.

Charging

Voltage rises exponentially: V(t)=V₀(1-e^(-t/τ)). Fast initial rise, approaches V₀.

Discharging

Voltage decays: V(t)=V₀×e^(-t/τ). 36.8% at 1τ, near zero at 5τ.

Applications

Power-on reset, filters, 555 timers, PWM smoothing, soft-start, decoupling, and wave shaping.

💡 Example: R=10kΩ, C=100μF → τ=1s. Charge to 63.2% (3.16V) takes 1s. 90% = 2.303s. 5s = 99.3% (4.97V).

Applications

Power-On Reset RC Filters 555 Timers Wave Shaping Power Decoupling

Frequently Asked Questions

What is RC time constant τ?▼
Time constant τ = R×C (seconds). It is the time for a capacitor to charge to 63.2% or discharge to 36.8%. After 5τ, the capacitor is ~99.3% charged/discharged. Larger τ = slower response.
How long to charge to a target voltage?▼
Charge formula: V(t)=V₀(1-e^(-t/τ)). Solve for t: t=-τ×ln(1-V/V₀). 50% = 0.693τ, 90% = 2.303τ, 99% = 4.605τ.
What are RC circuit uses?▼
RC circuits are used for: delay circuits (power-on reset), filters (low/high pass), timers (555 IC), integrators/differentiators, decoupling, signal coupling, and soft-start circuits.
Why wait for capacitor measurements?▼
Multimeters charge the capacitor with a fixed current. Larger capacitors have bigger τ=RC, requiring more time to reach the measurement threshold for a stable reading.

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