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RC Circuit Calculator

Calculate voltage and current over time in an RC (Resistor-Capacitor) circuit during charging and discharging.

Interactive Circuit

Voltage vs Time Graph

Understanding RC Circuits

An RC circuit consists of a resistor (R) and capacitor (C) in series. The behavior is governed by these equations:

Charging

v(t) = V(1 - e^(-t/τ))

i(t) = (V/R)e^(-t/τ)

Discharging

v(t) = Ve^(-t/τ)

i(t) = -(V/R)e^(-t/τ)

τ = RC

Time constant (τ) determines how quickly the circuit responds

V

Supply voltage

R

Resistance (Ω)

C

Capacitance (F)

t

Time (s)

RC Circuit Behavior Guide

Time Constants (τ)

Charging

  • 1τ: 63.2% of final voltage
  • 2τ: 86.5% of final voltage
  • 3τ: 95.0% of final voltage
  • 4τ: 98.2% of final voltage
  • 5τ: 99.3% of final voltage

Discharging

  • 1τ: 36.8% of initial voltage
  • 2τ: 13.5% of initial voltage
  • 3τ: 5.0% of initial voltage
  • 4τ: 1.8% of initial voltage
  • 5τ: 0.7% of initial voltage

Common Applications

Timing Circuits

Creating delays and oscillators in digital circuits.

Filtering

Smoothing power supply output and signal filtering.

Coupling

Blocking DC while passing AC signals between circuits.

Design Considerations

Component Selection

  • • Choose capacitor voltage rating > supply voltage
  • • Consider capacitor leakage current
  • • Account for resistor power dissipation
  • • Use low-tolerance components for timing

Circuit Analysis

  • • Allow 5τ for full charge/discharge
  • • Consider temperature effects
  • • Account for parasitic capacitance
  • • Monitor power supply stability