FREE ENGINEERING CALCULATOR · BILINGUAL
Capacitor Current Calculator: AC Ripple & ESR Loss
Calculate capacitor RMS current, peak current and ESR heating from capacitance, frequency and sinusoidal AC voltage, or solve for voltage from current. Supports ideal capacitance and a series ESR model.
Enter parameters
Or load an example:
Calculated results
Parameters changed. Select Calculate to update the results.
| RMS current | 0.0628306129 A |
|---|---|
| Peak current | 0.0888559048 A |
| Terminal AC voltage RMS | 1 V |
| Capacitive reactance |Xc| | 15.9154943 Ω |
| Total impedance |Z| | 15.9158085 Ω |
| Ideal capacitor voltage RMS | 0.999980261 V |
| ESR power dissipation | 0.000394768591 W |
Single-frequency sinusoidal AC component only. Voltage is RMS across the complete series C + ESR model, not the DC bus voltage.
Calculation formulas
Xc = 1/(2πfC) · |Z| = √(ESR² + Xc²) · Irms = Vrms/|Z| · Ploss = Irms² × ESR
How is capacitor current calculated?
Starting with i = C·dv/dt, differentiating a sine voltage gives the ideal relation Irms = 2πfCVrms. With ESR, the resistive and capacitive voltage drops are 90° apart, so their magnitudes combine in quadrature. Set ESR to zero to recover the ideal equation.
Example: 1 μF, 50 Hz, 10 V RMS
An ideal capacitor has about 3183.10 Ω reactance, 3.14159 mA RMS current and 4.44288 mA peak current. Doubling frequency or capacitance doubles ideal current. Significant nonzero ESR limits that proportional relationship.
Can I enter switching-supply ripple?
A single sinusoidal ripple component fits this model. Triangular, pulsed and rectifier charging waveforms contain multiple harmonics; their total RMS voltage and switching frequency alone are insufficient. Analyze the harmonics or the circuit current waveform. DC bias is excluded from steady AC current but can affect capacitance and component ratings.
Does ESR loss determine the ripple rating?
The result is dissipation at the entered operating point, not an allowable-current rating. ESR changes with frequency and temperature; allowable ripple also depends on heat removal and the datasheet. Near self-resonance, parasitic inductance matters and this series RC model is insufficient.
Quick reference
Fixed ideal capacitance 1 μF, sinusoidal voltage 1 V RMS, ESR = 0.
| f (Hz) | |Xc| (Ω) | Irms (mA) |
|---|---|---|
| 50 | 3183.09886 | 0.314159265 |
| 60 | 2652.58238 | 0.376991118 |
| 100 | 1591.54943 | 0.628318531 |
| 1000 | 159.154943 | 6.28318531 |
| 10000 | 15.9154943 | 62.8318531 |