Smoothing Capacitor Calculator

A smoothing capacitor in a power supply filters the pulsating DC output of a rectifier into a steady voltage — the Smoothing Capacitor Calculator tells you exactly what capacitance you need. Enter your supply voltage, load current, line frequency, rectifier type, maximum ripple %, and diode voltage drop to get the required capacitance in µF. Secondary outputs include peak output voltage, average output voltage, ripple voltage, and ripple frequency. Also try the Capacitive Reactance Calculator.

V

RMS voltage from transformer

A

Current drawn by the load

%

Percentage of peak-to-peak ripple voltage

V

Forward voltage drop per diode

Results

Required Capacitance

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Peak Output Voltage

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Average Output Voltage

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Ripple Voltage (pk-pk)

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Ripple Frequency

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Frequently Asked Questions

What is a smoothing capacitor?

A smoothing capacitor is used in rectifier circuits to reduce voltage ripple and provide a more stable DC output. It stores energy when the rectified voltage is high and releases it when the voltage drops, smoothing out the variations. See also our Spherical Capacitor Calculator.

How does rectifier type affect capacitor sizing?

Full-wave rectifiers require smaller capacitors than half-wave rectifiers because they have twice the ripple frequency, allowing less time for the capacitor to discharge between charging cycles.

Why is ripple frequency important in capacitor calculation?

Higher ripple frequency means the capacitor has less time to discharge, so a smaller capacitance is needed to maintain the same ripple level. Full-wave rectifiers operate at twice the line frequency.

What happens if I use a capacitor that's too small?

Using an undersized capacitor will result in higher ripple voltage, poor regulation, and potentially unstable operation of circuits powered by the supply. You might also find our Capacitor Discharge Calculator useful.

Should I use a higher voltage rating for the capacitor?

Yes, always use a capacitor with a voltage rating at least 25-50% higher than the peak output voltage to ensure reliability and account for voltage variations.

How does load current affect capacitor requirements?

Higher load current causes the capacitor to discharge faster, requiring a larger capacitance to maintain the same ripple level. The capacitance requirement is directly proportional to load current.

What is the difference between peak and average voltage?

Peak voltage is the maximum instantaneous voltage, while average voltage is the effective DC level. With proper filtering, the average voltage approaches the peak voltage minus diode drops.