Capacitor Size Calculator

Power Supply Filter Capacitors

After rectification, a filter capacitor smooths DC output by supplying current during voltage valleys. The required capacitance depends on load current, ripple frequency, and the maximum acceptable ripple voltage.

Capacitor Size Formula

$$C = \frac{I}{f \cdot \Delta V_{\text{ripple}}}$$

$I$ is load current in amperes, $f$ is ripple frequency in hertz, and $\Delta V_{\text{ripple}}$ is peak-to-peak ripple in volts. For full-wave rectified 50 Hz mains, use $f = 100$ Hz.

Example: 1 A load, 100 Hz ripple frequency, and 0.5 V acceptable ripple gives $C = 1 / (100 \times 0.5) = 20$ mF.

Frequently Asked Questions

What ripple frequency should I use?

For full-wave rectified AC, ripple frequency is twice the line frequency: 100 Hz for 50 Hz mains or 120 Hz for 60 Hz mains. Half-wave rectification uses the line frequency.

How much ripple is acceptable?

Depends on the load. Analog audio circuits may need under 10 mV ripple; general DC supplies often tolerate 0.1–1 V. Tighter ripple requires larger capacitors.

Why is my calculated capacitance so large?

High current and low ripple tolerance demand large capacitors. Reducing load current or accepting more ripple lowers the required value.

Can I use this for switching regulators?

This formula targets linear rectifier-filter supplies. Switching regulators have different input capacitor requirements based on duty cycle and switching frequency.

What capacitor type should I choose?

Low-ESR aluminum electrolytics are common for bulk filtering. Check voltage rating (typically 1.5–2× DC output) and ripple current rating for your load.

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Power Supply Filter Capacitors

Capacitor Size Formula

Frequently Asked Questions

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