Capacitor Ripple Estimate: Charge Loss Depends on Load and the Gap Between Charging Events

Define the charge-loss approximation

Capacitance relates charge and voltage through Q = CV. With constant load current over a defined discharge interval, charge loss IΔt gives an ideal voltage-change magnitude IΔt/C. Primary reference: charge and capacitance.

This comparison assumes the capacitor supplies that current for the stated time. It does not include its equivalent series resistance, leakage, changing capacitance or the detailed replenishment waveform. Those effects belong in the actual supply analysis.

A hypothetical storage calculation

Suppose a fictional constant load draws 0.020 A for 8 ms from a 100 µF ideal capacitor. Charge loss is 0.020×0.008 =0.00016 C, and modeled voltage reduction is 1.6 V. Doubling only capacitance to 200 µF reduces the estimate to 0.8 V.

Using 10 ms instead of 8 ms with the original capacitance gives 2.0 V. The time basis matters independently of capacitor size. These invented cases do not select a smoothing capacitor, guarantee a supply output or account for its charging-current stresses.

Keep the interval traceable

Write the load-current assumption, actual discharge window, capacitance condition and calculated change in separate fields. Identify the event that starts and ends the window.

If a proposal names only source frequency, ask how its actual charging interval establishes the gap used in the estimate. Keep the simplified arithmetic beside the omitted effects so a reviewer can decide what additional waveform or component evidence the application needs.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: charge and capacitance