Capacitor Ripple Voltage Calculator
Peak-to-peak ripple on a bulk or switching capacitor.
How to Use
- Enter I load, frequency, cap, and ESR.
- Vr = I/(f·C) + I·ESR. Switch ESR term often dominates.
Show Work
Notes
History of ESR and Capacitor Evolution
Equivalent Series Resistance became a critical spec in the 1990s with the rise of high-frequency SMPS. A reservoir capacitor at 50 Hz mains is dominated by the capacitive-reactance ripple term I/(f·C); at 500 kHz switcher frequency, that term vanishes and the resistive ESR term I·ESR dominates. Suddenly the capacitor's effective impedance floor (its ESR) set the output ripple, regardless of how many more microfarads you added.
The "capacitor plague" of 1999-2007 was an industry-wide failure cascade: conventional aluminum electrolytic capacitors made with a defective electrolyte formulation bulged, leaked, and failed prematurely on motherboards, graphics cards, and consumer electronics worldwide. The root cause was a stolen-and-botched formulation from Rubycon's aqueous electrolyte. The response accelerated adoption of conductive polymer capacitors (OS-CON, Poscap) which have 1/10th the ESR and ~10× the life of conventional aluminum.
Modern SMPS designs use a hybrid approach: bulk aluminum polymer (low ESR for ripple current) paralleled with ceramic multi-layer caps (extremely low ESR at > 1 MHz) to handle transient currents from fast load steps. The X7R/X5R ceramic capacitor revolution (1990s onward) pushed per-piece capacitance from 1 µF to 47 µF in standard 1206 packages — making polymer-aluminum bulk caps optional on point-of-load converters.
About This Calculator
Enter the ripple current, operating frequency, capacitance, and equivalent series resistance (ESR). The tool computes capacitive ripple Vc = I/(f·C), resistive ripple Ve = I·ESR, total ripple Vt (worst-case sum), and the capacitor's reactance Xc = 1/(2πfC). Typical ESR values: aluminum electrolytic 50-200 mΩ, polymer 10-30 mΩ, ceramic 1-10 mΩ.
Rule of thumb: if Ve > Vc by 3× or more, adding more capacitance won't help — you need lower ESR, i.e., polymer or parallel ceramics. For typical buck converter output, place a 47-100 µF polymer in parallel with 2-4 × 10 µF ceramics to cover both low-frequency ripple and high-frequency transients. Everything runs client-side; no values leave your browser.
About the Capacitor Ripple Voltage Calculator
Capacitor Ripple Voltage Calculator is a quick, free tool for electronics and circuit design. It works in your browser and keeps everything on your device. Peak-to-peak ripple on a bulk or switching capacitor.
How it works
Enter your figures and the result appears instantly, updating the moment you change anything. There is no submit button and nothing to wait for, so it is easy to try a few what-if numbers and compare the results. Just check each box holds the kind of value it expects.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Why ESR dominates?
Modern high-frequency converters — capacitive term is already tiny.
Buck ripple?
Vr ≈ I_L_pp/(8·fsw·C) + ESR·I_L_pp.
How do I use the Capacitor Ripple Voltage Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
Linear PSU
120 Hz ripple.
Buck Output
ESR-dominated.
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