Ripple Voltage Calculator

Estimate ripple for a capacitor-input filter using load current, capacitance, and ripple frequency (half-wave / full-wave). Includes “solve for C” and Show Work.

How to Use

  1. Choose a mode: compute ripple from C, or compute required C from ripple.
  2. Enter load current and ripple frequency (or choose half-wave/full-wave based on mains frequency).
  3. Enter capacitance (or target ripple Vpp).
  4. Read outputs (Vpp, Vrms approx, ripple %) and open “Show Work” for steps.

This tool models the common capacitor-input discharge approximation (capacitor discharges between peaks). Real circuits can differ due to diode drops, transformer regulation, ESR/ESL, and load dynamics.

Filter Snapshot
Capacitor-input ripple estimate (discharge between peaks).
Vpp
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Vrms
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C req
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Ripple %
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Approx ripple (capacitor discharge) Vpp Uses: Vpp ≈ I / (f · C)
Inputs & Settings
Choose a mode, then enter values. Results update instantly.
Average load current (approx). Example: 0.2A, 1A, 5A
For mains rectifier: full-wave is 2× line freq (50→100Hz, 60→120Hz)
Bulk electrolytic examples: 470µF, 1000µF, 2200µF, 10000µF
Used only in “Solve C” mode
If provided, tool can compute ripple % = (Vpp / Vdc) × 100
Vrms approximations depend on shape (used for Vrms estimate only)
Show Work (step-by-step)
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Work is shown in base units (A, Hz, F, V) for clarity and consistency.

Reference (Capacitor-Input Approximation)

In a common approximation, the capacitor discharges between peaks by ΔV ≈ I · Δt / C. With ripple frequency f, Δt ≈ 1 / f, so:

  • Ripple (peak-to-peak): Vpp ≈ I / (f · C)
  • Required capacitance: C ≈ I / (f · Vpp)
  • Ripple percent (optional): % ≈ (Vpp / Vdc) × 100
For full-wave rectifiers, ripple frequency is typically f_ripple = 2 × f_line.

FAQ

Half-wave vs full-wave: what should I choose?

Half-wave ripple frequency is about the line frequency (50/60Hz). Full-wave is about 2× line frequency (100/120Hz), which reduces ripple for the same capacitance.

Why doesn’t this match my scope perfectly?

Real ripple includes diode drops, transformer regulation, capacitor ESR/ESL, wiring resistance, and non-constant load current. This tool is meant for fast estimating and sizing.

Does switching power supply ripple use the same formula?

Not directly. Switching ripple depends on topology, control loop, inductor ripple current, ESR/ESL, and load transients. This tool focuses on the capacitor discharge model; use it as a rough baseline unless you’re specifically in a “bulk cap between pulses” scenario.

Tool Info

Last updated:

Updates may include better ripple-shape modeling, ESR handling, and additional output formats.