Ripple current calculator
Estimate capacitor ripple voltage and ripple (AC) current for rectifiers and switching converters. Enter load, frequency, C, and topology to get ΔVₚₚ and Iᵣ(rms).
buck converter ripple current
The speed with which the capacitor empties between pulses of recharging determines the capacitor ripple ( 1/C). In the case of rectifiers, 1/f (half-wave), 1/2 f (full-wave) is the time between peaks in conduction. Heating is defined by ripple current (the AC part of the current flowing through the capacitor). So topology-specific approximations (e.g., I_c,rms = 0.483 I_load for full-wave) should apply, compared to ratings of the capacitor (RMS current or ESR value)
Formula & Table Summary:
Rectifier: ΔVpp = I_load · Δt / C (half-wave Δt=1/f ; full-wave Δt=1/(2f)) C = I_load · Δt / ΔVpp I_c,rms ≈ 0.483·I_load (full-wave), ≈0.707·I_load (half-wave) Buck converter: ΔI_L = (Vin - Vout)/L · D / f_s I_c,rms ≈ ΔI_L / (2√3) ΔVpp ≈ ΔI_L / (8 f_s C) + (ΔI_L/2)·ESR
capacitor ripple voltage formula
Calculate the capacitor ripple voltage 1vpp and capacitor RMS ripple current (estimate) of rectifiers (half/full wave) and switching converters (buck). To verify the ripple and thermal limits, enter load/current, line/switching frequency, C, L (for converters), VIN/VOUT and ESR.
capacitor ripple calculator
| Topology | Inputs | Computed | Result |
|---|---|---|---|
| Full-wave rectifier | I=1.0 A, f=50 Hz, C=1000 μF | ΔVpp = I/(2fC); I_c,rms≈0.483·I | ΔVpp=1/(2·50·1000e-6)=0.01 V; I_c,rms≈0.483 A |
| Half-wave rectifier | I=0.5 A, f=60 Hz, C=470 μF | ΔVpp = I/(fC); I_c,rms≈0.707·I | ΔVpp=0.5/(60·470e-6)=17.7 mV; I_c,rms≈0.3535 A |
| Buck converter | Vin=12 V, Vout=5 V, L=10 μH, fs=500 kHz, C=47 μF | D=5/12, ΔI_L=(Vin-Vout)/L·D/fs | ΔI_L≈(7/10e-6)*(0.4167/5e5)=0.583 A; I_c,rms≈0.583/(2√3)=0.168 A; ΔVpp≈0.583/(8·5e5·47e-6)=0.0031 V + ESR term |
| Large smoothing cap | I=10 A, f=50 Hz, C=10000 μF | ΔVpp=I/(2fC) | ΔVpp=10/(2·50·1e-2)=0.10 V; I_c,rms≈4.83 A |
| Small converter cap | ΔI_L=0.2 A, fs=200 kHz, C=10 μF | I_c,rms≈ΔI_L/(2√3) | I_c,rms≈0.2/(2·1.732)=0.0577 A; ΔVpp≈0.2/(8·2e5·10e-6)=0.0156 V |
Frequently Asked Questions - Ripple current calculator:
What is ripple current?
Ripple current is the AC component of current that flows through a capacitor; it causes heating and limits capacitor life.
How do I compute peak-to-peak ripple voltage for a capacitor on a rectifier?
Use ΔVpp = I_load·Δt/C. For full-wave Δt=1/(2f); for half-wave Δt=1/f.
How do I size C to meet a ripple spec?
Rearrange: C = I_load·Δt / ΔVpp using the correct Δt for your topology.
What is capacitor RMS ripple current and why does it matter?
I_c,rms quantifies heating in the capacitor from AC current. Use the capacitor’s RMS/ESR rating to avoid overheating.
What approximate RMS factors apply for rectifiers?
For large-C capacitor input filters: full-wave I_c,rms≈0.483·I_load; half-wave I_c,rms≈0.707·I_load (engineering approximations).
How to estimate ripple current for a buck converter output cap?
Compute inductor ΔI_L, then I_c,rms≈ΔI_L/(2√3) (triangular approximation) and ΔVpp≈ΔI_L/(8 f_s C)+ESR·(ΔI_L/2).
Does ESR affect voltage ripple?
Yes. ESR causes an instantaneous voltage drop from ripple current: V_ESR_peak ≈ I_c,pk · ESR; include it when checking ΔVpp.
Can I use these formulas for electrolytic and ceramic capacitors?
Yes for voltage ripple and ripple current estimates, but check manufacturer RMS/ESR and temperature derating — ceramics have low ESR but may have capacitance change with voltage.
What if capacitor heating is high from ripple current?
Select capacitors with adequate ripple-current rating, parallel multiple caps to share ripple, reduce ESR, or increase switching frequency to lower ΔI impact.
Are these formulas exact?
They are engineering approximations valid for common waveforms (short recharge pulses or triangular inductor ripple). For precise design use waveform integration, simulation, or measurements.
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