Calculator Inputs
The page uses a single-column flow, while the input controls switch to 3 columns on large screens, 2 on medium, and 1 on mobile.
Formula Used
Buck Converter
Duty cycle: D = Vout / Vin
Inductor ripple current: ΔIL = ((Vin − Vout) × D) / (L × f)
Capacitive ripple: Vr(cap) = ΔIL / (8 × f × C)
ESR ripple: Vr(ESR) = ΔIL × ESR
Boost and Buck-Boost Converters
Boost duty cycle: D = 1 − Vin / Vout
Buck-boost duty cycle magnitude: D = Vout / (Vin + Vout)
Capacitive ripple: Vr(cap) = (Iout × D) / (f × C)
ESR ripple: Vr(ESR) ≈ Iout × ESR
Rectifier Capacitor Filters
Half-wave ripple frequency: fr = fline
Full-wave ripple frequency: fr = 2 × fline
Capacitive ripple: Vr(cap) = Iout / (fr × C)
Total ripple estimate: Vr(total) ≈ Vr(cap) + Vr(ESR)
These are engineering estimates. Real ripple depends on control loop behavior, parasitics, output current waveform, capacitor aging, layout, and measurement bandwidth.
How to Use This Calculator
- Select the output stage type that matches your design.
- Enter the nominal output voltage and load current.
- For converter modes, enter input voltage, switching frequency, and inductance.
- For rectifiers, enter the AC line frequency in the frequency field.
- Enter output capacitance and ESR from the capacitor datasheet.
- Leave duty cycle blank to let the calculator estimate it automatically.
- Press Calculate Ripple to show the result above the form.
- Review the summary, the steps, and the Plotly graph.
- Use the CSV or PDF buttons to save the current result.
Example Data Table
| Case | Topology | Key Inputs | Estimated Total Ripple |
|---|---|---|---|
| 1 | Buck | 12V to 5V, 2A, 300kHz, 220µF, 47µH, 0.03Ω ESR | 0.00660 Vpp |
| 2 | Boost | 12V to 24V, 1.5A, 200kHz, 470µF, 68µH, 0.02Ω ESR | 0.03798 Vpp |
| 3 | Buck-Boost | 12V to 18V, 1.2A, 250kHz, 330µF, 56µH, 0.025Ω ESR | 0.03873 Vpp |
| 4 | Full-Wave Rectifier | 12V output, 0.5A, 50Hz line, 2200µF, 0.08Ω ESR | 2.31273 Vpp |
FAQs
1. What is output voltage ripple?
Output voltage ripple is the periodic variation riding on a DC output. It is usually measured peak-to-peak and results from charging, discharging, switching, and capacitor ESR effects.
2. Why does ESR matter so much?
ESR converts ripple current into immediate voltage ripple. Even large capacitance can underperform if ESR stays high. Low-ESR capacitors often reduce ripple faster than simply adding more capacitance.
3. Does increasing capacitance always reduce ripple?
It reduces the capacitive part of ripple, but not all ripple sources equally. ESR ripple, layout noise, control loop behavior, and switching spikes can still dominate the final waveform.
4. Why is full-wave rectifier ripple frequency doubled?
A full-wave rectifier refreshes the capacitor on both halves of the AC waveform. That means the capacitor gets recharged twice each line cycle, so ripple frequency becomes two times line frequency.
5. When should I override duty cycle manually?
Override duty cycle when your controller uses a known operating point, when losses are significant, or when you want to compare ideal voltage-derived duty against measured or simulated duty.
6. Can this calculator replace oscilloscope measurements?
No. It provides engineering estimates for planning and comparison. Final verification should come from measurement using proper probing, bandwidth limits, grounding technique, and real load conditions.
7. What is the fastest way to reduce ripple?
Common fixes include lowering ESR, increasing capacitance, increasing switching frequency, optimizing inductance, improving PCB layout, and reducing current pulses seen by the output capacitor.
8. Why can simulation and real hardware differ?
Real parts have tolerance, temperature drift, parasitic inductance, aging, and nonlinear behavior. Layout coupling and measurement technique also introduce differences that ideal formulas and simplified models do not capture.