Power Supply Ripple and Filter Calculator
Find the ripple voltage of a rectifier-capacitor filter from load current, filter capacitance, line frequency, and rectifier type.
🔋 What is Power Supply Ripple?
Power supply ripple is the small residual AC voltage variation left on a rectified DC output after filtering, caused by a capacitor discharging into the load between the brief pulses when the rectifier conducts and recharges it. It appears as a sawtooth-shaped waveform superimposed on the average DC level, with amplitude given by Vripple(pp) = Iload / (fr * C).
Power supply designers use this calculation to size filter capacitors for linear power supplies, predict hum and noise on unregulated rail voltages, verify a downstream regulator's dropout margin (the regulator must tolerate the ripple's lowest point, not just the average), and compare half-wave versus full-wave rectifier topologies.
A common point of confusion is applying the same ripple frequency to both rectifier types. Full-wave rectification (bridge or center-tapped) delivers two conduction pulses per AC cycle, doubling the ripple frequency to 100 Hz or 120 Hz, while half-wave rectification only delivers one pulse per cycle, at the line frequency itself, requiring roughly twice the capacitance for the same ripple target.
This calculator computes peak-to-peak and RMS ripple voltage from your load current, filter capacitance, line frequency, and rectifier type, plus ripple as a percentage of DC output voltage when you provide it, and plots how ripple voltage falls as filter capacitance increases.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Full-Wave 1 A Supply with 1000 µF Filter
Full-wave, Iload = 1 A, C = 1,000 µF, fline = 50 Hz, Vdc = 12 V
Example 2 — Half-Wave 0.5 A Supply at 60 Hz
Half-wave, Iload = 0.5 A, C = 2,200 µF, fline = 60 Hz, Vdc = 9 V
Example 3 — Under-Filtered Full-Wave 2 A Supply
Full-wave, Iload = 2 A, C = 470 µF, fline = 50 Hz, Vdc = 24 V
❓ Frequently Asked Questions
🔗 Related Calculators
What is power supply ripple?
Power supply ripple is the small residual AC voltage variation that remains on a rectified DC output because a filter capacitor cannot fully smooth the pulsating output of a rectifier between successive conduction pulses. It appears as a sawtooth-like waveform riding on the average DC level.
What is the formula for ripple voltage?
The standard linear approximation is Vripple(pp) = Iload / (fr * C), where Iload is the DC load current, fr is the ripple frequency (twice the line frequency for full-wave, equal to line frequency for half-wave), and C is the filter capacitance.
Why does full-wave rectification reduce ripple?
A full-wave rectifier (bridge or center-tapped) delivers two current pulses per AC line cycle instead of one, doubling the ripple frequency. Since ripple voltage is inversely proportional to ripple frequency, this alone roughly halves the ripple voltage for the same load current and filter capacitance.
How do I convert peak-to-peak ripple to RMS ripple?
For the sawtooth-shaped ripple waveform typical of a capacitor-input filter, RMS ripple voltage is approximately Vripple(pp) / (2*sqrt(3)), about 0.289 times the peak-to-peak value. This RMS figure is more directly comparable to a hum specification measured with an AC voltmeter.
How much filter capacitance do I need for a target ripple voltage?
Rearrange the ripple formula: C = Iload / (fr * Vripple(pp)). Enter your target peak-to-peak ripple voltage instead of a trial capacitance, then solve for C directly, or read the required capacitance off the ripple-vs-capacitance chart above.
What ripple percentage is acceptable for a linear power supply?
For general-purpose linear supplies feeding a regulator, 5 to 10% ripple relative to the DC output is a common design target, since the downstream regulator's ripple rejection handles the rest. For unregulated supplies or audio applications, ripple well under 1% is usually required.
Does the ripple formula apply to switch-mode power supplies?
No, this formula models the classic linear rectifier-capacitor filter topology, where mains-frequency AC is rectified directly. Switch-mode supplies filter at their much higher switching frequency using a different topology and require separate ripple analysis based on switching frequency and output filter design.
Why does higher load current increase ripple?
Between rectifier conduction pulses, the filter capacitor supplies the load current entirely on its own, discharging linearly. A higher load current drains the capacitor faster during that interval, producing a larger voltage drop (ripple) before the next conduction pulse recharges it.
What line frequency should I use?
Use your actual AC mains frequency, 50 Hz in most of the world including India, Europe, and Australia, or 60 Hz in North America and parts of South America and Asia. The full-wave ripple frequency is then 100 Hz or 120 Hz respectively.
Is a larger filter capacitor always better?
Not entirely. A larger capacitor reduces ripple but also draws a higher, narrower peak charging current pulse from the rectifier and transformer each cycle, increasing diode and transformer stress and generating more conducted electrical noise, so capacitor sizing is a practical trade-off, not simply 'as large as possible'.