Calculate the residual "ripple voltage" left on a DC supply built from a diode bridge plus a smoothing capacitor. Vary the line frequency, load current, capacitance and rectifier type and the peak-to-peak ripple, mean DC voltage and ripple factor update in real time, helping you design a low-ripple supply.
Parameters
Line frequency f_line
Mains frequency, fixed by region
Load current I_L
A
Mean current drawn on the DC side
Filter capacitance C
µF
Smoothing capacitor that absorbs the rectified ripple
Peak voltage V_peak
V
Crest value of the transformer secondary (V_rms·√2 − V_f)
Rectifier type
Full-wave uses a 4-diode bridge, half-wave uses a single diode
Results
—
Ripple frequency (Hz)
—
Ripple voltage (peak-to-peak) (V)
—
DC output voltage (mean) (V)
—
Ripple RMS (V)
—
Ripple factor (%)
—
Ripple quality grade
—
Rectifier circuit and output waveform — animation
Left: transformer + diode bridge + smoothing capacitor + load. Right: the rectified waveform and the triangular ripple traced as the capacitor voltage discharges to the next crest.
Peak-to-peak ripple voltage V_pp and the ripple frequency f_ripple. I_L: load current, C: smoothing capacitance, f_line: line frequency. Ripple is inversely proportional to both C and f_ripple.
Ripple factor r. General-purpose equipment targets a few %, while instrumentation and audio aim for under 1%.
What is the rectifier ripple voltage?
🙋
Inside an AC adapter or a power supply there's always a diode and a big capacitor. What are those doing exactly?
🎓
That's the classic "rectify + smooth" circuit. The electricity from a wall socket is AC — plus and minus swap 50 to 60 times per second. But LEDs and microcontrollers only run on DC. So first the diodes "flip the negative half to the positive side" — that's rectification. Then a large electrolytic capacitor "fills the troughs and flattens the wave" — that's smoothing. Those two stages turn AC into something close to DC.
🙋
But even with "peak voltage 17 V" on the left, the DC output reads 14.9 V — a bit lower. If the capacitor is supposed to flatten everything, shouldn't it stay at 17 V?
🎓
Good catch. Perfectly flattening it would need an infinite capacitor. In reality the voltage drops a little while the load is pulling current out, and each time the next AC crest arrives, it gets recharged with a quick spike. That sawtooth pattern of charge and discharge is the "ripple voltage". So the output sits at roughly "peak voltage minus half the ripple". The larger C is, the smaller the ripple and the closer the output to the peak.
🙋
Then why not just crank C way up? Sliding it to the top makes the ripple factor drop fast.
🎓
Yes, but making C bigger brings other problems. First, "inrush current". The moment you switch on, an empty giant capacitor charges to the peak voltage all at once, so tens of amps flow through the transformer and diodes. That blows fuses or destroys diodes. Second is physical size and lifetime — large electrolytic capacitors eat board space and their life shortens with heat. So in the field the rule is "use just enough C, and if it isn't enough, add a 3-terminal regulator or LDO downstream".
🙋
Switching "Rectifier type" from full-wave to half-wave at the top right halves the ripple frequency from 120 Hz to 60 Hz. What's the practical difference?
🎓
Full-wave uses 4 diodes as a bridge and charges the capacitor on both halves of the AC cycle. Half-wave uses one diode and only uses the positive half. So full-wave tops up the capacitor 120 times per second, while half-wave only 60 times. The longer the gap between top-ups, the more the capacitor discharges, so half-wave ripple is twice as large. That's why almost every supply uses full-wave rectification; half-wave is reserved for signal detection or extremely low-current uses.
🙋
The verdict says "above 15% needs additional filtering". What is "additional filtering"?
🎓
There are three main options. The simplest is to make C even bigger. Next is an "LC filter" — putting an inductor in series after the capacitor to block higher-frequency content. The most powerful is to add a "linear regulator" or a "switching DC-DC converter" downstream. For a microcontroller, the classic recipe is bridge + smoothing C to make ~20 V DC with ripple, then a 7805 3-terminal regulator behind it to deliver a clean 5 V with only a few mV of ripple.
Frequently Asked Questions
From the charge balance between the smoothing capacitor and the load, the peak-to-peak ripple voltage is approximated as ΔV_pp = I_L /(f_ripple · C), where I_L is the load current, C is the capacitance and f_ripple is the ripple frequency — 2·f_line for full-wave and f_line for half-wave rectifiers. For example at 60 Hz, full-wave, 0.5 A and 1000 µF, f_ripple = 120 Hz and ΔV_pp = 0.5/(120·1e-3) ≈ 4.17 V. This tool uses that formula to compute V_pp, V_rms and the ripple factor automatically.
The ripple factor is V_rms_ripple / V_dc expressed as a percentage and shows the size of the ripple relative to the DC output. As a practical guide: below 1% is "very low (good for audio and instrumentation)", 1-5% is "practically good (general equipment, motor drives)", 5-15% is "moderate (extra smoothing recommended)", and 15% or above is "large ripple (additional filtering required)". This tool computes the ripple factor from your inputs and grades it in four levels.
The ripple frequency is 2·f_line for full-wave but only f_line for half-wave, so for the same C and I_L the full-wave ripple is half. In addition, a half-wave rectifier charges the capacitor for only half of each cycle, giving a lower mean DC voltage and causing DC magnetisation of the transformer. In practice, four-diode bridge (full-wave) rectifiers are standard, and half-wave is limited to signal or very low-current applications. This tool lets you switch the rectifier type to see the difference.
From ΔV_pp = I_L /(f_ripple · C), there are three ways to lower the ripple: (1) increase the capacitance C, (2) raise the ripple frequency f_ripple (half-wave → full-wave, line frequency → switching supply), and (3) reduce the load current I_L. Increasing C is the easiest, but it trades off against inrush current at power-on (tens of A peak), physical size and capacitor lifetime. If even lower ripple is needed, add an LC filter, a 3-terminal regulator, an LDO or a switching converter downstream.
Real-World Applications
AC-DC adapters and linear supplies: Almost every laptop or router AC adapter, and the power section of any radio or analog audio gear, contains exactly this "bridge rectifier + smoothing capacitor". A transformer steps the mains down to a few V to tens of V AC, the bridge full-wave rectifies it, hundreds to thousands of µF smooth it, and a 3-terminal regulator (7805 etc.) or DC-DC converter stabilises the result. This tool is useful for estimating the rough DC voltage the front-end "rectifier + smoothing" stage delivers and the ripple budget that the downstream regulator must absorb.
Audio amplifiers and instrumentation: In vacuum-tube amps and analog audio, supply ripple shows up directly as hum (50/60 Hz, 100/120 Hz "buzz") at the output. Even a 1 W class commercial product targets a ripple factor below 1%, and high-end gear pursues below 0.1%, which is why they use tens of thousands of µF of electrolytics or CLC filters (capacitor → inductor → capacitor). Sweeping C and I_L with this tool is the first step toward sizing capacitance that meets your ripple target.
Motor drives and industrial rectifiers: A three-phase motor inverter starts by full-wave rectifying three-phase AC to a smoothed DC bus of several hundred volts. For three-phase full-wave, f_ripple = 6·f_line, which makes smoothing easy and avoids the need for very large C. This tool covers single-phase rectifiers, but the relationship between ripple frequency and C is the same fundamental study. It is also handy for benchtop rectifier experiments and DIY supplies that replace batteries.
Pre-study for power-supply boards: Before laying out a new supply PCB, you want to estimate "how many µF do I need to hit my ripple target?", "how big is the peak current?", and "do I still meet the dropout voltage of the 3-terminal regulator?". This tool serves as the back-of-the-envelope check for that initial sizing. The waveform-level work later moves to LTspice or PLECS, but having the order-of-magnitude right beforehand prevents parameter mistakes.
Common Misconceptions and Pitfalls
The biggest pitfall is "treating ΔV_pp = I_L/(f·C) as an exact equation". It is an approximation that assumes a triangular ripple from linear capacitor discharge and ignores the short conduction window during which the diodes recharge the capacitor. Under high load current, small C or high transformer source resistance, that conduction window can no longer be ignored, and the approximation error reaches 10-30%. Use this tool's numbers as a "starting-point, order-of-magnitude estimate" and confirm the final design with waveform-level simulators such as LTspice.
Next is the misconception that "a bigger capacitor solves everything". Doubling C halves the ripple, but it also doubles the inrush current at power-on. A 100 W linear supply with C above 10,000 µF can draw tens of amps of inrush, destroying the bridge diodes beyond their rating or making nearby lights flicker. The standard fix is to put an "inrush limiter" (NTC thermistor) in series with the input, or build a soft-start circuit. When choosing capacitance, consider not just ripple but also inrush, the capacitor's rated ripple current, board area and lifetime (the 10°C-doubling rule for electrolytics).
Finally, "peak voltage = DC output voltage". If the transformer secondary RMS is 12 V, the peak is 12·√2 ≈ 17 V, but the diode forward drop (0.7 V × 2 = 1.4 V across a full-wave bridge in silicon) subtracts off, and so does half the ripple (V_pp/2). The actual DC output is often more like 17 − 1.4 − V_pp/2 ≈ 13-14 V, and design mistakes that fail the dropout voltage (2 V for a 7805) of a downstream regulator are common. Always verify that "peak voltage − ripple width − diode drop − regulator dropout > target DC voltage" holds under the worst case (high load, low AC input).
How to Use
Select number of diodes in the rectifier bridge (iNum: 2 for half-wave, 4 for full-wave) and input AC supply frequency (iRange: typically 50 Hz or 60 Hz)
Enter smoothing capacitor value (cNum and cRange: e.g., 1000 µF, 2200 µF) and load resistance or current draw (vNum and vRange in ohms or amps)
Read output metrics: ripple frequency increases with diode count, ripple voltage (peak-to-peak) decreases with larger capacitance, and ripple factor (%) quantifies quality
Worked Example
Full-wave rectifier (4 diodes) from 230 V AC 50 Hz supply with 2200 µF electrolytic capacitor and 100 Ω load resistance yields: ripple frequency 100 Hz (double line frequency), DC output ~320 V (mean), ripple voltage peak-to-peak ≈ 4.2 V, ripple RMS ≈ 1.4 V, ripple factor ≈ 0.44%. Half-wave (2 diodes) same conditions produces ripple frequency 50 Hz and ripple voltage ~8.5 V peak-to-peak due to single pulse per cycle.
Practical Notes
Larger capacitors reduce ripple but increase inrush current at switch-on; use soft-start or series resistor (2–10 Ω) for 1000+ µF in industrial power supplies
Ripple factor below 5% suits audio amplifiers; below 1% required for precision DC instruments and analog sensor circuits
Load resistance affects RC time constant—light loads (high R) allow capacitor voltage to drop more between pulses, worsening ripple; heavy loads demand larger capacitors
Electrolytic capacitors degrade; assume 20% capacitance loss over 5 years in thermal environments (>60°C)