Rectifier Ripple Calculator (Smoothing Capacitor)
Peak-to-peak ripple voltage on the smoothing capacitor of a half-wave or full-wave rectifier, and the capacitance needed for a ripple you can accept.
Results
The dashed line marks the value you entered.
What this tool does
Between the peaks of the rectified voltage the capacitor supplies the load alone, so it loses a charge of about I × t: the ripple is I ÷ (f × C) for a half-wave rectifier, which recharges once per mains cycle, and half that, I ÷ (2 f × C), for a full-wave one, which recharges twice. The ripple frequency is 50 or 60 Hz for half-wave and 100 or 120 Hz for full-wave. The formula takes the capacitor as discharging for the whole period, so it slightly overestimates the ripple; the diodes meanwhile conduct in short pulses much larger than the load current.
Formula
ΔV ≈ I ÷ (f × C) half-wave · ΔV ≈ I ÷ (2 f × C) full-wave · C = I ÷ (k f ΔV) · Vrms ≈ ΔV ÷ (2√3)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
i | Load current | A |
f | Mains frequency | Hz |
c | Capacitance | µF |
ty | Rectifier | — |
vt | Ripple you can accept, peak to peak | V |
VP | Ripple voltage, peak to peak | V |
VR | Ripple voltage, about rms | V |
FR | Ripple frequency | Hz |
CN | Capacitance for the ripple you accept | µF |
Worked example
- Load current1 A
- Mains frequency50 Hz
- Capacitance4700 µF
- Rectifier2
- Ripple you can accept, peak to peak1 V
- Ripple voltage, peak to peak2.13 V
- Ripple voltage, about rms0.614 V
- Ripple frequency100 Hz
- Capacitance for the ripple you accept10,000 µF
Limitations
- Electrical installations are governed by national wiring rules. Cable sizing also depends on installation method, grouping, ambient temperature and protection devices, which this calculator does not evaluate.
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.