Power Supply Ripple Calculator Formula
Understand the math behind the power supply ripple calculator. Each variable explained with a worked example.
Formulas Used
Ripple Voltage (Vpp)
ripple_vpp = load_current_a / (cap_farads * frequency_hz)Ripple Voltage (Vrms)
ripple_vrms = load_current_a / (cap_farads * frequency_hz) / (2 * sqrt(3))Variables
| Variable | Description | Default |
|---|---|---|
load_current_a | Load Current(A) | 1 |
filter_cap_uf | Filter Capacitance(µF) | 1000 |
frequency_hz | Ripple Frequency(Hz) | 120 |
cap_farads | Derived value= filter_cap_uf / 1000000 | calculated |
How It Works
Power Supply Ripple
Formula
V_ripple = I_load / (C x f)
Where f is the ripple frequency (120 Hz for full-bridge rectifier on 60 Hz mains). Larger capacitance or lower current reduces ripple.
Worked Example
1 A load, 1000 uF filter cap, 120 Hz ripple (full-bridge on 60 Hz).
load_current_a = 1filter_cap_uf = 1000frequency_hz = 120
- 01C = 1000 / 1000000 = 0.001 F
- 02V_ripple = 1 / (0.001 x 120) = 8.33 Vpp
- 03V_rms = 8.33 / (2 x 1.732) = 2.406 V
Frequently Asked Questions
Why 120 Hz for 60 Hz mains?
A full-bridge rectifier produces two pulses per cycle, doubling the ripple frequency. Half-bridge gives 60 Hz ripple.
How much ripple is acceptable?
Depends on the load. Typically under 5% of DC voltage. Sensitive circuits need millivolt-level ripple from additional regulation.
Does adding more capacitance always help?
Yes for ripple, but very large caps draw high inrush current and may exceed rectifier surge ratings.
Ready to run the numbers?
Open Power Supply Ripple Calculator