Buck Output Inductor Ripple Calculator

Calculate peak-to-peak inductor current ripple for a buck converter output choke. Verifies against inductor saturation current and output capacitor ESR.

Calculator Electronics Updated Apr 23, 2026
X Facebook LinkedIn Reddit Email
How to Use
  1. Enter input voltage, output voltage, switching frequency, inductor value, and load current.
  2. Tool computes ΔI_L pp and peak inductor current to verify against I_sat.
Input
V
V
Hz (kHz OK)
H (µH OK)
A
A
Presets
Inductor Current
ΔI_L pp
—A
% of I_out
—%
I_peak
—A
Duty D
—

Show Work

Enter values.

Formulas

Duty cycle
D = V_out / V_in
Ideal buck.
ΔI_L
V_out · (1 − D) / (f_sw · L)
Peak-to-peak ripple.
I_peak
I_out + ΔI_L / 2
Check vs I_sat.
CCM/DCM
CCM if I_out > ΔI_L/2
Else DCM.
Solve L
L = V_out·(1-D) / (f·ΔI_L_target)
Size for 30% ripple.
Output ripple V
ΔI_L · ESR + ΔI_L / (8·f·C)
ESR + capacitive terms.

History of Output Inductor Sizing

Middlebrook and Cuk's state-space averaging (1976) at Caltech gave power electronics engineers the rigorous framework for analyzing ripple, transient response, and stability of switch-mode converters. The rule-of-thumb target 20-40% inductor current ripple came from TI and National Semiconductor's application notes of the 1980s - balancing inductor size against output capacitor stress. Modern high-frequency GaN converters shrink output inductors to nH range, but the same ripple target guides component selection.

About This Calculator

Enter V_in, V_out, f_sw, inductor value L, and load current I_out. The tool computes duty cycle D = V_out/V_in, peak-to-peak ripple ΔI_L = V_out·(1-D)/(f·L), peak inductor current I_peak = I_out + ΔI_L/2, and checks against your datasheet I_sat.

For lowest ripple: increase L (larger, more expensive) or raise switching frequency. For production, specify I_sat ≥ 1.3·I_peak and I_rms ≥ I_out for thermal derating. Everything runs client-side.

Frequently Asked Questions

Ripple rule of thumb?

Target ΔI_L ≈ 20-40% of full-load current. Too little ripple = large/expensive inductor; too much = need higher-current rating and more output cap.

CCM vs DCM?

Continuous-Conduction Mode (CCM): I_L never reaches zero, ripple overlays the DC current. DCM: I_L hits zero each cycle, higher ripple, different math. Most buck converters operate CCM at full load.

I_peak headroom?

Size inductor such that I_peak = I_out + ΔI_L/2 < 0.8·I_sat. 20% margin accounts for transient overshoot during load steps.

Common Use Cases

12 V → 3.3 V Buck

V_in=12 V, V_out=3.3 V, f=500 kHz, L=4.7 µH, I_out=2 A: ΔI_L ≈ 1 A pp (50% ripple).

24 V → 5 V Industrial

Pick L for 30% ripple at max load. Lower-ripple designs: larger L, more cost.

5 V USB-PD 20 V output

Boost from 12 V to 20 V; different equation (boost, not buck).

Last updated: