SMPS Inductor Current Ripple

ΔI = Vin × D / (f × L)

Quick answer

This calculator solves ΔI = Vin × D / (f × L) for Current Ripple. With Input Voltage 12 V, Duty Cycle 50 %, Switching Frequency 100 kHz, Inductance 100 µH, the result is 0.6 A. It solves in 5 directions, so you can enter the values you have and get the one you need.

Calculator

Current Ripple (A)
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Formula

ΔI = Vin × D / (f × L)

Description

During the on-time of a buck converter, the voltage across the inductor is (Vin - Vout), causing the current to ramp up linearly. The peak-to-peak inductor current ripple determines whether the converter operates in continuous conduction mode (CCM) and affects output voltage ripple, core losses, and EMI. A common design target is 20-40% ripple relative to the DC output current. Higher ripple allows a smaller inductor but increases RMS current losses and output ripple. Lower ripple requires a larger, more expensive inductor but improves efficiency.

Variables

  • ΔI — Peak-to-peak inductor current ripple (A)
  • Vin — Input voltage (V)
  • D — Duty cycle (0 to 1)
  • f — Switching frequency (Hz)
  • L — Inductance (H)

Practical Notes

The inductor must handle a peak current of Iout + ΔI/2 without saturating. Inductor saturation current rating should have at least 20% margin above peak current. Core losses increase with ripple amplitude and frequency. For critical-mode (boundary) converters, ΔI = 2 × Iout by design.

Symbols and units

Symbol Meaning Default unit Accepted units
dI Current Ripple A pA, nA, µA, mA, A, kA
Vin Input Voltage V pV, nV, µV, mV, V, kV
D Duty Cycle — —, %
f Switching Frequency kHz Hz, kHz, MHz, GHz
L Inductance µH nH, µH, mH, H

Step by step

  1. 1. What you know: Input Voltage 12 V, Duty Cycle 50 %, Switching Frequency 100 kHz, Inductance 100 µH
  2. 2. The relation: ΔI = Vin × D / (f × L)
  3. 3. Substitute: Vin = 12 V, D = 50 %, f = 100 kHz, L = 100 µH
  4. 4. Result: Current Ripple = 0.6 A

Related quantities from the same inputs

  • P = V × I = 7.2 W

Worked examples

Minimum range

Given: Input Voltage 0.33 V, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Inductance 100 nH

Result: Current Ripple = 0.825 kA

Low range

Given: Input Voltage 3.3 V, Duty Cycle 25 %, Switching Frequency 1 kHz, Inductance 1 µH

Result: Current Ripple = 0.825 kA

Typical

Given: Input Voltage 12 V, Duty Cycle 50 %, Switching Frequency 100 kHz, Inductance 100 µH

Result: Current Ripple = 0.6 A

High range

Given: Input Voltage 0.23 kV, Duty Cycle 0.8, Switching Frequency 0.5 MHz, Inductance 0.47 mH

Result: Current Ripple = 0.783 A

Maximum range

Given: Input Voltage 2.3 kV, Duty Cycle 8, Switching Frequency 5 MHz, Inductance 4.7 mH

Result: Current Ripple = 0.783 A

Solving for each variable

Solve for Current Ripple

Input Voltage 0.33 V, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Inductance 100 nH → 0.825 kA

Solve for Input Voltage

Current Ripple 2 mA, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Inductance 100 nH → 0.8 µV

Solve for Duty Cycle

Current Ripple 2 mA, Input Voltage 0.33 V, Switching Frequency 100 Hz, Inductance 100 nH → 6.06 × 10⁻⁶ %

Solve for Switching Frequency

Current Ripple 2 mA, Input Voltage 0.33 V, Duty Cycle 2.5 %, Inductance 100 nH → 41.25 MHz

Solve for Inductance

Current Ripple 2 mA, Input Voltage 0.33 V, Duty Cycle 2.5 %, Switching Frequency 100 Hz → 41.25 mH

How Current Ripple changes with Input Voltage

Input Voltage (input) Current Ripple (result)
1.2 V 60 mA
3 V 150 mA
6 V 0.3 A
9 V 0.45 A
12 V 0.6 A
18 V 0.9 A
24 V 1.2 A
48 V 2.4 A
84 V 4.2 A
120 V 6 A

The same result in other units

Unit Value
µA 600000
mA 600
A 0.6
kA 0.0006

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Frequently asked questions

How do you calculate SMPS Inductor Current Ripple?

Use ΔI = Vin × D / (f × L). With Input Voltage 12 V, Duty Cycle 50 %, Switching Frequency 100 kHz, Inductance 100 µH, Current Ripple works out to 0.6 A.

What is the formula for SMPS Inductor Current Ripple?

The formula is ΔI = Vin × D / (f × L). During the on-time of a buck converter, the voltage across the inductor is (Vin - Vout), causing the current to ramp up linearly.

How do you find Input Voltage when you know the other values?

Rearrange for Input Voltage: with Current Ripple 2 mA, Duty Cycle 2.5 %, Switching Frequency 100 Hz, Inductance 100 nH, Input Voltage is 0.8 µV.

How do you find Duty Cycle when you know the other values?

Rearrange for Duty Cycle: with Current Ripple 2 mA, Input Voltage 0.33 V, Switching Frequency 100 Hz, Inductance 100 nH, Duty Cycle is 6.06 × 10⁻⁶ %.

What units does SMPS Inductor Current Ripple use?

Current Ripple is shown in µA, mA, A, kA. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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