SMPS Inductor Current Ripple

ΔI = Vin × D / (f × L)

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Result
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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.

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