What is the formula for Inductor AC Winding Loss?

The Inductor AC Winding Loss formula is Pac = Iac(rms)² × Rac, where Pac—AC winding loss (W); Iac—RMS ripple current at the switching frequency (A); Rac—AC resistance at that frequency (Ω).

Inductor AC Winding Loss

Q: How do you calculate Inductor AC Winding Loss?

Use the formula Pac = Iac(rms)² × Rac. At the switching frequency a winding’s effective resistance rises far above its DC value because of skin and proximity effects that crowd current into the conductor surface. Enter the values you know in the calculator above and it solves for the remaining variable.

Pac = Iac² · Rac

Calculator

AC Loss

AC RMS Current

AC Resistance

Result

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Formula

Pac = Iac(rms)² × Rac

Description

At the switching frequency a winding’s effective resistance rises far above its DC value because of skin and proximity effects that crowd current into the conductor surface. The AC winding loss is the AC ripple current squared times this elevated AC resistance. In high-frequency converters this loss can rival or exceed the DC (I²·DCR) loss and is easy to overlook.

Variables

Pac — AC winding loss (W)
Iac — RMS ripple current at the switching frequency (A)
Rac — AC resistance at that frequency (Ω)

Practical Notes

Rac/Rdc grows with frequency and conductor thickness; litz wire or thinner strands reduce it. Add Pac to the DC copper loss (Idc²·DCR) and core loss for the total.

Related Concepts

All Inductors formulas →

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