Determining Inductor
Power Losses

Core, DCR and ACR Losses
Abstract

which are unique to each core material.

As power supply output current requirements continue
to increase, it is important for the design engineer to pay
close attention to inductor power losses and their affecton overall power supply efficiency. This paper introduces
the basic formulas to determine the approximate inductor
power losses.

Pdcr

Introduction
The demand for an improvement in power supply efficiency, and therefore, inductor efficiency has increased quite
rapidly. This demand has come as a result of an increasein power supply output current. At the same time, there
has been a renewed effort to reduce the amount of heatthat power supplies have to dissipate, which has a direct
effect on overall power supply efficiency. The reductionin heat creation is especially important to laptop users.
Since heat creation and inductor power loss are directlyrelated, it is extremely important to reduce inductor
power losses. To reduce these losses, it is necessary
to understand where the they come from.

Inductor Power Loss
The power loss of an inductor is defined by the basic
formula:PlossInductor = Pcore + Pdcr + Pacr
Each component of this formula is discussed below.

PcoreThe calculated and/or measured core loss is often directly
provided by the inductor supplier. If not, a formula canbe used to calculate the core loss. Measuring core loss
and getting repeatable results can be a tedious task
depending on the test frequency. A general form of thecore loss formula for ferrite cores is:
Pcore (mW) = K1f xBy × Ve
Where:
K1 = Constant for core materialf = Frequency in kHz
B = Peak Flux Density in kGauss
x = Frequency exponenty = Flux Density exponent
Ve = Effective core volume (cm3)

The wire loss caused by dc resistance is easy to calculate.
It is defined by this basic formula:Pdcr (W) = Irms2 × DCR
Where:
Irms = The rms value of the peak current applied tothe inductor
DCR = The dc resistance of the inductor

Pacr
The wire loss caused by ac resistance is more difficult
to calculate since ac winding resistance values are notalways readily available from magnetics vendors. Pacr isdefined by the following formula:
Pacr (W) = Irms2 × ACR
Where:
Irms = The rms value of the peak-peak ripple current
applied to the inductor
ACR = The ac resistance of the inductor
The inductor power loss information can be often be
provided by inductor suppliers for most of their products.
In an effort to speed up the design process for engineers
using inductors, Coilcraft has developed a calculator for
estimating inductor core and winding loss. The calculator
is based on the formula:
PlossInductor = Pcore + Pdcr + Pacr

Conclusion
This paper has introduced the basic formulas used indetermining inductor power loss. It also discussed theimportance of knowing where inductor power losses
come from in order to reduce heat creation and thus
improve overall efficiency.
For a more thorough discussion on ac losses refer to:Document 1400, titled Choosing Inductors for Energy
Efficient Power Applications.

The core loss can be calculated by entering the K1 coefficient and the frequency and flux density exponents,
Document 486

Revised 05/17/18