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range so that extreme scenarios can
be taken into consideration. This
allows the most energy-efficient
power inductor to be selected for the
respective application.
To determine the right inductor for
a buck converter, the existing input
voltage range and the output voltage
and current are entered into the
user-interface, as well as switching
frequency, diode flow voltage and
targeted ripple current of the inductor.
A simple click on "Display Details"
reveals the most suitable power
inductor, including its anticipated
ripple currents and the losses in the
application.
A manual loss calculator is also
available to determine the losses for
power inductors independent of the
topology. Only frequency, duty cycle
and ripple current, or voltage drop,
need to be entered and REDEXPERT
takes care of the rest. A useful
feature immediately displays the
entries graphically below the data
entry screen.
As REDEXPERT is a web-based tool,
there is no need to download or worry
about updating the tool. Registered
users have access to further features,
such as determination of inductance
value or temperature increase of the
inductor for every possible current
value.
amperes (A).
There are other models that attempt
to tackle the problemof non-sinusoidal
waveforms by separating hysteresis
and eddy current losses. The empirical
Steinmetz equation has proven to
be a useful variant, but offers high
accuracy only for sinusoidal currents.
However, the various Steinmetz
models only work optimally with a
duty cycle of 50 percent and within
a limited frequency range. Moreover,
determining the magnetic path length
is highly complex. Subsequently the
determination of core losses with
the help of existing models for iron
powder and metal alloys is not only
demanding, but the accuracy is also
subject to significant fluctuations.
For inductors that consist of several
different core materials, an estimation
of the losses is not possible, or at the
very least highly complicated.
Empirical data-based AC-
loss model
Würth Elektronik eiSos has developed
a sophisticated model capable of
accurately measuring the complete
AC losses in inductors. It is based on
empirical data generated by real-time
application set-ups. Here the total
losses of the inductor are divided into
AC- and DC-losses.
Empirical data is captured with a
DC/DC converter. A pulsed voltage
is applied to the inductor, whereby
the input power Pin and the output
power Pout are measured. On this
basis Ploss = Pin - Pout is determined
and the AC losses of the coil PAC are
separated. This procedure is used
to measure and capture empirical
data for various parameter settings
such as fluctuations in the magnetic
modulation, switching frequency,
ripple current, etc. A model for the
calculation of the AC losses is then
created with the use of this empirical
data.
Determining losses online
REDEXPERT is an online design tool
from Würth Elektronik eiSos to select
the most suitable power inductor
for the respective application. It is
an intuitive and effective tool that
enables component comparison at
the click of a button.
The calculation of AC losses in
magnetic components is just as
critical as it is complex - but not with
REDEXPERT, as the AC loss model
from Würth Elektronik is integrated
into the tool. The calculation accuracy
of the complete AC losses also
makes the application suitable for
temperature estimation.
Currently three topologies are
supported in which the component
can be selected for the application:
buck, boost and SEPIC converters.
The losses are displayed graphically
over the complete input voltage
Empirical data is based on a DC/DC converter
Accurate determination of losses for every given
duty cycle
Accurate across a wide frequency range (10 kHz to
10 MHz)
Considers the smallest changes in the core material
and the winding structure
Applicable for components where more than one
material is used
Accurate determination of losses in components
with iron powder and metal alloys
Applicable for every possible core design and
winding structure
Includes AC winding losses
Advantages of the AC loss model:
New-Tech Magazine Europe l 19