Welcome to the Würth Elektronik WE-PDF Flatwire Inductor product ...

Welcome to the Würth Elektronik WE-PDF Flatwire Inductor product
training module. This module will overview the available products, explain
the key features and technical background, show customers the
advantages of using a flatwire and last but not least, discuss their main
applications.
1

Würth Elektronik has recently released the WE-PDF series of high
performance flatwire inductors. It is available in two different sizes, 10mm
x 10mm x 4mm and 10mm x 10mm x 6mm. The WE-PDF consists of a
ferrite material which has significantly lower core losses than iron powder
inductors and is mainly used in high current inductor designs. The WE-
PDF series is optimized for power supplies running high switching
frequencies. In particular by using a flatwire construction, the frequency
dependent resistance of the wire is significantly lower than using a
roundwire. Due to the focus on high performance partial components for
the design, the WE-PDF series has been released for an extended
temperature range up to 150 degrees Celsius.
2

The WE-PDF series is suitable for applications with switching frequencies
up to 10MHz such as the new generation of high frequency switching
regulators. The maximum operating temperature of the WE-PDF series is
150°C and it can handle continuous DC currents of up to 10.3A.
Additionally, due to the design and material, this series has a saturation
current of up to 30A.
3

Flatwire in an inductor design is much more efficient than using roundwire.
The reason for this will be explained in the next six slides. In general, it
can be said that the whole amount of losses of an inductor are created by
copper losses and core losses. The copper losses depend on resistance,
both DC and AC. While the DC resistance is a stable value, the AC
resistance is frequency dependent and based on the Skin and Proximity
Effect. The AC-resistance will increase with an increase of the frequency.
Core losses will not be discussed here as the wire type has no influence
on the core losses.
4

Most people do NOT consider the AC resistance because the most
common assumption is that ONLY the DC resistance determines the
copper losses. As a result of this assumption, target number one would be
to increase the diameter of the copper wire to increase the cross section.
An increase of the cross section results in a reduction of DCR and lower
copper losses.
5

There are different ways to obtain target number one. The diameter of the
wire itself can be increased or multiple wires in parallel could be used
instead. Using multiple wires in parallel is nothing else than switching
multiple DC resistances in parallel, which will result in a much lower overall
DCR. Now, by pointing out that multiple wires in parallel and in
particular in a row can be used, it can be seen that there is still room
between the wires to fulfill the winding window exactly. Instead of using a
bunch of roundwires, a flatwire can be used. The outer dimensions, in this
example of four roundwires or one flatwire, will be the same. However, by
using a flatwire, the entire possible area can be used resulting in a much
lower DCR.
6

This slide will focus on the frequency dependent AC resistance. Because
of eddy currents in the wire, which is a result of the AC-current, the current
will be pushed to the outside skin of the wire. This effectively results in a
reduction of the area that current can flow. Pointing out the equation of the
skin depth, the higher the frequency the lower the skin depth. Coming
back to the equation of calculating the resistance of a wire, the smaller the
conductive surface, the higher the resistance. Since this resistance will
only appear when driving an AC-current through wire, like the ripple
current in a switch mode power supply, this resistance is called ACresistance.
7

The Proximity Effect increases the AC-resistance as well. A current driven
wire creates a magnetic field around the wire which also creates eddy
currents. By using two wires in parallel, the magnetic field of both wires
influence the eddy currents resulting in the current not being pushed to the
entire skin of the wire. This causes the proximity effect to increase which
results in a much higher AC resistance. To summarize, the higher the
frequency, the smaller the AC current driven surface, the larger the AC
resistance. The higher the AC resistance, the higher the copper losses. To
somewhat mitigate this problem, the WE-PDF uses a flatwire where the
AC copper losses are minimized in comparison to inductors using one or
multiple roundwires.
8

The AC resistance of an inductor is sometimes called Equivalent Series
Resistance. This is the resistance in the equivalent circuit of an inductor
which represents the copper losses with an increase of frequency.
9

From the physical point of view, considering the same cross section of a
flatwire and a roundwire, e.g. 10mm², the flatwire can offer about 20%
more surface area. Because of the fact that high frequency currents only
use the surface due to the skin and proximity effects, the WE-PDF flatwire
inductor can offer a higher performance to an application by using a
different type of wire.
10

This page summarizes the advantage of using the flatwire inductor WE-
PDF series. The flatwire uses the whole winding window, maximizing the
available area on the core to reach the minimum DCR possible. Secondly,
by using the flatwire, the AC resistance is much lower than that of
roundwire inductor designs.
11

This page shows an extract of the typical applications for the WE-PDF
Flatwire inductor series.
12

Additionally, Wurth would like to point out that the WE-PDF flatwire
inductor is rated up to 150°C. Also, the component series WE-PDF is
designed for a high degree of robustness and for use in adverse
environmental conditions or other extreme conditions that exceed the
ratings of standard components
13

The WE-PDF series is available in the package sizes 10mm x 10mm x
4.5mm and 10mm x 10mm x 6.4mm. Each package size carries a broad
range of inductance values to provide the optimum solution for a
customer‘s application. All values are in stock and available from Digikey.
14

The Wurth Electronics WE-HC/WE-HCA series is also equipped with Flat
Wire and delivers the performance users need in their power supply. The
available core materials are Superflux and WE-PERM which
characteristically have low core losses and high saturation currents. The
HC series parts are available in either a 7mm x 7mm or 10mm x 10mm
package size and are rated up to 150°C.
15

In addition, Wurth Electronics carries the WE-HCA series which is
available in 13mm x 13mm package size and three different profiles. The
maximum saturation current is rated at 65A and the 13mm x 13mm parts,
which often are used in high temperature applications, are rated at up to
150°C. The WE-HCB series is the largest family of Flatwire Inductors
manufactured by Wurth Electronics. With its 18mm x 18mm package and
outstanding current handling capabilities it is the top of the line product for
high current DC/DC converters without external cooling. The parts have a
temperature rating of up to 125°C. All products of the Wurth Electronics
WE-PDF, WE-HC, WE-HCA and WE-HCB lines are available in stock at
www.digikey.com.
16

In summary, the WE-PDF series from Wurth Electronics Midcom can
increase, with Flat Wire Technology, the efficiency of a given application.
The series is available in a low profile 1045 package along with the
standard 1064 size.
17