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ETD Series Ferrite Cores

The ETD series of cores with their associated bobbins and clips are suitable for the design and construction of inductors and transformers that are a little larger than the RM types.

The ones listed here are made in accordance with IEC standard 1185, my local supplier is RS Components as linked top left.

I have used this style of core, in a few applications, mainly in inverter type power supplies as the power transformer (at about 40 kHz chop frequency).

Generally the mating surfaces are ground flat for minimum reluctance, but some types have deliberately shorter central limbs in order to provide a central air gap... This increases the reluctance, but improves the tolerance on the reluctance.
typical ETD ferrite cores


typical ETD winding bobbin
The moulded bobbin shown here fits the centre limb that occurs when a pair of cores are placed face to face. The pins are arranged as 'dual in line'. This particular one is Part Number: FD9630 from MILES - PLATTS Ltd.

The version illustrated at left has vertical core orientation, but other types exist where the core is held horizontally, usually the distance between the rows of pins is greater for the horizontal type.
The completed assembly is held together by spring steel clips of the shape indicated at right, the dimensions are those that apply to an ETD29 clip that latches on to small lugs moulded into the bobbin. Two are required. ETD29 core assemby clip
assembled ETD core transformer A finished transformer is shown in this picture. Note that it has a different style of clip to the one illustrated above, such variations occur between different manufacturers.

The examples quoted throughout the rest of this page are those of the particular versions offered by RS Components They are a supplier that is local to where I live and their website has been provided some of the information given here. If you use components from a different supplier then you must use the design parameters published by your supplier rather than any figures quoted here.


Tolerance... +30%/ -20% for all ungapped cores. The tolerance on gapped cores will vary between 10% for large gaps and 20% for small gaps.

Frequency range... for all types is generally between 16 kHz and 400 kHz.

Un-gapped information
Size DesignationPara
meter
ETD 29ETD 34ETD 39
Core Material F47F44F5F5AF47F44F5F5AF47F44F5F5A
Inductance factor (nH/turns2)AL180019502000235021502250240024802440247027003120
Permeability (effective)e133214431480174013851450155016001435145515901835
Path length (effective)mm70.470.470.470.478.678.678.678.692.292.292.292.2
Path area (effective)mm276.076.076.076.097.197.197.197.1125125125125
Winding area (single section bobbin)mm289898989123123123123177177177177

Gapped information
Size DesignationPara
meter
ETD 29ETD 34ETD 39
Inductance factor (nH/turns2)AL180019502000235021502250240024802440247027003120
Centre limb gapmm0.10.20.51.00.10.20.51.00.10.20.51.0
Core Material F44F44F44F44F44F44F44F44F44F44F44F44
Permeability (effective)e59034016092645375175100735425205120
Path length (effective)mm70.470.470.470.478.678.678.678.692.292.292.292.2
Path area (effective)mm276.076.076.076.097.197.197.197.1125125125125
Winding area (single section bobbin)mm289898989123123123123177177177177


Designing an inductor using these types of core is similar to the process described on RM calculations.

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Written... 26 April 2002, New Domain 20 April 2004,

Electronics Favicon Coding Standard 2003 Issue 5