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ETD Series Ferrite Cores

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.

	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.

	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.

Size Designation	Para meter	ETD 29	ETD 34	ETD 39
Core Material		F47	F44	F5	F5A	F47	F44	F5	F5A	F47	F44	F5	F5A
Inductance factor (nH/turns²)	A_L	1800	1950	2000	2350	2150	2250	2400	2480	2440	2470	2700	3120
Permeability (effective)	ľ_e	1332	1443	1480	1740	1385	1450	1550	1600	1435	1455	1590	1835
Path length (effective)	mm	70.4	70.4	70.4	70.4	78.6	78.6	78.6	78.6	92.2	92.2	92.2	92.2
Path area (effective)	mm²	76.0	76.0	76.0	76.0	97.1	97.1	97.1	97.1	125	125	125	125
Winding area (single section bobbin)	mm²	89	89	89	89	123	123	123	123	177	177	177	177

Size Designation	Para meter	ETD 29	ETD 34	ETD 39
Inductance factor (nH/turns²)	A_L	1800	1950	2000	2350	2150	2250	2400	2480	2440	2470	2700	3120
Centre limb gap	mm	0.1	0.2	0.5	1.0	0.1	0.2	0.5	1.0	0.1	0.2	0.5	1.0
Core Material		F44	F44	F44	F44	F44	F44	F44	F44	F44	F44	F44	F44
Permeability (effective)	ľ_e	590	340	160	92	645	375	175	100	735	425	205	120
Path length (effective)	mm	70.4	70.4	70.4	70.4	78.6	78.6	78.6	78.6	92.2	92.2	92.2	92.2
Path area (effective)	mm²	76.0	76.0	76.0	76.0	97.1	97.1	97.1	97.1	125	125	125	125
Winding area (single section bobbin)	mm²	89	89	89	89	123	123	123	123	177	177	177	177

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.

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.

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 ą10% for large gaps and ą20% for small gaps.

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

Un-gapped information

Size Designation Para
meter ETD 29 ETD 34 ETD 39

Core Material F47 F44 F5 F5A F47 F44 F5 F5A F47 F44 F5 F5A

Inductance factor (nH/turns²) A_L 1800 1950 2000 2350 2150 2250 2400 2480 2440 2470 2700 3120

Permeability (effective) ľ_e 1332 1443 1480 1740 1385 1450 1550 1600 1435 1455 1590 1835

Path length (effective) mm 70.4 70.4 70.4 70.4 78.6 78.6 78.6 78.6 92.2 92.2 92.2 92.2

Path area (effective) mm² 76.0 76.0 76.0 76.0 97.1 97.1 97.1 97.1 125 125 125 125

Winding area (single section bobbin) mm² 89 89 89 89 123 123 123 123 177 177 177 177

Gapped information

Size Designation Para
meter ETD 29 ETD 34 ETD 39

Inductance factor (nH/turns²) A_L 1800 1950 2000 2350 2150 2250 2400 2480 2440 2470 2700 3120

Centre limb gap mm 0.1 0.2 0.5 1.0 0.1 0.2 0.5 1.0 0.1 0.2 0.5 1.0

Core Material F44 F44 F44 F44 F44 F44 F44 F44 F44 F44 F44 F44

Permeability (effective) ľ_e 590 340 160 92 645 375 175 100 735 425 205 120

Path length (effective) mm 70.4 70.4 70.4 70.4 78.6 78.6 78.6 78.6 92.2 92.2 92.2 92.2

Path area (effective) mm² 76.0 76.0 76.0 76.0 97.1 97.1 97.1 97.1 125 125 125 125

Winding area (single section bobbin) mm² 89 89 89 89 123 123 123 123 177 177 177 177

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,