---- April 21st 2024 ----

CAGE Code: 5DME2
ITAR Registration Code: M28889
Call: 1 (800) 377-3244
Monday to Friday 8 A.M. - 5 P.M. (Pacific Time)
E-mail questions and requirements to: sales@coilws.com

Pricing is subject to change depending on product availability and backorders.
*Please Note: Items without price are listed for CWS' capability purposes.

Custom Power Transformers Sizes & Dimensions


Custom transformers are usually built with some standardized ferrite core sizes with or without bobbins. If a custom transformer is for RF (radio frequency) application, it is usually designed and built with toroidal core for high frequency operations. CWS stocks thousands of such toroidal cores for these RF applications, and we will design and do winding for our customers with the fastest possible delivery. For more information or to purchase over the internet the various types of toroidal core, please visit: www.cwsbytemark.com

However, if a custom transformer is for switch mode power application, or application where the switching frequency is below 500 Khz, paired core is usually used. The paired core use a bobbin to put the windings on. These bobbins have pins for either through hole mount or surface mount. Paired cores are available in hundreds of different shapes and sizes, ranging from EFD, to PQ to TF. The ferrite industry has adopted some standardized core shapes and sizes. For example, the EFD20's core is shaped like a "EFD" with a size of 20mm in usually the largest dimension. Every ferrite manufacturer's EFD20 will have the same dimension, and common third party bobbins can therefore be used. The advantage of using paired core is lower cost and ease in manufacturing, especially for high volume. Because of lower cost, if the volume is very large, paired core custom transformer is the way to go. For small size types, the packaging can also be in tape and reel.

The list below shows 41 different types of standardized sizes in PDF format that are maintained at CWS' facilities in California, Malaysia, Taiwan or China. The ferrite core material used in these transformers are industry standard MnZn with permeabilities of 2000 to 2500. The cores used are from manufacturers such as Magnetics Inc, Epcos, TDK, Tokin, Kawatetsu, Siemens, Philips ( Ferroxcube), etc. Depending on the application and switching frequencies, most of these manufacturers' product has similar characteristics. Some may have lower losses when frequency increases, while others have lower losses when operating at higher flux densities and ambient temperatures, etc.

When we receive a request for custom built transformers using paired cores, we will try to use one of the core types listed below. In this way, we can deliver final products to our customer with the shortest lead time. The critical dimensions are shown in the drawings. These include the maximum height and width, and pin size and spacing. These data are important for design engineers to plan the space on the PCB's.

The number of pins on the bobbins are shown inside the parenthesis beside the core type. i.e. EFD30(12P) means the core is EFD, size is 30mm width and bobbin has 12 pins. The number of pins are just a guide. Depending on the requirement, we can choose other types of bobbins with different number of pins. In many cases, surface mount bobbins are also available, even though they are not listed here.


EFD20 (8P) EFD25 (10P) EFD30 (12P)
EI10 (8P) EI13 (10P) EI14 (6P)
EI16 (10P) EI19 (6P) EI22 (10P)
EI24 (6P) EI25 (8P) EI30 (10P)
EI33 (12P) EI33 (14P) EI40 (12P)
EI40 (16P) EL19 (10P) EL19 (7P)
EL25 (10P) EL25 (7P) EP10 (8P)
EP13 (10P) EPC19 (11P) ER11.5 (10P)
ER14.5 (10P) ER28 (10P) ER28 (12P)
ER28 (13P) ER35 (12P) ER35 (14P)
ER35 (16P) ER9.5 (8P) PQ2020 (16P)
PQ2620 (12P) PQ32 (12P) RM08 (12P)
RM10 (12P) TF16 (10P) TF16 (5P)
UI-15 UU10.5 (4P)    

You can download Acrobat Reader from this site to view PDF file. http://www.adobe.com/products/acrobat/readstep.html



Disclaimer: Coil Winding Specialist, Inc., its affiliates, agents, and employees acting on behalf of Coil Winding Specialist, Inc. (collectively, CWS) disclaim any and all liability for any errors, inaccuracies or incompleteness contained herein or in any other disclosure relating to any product. CWS reserves the right at any time and from time to time to make changes to design, technical specification, or construction of any product listed on this website without notice. CWS also reserves the right to discontinue or limit sale of any product or service available throughout this website on temporary or permanently basis without notice. CWS highly recommends customers not to use its products offered on this website for inappropriate use and applications. Products should be tested for its suitability by prospective customers in all possible applications and conditions. Customers using or selling CWS products for use in other than recommended applications do so entirely at their own risk and agree to fully indemnify CWS from any damages arising or resulting from such use or sale.

WARNING: This product can expose you to chemicals which is [are] known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go towww.P65Warnings.ca.gov.

Any Comments, Suggestions or Questions? Contact us!
Email: sales@coilws.com
CWS 353 West Grove Ave. Orange, California 92865
Call us Toll Free: 1-800-679-3184 or 1 (800) 377-3244

Tel: (714) 279-9010, Fax: (714) 279-9482

Copyright 2008, Coil Winding Specialist, Inc
Updated July, 2013

CAGE Code: 5DME2(Registered with www.ccr.gov)