Bobbin Wound Transformer Theory


Electronic transformers can be classified in several ways:
ViewTheoryPages_btnby power rating, by type of application, by type of construction,
by industry, and others. Bobbin wound electronic transformers refers to a type (or method) of construction. Toroidal coils are wound Request_a_quote_btndirectly onto a toroidal core. The core may be coated or boxed to insulate it form the coil windings. In contrast, bobbin wound electronic transformer coils are wound independently of the core. The coil must hold its shape (or form) until the coil is assembled onto the transformer core. One common method of doing this is to wind the coil onto a bobbin (also referred to as a spool), hence the term “bobbin wound transformer”. The bobbin is a pre-formed reasonably rigid part. The bobbin material is usually (but not always) an insulating material, hence it can provide electrical isolation between the coil and the adjoining core material provided suitable creepage distance is used. Multi-section bobbins are available to provide increased electrical isolation between coil windings.

Bobbin wound electronic transformers are used in a variety of applications, hence bobbins are made from a variety of materials: plastics, phenolic, glass, Teflon and others. Most bobbins are molded. Some are fabricated. Bobbin designs for bobbin wound transformers often provide terminals, pins, and/or surface mount pads to ease wire termination and to facilitate printed circuit board mounting.

Bobbin wound transformers (and inductors) are available in a variety of shapes. Bobbin wound transformers shapes include pot cores (round), “RM” (square pot cores), “RS” (round slab pot cores) and “DS” (double slab pot cores), “EP”, “PQ”, “E”, “EI”, “EEM”, “EFD”, “U”, “UI”, “EC”, “ETD”, “ER”, “EER”, and some others including custom shapes. Bobbin wound transformers in these shapes are available in several different sizes.


Butler Winding can make (and has made) bobbin wound transformers (and inductors) in a wide variety of materials and sizes with pin-thru, surface mount, and/or flying leads terminations. Butler Winding also does “tube wound” transformers (and inductors) and air core coils. Our upper limits are 40 pounds of weight and 2 kilowatts of power. We have experience with foil windings, litz wire windings, and perfect layering. For toroids, we can (and have done) sector winding, progressive winding, bank winding, and progressive bank winding. Butler winding has a variety of winding machines, bobbin/tube and toroid. That includes two programmable automated machines and a taping machine for toroids. Butler Winding has vacuum chamber(s) for vacuum impregnation and can also encapsulate. To ensure quality, Butler Winding purchased two programmable automated testing machines. Most of our production is 100% tested on these machines.