Bobbin Wound Inductor Theory

Bobbin Wound Inductor Theory

Bobbin wound inductors refers to a type or method of constructin of winding inductors chokes and reactors. Toroidal coils are wound directly onto a toroidal core. The core may be coated or boxed to insulate it from the coil windings. In contrast, bobbin wound inductor coils are wound independently of the core. The coil must hold its shape or form until the coil is assembled onto the inductor 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 winding inductor”. 

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 inductors 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 inductors often provide terminals, pins, and/or surface mount pads to ease wire termination and to facilitate printed circuit board mounting.

Bobbin winding inductors (and transformers) are available in a variety of shapes. Bobbin wound inductor 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 inductors in these shapes are available in several different sizes.

Bobbin wound inductors (and transformers) can also use a variety of core materials: laminated or taped wound silicon steel alloys, nickel-iron alloys, cobalt alloys; powdered irons and nickels; ferrite; air core; core materials processed for square loop or round loop properties; and others.

Butler Winding makes bobbin wound winding inductors chokes and reactors in a wide variety of materials and sizes with pin-thru, surface mount, and/or flying leads terminations. Butler Winding also does “tube wound” 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. Most of our production is 100% tested on these machines.

If you need assistance with your design, please contact Butler Winding and ask for Engineering.