Xmultiple Engineering Dept.
has a complete produced line of transformer products.
In the case of an electrical transformer, inductor or
relay, the bobbin is a permanent container for the wire,
acting to form the shape of the coil (and ease assembly
of the windings into or onto the magnetic core). The
bobbin may be made of thermoplastic or thermosetting
(for example, phenolic) materials. This plastic often
has to have a UL or other regulatory agency flammability
rating for safety reasons. Bobbins provide the alignment
for the cores and therefore the bobbin is the critical
element of any transformer. The bobbin or coil former
are at the heart of the transformer and serves as its
winding and termination platform. The bobbin or coil
former supports the winding, channels the winding and
provides a termination and connection method. Each bobbin
is designed for use with a specific core shape, whether
that core is ferrite, stacked laminations, or tape wound.
There are many ways to design a transformer, so it is
important to make the best bobbin and core combination
selection. Product cost, availability, material limitations,
safety agency requirements and, ease of production are
designing products may ask which bobbin and core combination
meet the form, fit and function of the design. However,
cost considerations will not be far behind. The lowest
cost core and bobbin combination with the widest availability
are based on the square stack lamination sizes like
E187, E24/25, E375, E21, E42/15. However, these square
or rectangular center leg shapes may need to be shielded
around the core with copper foil to reduce EMI, which
will increase cost. Some
Industry standards require 3750Vrms dielectric between
the core and windings, and from winding to winding.
To accomplish this effectively, a 3mm-isolation margin
must exist on each side of the bobbin.
designing and specifying a bobbin and core combination,
attention is initially paid to the performance of the
core. The designer must realize that the bobbin, and
not the core, will have the greatest impact on the nature
and ease of the winding operation, the winding lead
termination, safety regulations and printed circuit
board insertion. The bobbin will have a larger impact
on the cost of manufacturing the assembly than the core.