Although toroidal transformers emit minimal stray
magnetic fields by their nature, a certain amount will
always be present as with all magnetic devices. For the
vast majority of applications, toroidal emissions are
far too low to affect circuit operation, but there are
some applications that are especially
sensitive.
These include wideband, high-gain
instrumentation and preamplification, high-end audio,
and high-resolution CRT circuits. In this case, magnetic
shielding can be applied around the toroid in the form
of a high-permeability metal band. This can be Silicon
Steel for the majority of cases or Mu Metal for
sensitive applications. For extremely sensitive
circuits, total encapsulation in a steel can or case may
be the only option. There are ways to reduce emissions
by design (before any protection is added to the
transformer), so if your circuit is prone to magnetic
interference, please include this information in
specifications when requesting a quotation.
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