Re: Power Supply

--- In CAD_CAM_EDM_DRO@y..., "kilroy2k1" <tszaran@c...> wrote:

> I'll toss this out to the EE's out there..

Low frequency transformers can be constructed several ways. The
magnetic field in a transformer is supported by the "core" sort of
like a flywheel. The cores are made of a special iron and the most
common configuration is to stamp a bunch out as E shaped flat
pieces. You get a bobbin and wind the coils (with thin insulation
between each coil) on it, then you can stack the laminations by
alternating each one until you fill the center of the bobbin and you
end up with the normal square shape. The result is an easy to
construct, if not optimal magnetic device. Since each lamination has
some air between it and the next one, it has a natural "air gap".
Air acts as a high impedence path to magnetic lines of flux so that
it prevents the core from saturating (a bad thing). Of course the
air also introduces losses and the laminations have a tendency to
flex and bang together creating some heat and noise.

The toroid is a molded piece of magnetic material where the air gap
is highly predictable and is designed to focus to magnetic field into
the center. The result of that is that toroids are slightly more
efficient, have less electromagnetic radiation and no "moving" parts
to make noise. They can be built in a lower profile that resembles a
donut rather that a cube. They also cost more to build since there
is no bobbin you can chuck in a lathe and quickly wind. You have to
thread each wrap of the transformer through the center of the core.
High frequency power circuits (above about 400HZ)need less and less
magnetic core and both toroids and molded E (with an "I" end piece)
are used for those types of circuits.

If you were building audio circuits where the 60hz of the stray
magnetic field from the power transformer can create real hum and
noise issues, you might want to either sheild the transformer or use
a toroid. In the case of building a bulk supply for driving steppers
or servo's the low frequency stray field is of little concern. The
noise issue is of less concern considering the environment of motors,
moving parts and screaming routers or plasma cutters! That leaves
the other reasons to use a toroid: slightly more efficient and easier
to mount. If you can justify spending the premium for the toroid for
those benefits that by all means do it, but don't loose sleep over
not doing it either.

The Triac, SCR issue is something completely different and has to do
with building power supplies that need forms of control and
regulation. Both of those devices are basic AC low frequency
components and entire books exist of how to use them to control
power. Of course there are high voltage transistors, FETS, IGFETS
and other devices but I doubt the group wants to start a discourse
about the use and abuse of those devices :-)