[GreenKeys] Loop supplies, or how to drive a selector, magnet.

[John Nagle]

From:hwhall at compuserve.com

>>> the efficient way to run a selector magnet
> If a huge increase in circuit complexity and cost meet one's
> definition of "efficient." :-) The new design gets the selector
> magnet current up faster because, as shown, it holds the applied
> voltage across the magnet higher for longer than the traditional
> all-passive-component circuit. An alternative approach might take the
> form of an active shunt around the current limiting resistor, or an
> active current limiter instead of a resistor, that only applies
> current limiting after the magnet current hits 60mA.
>
> Wayne WB4OGM

You don't need to push the rise time that hard; this is just
an example circuit.  My point with this is that it's quite possible
to build a board with both power supply and USB to serial converter
on one small board, and eliminate the need for a separate loop
supply.

If I could find a way to do this with through-hole parts, I'd
build this. But most switching power supply parts are surface
mount.

				John Nagle