[sdiy] Power Supply Design Questions

[patchell]

If you go here:

    http://www.silcom.com/~patchell/powersupply/powersupply.html

    You will find a scan of something I wrote up on how to select a
filter capacitor for a three terminal type regulator.  I generally allow
for 3 volts drop, sort of a margin of saftety.  You have to remember
that there will be supply ripple going into the regulator, and you need
to make sure that the voltage never goes below that magic point.  So, it
is not so much the transformer you have to select, but rather, the
filter capacitor.

Scott Gravenhorst wrote:

> Some questions I have:
>
> At what input voltage should a LM78xx or LM79xx type
> regulator be run for minimum heat?
>
> I read in data sheets that 2 volts is the usual value for
> dropout voltage (at 1A).
>
> Would this be the point (well, somewhat above it) at which
> the regulator would heat up the least?
>
> Operated so, does this also mean using a transformer with
> better current capabilities?
>
> Thanks all.
>
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> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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--
 -Jim
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