About the series resistor... if I am operating at full load, 1.5A, since the
resistor will essentially be in the path of the current, won't that 1.5A pass
through the resistor... basically frying it? Unless I get a huge wattage
resistor??? Or am I missing something here.

Quoting "Thomas C. Sefranek" <tcs@CMCORP.COM>:

> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jai Dhar
> > Sent: Monday, January 27, 2003 9:54 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: [OT]: Linear regulator question
> >
> >
> > Hello,
> >
> >  I am using a +12 and +5V regulator in my psu, and both are being
> > fed from a
> > full wave bridge rectifier ( I guess I don't need the negative
> > part ).
>
> Skip the nonsense about "the negative part".
> A full wave bridge makes the "negative part" positive.
>
> > Anyway,
> > My transformer ends up putting out 30V at the positive end of the
> > rectifier.
> > The specs for the +5 regulator say that 25V should be the max for
> > input, but
> > the +12 is ok.
>
> If you have a center tap transformer, you could get 15 volts for your
> 5 volt regulator from a wire connected to the center tap.
> (Add another filter cap on the line.)
>
> > My question is that would it be fesable to feed the +5V
> > regulator from the +12V one? I suppose this would mean that both
> > my 5 and 12
> > outputs could only have a max. current of 1.5A out since they are
> > being fed
> > off the same regulator... this correct?
>
> Basicly correct...
>
> > If this isn't fesable, how can I use
> > the +5 regulator safely. Would a voltage divider do? It seems too
> > simple, I
> > don't know, there are a lot I do'nt know about regulators, and maybe this
> > wouldn't work. Anyway, all your help is appreciated.
>
> Use a series resistor to drop some of the voltage before the regulator.
> You could even hang a zener after the resistor as a shunt pre-regulator.
> >
> > Jai
> >
> >
> > ----------------------------------------
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>
>   *
>   |  __O    Thomas C. Sefranek   WA1RHP@ARRL.NET
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