Voltage regulator with alternate voltage source...
wh.sudbrink at verizon.net
Fri Apr 8 13:50:26 CDT 2016
William Donzelli wrote:
> > 1) The 7805 is actually a Motorola MC7805CP, date
> > code 7308 with gold leads. Very hard to exactly
> > replace.
> Is that the big flat plastic package with the wide
> flat leads?
Nope, purple ceramic. The heat transfer plate is gold
> > 1) I have a 12 volt DC supply. 12 volts seems to be
> > within the VIN range for the 7805s whose data
> > sheets I've now read. Can I simply apply 12 volts?
> Yes, but that regulator might get mighty hot! I would
> not do this for fear of cooking the poor thing.
That's what I figured to start with, before reading the
> > 2) Could I place a resistor in series between the 12V
> > supply and the 7805 to drop the voltage at the 7805
> > to somewhere around 8?
> Yes, you could do this. Pick an appropriate power resistor,
> or use a big wirewound rheostat.
At this point, I think I'll just wait till Monday and work
on other things.
> > 3) If I was to "tack on" a jumper between VIN and VOUT,
> > would that protect the 7805 and allow me to power the
> > circuit with 5 volts?
> I would not do this at all.
I didn't think so.
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