piclist 2002\01\11\215938a >
Thread: Car power supply challenges
www.piclist.com/techref/power/actodc.htm?key=power
picon face BY : Russell McMahon email (remove spam text)



> > > Actually the normal draw on the 5V line is about 4A. I measured it
during
> > > testing of Russell's 2 transistor SMPS. BTW the MB would consistently
boot
> > > from that power supply.
> >
> > I'd like to see the circuit you built, i'm curious
> > about the regulation and also the type and performance
> > of the inductor.
>
> Let me know what you want me to measure.
>
> The inductor is a J.W. Miller high current toroid pushed from
RadioShack.com
> IIRC it's a 50 mH 10A inductor.



What would be interesting would be

1    Output voltage at a number of combinations of input voltage and output
current.
2    It would also be interesting to know input current as well in each
case.
3    For the really keen,  the performance under sudden steps in load and
input voltage would be of interest.

1. is best presented as a table with Vin and Iout as table axes and Vout for
each combination.

I found my original design to have amazingly good Vout regulation with Vin
and Iout CONSIDERING HOW SIMPLE THE CIRCUIT IS. I "shout" this as I don't
want people to think I am saying it is a high performance design in absolute
terms compared with sophisticated IC based designs - just amazingly good for
what it is. For example, *from memory*, with Vin ranging from about 12 volts
to 200 volts I was getting Vout of better than +/- 0.1 volt. Can't remember
regulation with load but can always measure with a working design or dig up
notebooks if of great interest. Byron's figures would be more apposite in
the present case.

2. above allows efficiency to be determined.

3. - transient performance (scope or similar needed) allows you to determine
if there are any nasty surprises lurking. An apparently well performed
design may provide a voltage spike on step removal of load (or on
application!)  or Vout may drop substantially during load changes.


regards,


       Russell McMahon

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