Got this response offlist - probably thought my offlist request re religious
stuff related to technical matters as well.
I told them I would respond on list but not identify them. They can self
identify if they wish,.


_____________________

Hello,

I am very interested of one of those regulators, for a power supply I want
to build, where the cost is most important, and after that the efficiency.
Around which value is the efficiency though ? I guess that's more than a
linear power supply...

I am beginner with electronics, so I have a limited capacity to understand
your circuit. I want to build a 13.8V power supply, that would be capable of
giving at maximum 3A of current. Could you indicate me the key parts that
need to be changed for that job ? And in the schematic, there is the
complete circuit ? Or just a part of it ?

Thank you for answering !

_______________________________________________

That is more or less the whole circuit - although there are always bits and
pieces that need adding on in a real circuit.
A filter capacitor on Vin is a very good idea.  Depending on what the load
is it MAY be a good idea to add a small output resistor in series with the
output with a larger filter capacitor to ground after it.

You don't say whether 13.8v is input or output.
What are your desired input and output voltages?
What is the circuit to be used for?
The more you can tell about your application the easier it is to give good
answers.

Why is the cost important? - are you wanting to build many or just a few or
one? If a few or one then you MAY find that a commercial circuit or an IC is
still an OK solution.

The efficiency can probably reach 80%+ depending on many factors. I suspect
it would never get to 90%+. My friend who is using it to give 12v from 20v
to 35v in is getting 70%+.

For a 3A design using a FET may be a good idea. A P channel FET is needed -
which one depends on the required Vin .

NOTE - while this circuit COULD be used from rectified mains to 13.8 volts
DC I would not recommend doing so! The output is not isolated and the
circuit is "unusual" enough that you would want to have lots of confidence
that the design worked under all conditions. Mains can be very tricky.

Tell us more and see how it goes. If you don't want the list to know who you
are you can ask me offlist and I'll answer on list. For technical things
like this it's a very good idea to ask onlist so all can share with you.

What I said at the start about answering me offlist only applied to anything
applying to how God related to the design  - some people get extremely
annoyed when such things are discussed onlist.



        Russell McMahon





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