[sdiy] Power Supply Design Questions

[Scott Gravenhorst]

Paul Perry <pfperry at melbpc.org.au> wrote:
>The heat generated is EXACTLY the product of the current, times the 
>voltage drop across.
>
>The voltage drop must always be more than the drop out, naturally.
>If you pay more, you can get lower dropout chips.
>
>Worry about:
>the lowest & highest mains voltage you are likely to see. It varies
>more than you might think.
>
>A heavier mains tranny will allow more current to be sucked without 
>sagging. But if the current is largely constant, then that isn't a 
>problem.
>
>Are you trying to run a huge amount of stuff from one tranny?
>It is often better to distribute regulators around the different
>boards, rather than run regulated voltage from a central point.

Ah thanks, good point about mains hi/lo, I hadn't thought about that
much.  This says for the device to be portable, i.e., runs in other
people's houses or whatever, you need to run above dropout a
sufficient amount.  

What happens here, is a creeping thing.  I must admit that what I do
is build a supply and start adding loads to it; a VCO here, an ADSR
there, etc.  If I built one huge project, I'd plan this better.  The
regulator ICs always have small heatsinks on them and when I add
enough load to it that it becomes warm (not hot) to the touch I think
about building another one.  Another other issue for me is that I
have a rather large collection of used/discarded wall warts that work
just fine.  They are all of rather random voltages and current
capacities, so I try to pick ones that will best fit what I'm trying
to make.  Numerous wallwarts are not a big problem for me.  So I
guess I already distribute the loads; FatMan One has 3 bipolar
supplies in all.

I need to build another one (for FatMan Two), and I got curious as to
the best way to do it, even though what I've done works.

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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