[sdiy] Switching power supply transformers

[Harry Bissell Jr]

Another note is to consider the symptoms of an
under-loaded supply.

The voltage may become unstable (which could mean doom
for the 5V logic)... 

The supply may operate in what is known as "burst
mode"
the supply will run at the normal switching frequency
until the 5V level is reached, then shut offf while
the
DC voltage bleeds down, and starting the cycle over.

Most switchers rub well above the audio frequency...
but if they go into burst mode they will probably
cause
audible sound, as well as interference with the rest
of the synth circuit as a whole.

Even if the burst mode does not kill you, you may wish
you were dead...   :^P

H^) harry



--- "Roy J. Tellason" <rtellason at blazenet.net> wrote:

> On Thursday 13 January 2005 11:28 am, Karl Ekdahl
> wrote:
> 
> > > You should be alright in terms of the 5 volt
> supply for the logic, Though
> > > it would be prudent to observe the rules for
> mixed signal PSU routing
> > > overall. That is. Separate termination for
> analogue and digital grounds.
> >
> > This is one of the issues i was thinking of. I'm
> doing a analog drummachine 
> > with a digital sequencer and the only signal i
> need to connect from the 
> > digital part to the analog is the triggers (8 of
> them). How do i realize 
> > this without mixing the grounds? Optocouplers? Or
> is there any even simpler 
> > method?
> 
> You can connect the two grounds together,  just do
> it at *one* point to avoid 
> ground loops.  The main thing with that is not so
> much that you don't want 
> them connected as that you don't want the sort of
> nonsense that digital 
> signals can do (including "ground lift",  where
> transient currents actually 
> raise "ground" by a bit) getting into your analog
> circuitry.  Just thinking a 
> bit about where that current is flowing should make
> it clearer.
> 
> > What i found is a wallwart transformer on a flee
> market. I bent it open and 
> > it's shielded and everything so i'll probably just
> glue it back together and 
> > use it as it is. If 20% of usage is the
> requirement, then out of 2A i have 
> > to use 200mA, right? My application is allready
> consuming well over 500ma so 
> > that should be O.K. i guess..
> 
> The 20% figure is a guess,  some of the real early
> stuff needed closer to full 
> load,  some supplies can go as low as 5% without any
> trouble.  Best thing to 
> do is to hook up some sort of a dummy load to it
> (use light bulbs,  handy 
> power resistors,  whatever) to it in stages, 
> testing the output voltage at 
> various loads to see how well it works out.  Or just
> test it with something 
> that's close to the load you plan to use it at,  to
> see if it works.
> 
> 
> 
> 
> 
> 
>