Most amusing!
It can and has been done. Would you believe it, there's a range of I.S.
safety barriers from MTL instruments
with such functionality. I phoned them up and asked if they could let me
know how they do it... I didn't expect an answer and needless to say I
didn't get one.
Maybe i'll buy a barrier and take it apart, but then i guess all i'll see if
a blob of epoxy, encased in a mound of epoxy.
-----Original Message-----
Sent: 18 December 2003 13:24
To: Multiple recipients of list CHIPDIR-L
On Thu, Dec 18, 2003 at 02:49:19AM -0800, Darren Logan enlightened us
thusly
> Hello,
>
> The circuit requires regulated 12V DC but must be either mains or DC
> (for want of a better word) "powerable".
>
> Instead of having two separate connections (one for mains and another
> for DC) i want both on the same connection!.
>
> I.e. you can stick mains or DC in the same socket and the instrument
> wont mind!.
It _is_ madness - you understand that safety people will freak. The
worst case analysis gives A.C. into battery, explosion, and sulphuric
acid in your eyes. I did explode the top off a lead acid battery by
touching jump leads together as I was extracting them from the back seat
of a skoda. The bits hit the raised bonnet!
Nevertheless, The way to do that is as follows. Put your input into the
A.C. points on a bridge rectifier. gqap a feed from '+' and '-' and as
long as DCV is between ACV RMS and peak, there shouldn't be too much of
a jump.
Given the figures you suggest(12VDC and 230VAC), however, your
input now will be 10V (12V-2V dropped on the bridge), or
325v(230V*1.414) If your smps can handle that, post a link to the
circuit. We'd all like to know how you did it.
The sane way to do it is use two plugs and a diode & supervisory IC to
change the regulated 12V from a mains supply or the battery. That way
your messing is at 12V
Let us know how it blows up :-).
>
>
> On Thu, Dec 18, 2003 at 01:54:20AM -0800, Darren Logan enlightened us
> thusly
> > Hello,
> >
> > Does anybody have any idea how one can go about designing a power
> > supply which can run from AC mains or DC - automatically switching
> > itself for either input. For example 90-260V AC and 8 to 24V DC
> > (output 12V, 1A)?
> >
> > I guess there will be some kind of front end detection circuit (of
> > AC or DC) which controls how the input is converted.
>
> Clarify exactly what you are up to.
>
> Are you switching power sources for a low voltage circuit, or doing a
> step down/step up smps?
>
> Are you connecting mains and battery to the same pine (Joe public will
> love that!)
>
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
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Author: Darren Logan
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