From: John Popelish
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Subject: Re: Switching supply w/ 48v to 240v input?
References: <3E26E12F.1C5815AC@y.z> <3E2833D8.507C2616@rica.net> <3E271E33.897A9CAC@y.z>
Date: Thu, 16 Jan 2003 21:41:20 GMT
NNTP-Posting-Date: Thu, 16 Jan 2003 16:41:20 EST
> John Popelish wrote:
> > The wider the supply range, the bigger the compromises at the
> > extremes. The 100 to 240 volt range covers almost all residential
> > line voltages, worldwide (not counting their tolerance).
> With 4-8 watts output at 5v, where would the compromises be? Is it an
> issue with more ripple at one end of the range? Could it even be done
> with common parts, or would it require odd transformer ratios, etc.?
It can almost certainly be done. The compromises are mostly cost. To
get 8 watts from 48 volts, you need a transformer and switching device
that can handle about .2 amps average (several times that, peak). But
at 240 volts you need only an average current capability of .04 amps,
but a voltage capability of something like 600 volts peak. To cover
both ends of this range, you need a device with both the high current
and the high voltage capability, and magnetics that also handle those
extremes. That means that at both ends, of the range only a fraction
of some of the limitations of the devices are approached. At 500
watts, that amounts to quite a bit of extra capability and expense.
At 8 watts, not so much. A flyback isolated regulator with non
continuous inductor current is probably the best way to achieve this
small supply. However, doing this the first time (and dealing with
240 volts and the safety implications of that voltage) is a pretty big
hill to climb.
The basics of the flyback isolated regulator can be found at: