wrote:

wrote:

I have a collection of "wall wart" (others may call them "transformers")
and I'd like to use one to cobble a little power supply. I've never
opened any to see what's really in them (and suspect it'll be quite a
chore), but I'm quite sure they are not ALL "transformers", because some
claim AC and some claim DC output, yet the first I grabbed out of the
junkbox claimed DC AND ALSO provided a HEALTHY AC output on the same
two wires! Furthermore, NONE of them seem to be voltage regulated!
(But if one says "X volts at Y milliamps", then loading it to Y mils
usually gives an output close to X volts.)


So what IS in them? Do the really light-weight ones, for example,
use a capacitor for relatively low-loss voltage dropping? And
why would one give *BOTH* AC and DC? Bad diode(s)?


--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member and Rifle, Pistol, & Home Firearm Safety Certified Instructor
Certified Instructor for the Kansas Concealed-Carry Handgun license


It depends...

The AC ones are just a transformer.

The DC ones contain a transformer and diode(s).

The cheapies usually don't contain any capacitors or regulators, hence
there is significant AC on the DC.


And AFAIK most of them achieve current limiting by intentionally making
the windings lossy, so you can't burn down your house by shorting the
leads together.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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