W3JDR wrote:
There are also some transformer-input types that produce well-regulated DC
outputs using linear regulator technology, and a growing number of units
that use switching regulator technology to make the transfoprmer so small
that it's hard to tell from the outside that there's even a transformer in
it.. The latter are easily distinguishable because they put out quite a bit
of power, yet are smaller and much lighter in weight than traditional units
with equivalent power capability.
Joe
W3JDR
wrote in message
...
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.
--
Jim Pennino
Remove .spam.sux to reply.
Such units actually have a bridge rectifier across the AC mains and
supply DC to a switching regulator running at 20-50khz. There is an
isolation transformer running at this frequency (it's core is just a
small bit of lightweight ferrite). The output of the isolation
transformer feeds another bridge rectifier and filter (at ~40khz not
much of a filter is needed, small caps and chokes!). There may then
be a linear or switching regulator. If the later, it may actually
regulate by changing the switching frequency/duty cycle of the
original switcher at the AC mains input. In this case the feedback
is by means of an opto-isolator for safety.