> The better ones have full wave rectification. The cheaper ones have half
> wave.
I can't prove that none of them have only half-wave rectification, but I doubt
it. Mine is certainly a cheap unit, and has full wave.
> A single diode is less expensive than two (or four).
That's true, but the heavier transformer required to achieve a particular
current rating with only half wave rectification more than offsets the cost of
one more diode. Diodes are pretty dang cheap, while the transformer is the most
expensive item in the unit. Even $3 "wall warts" have full wave rectifiers.
Randall
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