piclist 1999\10\30\035930a >
Thread: power supply
face picon face BY : Jinx email (remove spam text)

Correct, I know exactly what you mean about DC plugpacks. I would
still not trust a label and consider it prudent to measure the AC voltage.
You never know what, if any, standards the manufacturer has. If you'd
agree that a loaded transformer's voltage will drop, then it's not
unreasonable to suggest that a manufacturer could install one with a
higher voltage that will drop to the stated voltage at the stated load.
As an example I have a small labelled 18V 0.3A AC adaptor for a
UV EPROM eraser (no retification or caps at all). It measures 20.3VAC
unloaded but 17.4VAC in use.

Whether we agree or agree to disagree I think a point about not
assuming labelled voltages on plugpacks is worth mentioning. I've
stopped at least one of my customers blowing a circuit I'd made for
him by checking his chosen 4.5V plugpack before he used it. Admittedly
it was a DC one and if he'd been in the know he could have expected
it to be as high as it was (7.5V). With so many low voltage CMOS
devices now on PCBs and the consequent general reduction in current
required, if you aren't using a regulator you'd be ill-advised not to check
a bought plugpack (please don't think I just said you give ill advice).

All of this is academic in Chris' case. It looks as though the supply he's
got will be inadequate anyway.

WBR Jinx.
{Quote hidden}

<00b001bf22ac$903b7c00$703761cb@joec> 7bit

See also: www.piclist.com/techref/power/actodc.htm?key=power
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