HV stories

[Mark A Moss]

>That is assuming you are not messing about inside the switch mode
>power
>supply in the PC.   They often rectify the line AC and use that
>voltage
>to drive the switcher.  This could lay you flat if you aren't looking
>for it.
>
>I've been bit a few times, always because I got in a hurry and was
>not paying attention to what I was doing.   Never work on any power
>supply when you are tired, have had a few beers, or are in a hurry.
>You only live once.

Exactly.  Most switchers I work with (30 or 40V at several amps) convert
the line voltage up to about 300VDC using diodes and caps, then back down
to the desired DC voltage.  The caps in the 300V section can hold their
charge for a long time, so check that the bleeder resistors _have_
actually discharged the caps before going to work.  Also, there often
isn't any guard, shielding, or interlocks to protect you from
accidentally contacting the high voltage while making adjustments to
other parts of the circuit.

Mark Moss, KC8DEI
Kalamazoo, MI
U.S.A.
Grid EN72eh
www.qsl.net/kc8dei

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