On 23/04/2015 03:13, JohnK wrote:
A similar 'nasty' can happen to experimenters - if multiple voltages
are required on a board, don't 'common up' at the bench supplies with
only one common taken to the board. Lifting that common causes the
'total' voltage to distribute according to the various resistances -
eg your 3V ICs could get most of the 12V IC's voltage.
[If you are new to electronics, try some calculations. OR just take my
word for it.]
John
Thanks for this warning. It makes complete sense the way you have
descibed it (I'm not new to electronics but then I'm not a EE). My bench
PSU is currently powering an experimental board using -12, +12 and +5V.
Loss of the ground connection would not at all be good for the
(expensive) 5V parts. But how to mitigate the risk? The PSU has a common
ground so I have just run one ground wire to the board. I guess I must
be doubly sure that the connection is secure before I power up and while
I use the board. Also, I suppose I could put a 5V1 or 5V6 zener on the
experimental board to try to clamp the drop across the 5V-to-ground at
the board (cheap and reusable between experiments). Any other protection
ideas would be good!
Grahame
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