[hpsdr] [ATLAS] - Watch the TOES!, (was proposed physical bus/pcb design 03March2006)

[Lyle Johnson]

> I sort of suspected a fuse in the power supply ground connection was a 
> bad idea, but not sure why.  Is the danger that the chasis will then be 
> floating and could obtain a voltage ... or is there a danger of some of 
> the supply lines effectively becoming the return?
> 
> Mostly a software guy here ... as they say, beware programmers wielding 
> soldering irons!

Let's say you have +12V and -12V being used in your widget and the open 
the ground.  The +12 and -12 are in series and in a series circuit the 
current is the same.  This will cause the "floating" ground to shift 
around until the load is happy, e.g. the current is the same from the 
+12 and -12 sources.  But this might mean that you have, from the 
perspective of the "floating" ground a +3 and -21V supply, or a +19 and 
-5V, or ...  Some parts may then have their voltage rating exceeded, and 
do something dramatic but unintended.

Alternately, if the power supply has its ground somehow tied back to the 
"chassis" and you connect and audio cable with a ground to something 
that the power supply is grounded to, the cable is now completing the 
path around the fuse...

73,

Lyle KK7P


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