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Re: gEDA-user: gschem vs. PCB diode pin numbering - anode/cathode definition

On 08/24/2011 01:15 PM, Colin D Bennett wrote:

On Wed, 24 Aug 2011 08:21:17 -0400
Ethan Swint<eswint.ramu@xxxxxxxxxxx>  wrote:


On 08/23/2011 08:47 PM, Matthew Lewis wrote:

I was double checking a pcb layout today and I discovered a rather
nasty gotcha. It seems that gschem and PCB don't agree on which end
of a diode should be pin 1. Gschem views pin 1 as the anode and PCB
considers pin 1 to be the cathode. It doesn't prevent you from
laying out a board correctly, but it does cause the silkscreen
polarity to be printed backwards (for the SOD devices at least).

I've defined my own symbols and footprints to use 'A' and 'K' instead
of 1 and 2.

That's a good idea.  Anything you can do to error-proof yourself is
a Good Thing.

However, I refuse to use âanodeâ and âcathodeâ for diode symbols, since
these terms refer to electron flow and are _incorrect_ when the diode is
reverse-biased (most obvious for common Zener diode circuits).




I understand that it is electrical convention to name diode terminal
anode and cathode, but I reject it as a confusing and ambiguous naming
convention.
Yes, it's not quite correct, but it is a widely held convention, unlike numbering the pins 1 and 2 (or 3 or 4). 
For my diode symbols and footprints, I choose to name the terminals
âPâ and âNâ (for the p-type doped side and the n-type doped side).

If you use "P" and "N", Schottky diodes are now in error.  ;)


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