Welcome to the CADSTARguys Blog - Information, hints, tips and my waffle on the CADSTAR Printed Circuit Board design suite.

Please note that all names used are completely fictitious and any thing written is my own personal opinion or knowledge and not related in any way to either my employers or their customers (or Zuken).
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Wednesday, 17 November 2010

Dangerous Diodes!

Just a little something that I noticed in a CADSTAR library I was browsing through.

How do you draw your diodes? Although there is an obvious choice of whether you want them filled or clear some disastrous mistakes have been made because of bad choices made when creating the simple diode symbol.

In essence, a line has been drawn through the centre of the diode - this is not the first time I have come across this in peoples libraries and it can enable a very easy mistake to be made.

Let me show you what I mean.

Why one earth would you need to draw a line through an open diode?
It makes it look as if the connection is going straight through it, however if it is in a circuit and it is rotated 180 degrees the connections at each end actually do go through the middle of the diode and although your circuit may look correct when it gets onto the actual PCB the legend is the wrong way around as is the placement information and the diode gets fitted wrongly - and that possibly leads to either something not working or it going bang!

In this example I have offset the diode slightly.

I have seen this cause problems with other peoples designs - it was hard to track down because the schematic looks correct, ECO updates and design checks all come back correct.

The same goes for filling them, as well as using up more ink when printing them (lol) they can also be rotated and not show the true connection.

So please - do not put a line through the middle of your diodes
it is dangerous.

So instead  make them like this:
(Different type - but clear inside the body).

This way if it is rotated then it does look like this:

And you can easily see it as a short!

It's not hard to figure this out however so many seem to miss it - so go on - please change the diodes in your library before you too suffer from the mistakes that this can cause.


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