Roman,

> The zero cross detect, the power supply is a capacitve reactance type.

You have no issues with these?

> I know. It's an expression of speech. :o)

Yes, I know. But you came across as if I was trying to shove this upon
the list, and that is not what I was trying to do.

> Yes opinions vary, we have been discussing this
> for months (years?) now on the list with wide
> varying opinions.

Sorry. I did not realise it was an old topic. I must have been napping.
I will try to search my archives, then the PIClist.

> The PIC doesn't have a zener.

I was referring to the Zener in Paul Benford's circuit. Isn't it
holding VDD at 5.6 volts relative to "0 volts" connected to VSS? But
then this would also mean that the neutral can swing from zero to
(339.5 - 5.6) as referenced to zero volts right? And that is what you
are getting at. You do not trust the internal clamp diodes to clamp
this off - even when it appears in many Microchip application notes and
those of third parties?

>  It has clamp diodes,
> very different story. :o) In the circuit you posted
> (yes I know it's not your circuit, sorry if I gave
> that impression)

No. I just don't want to be seen to be putting up someone else's work
without giving them the credit - whether it's good or bad! :-)

> the circuit is live to AC mains
> active, and the Xc supply and zero cross detect
> are driven from the neutral. This has EXACTLY the
> same effect as ac mains is, well, ac. :o)

Yes. Agree.

> The PIC pin is connected to the AC mains full potential
> via just one series resistor.

Yes.
>
> My reasons for an external zener;
> * much larger silicon and testable
> * can be physically away from PIC
> * WILL clamp 5.1v, even fast spikes

OK, thanks.

> And a capacitor across the zener will give some
> spike protection for negative spikes and reduce
> zener surge current for all spikes + and -.
> These two parts cost a few cents and go some way
> to preventing the AC mains killing the PIC. :o)

OK, Agreed. I don't care about the PIC as much as I do as making a safe
product and one that will pass standards.

> I've changed the topic as I know lots of people
> have their own ideas and may want to add...

OK

> Russell has posted a long and detailed post on
> the topic recently.

What was the subject? I can not find it on my machine at home. Will
check in the office tomorrow.

Regards,

Sean

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics