> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Dario Greggio
> Sent: 23 April 2010 16:03
> To: Microcontroller discussion list - Public.
> Subject: Re: measuring 36-72VDC
> 
> M.L. ha scritto:
> > Also I don't really see how a 33 volt zener is going to allow your
78L05
> to
> > work from 36v to 72v. The abs. max of a 78L05 input is 35v and you
want
> it
> > to actually work at 39V.
> 
> 
> That part is indeed a bit of cumbersome, Martin and Bob.
> I may use a small DC-DC converter with a larger range. Again, I still
> stress the point that I'd have liked this circuit to be more cheap and
> "concise" as possible.

Why not use a shunt regulator like a TL431? All the power dissipation is
them in a resistor rather than in the same device that is going to be
your reference voltage.

 There are even PICs with built in shunt regulators 12HV6xx, but I dount
they will be suitable for a reference without some calibration as they
don't have very good initial accuracy.

Mike

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