> -----Original Message-----
> From: Olin Lathrop [SMTP:olin_piclist@EMBEDINC.COM]
> Sent: Friday, April 11, 2003 8:20 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [EE]: Detecting low input voltage
>
> > I don't understand how this circuit works.  Assuming (dangerous!) that
> > the
> > regulator will always have at least it's dropout voltage between it's
> > intput
> > and output,
>
> The point was to test whether the input voltage is too low.  If the
> regulator always has enough voltage to work with, then there isn't a
> problem.  This circuit will start raising UNREG-OK when the drop on the
> regulator gets to around 1.4V.  UNREG-OK should be fully high when the
> drop is about 1.9V.  You can add another diode in series with D1 if you
> want the thresholds to be a little higher 600mV to 700mV higher.
>
The point I was trying to make is that the drop accross the regulator is
pretty constant once it goes out of regulation.  For a 7805 this is over 2
volts so the circuit wouldn't work, but as already explained by someone,
this application is for an LDO.

Regards

Mike


=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================
Any questions about Bookham's E-Mail service should be directed to postmaster@bookham.com.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.