Kevin,

     I've evaluated the three circuits in AN-552, and basically they do as
     the book says.  They are cheaper than the MC34064 (max $0.30 instead
     of $0.90) but require certain characteristics from your power supply
     to work reliably.  Figure 5 (the diode, resistors & cap) helps only
     when your power supply is slow to ramp up, it gives zero brown-out
     protection.  Figures 6 & 7 help with the brownout and slow power
     supply ramp up, but use a few too many parts for my liking.  Also, if
     you need hysteresis and/or power-on delays, you need even more parts.

     Basically, before you pick protection, know thy power supply....

     -Ed VanderPloeg


______________________________ Reply Separator _________________________________
Subject: Re: brownout protection
Author:  pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU> at
InterNet
Date:    4/22/96 2:22 PM


>At 11:10 AM 4/22/96, Kevin Rhoades wrote:
>>Has anyone out there used the brownout protection circuits in AN-522 (figure
>>6 and figure 7)?.
>
At 11:59 AM 4/22/96 -0700, you wrote:
>Having been down the road before, my question is "Why do you think
>you need brownout protection?"
>
>eric
>
Cheap, unpredictable, already existing power supply located in various and
probably noisy (electrically) locations.  I feel the new processor board I'm
designing for an existing device needs all the help it can get.  Cheap
insurance for a fairly low volume project (<200).

Actually I sorta jumped the gun a little with my question.  I went back over
the older messages posted to the list and found the one that references the
motorola MC34064 device.  I'm still curious though about the circuits shown
though...K.R...