Thanks Gerald. You make a good point about the returns you see. It would be interesting to know if those numbers are due to many if not most powering boards from usb due to it's immense ubiquity and popularity. While I generally try to be careful in getting things right including checking things multiple ways with VOM prior to, during and, after assembly I can say it has happened where a power cord on some item has been assembled or hooked up improperly such that polarity ends up reversed.
I'm aware of the voltage drop issue with a rectifier which is why I was thinking single diode placed across the input (basicly as a crowbar to the supply) as the point is protection but again with the rma levels seen I can see how that dictates economics. Eric On Thu, May 22, 2014 at 6:14 AM, Gerald Coley <ger...@beagleboard.org>wrote: > It will not protect against reverse polarity.A full > wave rectifier will cause a voltage drop and then you o longer have 5V. Yes > I could have added some reverse protection, but I must admit out of 200,00 > boards shipped I have sen about 10 cases of reverse polarity. So adding he > cost to all boards for that feature does not make a lot of sense. I removed > the NCP349 on the BBB..Out of the 150,000 of those shipped, I think we > maybe had 3 cases of reverse polarity. > > Gerald > > > On Thu, May 22, 2014 at 2:15 AM, Eric Fort <eric.f...@gmail.com> wrote: > >> are you saying that the ncp349 *CONTAINS* a full wave bridge rectifier? >> I certainly didn't see that in the data sheet. Note the point is >> protection from overvoltage and possibly, thus the question, polarity >> reversal which may or may not be the same as severe under voltage. >> >> Eric >> >> >> On Wed, May 21, 2014 at 11:18 PM, Bayani Custodio < >> bayani.p.custo...@gmail.com> wrote: >> >>> Full wave bridge rectifier, if they make 'me small enough would be the >>> cat's meow. Worked we'll on an old project back in the op amp days. >>> >>> Sent from my iPad >>> >>> On May 21, 2014, at 11:41 PM, Eric Fort <eric.f...@gmail.com> wrote: >>> >>> the ncp349 chip used for overvoltage protection on the dc power input >>> for the beaglebone seems to do a good job of providing overvoltage >>> protection. Even looking at it's datasheet though, I'm not completely sure >>> if it will protect the board against reverse polarity. (I'm not out to >>> overtly or purposely try this but I too have occasionally made mistakes...) >>> >>> so should the beagle bone white/black be protected from application of >>> reverse polarity being applied, i.e. powering it with -5v instead of +5v, >>> by the ncp349 (or might it be a good idea to add a reverse polarity diode >>> across DC in that will pop the power supply & save the board. >>> >>> Eric >>> >>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "BeagleBoard" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to beagleboard+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "BeagleBoard" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to beagleboard+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- >> For more options, visit http://beagleboard.org/discuss >> --- >> You received this message because you are subscribed to the Google Groups >> "BeagleBoard" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to beagleboard+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to beagleboard+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
