take a look to the attach, maybe will be useful if understand. vasile
On Sat, Feb 5, 2011 at 9:37 AM, Sebastien Lelong <[email protected] > wrote: > Sure, I understand what you mean. So here's some self-enligthenment :) > > I want the board to be safe: it should never damage USB host for instance > (this is the most important point). It must also be fool proof: a short > circuit should just blow a fuse. Ideally reverse polarity shouldn't be a > problem. > > I know this is still fuzzy, from what your say, Kiste, blow speed is also > important. I just don't have enough knowledge to pick the better solution, > the better compromise. > > In my opinion, 500mA should protect the load for extra current (user load) > *and* board itself (PIC, etc...) *and* the power supplies. > > Cheers, > Seb > > 2011/2/5 vasile surducan <[email protected]> > >> Seb, it's yours design so you have to enlighten us. >> You want three power supplies: one battery, one external supply, one USB. >> The load is one nanowatt PIC and one XBEE which draw max 270mA on TX and >> the user unknown load. >> In your opinion the 500mA fuse should protect the load for the extra >> drawn current, the power supplies or all of them? >> >> Vasile >> >> >> >> On Sat, Feb 5, 2011 at 5:00 AM, Sebastien Lelong < >> [email protected]> wrote: >> >>> Or, should I keep another fuse at its first place, after regulation ? I >>> first thought that put this fue here would protect USB (but not the >>> regulation part) and the whole circuit. >>> >>> Please enlighten me ! >>> >>> Seb >>> >>> 2011/2/5 Sebastien Lelong <[email protected]> >>> >>> Hi Kiste, >>>> >>>> 2011/2/5 Oliver Seitz <[email protected]> >>>> >>>> >> Both USB and U1 have short circuit protected outputs. >>>>> >>>>> You mean, power rails on USB connectors at a computer are short-circuit >>>>> protected? This is true, but the protection is often a non-resettable SMD >>>>> fuse somewhere in the middle of a very big PCB called mainboard... I'd >>>>> prefer not to blow that one. >>>>> >>>> >>>> :) >>>> >>>> OK, so I can put another SMD fuse for USB. >>>> >>>> >The trouble with polarity protection (this is what we're talking about >>>>> isn't ?) is the drop voltage involved with diode. >>>>> >>>>> Only if you're using a diode in series. You could also use the fuse and >>>>> a reasonably strong schottky diode from ground. So, reverse polarity will >>>>> not go beyond 0.5V, and the fuse will blow when strong reverse power is >>>>> applied. >>>>> >>>> >>>> Thanks for the tip. Could you point to some direction about this diode ? >>>> >>>> I was also thinking about using a schottky diode to regulate max 3.3V. I >>>> mean, according to my last power supply schematic, if user select USB but >>>> no >>>> regulation, xbee could be damaged for instance. Could a 3.3V schottky diode >>>> be used for thi purpose ? (make sure it won't be more than 3.3V ?) >>>> >>>> >>>> Cheers, >>>> Seb >>>> >>> >>> >>> >>> -- >>> Sébastien Lelong >>> http://www.sirloon.net >>> http://sirbot.org >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "jallib" group. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]<jallib%[email protected]> >>> . >>> For more options, visit this group at >>> http://groups.google.com/group/jallib?hl=en. >>> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "jallib" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]<jallib%[email protected]> >> . >> For more options, visit this group at >> http://groups.google.com/group/jallib?hl=en. >> > > > > -- > Sébastien Lelong > http://www.sirloon.net > http://sirbot.org > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<jallib%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/jallib?hl=en. > -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
<<attachment: three pwr-small.jpg>>
