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]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
