OK, this one should protect both battery and USB (not considering blow speed):
[image: power2.png] If it sounds ok to you, I'll keep this one. cheers, seb 2011/2/5 Sebastien Lelong <[email protected]> > Typically I wanted to use this kind of fuse: > http://cgi.ebay.com/10pcs-Little-fuse-notebook-repair-LF-Fuse-SMD-1206-0-5A-/220725125732?pt=LH_DefaultDomain_0&hash=item33643e2264#ht_1113wt_754 > > Seb > > 2011/2/5 Sebastien Lelong <[email protected]> > >> 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 >> > > > > -- > Sébastien Lelong > http://www.sirloon.net > http://sirbot.org > -- 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.
<<power2.png>>
