On Sat, Feb 5, 2011 at 10:30 AM, Sebastien Lelong < [email protected]> wrote:
> Thanks ! > > Why using a coil (L1 ?) with USB ? > L1 + C2 is a filter, for the noise coming from the computer. Also the USB connector ground can be AC or DC coupled to avoid noises, read the USB2.0 specifications... > And how it's 1A protected while using 0.8A fuse ? > because a 0.8A regular fuse will never blow at 0.8 A, but you need 20 years of work and 1000 fuses to know that (or a good fuse datasheet to read before starting your design) So, I understand you're using 2 zener diodes 20V/1A for polarity protection, > is that right ? > you still don't know (after Oliver's message) which is difference between a zener symbol and a schottky simbol and still trying to design board for selling, capitalist economy it's amazing ...fortunately the buyers will don't know either those un-interesting things... A schottky is protecting the silly user only for reversing the polarity of the power supply, by blowing the fuse if it's reversed. A zener needs a series resistor to limit the current after the voltage is increased above the zenner thresold limit. Vasile > > > Cheers > Seb > > 2011/2/5 vasile surducan <[email protected]> > >> 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]. >>>>> 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. >>>> >>> >>> >>> >>> -- >>> 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. >>> >> >> -- >> 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. >> > > > > -- > 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. > -- 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.
