2011/2/6 vasile surducan <[email protected]> > > >> 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'd need 300mA to protect 500mA ?... Or I could 500mA knowing it'll blow at 800mA > > 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 > Yes I do. Yours didn't look like Zener ones, but the "DZ" (ooops, D2) and the symbol trace fading way confused me (I had to use the same magnifier as the one I used to smd solder :)) > and still trying to design board for selling, capitalist economy it's > amazing ... > Impressive, I was wondering how many more posts you'd need before talking about capitalist economy :) Oh, should I repeat there's no profit around this project ? That makes it less capitalist, maybe... If you had read "The Cathedral and the Bazaar", you'd know how open source project communities work, the same applied to open hardware projects. Many human societies are based on owning things: the bigger and most, the better. There are different types of levels. In this book they also talk about another society (can't remember the name), this time based on gifts: the bigger the gift, the more valuable, the better, you, the giver, will be recognized as an important person in this society. Open source projects are le that (not every os projects though), so are open hardware projects. But for the latter, there's often some money around, as it's material. You can't download a PCB, unfortunately. S Well, you already know all of that, and I know you're joking. What you still don't know is I'm not trying to design boards for selling. And what could I say now ? Well, thanks Vasile for your highly valuable gift :) fortunately the buyers will don't know either those un-interesting things... > maybe, maybe not. I never expect anything from people who would be interested (call them "buyers"). > > 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. > OK, thanks also for the gift wrap :) So, reading Kiste's post, Shottky diodes have a lower drop voltage than other diodes, typically 0.3V. This means I'll have 3V - 0.3V = 2.7V when using battery, is that right ? If I add a schottky diode to my last power supply proposal, I can save one fuse and one diode. 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 >>>>>>> >>>>>> -- 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.
