Am Fr 21. November 2008 schrieb Tobias Diedrich: > Cédric Berger wrote: > > On Thu, Nov 20, 2008 at 17:24, DJDAS <[EMAIL PROTECTED]> wrote: > > > Cédric Berger ha scritto: > > >> I did not have a look at neo's circuitry. > > >> But whatever the method it uses, it cannot force 1A if 1A is not > > >> available (wall charger unplugged from the wall won't give 1A :-p ) ? > > >> > > > Uhm...not exactly true... Ohm Law says: V = R * I -> I = V/R, and if > > > R->0 then I->oo > > > In practice if you power a load with a little impedance (in real systems > > > the load is not always only resistive) the current requested will grow > > > and the source could be damaged (try to short circuit a normal battery, > > > you'll see a flash and if you maintain the circuit closed you'll meld > > > the battery). > > > This is why you should not ask 1000mA from the USB port (for example) > > > unless you're sure the hardware could give it. > > > Bye :) > > > > > > > Yes but I also have some car adapters that "did not mind" being > > shorted (12v to 5v adapter, given for 350mA). So I doubt a device > > wanting 1A would be worst than a short circuit... but what would be > > the output in such a case I do not know. > > According to the MAX756 datasheet (the step-up converter used in the > minty boost AFAICS), the switching mosfet should be protected due to > the operating principle: > The coil is shorted to ground until the current reaches about 1A, > then switched off automatically (and then the coil discharges in > series to the battery, effectively boosting the voltages). > > So the only things relevant to a overload situation are the > coil rating and the diode rating. > If both are capable of handling >1A continously, then switching > the Freerunner to 1A can't break anything. > The 1N5818 can handle 1A and the coil used has a saturation current > of 1.5A. > > (However, it is _not_ short-circuit-proof, since in that case the > current would flow directly from the battery over coil and diode to > ground and will likely destroy the diode first) > > Switching noise is nothing to worry about (Switching frequency depends > on load and battery voltage). > > Of course thermal dissipation can still be an issue.
you should use a polyfuse, to make device resistant against short on output /j
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