USB charging semantics

Discussion in 'General Electronics Chat' started by axeman22, Jun 29, 2012.

  1. axeman22

    Thread Starter Active Member

    Jun 8, 2009
    53
    0
    something that's on my electronic mind, bugging me.. I'm hoping you guys might be able to shed some light..

    USB - my favourite..

    USB charging actually. so the USB spec initially allows devices to pull 100mA - and do data transfer at the same time. Not enough power for most any device today - especially smart phones. so with a revision to the spec devices when they connect up look for les than 200Ohms between the data wires, if the case - for example short, then they will pull up to 5000mA - all good..

    so here;s what I want to do.. take a 12Vdc car battery - nice clean 12V .. put that into a 7905 reg (to-220), with required external caps as per the 7905 data sheet.. , short the two data wires - and then allow the phone to pull 500mA etc.. - sound simple sight - /? it does't work…..!!!!! phone goes all weird etc etc..

    can anyone tell me what is going on - what am I doing wrong..? my understanding is that the phone has internal charging circuits etc.. so just putting a nice clean 5Vdc into it should be all that is needed..?
     
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