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mobile charger circuit help

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RCinFLA

Well-Known Member
Any of those will work.

Keep in mind, it will eat up alot of AA batteries. An AA alkaline battery is about 2000 mA-hrs. The internal resistance of the alkaline batteries will result in a lot of voltage drop.

Assuming a 1000 mAH LiIon battery in phone:

5 vdc charging input is linearly regulated to charge battery in phone. Charging current is typically 500 mA to 750 mA of this 1000 mAH LiIon battery.

Boosting 3.0 vdc (two AA's) to 5vdc @ 700 mA requires 5v * 0.7 A = 3.5 watts * 85% switcher efficiency = 4.1 watts from two AA batteries. This is 1.37 amps from batteries. At that current the batteries will sag greatly in voltage due to their internal resistance. AA alkaline batteries start out new with about 0.4 ohms of internal resistance which rises to over 1 ohm at >80% state of discharge.

You will have a voltage drop of greater then 1.5 vdc so as soon as you draw that much current the voltage will drop from 3v to less then 1.5 vdc.

You are better off just stacking four or five AA batteries.
 

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yasir_ali

New Member
today i tried up with 7805 regulator. i attached that how i tried to wire the circuit But after all this the circuit is nor charging my nokia 1100. i checked the voltage when charging, it was exact 5v and then i checked the current unfortunatley i know why the current is not gong above 1.7mA. what could be the problem i am powering this circuit from my lab supply i designed. the input to the circuit if from 7812 Ic.

Thanks
 

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