From time to time many of us are facing the same problem when trying to charge your smartphone or tablet from the USB port â it just not charging. Recently I have bought USB car charger to power my Samsung Galaxy Tab 10.1 on the road just to discover it doesnât work. Even though the Galaxy actually sees the charger connected is just marking it as unrecognized power source. I was trying to power up my Motorola Droid 3 phone â it wonât work either. The reason is simple â the Galaxy Tab doesnât recognize the charging device as ânative chargerâ.
What is ânativeâ charger?
The native charger for smartphone or tablet often have a special voltage signature on USB data pins to let the device recognize the charger and figure out the maximum charging current it can consume from the power source. The intent is twofold. First, it is stopping the device from consuming too much current from the charger. Second, it is preventing the charging from unrecognized power sources. The âunrecognizedâ is the keyword here, as profiting from selling additional device accessories (chargers) is definitely a business strategy.
Samsung devices
I have figured the simple solution that will make the Samsung Galaxy pad device charge from USB port, see the schematic below. The R1/R2 voltage divider is providing the 1.2V voltage on the D+ and D- pins of the USB connector to be recognized as Samsung native charger. Thatâs it. The only issue is that completely discharged Galaxy tab battery might draw even more then 500 mA from the USB port, when the USB 2.0 specification limiting the maximum current load to 500 mA. Just be aware.
For more detail: Charging your Smartphone from USB without fear