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Precision Voltage Regulation

  1. Mar 22, 2014 #1


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    I have a nokia N8 cell phone and it is very precise about what it will allow to charge it. Mostly it will only accept wall chargers, not car power in any way. There is no way it knows the car charger isnt in the wall so all I can guess is the power is "dirty" and therefore it denies it. My question is how do I build one that is very precisely regulated? I found this http://www.brighthubengineering.com...13-make-yourself-a-d-c-mobile-charger/#imgn_0 but I am not sure that is different than any other car charger or if it is better. Sorry if this is overly simple. Thanks for any help.

    I also found this, might be of some help. http://www.herjulf.se/solar/charge-..._Charging_Interface_Specification_v1_2_en.pdf
    Last edited: Mar 22, 2014
  2. jcsd
  3. Mar 22, 2014 #2


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    If the phone is being charged through a USB port then it may require a conversation with the power source. Some in-car chargers simply loop the transmit and receive USB data back to signal a valid supply. They may also have a high value resistor in the charger on one of the USB pins. They can assess that from inside the phone to see if you have purchased their charger.
  4. Mar 22, 2014 #3


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    The car charger converts the battery to a "precision enough" voltage for charging, so that is not your issue.

    Nokia phones will charge with nokia car chargers.

    The issue is probably with the data pins on the USB connector. Different phones have different requirements in order to see a charger as a valid source.

    It could be as simple as Nokia requires DM/DP to be shorted, and your car charger has something different (is it apple, sony, or samsung?).
    Or even, the car charge is not working properly. Does it work on other devices?

    I don't know of any special Nokia requirements (based on a quick search).

    Here is a good analysis of chargers, and in the later sections it talks about the DP/DM pins and gives references.

    http://datasheets.maximintegrated.com/en/ds/MAX14578AE-MAX14578E.pdf shows how complicated all this can be.

    http://www.microchip.com/wwwproducts/Devices.aspx?product=UCS1002-2 emulates 9 different USB chargers.
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