Cell phone charger Design

Discussion in 'Power Electronics' started by ali_786, Aug 21, 2016.

  1. ali_786

    Thread Starter New Member

    Aug 5, 2016
    Hi everyone! i m designing a cell phone charger (zener based) but i have some queries in my mind:
    1: how can i measure the cell phone battery resistance because it will be used as RL (load resistor) in my design as well as in multisim.?
    2: choosing series resistor?
    3: zener slection?
    waiting for your valuable suggestions.....thanks
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Are you aware that cell phones incorporate their own charge controller, which (a) will prevent you measuring the battery resistance and (b) may check for a proprietary charger by looking for specific signal conditions on the USB D+ and D- lines? The controller will probably also negotiate via USB for a high charging current.
    A zener diode and series resistor based charger would seem suitable for low-current charging only. Have you considered using an off-the-shelf voltage regulator such as a 7805?
  3. ali_786

    Thread Starter New Member

    Aug 5, 2016
    thankx Alec_t...Actually my target is to charge simple Nokia mobile. Charging requirements are 5V , 400mA. it will charge via charger pin (jack) not via USB.
  4. NCSailor

    Active Member

    Jun 15, 2013
    While it may not use USB as a power source,and therefore need not negotiate, everything else Alec-t wrote still holds.
    I am assuming that you are basing the power supply requirements on the 5V and 400mA which is fine. However, that charger pin(jack) does not connect directly to the battery. It is simply a power supply for the onboard charging and battery management system. Current might rise up to 400 mA for a discharged battery, but it will also likely drop to near 0 mA once the battery is fully charged.
    The charging requirements of Li-Ion batteries are actually fairly simple, however, the current and voltage values are also critical for safety. In addition to the pre-charge, constant current, and constant voltage cycle, they should turn off once the battery is charged. In addition, many monitor battery temperature and will reduce current to avoid excessive temperatures. There are battery management IC's that do all this and they are included in the phone to avoid issues with consumers connecting incorrect chargers and creating fires or even explosions.

    Your power supply will see an effective resistance that is highly variable. A zener is not really a good solution for highly variable loads. Alec_t suggestion of a 7805 would be the simplest approach that would meet the requirements.