Resistance value to get 1.5 v output form a 2.8 v adapter?

Discussion in 'General Electronics Chat' started by meghama, Jun 11, 2010.

  1. meghama

    Thread Starter New Member

    Jun 11, 2010
    1
    0
    I have a 2.8 V ,150 mA charger . I need the out put voltage of 1.5 V . What is the value of resistance need to get 1.5 V output Voltage , Pls give the color code of the resistor.
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,176
    1,799
    There is no value of resistance that will give you that voltage for all possible loads. Familiarity with ohms law would reveal this salient fact.
     
  3. oidium45

    Active Member

    Apr 24, 2010
    130
    8
    This is correct.
    However, If you are going to use the adapter for one item. (hopefully not your cell phone or anything too important!) You could use ohms law to determine the value needed for the voltage drop. But keep in mind that as the current requirements change so will the needed resistor values unless you use a voltage regulator.There are a few 1.5v voltage regulators out there and the required circuits are pretty small, cheap, and simple. Search google for "1.5v voltage regulator".

    Good luck.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If it's a constant current charger, a 2.8v 150mA charger will overcharge a 1.5v battery.

    The charger will supply current at a controlled rate until the chargers' output voltage reaches the limit.

    A resistor in series with the charger will slow the rate of charge, but it will still overcharge the battery.

    You need the correct charger for your battery.
     
  5. Externet

    AAC Fanatic!

    Nov 29, 2005
    763
    57
    Instead of using a resistor, connect a couple of 1N4001 diodes in series and test if the voltage is close enough to your satisfaction when the unit is working.

    +2.8V---------|>|------|>|--------+1.5V
     
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