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.
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".
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.