I have this old power adapter with a rating of 6V 2.4 Amp. I used a voltage divider circuit made of two 1000 ohm and one 10000 ohm resistors. when i measured the voltage across the 10k resistance, I got an exact drop of 1 volt, i.e., it was reading 5 V. i connected the ends to the micro USB and connected to my windows phone. The phone was not charging. When i read the voltage with charger, the voltage was only 2.5 V instead of 5 V. What just happened here? the adapter was a 6 V adapter that was used for a router, why did stepping down voltage result in drop in voltage on connecting load. thanks for helping me out. How would i get a 5V to charge my cell phone from this adapter?
The basic assumption of a resistor divider is that the current flowing through both resistors is the same. When the current is not the same, the resistor divider equation does not work.
6V is pretty close to 5V. You almost don't need a regulator. Instead of a normal resistive divider, make a divider with a diode "on top" and a 1k resistor "on the bottom." An ordinary silicon diode. A nice big one that can dissipate lots of heat without a separate heatsink. Look for something rated at 10A or something.