I am trying to build a radio transceiver using the power from a cell phone type battery. I am wondering if anyone can help me with 1) What type of power supply is in a cell phone? 2) A schematic of a cell phone power "system"
I am using a micro-controller that can run between 3 - 3.6 volts. A cell phone battery is between 2.8 - 4.2 volts. The rest of the components Transmitter, LNA, possible GPS etc all run on 3.3 volts
My current plan is to run the micro-controller and the LNA off of the battery through an LDO so they (the LNA also has an enable line that can be toggled) will run until the power is gone. Then have a Buck/Boost enabled when the transmitter needs to send. The buck/boost is not very efficient.
If you are in a modern civilised country then your cell phone uses a Lithium-Ion or Lithium-Polymer battery that is 4.2V when fully-charged and drops to about 2.8V when its load must shut off. A lithium battery will catch on fire if it is improperly charged or discharged. (A very hot fire. Water makes it burn hotter.) I have cell phone Lithium battery that was made for extended time. It has two cells in parallel.
If you are in a poor 3rd-world country then your cell phone is nearly 20 years old and uses an old Ni-Cad "3.6V" battery that has three cells.
There are different batteries for different blackberries. One small one is only 900mAh and a "high capacity" battery is 1600mAh. You need a circuit that will disconnect its load when its voltage drops to 2.8v to 3.0V. You also need a suitable Lithium battery charger IC.
Those Li-Po batteries are powerful beasts, but they are a sensitive bunch. Charging and discharging must be done carfully. They can be made in many shapes and sizes. My Helicopter uses some cells in series and the unit is about the size of a matchbox. They can handle about 6A continuous for about 10min and transients greater than 20A so they must have a very low internal resistance or else the receiver resets when the blades start to spin (transient current causes a quick but big voltage drop on a low charge).
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Internal cell phone power supply
Posted - Mar 04 2010 : 12:34:55 PM
