circuit which will provide quite enough power in one charge cycle for charging your devices many times. Increasing the battery AH will more increase the backup. For example a 4.5AH will provide more backup than a 2.8AH.
The circuit is divided in three parts. The first part is a power supply which supplies the power to the circuit. The second part is an automatic battery charger built around two transistors and the third part is LM2940CT-5.0 efficient voltage regulator that provides neat and stable 5.0 volts.
The charging part of the circuit requires some simple adjustments at the first time. For adjusting the circuit connect the power supply directly with the battery and wait until the battery reached to 7.2V with power supply connected, for this purpose a millimeter should be used to check the voltage. When the battery reached to 7.2V then disconnect the direct connection of the power supply with the battery and connect it as shown in the schematic. Then again wait for few seconds until the meter shows 7.2V then adjust the 10K variable resistor till the charge indicator LED light up. After these adjustments your circuit will be ready to use.
For best performance fit the circuit in a suitable enclosure. The LM2940 voltage regulator IC will dissipate heat due to which a suitable heat sink will be required.
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This DIY cell phone battery bank can be used as a backup charger for your cell phones and other devices for example MP3 players, iPad, iPod and any device which require 5V input for charging. The circuit can be used on the places where no electrical outlet is present. A 2.8AH SLA battery is used in the
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