This is the schematic diagram of cellphone charger circuit which connecter to the USB as main power. Whit this circuit, you can charger your cell phone from USB port in your PC or notebook.
The majority of the cellphones battery is appraised 3.6 volts at 1000 to 1300 mah. These battery packs have 3 Nimh or Lithium cells having 1.2 volt rating. Generally the battery pack requires 4.5 volts and 300-500 mA current for quick charging. Anyway, low present charging is better to build the proficiency of the battery. The circuit depicted here gives 4.7 directed voltage and sufficient present for the moderate charging of the cellphone.
Transistor T1 is utilized to give the regulated output. Any medium power NPN transistor like TIP122, Cl100, BD139 could be utilized. Zener diode ZD controls the output voltage and D1 protects the polarity of the output supply. Front end of the circuit ought to be joined with A type USB plug. Connect a red wire to pin1 and black wire to pin 4 of the plug for easy polarity identification. Connect the output to a suitable charger pin to connect it with the mobile phone. After assembling the circuit, insert the USB plug into the socket and measure the output from the circuit. If the output is OK and polarity is correct, connect it with the cellphone.