SIMPLE CELLPHONE CHARGING CIRCUIT

             A simple mobile phone charging circuit can be constructed from basic components. Here a zener diode and a transistor are the key components of this project. It is NOT suitable for daily purpose usage, but can be used to charge old cellphones. I'am explaining this circuit to only understand the basic working principle only. The main components required are,

• BC 547 Transistor
  
• 4.7 V Zener diode
  
• 100uF Electrolytic Capacitor
• 470 Ω resistor
• Breadboard or PCB

CIRCUIT DIAGRAM

                The above figure is a series voltage regulator. The transistor is used as a control element and the zener used as a dtector. When the input supply voltage Vin increases the output voltage Vload also increases. This increase in Vload will cause a reduced voltage of the transistor base emitter voltage Vbe as the zener voltage Vzener is constant. This reduction in Vbe causes a decrease in the level of conduction which will further increase the collector-emitter resistance of the transistor and thus causing an increase in the transistor collector-emitter voltage and all of this causes the output voltage Vout to reduce. Thus, the output voltage remains constant.