USB to phone battery charger circuit

Without any  USB to phone battery charger circuit we can charging phone battery using port on USB computer , but it will quickly damage the phone battery, and the battery will bulge. Because the voltage which was issued on usb is 5 volts , while the average-voltage phone battery 3.5 - 3.7 volts. That's why this USB to phone battery charger circuit is required , this USB to phone battery charger circuit reduce votlage to 3.7 volt usb, but will not reduce currents and  will make a durable phone battery.

USB to phone battery charger circuit diagrams

List of components :

R1 : 1 K

R2 : 330 R

R3 : 4K7

R4 : 300 R

R5 : 27R

D1 : 4.7 volt zener /1W

C1 : 100uF/16V

Q1 : BC548

Q2 : BC558A

LED1 : Green Led

X1-1   : Vcc USB

X1-4   : Ground USB

X2-1 , X2-2 : To phone battery

See also this printed circuit board ( PCB ) of USB to phone battery charger :

USB to phone battery charger printed circuit board