This USB car charger circuit adapter from car cigar socket project is a DC DC power converter that safely converts the 12V car battery voltage into stable 5V. This circuit can be used to supply power from a car cigar lighter socket to a portable device that require a 5 volts . This circuit makes it possible to power/recharge any USB power-operated device, using in-dash board cigar lighter socket of your car.
The DC supply available from the cigar lighter socket is fed to an adjustable, three-pin regulator LM317L (IC1). R1 and R2 resistors regulate the output of IC1 to steady 5V, which is available at the ‘A’ type female USB socket. Red LED1 indicates the output status and zener diode ZD1 acts as a protector against high voltage.
As you can see in the circuit diagram , the circuit is very simple and require just few common cheap components . Even if this charger needs just few components , it has a high efficiency and is very easy to construct . Because this circuit not require many components , you can put all components in the cigar plug socket .