Schematic diagram of car cigarette lighter to USB power port

This is a schematic diagram of a car cigarette lighter to a USB power port. Nowadays, almost all computer systems have logic blocks for using USB ports. In practice, USB ports are capable of providing more than 100 mA of continuous current at 5V to peripheral devices connected to the bus. Therefore, a micro electronic device operating at 5V DC can be powered using a USB port without any problems.

Today, many handheld devices (e.g., portable reading lights, smartphones, tablets, iPods) utilize this resource of USB ports to charge their battery packs with the support of internal circuitry. Typically, 5V DC, 100mA current is required to meet the input power requirement.

The above picture is a universal USB power socket circuit that can correctly convert 12V battery voltage to a stable 5V voltage. This car cigarette lighter to USB circuit can power/charge any USB power operated device. It works with the dashboard cigarette lighter socket of the car.

The DC power supplied from the cigarette lighter socket is fed into an adjustable three-pin regulator LM317L (IC1).

Capacitor C1 buffers any disturbances in the input supply. Resistors R1 and R2 regulate the output of IC1 to a constant 5V, accessible via a type 'A' female USB socket. Red LED1 indicates the output status and Zener diode ZD1 acts as an overvoltage protector.

Assemble the circuit of the car cigarette lighter to the USB power socket on a generic PCB and enclosed in a slim plastic cabinet, along with the indicator lights and the USB socket. When wiring the USB socket, make sure the power polarity is correct. For the interconnection between the cigar plug pins and the device, use long coil wires as shown in the second picture.

Here is the pin configuration of the LM317L: