Build a 5V USB Power Socket with LM317L Circuit

Description

Currently, many personal computers incorporate logic blocks for implementing a USB port. A USB port, practically speaking, is able to supply more than 100 mA of continuous current at 5V to the connected peripherals within the bus. Consequently, a USB port can be employed, without difficulty, for powering 5V DC-operated miniature electronic devices. Presently, numerous handheld devices (for example, portable reading lamps) leverage this feature of the USB port to recharge their internal battery packs via internal circuitry.

Circuit diagram:

Typically, 5V DC, 100mA current is needed to fulfill the input power requirement. Figure 1 illustrates the design of a flexible USB power connector that safely transforms the 12V battery voltage into a consistent 5V. This circuit enables the powering/recharging of any USB power-operated device using the in-dash board cigar lighter socket of your vehicle. The DC supply obtainable from the cigar lighter socket is delivered to an adjustable, three-pin regulator LM317L (IC1). Capacitor C1 dampens any irregularities in the input supply.

LM317L

The LM317L is a versatile three-terminal adjustable voltage regulator. It’s a widely used integrated circuit (IC) that precisely controls the output voltage within a specific range, typically from 1.2V to 3.6V, depending on its control terminal setting. This IC is frequently utilized in power supply circuits to generate a stable and regulated DC voltage, making it ideal for applications needing a consistent voltage source. It is a monolithic integrated circuit that integrates a pre-regulator, a voltage reference, and a series of transistors for precise voltage control.

Resistors R1 and R2 stabilize the output of IC1 to ensure a steady 5V, which is available at the ‘A’ type female USB socket. Red LED1 indicates the output status and zener diode ZD1 functions as a safeguard against excessive voltage. Assemble the circuit on a general-purpose PCB and enclose it in a slim plastic casing together with the indicator and USB socket. While connecting the USB outlet, verify the correct polarity of the supply. For interconnection between the cigar plug pin and the device, use a long coil cord as shown in Figure 2. Pin configuration of LM317L is shown in Figure 3.