Power Supply from USB Port

Power supply from usb port

As in the title Power supply from usb port, the power supply circuit using a source from USB port, with an adjustable stabilizer can be obtained voltage from 1.25V to 3.75V. USB port can give power to peripherals of 500 mA at 5 V ± 5%. The USB port can be used to power external circuitry, which is useful when no other constant voltage source.

USB-port consists of supply line V BUS, GND return path and the two signal lines. If you only need 5 V, you can take them directly to a USB connector, you can put a 10 uF filter capacitor between the V BUS and GND.

If you use adjustable voltage regulator, you can get any voltage from 1.25 V to 3.75 V. This voltage is used to power many schemes. This scheme is shown in Figure above. Regulated output voltage trimmer R 3 according to the equation.

V OUT = 1.25 in × (1 + R 3 / R 2 ).

In this equation, “1.25” – Internal reference voltage source circuit LM1117-ADJ, measured between the terminal V OUT and adj. For this reason, the current through R 2 becomes permanent. Since adj current, resulting from the withdrawal ADJ, ignored, can be considered constant and the current flows through R 3. When R 2 = 100 ohms, this time is 5.12 mA. If you choose a trimmer resistance R 3 equal to 200 ohms, the output voltage adjustment range is from 1.25 at 0 to 3.75 at R 3 = R 3 = 200 ohms.

To protect the Power supply from usb port device from short circuit or overload can be added to the scheme, limiting current of 500 mA. This may be self-healing fuse, or a pair of transistors that can be easily inserted into the input line power.

The filter capacitor must not be greater than 10 microfarads. This value is sufficient to neutralize the current surge. Typically, the Power supply from usb port circuit operates normally when the capacitance of the filter from 1 to 10 uF.


Power supply is an electronic device that supplies electric energy to an electrical load. The primary function of a power supply is to convert one form of electrical energy to another and, as a result, power supplies are sometimes referred to as electric power converters. Some power supplies are discrete, stand-alone devices, whereas others are built into larger devices along with their loads. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.


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  1. author

    JHAKRI Khalid4 years ago

    hi…from the output can i connect a usb cable with it…
    because right now i’m searching a usb booster so that can use my wifi adapter from a 15m usb cable.
    thanks for the help in advance