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USB Lamp Circuit

Here is a simple USB lamp powered from the USB socket of PC. It uses 5mm high bright White LEDs to give ample light to work in the Keyboard if the room light is not sufficient. No PCB is required to make this circuit.

The circuit is too simple and can be wired through lead-to-lead soldering. The LEds are connected to current limiting resistors R1 through R4.The cathode of all LEDs are joined together and soldered to the black wire of USB cable. Free leads of all the resistors are joined together and connected to the Red wire of USB cable. You can use a discarded USB cable with Class A type connector. Cut the Green and White wires of the USB cable and use only Red and Black wires. USB socket of PC provides 5 volts so that the LEDs give bright light. LEDs can be fixed in the Key board by drilling 5 mm holes.

USB Lamp Circuit Schematic

usb lamp circuit schematic

USB Cable

Class A USB Connector

10 Comments

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  • mahesh kumawat

    sir,
    please tell me about how to operate a home appaliance using a CD4017 ic ?
    are there another way to do this ?
    thanks
    m waiting for ur reply…

  • Akila pramod

    This web site has so many importent things.this usb led lamp is very nice.I am making this usb led lamp and test it my self.thanks for the circuit.

    Akila pramod

  • ebin

    sir,
    i have an old card reader.can i use the pin of the cardreader.can u mail me the correct terminals among 4 terminals of the pin

  • uttam

    is there any problem by using 1k ohm resistor ? if yes then what ?

    • D.Mohankumar

      White LED requires 3 volts and 30-40 mA current to give full brightness. USB supply is 5 volts.IK resistor will drop much current, so brightness will be low.

  • ammar mahmood

    its reaaly an awesome thing i have made it my self its really awesome i have enjoyed it its an amazing thing to be used

  • D.Mohankumar

    Current limiting resistor is used to limit the LED current to 40mA for White and Blue and 20mA for ordinary LEDs.If we use a single resistor for all LEDs, brightness may vary, since each LED has some difference in light output.So it is always recommended to use separate resistors in LED array.Here the supply voltage is 5 volts.So 5 / 0.04A = 125ohms. But a 125 ohms is not available. So 100 ohms resistor is used eventhough the LED current increases to 50mA.It can handle up to 50mA. Resistor is mainly used to drop current .As per Ohms law V / I = R. V is the input supply voltage, I the LED current in Amps and R is the resistor value in ohms

    • Neon

      Sir , Thanks a lot for your reply . Here we are using Resistor to limit the current . That means – If we will limit the current then that resistor will automatically drop the voltage to 3.6V also . Am I right sir ?

      – Thanks
      – Neon

    • Neon

      Hello Sir ,
      Yesterday I saw a USB Lamp in a computer parts selling shop . In that USB Lamp , they used 14 LED’s !! How did they manage 14 LED’s within 100mA ?? Have they used any transistor or circuit to increase the ampere ?

      Sir , Please give us a such kind of circuit diagram , which can operate 14 or more LED’s from a computer USB port .

      – Thanks
      – Neon

  • Neon

    You are using 100 ohms Resistor for each LED . Why do we use resistor for each LED ? Instead of this , If we use just one(Single) 100 ohms & 1/2W resistor , then will be there any problem ?? And as far as I know – PC USB gives 5V 100mA current and White bright LED needs 3.6V 40mA current . Here is 4 LED’s . That means – it needs 4 x 40 = 160mA Current . And 5 – 3.6 = 1.4 Volts needs to be dropped . Then We need 1.4/0.16 = 8.75 ohms resistor of 1/4W (Just Single one) . If we use 100 ohms resistor , then will it not drop too much voltage ?

    Sir, What is the advantage for adding resistor for each LED and what is the dis-advantage using single resistor for all LEDs ?

    Waiting for your reply ………..

    – Thanks
    – Neon

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