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L88, USB Lamp

Here is a simple USB powered lamp that can be used to light your desktop during power failures. The circuit operates from the 5 Volt available from the USB port.The 5V from the USB port is passed through current limiting resistor R2 and transistor Q1.


  • USB socket (male)

  • Q1 = BC558

  • D1, D2 = 1N4007

  • R1 = 560R, R2 = 220R, R3 = 1K

  • C1 = 0.01uf

  • D3 = LED (Red)

  • D4, D5 = LEDs (White)

  • B1 = Battery (2.4v)

The base of transistor Q1 is grounded via R1 which provides a constant bias voltage for Q1 together with D2.The diode D1 prevents the reverse flow of current from battery.C1 is used as a noise filter.Two white LED’s are used here for lamp. You can also use a 2V torch bulb instead of LED’s. LED D3 indicates connection with USB port.


  • USB port is only able to provide up to 100 mA current. So don’t overload the circuit with more no of LED’s.

  • Before wiring the circuit confirm the positive and ground leads of USB by a multimeter.

  • Switch S1 can be used to turn on the lamp.

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