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.

Components-

• 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.

NOTE-

• 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.