Simple LED reading lamp

Simple LED reading lamp

This desk lamp can emit cold light suitable for reading. 50 white LEDs (LED1 to LED50) are arranged in an array to emit white light to cover the table.

As shown in the figure, 50 white LEDs are arranged in a 10×5 array, and then powered by a 220V AC power supply. The AC power supply is rectified by a bridge D1-D4, and a transistor T1 and a field effect transistor T2 are used to maintain a constant low voltage of the LED array. This allows the brightness of the desk lamp to remain stable even when the input power supply voltage changes.

The bridge rectifier converts the AC voltage into a pulsating DC voltage. When the voltage at the capacitor C1 exceeds 40V during each pulsation cycle, transistor T1 drives field effect transistor T2 into the non-conducting region to maintain a constant low voltage across the LED array. Resistors R5-R9 (220Ω each) are connected in series to their respective LED branches to limit the current flowing through the LED to a safe value.

During installation, 50 LEDs are arranged into a circular array on a PCB board, and the PCB board is mounted on the top of the desk lamp, and a circular reflector is added to increase the illumination.

Note: Since the circuit is not insulated from the AC power supply, do not touch any part of the circuit to avoid fatal electric shock.