The working principle of LED table lamp follows the design concept of safety first civil electrical appliances. LED light source is a kind of low-voltage DC constant current source light-emitting device, which can not be directly lit with 100 ~ 220V AC high-voltage electricity. Therefore, the design idea of LED table lamp scheme is that the high-voltage AC electricity should be converted into low-voltage DC constant current source first, so as to light up LED light source. Using the most economical and effective method to reduce voltage and carry out AC / DC converter is the primary consideration in the design. Nowadays, the AC / DC buck converter (adapter) of portable electronic products using AC power supply has become the first choice which is economical, ready-made and easy to use. The output voltage of the adapter shall be stable at DC12V, and the output current shall be selected according to the power of the LED light source. Generally, 30% margin shall be given. Take the 3 × 1W white LED light source as an example, the standard working current of the 1W white LED shall be 350mA, so the current required for the three LED light sources in series is 350mA. In consideration of prolonging the LED life and reducing the light decay, it can be designed as 300mA ~ 330mA, It will not affect the brightness of LED, so the output current of adapter should be 750ma ~ 1a.