LED（Light Emitting Diode）is a solid light source , it has an enormous application prospect because of its advantages , such as energy conservation, environmental protection, firm structure, long life, short start-up time, small volume, low voltage supply. So research of LED Drive Circuit has crucial significance of theory and value of application. Due to the disadvantages of the Linear Regulated Power Supply which has high power consumption and large volume, a PWM(Pulse Width Modulation) switch power supply has been designed with the characteristics of small volume, high efficiency, steady performance, low cost, used to drive LED by constant current which can be adjusted by regulating external potentiometer, and the light intensity also changes. Firstly this paper introduces the motivation, the purpose, the significance and the background of the research, then selects Buck topology DC/DC converter based on the study of the electrical characteristics and the driver’s characteristics of LED and the system requirements, takes LM2575-ADJ as the core control chip of the system, it designs a switch power supply which can convert 15 V～30 V DC power supply into 8 mA～40 mA DC output current. In this paper, the design process, the hardware making and the debugging methods of the system are introduced in detail. It proves that the power supply basically satisfied the requirement of constant current driving LED through testing and analyzing.
Keywords： LED PWM switch power supply constant current driving Buck DC-DC converter
