Aiming at the characteristics of LED lighting load, the topology of the current non-isolated constant current drive power supply is basically the Buck Buck structure. This article will divide the development of non-isolated LED constant current control technology into three generations, discuss the development of the principle of constant current control strategy, analyze the advantages and disadvantages of each generation, and what breakthrough progress each generation has. Based on the DU8623 / DU8633 chip of the duty cycle semiconductor company, it introduces the latest generation of integrated closed-loop current control technology and details how this control strategy can breakthroughly improve the accuracy of LED output current. From open-loop to closed-loop is its essential breakthrough. Introduced a 7W bulb lamp driving scheme with a very small circuit and a very small size. Because closed-loop control is not sensitive to inductance changes, a lower-cost I-shaped inductor is used, which improves reliability and accuracy while reducing Overall program cost. The development of third-generation non-isolated LED constant current control technology The first generation LED constant current chip: The main technical feature of this type of chip is based on a fixed frequency PWM chip (such as UC384X, etc.), by reducing the inductor ripple current, fixed inductor peak current to achieve constant current. However, due to the fixed switching frequency, in order to avoid sub-resonant oscillation, its maximum duty cycle can only be used to 50%, and its application range is very limited; in addition, because the inductor ripple is very small, then a larger inductor is required At the same time, there are shortcomings that EMI is more difficult to solve and the efficiency is not high. This type of chip mainly includes: HV9910 (American Super Branch), PT4107 (China Resources Silicon Micro), SMD802 (Taiwan Xinrui), FT870 (Feimang Micro), LNK506 (PI) and so on. The second generation LED constant current chip: The innovation of this kind of chip relative to the first generation is: fixed Toff technology. Fixing the off-time of the switch can allow a larger inductor ripple current, and the duty cycle can be close to 100%. Its scope of application is also relatively wide. However, this generation of products has several shortcomings, that is, when the output voltage changes or the inductance changes, it cannot be constant current. This type of chip mainly includes: HB9910B (Super Branch), SN3910 (Sion), LM3445 (National Half) and so on. The third generation LED constant current chip: This type of product can be called a real constant current source, because real-time cycle-by-cycle detection and control of the real output current will eventually achieve constant current regardless of changes in output voltage, inductance, or input voltage. Such chips include: DU8608, DU8623, DU8633, DU2701. Wuxi Motian Signage Co., Ltd , https://www.makesignage.com