The third generation of non-isolated LED constant current drive technology

In view of the characteristics of LED lighting loads, the topology of the current non-isolated constant current drive power supply is basically a BUCK step-down 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 breakthroughs each generation has made. Based on the DU8623/DU8633 chip of Duty Cycle Semiconductor, the latest generation of integrated closed-loop current control technology is introduced, and how this control strategy can improve the accuracy of LED output current is introduced in detail. The essential breakthrough is from open loop to closed loop. A 7W bulb driver solution with a minimalist circuit and extremely small size is introduced. Since the closed-loop control is insensitive to changes in inductance, a lower-priced I-shaped inductor is selected, which improves reliability and accuracy while reducing the overall solution cost.

Development of three generations of non-isolated LED constant current control technology

The first generation of LED constant current chips:

The main technical feature of this type of chip is that it is based on a fixed-frequency PWM chip (such as UC384X, etc.), which achieves constant current by reducing the inductor ripple current and fixing the inductor peak current. However, due to the fixed switching frequency, in order to avoid subharmonic oscillation, its maximum duty cycle can only be used to 50%, and its application range is very limited; in addition, since the inductor ripple is very small, a relatively large inductance is required, and there are also disadvantages such as EMI being difficult to solve and low efficiency. This type of chip mainly includes: HV9910 (American Super Technology), PT4107 (China Resources Silicon Micro), SMD802 (Taiwan Xinrui), FT870 (Huimang Micro), LNK506 (PI), etc.

Second generation LED constant current chip:

The innovation of this type of chip compared to the first generation is: fixed Toff technology. By fixing the off time of the switch tube, a larger inductor ripple current can be allowed, and the duty cycle can be close to 100%. Its application range is also relatively wide. However, this generation of products has several disadvantages, that is, when the output voltage changes or the inductance changes, the constant current cannot be maintained. This type of chip mainly includes: HB9910B (Supertech), SN3910 (Silicon), LM3445 (National Semiconductor), etc.

The third generation LED constant current chip:

This type of product can be called a true constant current source because it detects and controls the actual output current cycle by cycle in real time, and ultimately achieves constant current regardless of changes in output voltage, inductance, or input voltage. This type of chip includes:

DU8608、DU8623、DU8633、DU2701。