For the characteristics of LED lighting load, the topology of the current non-isolated constant current driving power supply is basically a BUCK buck structure. This paper will divide the development of non-isolated LED constant current control technology into three generations, discuss the development of the control strategy to achieve the principle of constant current, analyze the advantages and disadvantages of each generation, and make breakthrough progress in each generation. Based on the duty cycle semiconductor company's DU8623/DU8633 chip, introduce the latest generation of integrated closed-loop current control technology, detailing how this control strategy can improve the LED output current accuracy, from the open loop to the closed loop is its essential breakthrough. A 7W bulb lamp driving scheme with a very small size of a minimalist circuit is introduced. Since the closed-loop control is insensitive to inductance changes, a lower-priced I-shaped inductor is selected, which improves reliability and accuracy while reducing Overall program cost.

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

The first generation of LED constant current chips:

The main technical features of such chips are based on fixed-frequency PWM chips (such as UC384X), which achieve constant current by reducing the inductor ripple current and fixing the inductor peak current. However, because the switching frequency is fixed, in order to avoid sub-resonance, its maximum duty cycle can only be used up to 50%, and its application range is very limited; in addition, because the inductor ripple is small, it needs a relatively large inductor. Quantity, but also EMI is more difficult to solve, the efficiency is not high and so on. Such chips mainly include: HV9910 (American Super), PT4107 (China Resources Micro), SMD802 (Taiwan Core), FT870 (Fengmang), LNK506 (PI) and so on.

The second generation of LED constant current chip:

The relative innovation of this type of chip with the first generation is: fixed Toff technology. By setting the turn-off time of the switch, it is possible to allow a large inductor ripple current and the duty cycle can be close to 100%. Its application range is also wide. However, this generation of products has several disadvantages, that is, when the output voltage changes or the inductance changes, constant current cannot be achieved. These chips mainly include: HB9910B (Super Branch), SN3910 (矽恩), LM3445 (National Half) and so on.

The third generation of LED constant current chip:

This type of product can be called a true constant current source because real-time cycle-by-cycle detection controls the true output current and ultimately achieves constant current regardless of output voltage, inductance, or input voltage. Such chips include:

DU8608, DU8623, DU8633, DU2701.

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