Using DC/DC chip to make LED constant current drive circuit solution

Every DC/DC IC (whether step-up or step-down ) can be connected to drive a constant current LED. Now, we will take KZW3688 and CE9908 as examples to introduce their connection methods and features.

1. KZW3688 step-down IC, its connection method is as follows:

The principle is very simple, and you will know it at a glance, so I won't repeat it here. The value of R1 is calculated as 3.3V/required current . The figure above shows 2-5 connected, and multiple circuits can also be used in parallel . And here is a question for everyone: Is C2 needed? Take a look at the connection method in the figure below:

I removed C2 and connected one or even several LED strings in parallel. What do you think of the effect? ​​Are you interested in answering?

[page] There are too many circuits suitable for this connection . In addition to 3688, any step-down IC such as PT1102, 1101, lm2596, GA8512, 1016, 1014, 313, 1011 can be connected into such a circuit. The conversion efficiency of this circuit is as high as 95%, but the efficiency in actual use is between 36%-88%, which is not as high as some targeted linear efficiency. Think about why this is? At the same time, it is pointed out that many constant current circuits write the efficiency of LED drive circuit as the efficiency of IC conversion, which is wrong and misleading. I hope that the majority of engineers will pay attention to the parameters in these materials.

2. Boost IC, taking CE9908 as an example, the connection method is as follows:

Think about the principle. You can also connect them in series first, then connect them in parallel to form N branches. Here I intentionally do not talk about power factor, but only about efficiency. This efficiency is also between 36-88%. Do you understand now? The efficiency of the IC that we regard as "high efficiency" in our hearts must be measured in practice to see its actual effect on LEDs.

These two diagrams are just to illustrate the principle. They should be used flexibly in use. I believe that everyone will master more skills, such as using external MOS tubes to directly use low-voltage step-down ICs to connect to 220V direct input AC/DC (similar to 9910), using lower sampling voltage (FB end) to improve the efficiency of the entire circuit , using parallel resonance to combine IC characteristics, and specifically designing efficient and high-quality LED drive circuits.