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 characteristics.

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?

There are too many circuits suitable for this connection method. In addition to 3688, any step-down IC such as PT1102, 1101, lm2596, GA8512, 1016, 1014, 313, 1011, etc. can be connected into such a circuit. The conversion efficiency of this circuit is as high as over 95%, but in actual use, the efficiency is between 36% and 88%, which is not as high as some targeted linear efficiency. Why is this? At the same time, it is pointed out that many constant current circuits write the efficiency of the LED drive circuit as the efficiency of IC conversion. This is wrong and misleading. It is hoped that 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. The connection method can also be to connect them in series first, and then connect the series in parallel to form N branches. Here I intentionally do not talk about the power factor, but only talk about the 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 actually acts on the LED, and it must be measured in practice.

These two diagrams are just to illustrate the principles. They should be used flexibly in use. I believe that everyone will master more skills, such as using an external MOS tube to directly use a low-voltage step-down IC to connect to a 220V direct input AC/DC method (similar to 9910), using a lower sampling voltage (FB terminal) to improve the efficiency of the entire circuit, using parallel resonance combined with IC characteristics, and targeted design of efficient and high-quality LED drive circuits.