Operating frequency drops

This is also a common phenomenon in the process of debugging, frequency reduction is mainly caused by two aspects. The input voltage and load voltage ratio is small, the system interference is large. For the former, be careful not to set the load voltage too high, although the load voltage is high, the efficiency will be high. For the latter, try the following:

1. Set the small current lower;

2. Clean wiring, especially the critical path of sense;

3. Select a small inductance or the inductance of a closed magnetic circuit;

4. Add RC low-pass filtering. The effect is a little bad. The consistency of C is not good and the deviation is a little large, but it should be enough for lighting.

There is no upside to downscaling anyway, only downside, so be sure to fix it.

Choice of inductor or transformer

With the same drive circuit, the inductance produced by a has no problem, and the inductance current produced by b becomes smaller. In this case, look at the inductive current waveform. Some do not notice this phenomenon, directly adjust the sense resistance or working frequency to reach the required current, which may seriously affect the service life of LED.

Therefore, before the design, reasonable calculation is perfect, if the theoretical calculation parameters and debugging parameters are a little far away, to consider whether the frequency reduction and transformer saturation. When the transformer is saturated, L will become smaller, resulting in a sharp rise in the peak current increment caused by transmission delay, so the peak current of LED will also increase. If the average current stays the same, you can only watch the light fade.

LED current size

We all know that if the LED ripple is too large, the LED life will be affected, how much impact, have not seen which said. I have asked the LED factory about this data before, and they said it is acceptable within 30%, but it has not been verified later. I suggest keeping it as small as possible. If the heat dissipation is not solved well, the LED must be derated. I also hope to have a specific index, otherwise it will affect the promotion of LED.

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