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Maybe this is a big topic, I will explain my problem.

(Reworded)

If you want to adjust the distance IR communication can reach, you will face this problem: transmission power adjustment.

That means we need to control the current through the IR led – a tsal6100 for my example. As a software engineer what I can think of is dc-dc switch power solution. I found AL8861 and composed the circuit based on datasheet info. My question is: can this circuit work? my circuit

Why I asked this question? According to my understanding, for the nature of switch power, there are ripples on the output,usually few handreds mA, this will lead to the transmission distance vary too? ripples on output

(Appended on 5/1)

Transistor is right,we should use analog dimming instead of pwm dimming.for the programmable resister is a little expensive,I planned to create my own one:

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The unit of resist is K , try to get a series of voltages allocated from 0.3 to 2.5V .(the analog dimming range of Vset defined in datasheet of AL8861.)

(Appended 5/1)

If build base on LDO (ZLDO1117),this is right?

LDO version

In order to get rid of influence of resist from CD4052B,I should use big resister (in Ks), is that ok?