I'm confused about the cause of noise when PWM dimming


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I'm working on an constant current led driver, in particular the TPS92512. After reading TPS92512's datasheet (http://www.kynix.com/uploadfiles/pdf65976/TPS92512HVDGQT.pdf), I started my work,and I got some problems.

 

Uz3IT.thumb.png.3be046383aba424bf94b0cfe8f53c5f0.png

There's audible noise when PWM dimming.

I think that the problem is on the inductor, but I don't know how to solve it, I mean, do I have to pick an inductor with higher DCR, higher Isat, or what?

I4Qjw.thumb.jpg.68cec7e4d0ca05283678f4fcb523484a.jpg

Here is the LED driver. I changed the inductor to SRR0805-150M.

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13 hours ago, fanja said:

I'm working on an constant current led driver, in particular the TPS92512. After reading TPS92512's datasheet (http://www.kynix.com/uploadfiles/pdf65976/TPS92512HVDGQT.pdf), I started my work,and I got some problems.

 

Uz3IT.thumb.png.3be046383aba424bf94b0cfe8f53c5f0.png

There's audible noise when PWM dimming.

I think that the problem is on the inductor, but I don't know how to solve it, I mean, do I have to pick an inductor with higher DCR, higher Isat, or what?

I4Qjw.thumb.jpg.68cec7e4d0ca05283678f4fcb523484a.jpg

Here is the LED driver. I changed the inductor to SRR0805-150M.

Audible noise means that something is physically vibrating.

 

It is most likely the inductor and it is vibrating to your PWM frequency or else a harmonic of it. Most likely due to a resonance effect so changing the frequency range could help.

 

Or the brand of inductor since the windings are probably shifting. Sometimes just applying some silicon caulking damps the vibration.

 

You have a mini-Tacoma Narrows to deal with!

 

https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)

 

Also, if this is for real world usage, beware of giving your users severe headaches!

 

https://www.notebookcheck.net/PWM-Ranking-Notebooks-Smartphones-and-Tablets-with-PWM.163979.0.html

 

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