How to solve power supply whine with continuous dimming LED?

Submitted ⁨⁨1⁩ ⁨year⁩ ago⁩ by ⁨nucleative@lemmy.world⁩ to ⁨askelectronics@discuss.tchncs.de⁩

My project is a “breathing” white 12v LED strip controlled by an esp32 on a dev board, and switched with an IFLZ44N mosfet.

In my video you can see it working but also hear the power supply complaining.

I’m using the LEDC Arduino library which allows me to select the frequency and resolution for PWM.

If I set the frequency too low the whine is extreme, but at this setting it’s the best I’ve been able to achieve, which is about 9000Hz. Unfortunately you can still hear the sound from across the room!

It is a cheapo solid state power supply that claims it can output 12v up to 25A. I tried my desktop supply and it emits some whine too, so I don’t think replacing the power will totally fix this.

Is there a technique for tuning the frequency or even just masking it somehow?

source

Comments

Sort:hotnew top

sramder@lemmy.world ⁨1⁩ ⁨year⁩ ago
What’s limiting your PWM frequency? You want it above 25 KHz so it’s outside the range of human hearing.

source
- nucleative@lemmy.world ⁨1⁩ ⁨year⁩ ago
  I think the limitation is my own knowledge of this LEDC library. When I run it with the frequency value of 25,000 it doesn’t output anything on my GPIO pin that I can detect with my multimeter.
  
  source
  - sramder@lemmy.world ⁨1⁩ ⁨year⁩ ago
    I’m reading the docs and it seems capable of running up into the MHz range although at higher frequencies the duty cycle resolution is reduced. Although I wouldn’t expect most multimeters to detect a frequency that high, anything should pick up the voltage.
    
    Do you get an error on the serial monitor? It should report if the frequency/duty-cycle range you’re requesting isn’t possible.
    
    E (196) ledc: requested frequency and duty resolution cannot be achieved, try reducing freq_hz or duty_resolution. div_param=128
    
    source
cmnybo@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago
Try adding a large, low ESR capacitor across the power rails on your board. Preferably a polymer electrolytic if you have some.

source
- nucleative@lemmy.world ⁨1⁩ ⁨year⁩ ago
  Thanks for the idea, I’ll give this a try but have to go and get some
  
  source
  - draz@lemmy.world ⁨1⁩ ⁨year⁩ ago
    Caps are definitely the first thing to try. To add on, the higher your frequency, the smaller caps you’ll need. At 10kHz you’ll need around 200uF of decoupling but at 50kHz you’d only need around 40uF. The smaller capacitance means you can find caps with better ESR, or just fit into a smaller space in general.
    
    source
    -> View More Comments
BigDanishGuy@sh.itjust.works ⁨1⁩ ⁨year⁩ ago
Is the changes in pitch alone, or does the amplitude change as well?

Have you located the source of the whine? I think most of us just assume it’s the psu, because it’s always the psu, but does the whine actually come from the psu? Don’t open the psu and start poking about while it’s on, just listen for it from the OUTSIDE of the casing.

What happens if you set the frequency to something extremely low? I know that 50Hz is unusable, it will flicker, but does something still hum at 50Hz? What about if you increase the frequency in steps until you approach 200Hz?

Your multimeter couldn’t measure anything when you went to 50kHz? That may be an issue of the microcontroller not supplying enough current to charge the gate capacitance on the mosfet in time, or not drain it fast enough to turn it off. If you disconnect the esp from the rest of the circuit, can you measure something then?

If yes, then you’ll want to use a push pull pair for driving the mosfet. Or get a mosfet driver, but a bc547/bc549 pair and a bit of passives will be fine, available in through hole, and considerably cheaper.

If no, then either the esp can’t go that fast in this implementation or your multimeter doesn’t work in that range.

source
- nucleative@lemmy.world ⁨1⁩ ⁨year⁩ ago
  Interesting suggestions, I would not have tried such low frequencies except based on your suggestion and it turns out that going very low, below 1000Hz and even down to 100Hz causes the power supply whine to almost entirely go away. I also have a 470uF capacitor in between the power rails now too.
  
  This range is a usable - there is no visible flickering even at very low duty cycles.
  
  From what I understand in the reference guides the LEDC library attaches directly to the 80mhz or 40mhz esp32 hardware clock for PWM. Intuitively I’d have guessed that higher frequency would always mean less discernable audible feedback, but seems not in this case.
  
  source
  - BigDanishGuy@sh.itjust.works ⁨1⁩ ⁨year⁩ ago
    
    This range is a usable - there is no visible flickering even at very low duty cycles.
    
    Before deciding on the frequency, and then mounting the strip in a position where the LEDs are directly observable, you should try moving the LEDs fast relative to your eyes. Eg. take the end of the strip and wave it from side to side. You may notice flicker at frequencies below 200Hz.
    
    source
    -> View More Comments
XTL@sopuli.xyz ⁨1⁩ ⁨year⁩ ago
It might be doing the PWM in software somehow, making it useless for this kind of control.

You could see if there’s some other class or library or option or particular pin that can use a pulse generator or timer to do PWM instead.

I’m not really familiar with the exact environment but that’s just what comes to mind.

source