LM3429: LED driver make a lot of noise on FM-radio

Thread Starter

SHTIRLIZnid

Joined Nov 11, 2021
3
Hi, everyone!

I've made a LED buck-boost (BB) driver based on LM3429. It's for automotive lighting, so Vin = 9-14.5 V, LED string consist of 10 white leds. V_out is about 30V, I_out=1.3A. All components were calculated according to LM3429 datasheet for BB topology. All datasheet recommendations for PCB design were also used (I think so))). Prototype of PCB has factory execution.

During the tests there is a lot of noise on FM frequency, however driver works properly at everything else. Noise on FM radio comes from induction - it sounds different in speakers when touched. But seems like it comes from all high frequency circuit with MOSFET and LM3429.
Currently I have no idea on how to remove this noise, where could be our mistake?
Led string is separated from the LED driver into a separate cooper board, wire length is about 25-30 centimeters.

Attaching schematic, PCB, operating conditions and component values for reference. Thanks in advance!
 

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DickCappels

Joined Aug 21, 2008
8,685
Hooooboy... my advice is to move the radio further away from the LEDs and driver. If you have not reduced radio interference from a power supply before, you are probably in for a great learning experience. Make sure you have bypass capacitors on all chips that show bypass capacitors in their example. You might find that an RC snubber across L1 helps.
 

Thread Starter

SHTIRLIZnid

Joined Nov 11, 2021
3
Hooooboy... my advice is to move the radio further away from the LEDs and driver. If you have not reduced radio interference from a power supply before, you are probably in for a great learning experience. Make sure you have bypass capacitors on all chips that show bypass capacitors in their example. You might find that an RC snubber across L1 helps.
Unfortunately, radio is a part of vehicle)
For now I'm learning about ferrite bead and bypass capacitors... What do u think, can I use here some ferrite bead?
All capacitors which are used in datasheet recommendations are on their places...
Can you tell a little bit more about RC snubber?
 

Dodgydave

Joined Jun 22, 2012
10,244
Are you using the same supply for the Radio as the led driver?
What happens if you use a different supply for the led driver, does the noise still appear?
 

Dodgydave

Joined Jun 22, 2012
10,244
Ok, so you could try making a Faraday cage with tin foil , to see if if stops the RF radiation, ideally you need a spectrum analyser.
 

DickCappels

Joined Aug 21, 2008
8,685
Since it is coming in through the MP3 player, I would probably turn my attention to scrubbing the power wire and power return. You can put chokes in series with each of the power input lines and the put a common mode choke in series with the input to keep the noise from "wandering" - getting picked up by ground and other conductors.

1636666903888.png
You might be able to find or make one of these. It is good if during winding you do not allow the wire to overlap previous turns.
Dodgydave makes a good point in the post above. A scope or spectrum analyzer (or scope with fft display mode) would be a very useful tool at this point.
 
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