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LM3431： LM3431 Abnormal sound problem

JOE SUNG
Prodigy 20 points
Part Number: LM3431

Provide complete circuit diagram: Provide complete circuit diagram

Problem 1: There is a strange sound when the light is on.

The picture shows the measurement waveform of Q 5-D terminal

 

Adjusted 1.R39, R37 frequency part without improvement

             2.R31, R26 total watts part no improvementTURN-SCH.pdf

             3.R71, R73, R75 have not improved

Please help to see if there is any adjustment needed

  • 0
    TI__Mastermind 28655 points

    Hello Joe,

    When do you hear the strange sound, just at turn on or all the time?  What is the sound and where is it coming from?

    What is the waveform above supposed to show.  It is turning on and starting to regulate the boost, this is what it should do.  Is C6 47 nF or a lower value?  You can try making C6 larger if turn-on is causing your issue.

    I'm not sure why you are using such a large MOSFET.  Qgate is rather high for less than 5 watts output power.  I cannot find information on D6.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 20 points

    HI Lrwin Nederbragt

    The abnormal part is adjusted as follows
    1. Currently I have adjusted the C6 part to 1uF
    2.R71, R73, R75 are adjusted to 2R4
    Reference: Figure 1,2

    Current partial adjustment (DIM) R10, abnormal noise will appear 

     

     

    Figure 1


    Figure 2

    D5V100SP.pdf

  • 0 in reply to JOE SUNG
    TI__Mastermind 28655 points

    Hello Joe,

    When do you hear the strange sound, just at turn on or all the time?  What is the sound and where is it coming from?  Are you PWM dimming?  Is it a frequency you hear?

    What is the waveform above supposed to show?  Is the frequency varying?  It appears to be running discontinuous.  What is the output current and voltage of the LEDs?  WIth an inductor of 100 uH the peak to peak current ripple is less than 0.25A, if it is discontinuous either it is going unstable or the load is very low.

    I'm not sure why you are using such a large MOSFET.  Qgate is rather high for less than 5 watts output power.  I cannot find information on D6.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    TI__Mastermind 28655 points

    Hello,

    I haven’t heard back from you, I’m assuming you were able to resolve your issue.
    If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

    Best Regards,