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LM3464EVAL: AN-2102 LM3464 and LM5021 DHC 25W EVM

Sana rezgui
Intellectual 400 points
Part Number: LM3464EVAL
Other Parts Discussed in Thread: LM5021, LM3464, UCC28810, LM3450, LM3464A, LM3464AEVAL

Hello,

I'm having buzzing noise with the "AN-2102 LM3464 and LM5021 DHC 25W EVM" that I bought from TI. Any idea why?

The issue gets worse when using a triac dimmer. Can we use a triac dimmer with this board inserted in series with the L line?

Thanks

Sana

  • 0
    TI__Mastermind 28655 points

    Hello Sana,

    Where does this state it can be used with a triac dimmer? That requires different circuitry and control signals to adjust light output. It is a much more difficult design to be compatible with a triac dimmer and also control the secondary side current output. A better approach would be not to use a DHC regulator for the first stage, a voltage regulation PFC would be better. Then a secondary stage that consists of buck converters.  A DHC may not reject variances in a triac dimmer function causing light fluctuation.  A triac decoder would be needed to set the buck converter output power/current. The LM3450 data sheet has information on this though it may not be exactly what you are looking to do. There are also circuits with the UCC28810/11 that are two stage designs.

    Are you stating there is a buzzing noise when connected direct to AC (no dimmer in the circuit)? Buzzing is a common issue when triac dimming, this was not intended to be triac dimmed.

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Intellectual 400 points

    Hello Irwin,

    Thank you for taking the time to respond.

    The buzzing is existing with and w/o the trial dimmer at the input AC line. It is worse and very noticeable though with the triac dimmer.

    Is it normal to have buzzing w/o triac dimmer?

    Thank you.

    Sana Rezgui

  • 0 in reply to Sana rezgui
    TI__Mastermind 28655 points
    Hello Sana,

    It is possible, the triac causes a sharp rising edge that tends to excite certain components on a PCB causing audible noise. It's possible that the AC waveform could do this as well though it seems not as likely. A triac dimmer turned all the way up still will, most likely, have a rising edge. What frequency are you hearing? Where is the buzzing coming from? The AC portion, the LM3464 portion or somewhere else?

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Intellectual 400 points
    Hello Irwin,

    The buzzing is located at the AC area; I have no way to measure its frequency. Even when I have no triac dimer connected to the board, which is directly connected to the AC line, I have the buzzing. The AC line is quite clean, freq 60Hz.
    Having said that, I was hoping to know if I can use an external triac dimmer with the LM3464A? I have not seen anything that indicated that and this why I asked. As I said before, the buzzing gets worse with an external dimmer.

    The buzzing is quite noticeable and so I was wondering if that is normal. I have stoped all audio and other equipments next to it that may cause interference to see if the buzzing will go away but it was not the case.

    Do you think that it is general problem to all of these board layouts or is it just the one that I have? Can I return it or replace it?
    I'd like to use this part but the buzzing is an issue for me.


    I also have other questions about the LM3464AEVAL/NOPB, should I ask them to you?
    Thanks. Sana Rezgui
  • 0 in reply to Sana rezgui
    TI__Mastermind 28655 points
    Hello Sana,

    The LM5021 EVM was not intended for triac dimming, the LM3464A EVM was not intended for triac dimming either. There are other designs that exist specifically for triac dimming. Designing for triac dimming requires a different design approach. Can the LM3464A interface to a current source that is triac dimmed? Probably, however it probably doesn't make sense to do a design this way.

    You have to locate the noise. I would assume it's 60/120 Hz noise however it can be something else. Solving this is just trying to find the offending parts, changing them, mounting them to the PCB different or possibly pot/RTV the component.

    I support the LM3464/A parts so you can ask about them.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Intellectual 400 points

    "The LM5021 EVM was not intended for triac dimming, the LM3464A EVM was not intended for triac dimming either. There are other designs that exist specifically for triac dimming. Designing for triac dimming requires a different design approach."

    Understood.

    "Can the LM3464A interface to a current source that is triac dimmed? Probably, however it probably doesn't make sense to do a design this way."

    Understood.

    "You have to locate the noise. I would assume it's 60/120 Hz noise however it can be something else. Solving this is just trying to find the offending parts, changing them, mounting them to the PCB different or possibly pot/RTV the component."

    As I said, I believe the noise is coming from the transformer. I was hoping that the demo board would reflect a reference design with no issues.

    I have already filed another case for the second 3464A EVM (w/o the LM5021) board. You will see it probably soon.

    Thanks.

    Sana

  • 0 in reply to Sana rezgui
    TI__Mastermind 28655 points
    Hello Sana,

    If it is coming from the transformer there are things that can be done, such as vacuum varnishing the transformer. The EVMs are for evaluating the circuitry. When designing for production these things need to be taken into account.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    TI__Mastermind 28655 points
    Hello Sana,

    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,
  • 0 in reply to Irwin Nederbragt
    Intellectual 400 points

    Hi Irwin,

    The buzzing is really substantial, when I use the PWM dimmer as well. A demo board should reflect a typical well operating condition. 

    I'm glad that I know about the issue now. I'll try vacuuming but I don't think that it will solve such noise.

    Thank you through for trying to help.

    Sana