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LM3450: LM3450 Dimmer

Shlomi Yehezkia
Mastermind 6150 points
Part Number: LM3450

Hi Team,

I have the LM3450AEV120V30 kit, I have a question about that controller:

The Holding current mechanism is the bleeding circuit that sink current from the Dimmer to maintain proper work with Dimmers.

The disadvantage with the bleeder, is efficiency+PF+THD reduces,

When the dimmer in not present, the Bleeding in the LM3450 is still working even though it is not needed (I checked in the EVAL board).

I have a MCU that can detect when the Dimmer in Present or not. I would appreciate to get recommendation how the MCU can disable the Bleeding circuit in the LM3450?

Thanks,

Shlomi

 

  • 0
    TI__Mastermind 28655 points
    Hello,

    You should look at the LM3450 (non A) version. The 'A' version will always add load. A lot of this is explained in the datasheet (see page 26 as well as reading about all the differences between the 'A' version and the 'non-A' version in the datasheet).

    Also not there are 230 VAC dimmers that, when turned up all the way, do not show the triac rising edge making it hard to detect.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Mastermind 6150 points

     

    I work with 120V Traics.

    I understand that the "not A" version, minimized the power dissipation and target the 2 stage solution like I have. But according the datasheet, in some cases (didn't fully understand in what cases), it can cause the Triac to misfire. TI claim that in 2 stage driver it is not a problem, but in other part of the datasheet, TI cliam that misfire can cause inaccurate in the decoded phase angle. The decoded phase angle is used by my MCU.

    So I rather use the A version, without the misfire, and hopefully bypass when not Triac in presence.

    LM3450.docx

     

     

     

  • 0 in reply to Shlomi Yehezkia
    TI__Mastermind 28655 points
    Hello,

    Sorry, read that wrong.

    I would look at placing a switch in series with the Rhld resistor (by switch I mean transistor or MOSFET), it may still require a high value resistor connected which should affect efficiency much. Chld may also need something depending if you are using it or not.

    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,