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LM3445: Flicker and Jump-up at low dim level

K.Sakai
Prodigy 100 points
Part Number: LM3445

Hello,

I am now evaluating Dimming performance and have some problem.

My error might be equivalent to following case but there is not solution so Let me add this case.

"LM3445: Low dim level issue using"

I am using equivalent diagram as Evaluation Board and Valley Fill Capacitance is 10uF each and Trans value is 1.6mH.

At the region when valley fill change series to parallel connection, LED flicker is occurring like as following.

Isw peak is changed from 25mA to 7mA around this Error state.

I guess, there is a little light Jump-up around this region at normal state.

Is there any way to improve this error ?

Kind Regards,

K Sakai

  • 0
    TI__Mastermind 28655 points

    Hello,

    Can you take a few other measurements?

    What is the valley fill voltage?

    Can you look at FLTR1, FLTR2 and ASNS and see if there is variation?

    Can you look at DIM to see if the 5.9 KHz is changing?

    Can you look at the triac output voltage when this happens?

    You are at the low end of dimming, if the triac waveform varies a little it will show up in the light.  Angle sense should still be creating a low reference for LED current since it's detect range is 45 degrees to 135 degrees.

    90 VAC is on the low side, what is your input voltage range and line frequency?

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 100 points

    Hello,

    Thank you for your reply.

    Vin rage is 90-110V and freq is 50 & 60 Hz.

    I am afraid but what do you meant "What is the valley fill voltage?" ?

    Others might be described as followings but I cannot measure FTRL2.

    >Can you look at FLTR1, FLTR2 and ASNS and see if there is variation?

    >Can you look at DIM to see if the 5.9 KHz is changing?

    >Can you look at the triac output voltage when this happens?

    Kind Regards,

    K.Sakai

  • 0 in reply to K.Sakai
    TI__Mastermind 28655 points

    Hello,

    What are you testing, the EVM or your own board?  If it is the EVM have you changed anything on it?

    It looks like the angle sense, DIM and FLTR1 pins are operating correct.  I'm not sure why you cannot look at FLTR2, what does it do?  There is a large capacitor on that pin so I would suspect if anything happened the light level may change.  Seems everything is working up to the DIM pin which directly controls FLTR2 value

    If you look at the point you say there is frequency change there really is not.  What it looks like for mode 1 is half of the time the MOSFET turns on and reaches the peak curent threshold, the other half it is not.  On mode 2 it is reaching the peak current threshold every time.

    Best Regards,