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Lumen fluctuation at 60Hz line frequency

nitin gupta2
Prodigy 50 points
Other Parts Discussed in Thread: TPS92210
Hi,
With TPS92210 we are getting a constant lumen output at 50Hz line frequency but it is not stable at 60Hz line frequency.
FYI, 
1. Switching frequency of driver is 80Khz
2. Visually no parametric fluctuation has been observed.
To know the behavior of outputs ,we have monitored the following curves from oscilloscope
1. Output Voltage curve
2. Output Current curve
3. Drain Switching wave form
But we have not observed any fluctuations in any of the cases.
​
Please help to provide the root cause of this behavior.
1. Why Lumen is not coming constant at 60Hz? 
2. Which area i have to look and improve?
With Regards
Nitin Gupta
  • 0
    TI__Expert 3495 points
    Nitin:
    Please check the LED current again. If the LED current is stable, the LED lumen output should be stable unless there is something wrong with the LEDs.
    David Zhang
  • 0 in reply to David Zhang
    Prodigy 50 points
    Hi David,

    Thanks for your prompt reply..

    I have checked the current with the RMS multi-meter and current probe both but i have not found any fluctuations in the current values..

    Can you please help to elaborate more about, why Led's are giving inconsistent data at 60Hz line frequency only?

    With Regards
    Nitin
  • 0 in reply to nitin gupta2
    TI__Expert 3495 points
    Nitin: Can you show me the LED current waveform?David Zhang
  • 0 in reply to David Zhang
    Prodigy 50 points

    Please refer attached curve.

  • 0 in reply to nitin gupta2
    TI__Expert 3495 points

    Nitin:

     

       Can you please zoom in to show the current ripple? Also please tell me the time scale. The labels of this scope picture are not very clear.

     

    David Zhang

  • 0 in reply to David Zhang
    Prodigy 50 points

    Dear Zhang,

    Please refer below Curves  after 1 hr Burn In

    Curve 1: Lumen Output Curve at 60Hz

    Curve 2: Lumen Output Curve at 50Hz

    3: Output Current Curve at 60 Hz at 1s/div

    4: Output Current Curve at 60 Hz at 20ms/div

    Concern:

    1. Why at 60Hz line frequency Output Luman switching curve following Sinusoidal wave form and why it is not at 50Hz line frequency?

    2. Why Output Current & Voltage wave forms are not following the same pattern of Lumen Curve.( by the way , pattern of Output Voltage and current wave form are same )

    3. Why the Lumen Fluctuation at 60Hz is more than the 50Hz? Lumen Fluctuation at 60 Hz is 7000 Lumen where as at 50 Hz the fluctuation is 100 Lumen Max).

    Please let me know if you need any more information...

    With Regards

    Nitin Gupta

  • 0 in reply to nitin gupta2
    TI__Expert 3495 points

    Nitin:

     

         Are you doing power factor correction? If you are doing single stage power factor corrrection, you will see a sine wave ripple twice the line frequency. I measured the LED current ripple frequency of the scope shot. I was about 80Hz. So the ripple may not be caused by power factor correction. It could be the control loop is not stable and it osccilates at 80Hz. Please adjust the loop to see if the osscilation goes away.

        I can not answer you the question why the LED lumen changes over time even the system power remains relative constant. I think the LED supplier can better help you on this.

     

     

    David Zhang

       

  • 0 in reply to David Zhang
    Prodigy 50 points

    Dear Zhang,

    Can you please share your personal Email ID. I want to share the Schematic of the design to know which component we have to change to make the frequency with in a range.

    With Regards

    Nitin

  • 0 in reply to nitin gupta2
    TI__Expert 3495 points
    david.zhang@ti.com