PMP4334: LED's blink from time to time

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Replies: 18

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Part Number: PMP4334

Hi everyone,

I have stumbled upon an issue that is bothering me more than I expected.

I have noticed that my LED's blink from time to time (asynchronous intervals) all of them at the same time. I have already done some debug but so far cannot seem to understand the underlying reason. Do you have any idea of what could be the probable cause? 

As I mentioned the blink occurs for all LED's on all channels. It lasts some milliseconds (enough to be seen and to bother). 

If you could support me in this issue that would be much appreciated. 

Best regards,

José

18 Replies

  • Hi Jose,

        Glad to see you here. I will looping David here to resolve your problem.

    Thanks!

    Regards,

    Richard

  • Hi, Jose,

    Could you please share your schematic? That will help us to check whether there is any founding.

    How do you dimming your LED? PWM or Analog. If PWM, what is the duty cycle.

    Once blinking, do you have check the UCC28810 single stage flyback output voltage whether it is stable?

  • In reply to David Ji:

    Hi David,

    thank you for reaching out!

    I have been using PWM and the duty cycle range between 20 to 100%.

    Regarding the UCC28810, you mean checking the EAOUT (2) pin correct? I have not, I will have a look at it and let you know the typical values recorded. 

  • In reply to Jose Araujo2:

    Hi, Jose,

    Yes, we can check the EAOUT voltage to see whether it is stable. Also, we can check the VOUT DC voltage and ripple voltage when LED blinking.

    Thanks.

  • In reply to David Ji:

    hi David,

    Yes, I can confirm that the voltage on pin EAOUT is stable around 2.57V. Nevertheless I noticed some extra blinking just by making the measurement (it looks in a way that it got more interference). It is hard anyway to make a measurement while the blink happens once its asynchronous. The VOUT voltage on the LEDs varies from 45 to 48V. 

  • In reply to Jose Araujo2:

    Hi, Jose,

    Could you please test the current of blinking LED string also drive signal of this string PWM on FET?

    Thanks.

  • In reply to David Ji:

    Hi David,

    I am sorry for the delayed answer. The current of the LED string is 300mA at normal operation. Note that all strings blink simultaneously but its not predictable when they'll blink. Regarding your second question you're asking about the gate voltage of the MOSFETs after the LEDs correct? The gate voltage is 4.3V at normal operation 

  • In reply to Jose Araujo2:

    Hi, Jose,

    Thanks for measuring this parameters. However, could you please test the waveform instead of testing its value? The waveform will help us to analysis, thanks.

  • In reply to David Ji:

    Hi David,

    thanks for your previous message and sorry for the delay answering you.

    I have noticed that right before the LEDs blink, the voltage value on Rdhc (coming from the Outp pin) goes from around 3.5V to 0V. Due to this drop, the voltage on the external mosfets gates (in series with the LED lines)  go to 0V while the LEDs are blinking.

    Could this sudden drop on Outp be the reason for the blink? And if you, you have any idea why it happens?

    If you want I can also send you the screen shots took for further analysis. 

    Thanks a lot!

    Best regards,

    Jose 

  • In reply to Jose Araujo2:

    Hi, Jose,

    Please also send me the waveform, that will be helpful.

    1. In addition, it is recommended to test flyback by removing D1 firstly from no load to full load using E-load. Checking flyback stability.

    2. Check the C54 value to ensure it is over 4.7uF. The higher the capacitance of the CDHC, the lower the frequency response of the DHC loop, and vice versa. I am not sure how fast your flyback is, make sure CDHC cap bigger is more safe.