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TPS92512: TPS92512 flickering problem

Prodigy 120 points

Replies: 18

Views: 386

Part Number: TPS92512

hi,

i am using TPS92512 ,for dimming  purpose

i am using 24v supply and 4 X20 led matrics (4 series)

i get the flickering during the period when current in between 600mA and 800mA

i am using the same circuit given in the data sheet please give me a solution

total voltage 24

volatge across led 11V

no of led series 4 

  • Hello,

    It appears you are PWM dimming this circuit. What PWM frequency and duty cycle are you using?

    Can you get oscilloscope pictures of Vin, Vled, the switch node and inductor current?

    Best Regards,
  • In reply to Irwin Nederbragt:

    we are varying duty cycle from 0 to 100% at frequency 500 Hz

    Vin is 24 V

    VLed 11V

    indiactor current 0-3mA

    we are getting smooth dimming if risense is high value lke 1ohm but the current is low like 350mA

    our application needs atleast 1A maximum 

    flickering occures when current is between 750mA anf 800mA, we dont have problem when current in between 

    0-500mA and 800mA-1A which is between duty cycle 60-80%

  • In reply to Jishnu Prakash Nambiar:

    Hello Jishnu,

    It sounds like possibly a noise issue.  I cannot help without oscilloscope pictures showing waveforms asked for above.  I also don't know what indiactor current is?  If this is inductor current, 0-3 mA with a 800 mA current set point will not work.

    Best Regards,

  • In reply to Irwin Nederbragt:

    hi this is image of Vin at 50% PWM

  • In reply to Irwin Nederbragt:

    Vled at 50% PWM

  • In reply to Irwin Nederbragt:

    PWM SIGNAL

  • In reply to Jishnu Prakash Nambiar:

    Hello,

    I'm not sure what the Vin oscilloscope picture is, it states 50V/div and shows about 2.5 divisions. Regardless, if Vin looks like that it won't work, it needs to be DC. Why is Vin unstable? Do you have an input filter for EMI? What does the power source voltage look like?

    Best Regards,
  • In reply to Irwin Nederbragt:

    hi,

    these noises appear  when the flickering occurs else it is perfect DC 

  • In reply to Jishnu Prakash Nambiar:

    Hello,

    Doesn't matter, the input should not do that.  Or let me rephrase, the flickering occurs when the noise appears.  If the input moves that much it will flicker.  BTW can you get oscilloscope pictures of Vin with the correct voltage range.  I don't think your input is near 125 volts so I don't know if you have an offset or the V/div is wrong.  If it is there is too much impedance which can cause instability.  I can see instability in the waveforms.  Get a low impedance power source and see what happens, or bypass your EMI filter if that's what is causing this.

    Best Regards,

  • In reply to Irwin Nederbragt:

    vin when pwm signal is not applied sorry for image quality

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