Inductor electrical measurments

Discussion in 'The Projects Forum' started by spanker1, May 14, 2012.

  1. spanker1

    Thread Starter New Member

    May 2, 2012
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    Hi,
    I am working on a NCL30160 Led driver from On Semiconductor. I was told by my boss who is a mechanical engineer to measure all the electrical measurments you could possibly get from the inductor we are using. He told me to use the oscilloscope too see the waveforms and record the values.

    I measured the Iout.
    I am driving the LED's at 24V input

    Amplitude 200mV
    Rms =10.87V
    Freq.= 774.3 Mhz
    pk-pk 5.361V
    Cycle Rms = 11.23V

    I don't understand a single thing from these values.
    Can some one advice me on the kind of measurement should i do?.

    Thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
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    What is the purpose of these measurements, other than doing what your boss told you to do?
     
  3. spanker1

    Thread Starter New Member

    May 2, 2012
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    To select which inductor company we wanna go with..
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    1,605
    The inductor is working as a sort of buck regulator in that circuit. Going by the sample cuircuit in the data sheet when the Lx terminal is switched to CS the current will build up in the inductor via the internal MOSFET. When this fet opens the current in the inductor switches to the external diode D1 and decays. An induuctor here could give you problems by going into "saturation," meaning there is so much current flowing it no longer looks inductive and the current grows without (inductive) bounds. Then things smoke. Bad.

    You do have the CS terminal as a current sense point. Drop your scope on that amd make sure the current looks like a nice triangle wave. It should be offset from ground (or the value is too large) and the ramp should not show any tendence to rise at a faster rate at the end of the cycle or you are hitting the ban saturation region.

    From the peak value at RS you can compute the peak inductor current, make sure this is well below the inductor's peak and you should be OK.
     
  5. spanker1

    Thread Starter New Member

    May 2, 2012
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    That was really educational and appreciate your help. But i want to analyze the output current
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    There's a lot more to choosing a vendor than looking at an occasional part. What really matters is the statistical variation against a specification, along with all the service issues. The vendor should share with you their quality system checks and you should align their methods with your own, so that you can, at least in theory, keep them honest. If you have a need for something they're not measuring, that's a lot more valuable to investigate than the behavior of a single inductor.
     
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