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PFC Input Power Measure?

Kami Huang
Intellectual 455 points
Other Parts Discussed in Thread: UCD3138

Dear Sir/Ms.

I got UCD3138 E-Meter sample code. I have some question.

There are a lot of vars. in the variables.h about measurement.



How to design these parameter in different hardware circuit?

for example following is my design 

 According to my test result.

iin_slope should be 597. Do you have any ideal about the calculation formula?

Most ADC is zero gain calibration. How to design other vars. base on different R-C value?

  • 0
    Intellectual 455 points

    Following is 1 segment of UCD3138 reference code.

    iv.iin_squared_filtered is vector value from ADC.
    I don't know why shift right 15bit in code and need to shift iin_slope_shift bit.
    do you have ideal about it?

    BTW,May I know what's your topology?

  • 0
    TI__Expert 7060 points

    Hi, Huang,

     

    Due to the componant tolerance, the voltage and current sensing circuit need to be calibrated, these variables are used to store the calibration parameters. They cannot be done by calculation.

     

    Regards,

    Bosheng Sun

  • 0 in reply to Bosheng Sun
    Intellectual 455 points
    Hello Bosheng
    I total agree your words but the slope value can be predictable. How to calculate a roughly value of slope and shift_value? I have other question about Iin. Have you try Input current above then 4A. In GUI (fusion design online) the PFC input value will display negative value if iin over 4A.
    for example.
    3900mA display 3.9A.
    4100mA display -3.9A.
    4200mA display -3.8A.
  • 0 in reply to Kami Huang
    TI__Expert 7060 points

    Hi, Kami,

    the slope is the realtionship between ADC counts and the input currents (mA)

    Iin(mA) = iin_slope * ADC + iin_offset.

    the ADC is 12 bit with 2.5V reference, you know the current shunt value, and the current amplifier gain, then you can calculate the voltage signal applied to ADC pin, then you can calculate the slope.

    the slope may be a decimal, UCD3138 uses fixed point in mathematical calculation.To reduce the rounding errors and maintain enough accuracy in the calculations, the small decimal values are multiplied by 2N and then rounded to the closest integer. for example if slope = 1.59. then you 28 (left shift 8) and rounded to 407.

    for the negative input curretn dispaly, you need modify the related PMBus command, please refer PMBus protocal for PMBus data format.

     

    regards,

    Bosheng

     

  • 0 in reply to Bosheng Sun
    Intellectual 455 points

    Hello Bosheng
    I notice iin_slope and iin_slope_shift play as floating point value. What's iin_offset and iin_offset_shift units of measurement? Is the unit mA?
    The display issue I will check PM_read_iin function.
    I have the other issue in PFC PCB. The inductor current is  not sine wave so measure value is not a exact value. I'm studying TI's application report #SLUA709 (UCD3138 PFC Tuning). Do you have this document in Chinese version? 

    Best Regards,

    Kami Huang

  • 0 in reply to Bosheng Sun
    Intellectual 455 points
    Hello Bosheng
    I solve the GUI display issue. Other issue is still trying to solve.
    Best Regards,
    Kami Huang
  • 0 in reply to Kami Huang
    TI__Expert 7060 points

    Hi, Kami,

    yes, iin_offset is in mA.

    sorry we don't have Chinese vesrion for that application note.

    Just want to let you know, this PFC input power measurement method is TI's IP, TI applied patent for that. You can use it as far as you are using TI's controllers. The source code you have may not the latest, please contact TI Taiwan office for latest code and technique help.

     

    Regards,

    Bosheng

     

  • 0 in reply to Bosheng Sun
    Intellectual 455 points
    Hello Bosheng
    As I know, The latest E-meter code release by library not by C code. I would like to get C code. Of course, I got warning from TI disty. The E-meter code only using in TI's controller.
    You refer these application notes [3] [4].
    [3]TI application note: A Harmonic Injection Method to Reduce PFC Harmonics and Improve THD
    [4]TI application note: A Novel EMI Filter X-CAP Reactive Current Compensation Method to Increase PF
    May I get application note? Did you have the pdf hyperlink?
    BTW, how to determine EMI cap. value in C code?
    e2e.ti.com/.../427239
    only C5, C6 , C37 ,C38?
    Best Regards,
    Kami Huang
  • 0 in reply to Kami Huang
    TI__Expert 7060 points

    Hi, Kami,

     

    Please contact TI Taiwan office, they have all you need.

     

    regards,

    Bosheng