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TIDA-00443: What will be the total Power dissipation of three 220uF capacitor C4,C5 and C18 used in TIDA-00443

Aneesh TS
Expert 1735 points
Part Number: TIDA-00443

Dear TI Experts,

I was referring TIDA-00443 Reference design from TI. TI used three 220uF capacitor C4,C5 and C18 at the output of PFC. What is the total power dissipation in these capacitor?.

TI calculated the ripple current as 2.734A in these capacitor as per the below document

http://www.ti.com/lit/ug/tidu962b/tidu962b.pdf

Regards

Aneesh

  • 0
    TI__Intellectual 2585 points

    Hi, 

    If you wants to calculate the power dissapation of capacitor, you should know the ESR of the capacitor and use the formular: Pe=I^2*ESR to calculate it. 

    And for the PFC part, please seperate the frequency into 2 parts, line freq and high freq.

    B.R

    Hawken.

  • 0 in reply to Hawken Li
    Expert 1735 points

    Hi Hawken,

    Is the ESR of the capacitor as per the below calculation is correct?

    ESR=DF/(2*PI*Fl*C)

    Where DF=Dissipation factor

    Fl= 2 times line frequency(120Hz)

    C= capacitance

    So ESR= 0.2/(2*3.14*120*660uF)

    ESR=0.401 ohm

    Power dissipation= 2.734*2.734*0.401

    Power dissipation= 3W

    I the above calculation is correct?

    Regards

    Aneesh

          

  • 0 in reply to Aneesh TS
    TI__Intellectual 2585 points

    Hi, 

    The calculation basically is correct. You should take care of DF. Different freq has different tanδ.

    And if you wants to calculate the PD of each capacitor (usually we calculates each one), you need separate current. 

    Hawken.

  • 0 in reply to Hawken Li
    Expert 1735 points

    Hi Hawken,

    I could not find any graph relating DF and frequency in the datasheet of 220uF capacitor  450QXW220MEFC18X50.

    Kindly find the datasheet link of the capacitor below.

    http://www.rubycon.co.jp/en/catalog/e_pdfs/aluminum/e_qxw.pdf

    The datasheet says DF =0.2 at 120HZ and the double the line frequency is also 120Hz.

    IF DF is not 0.2 then what should be the DF we should take for our ESR calculation according to you?

    Regards

    Aneesh

  • 0 in reply to Aneesh TS
    TI__Intellectual 2585 points

    Hi,

    Firstly, please seperate the calculation for high freq and low freq. In the calculation table, we already provided the Icout_HF and Icout_2fline data. Please separate the calculation. For the ESR, here is a coefficient table in which, 120Hz = 1, >=10KHz = 1.5. Which means, the ESR for 100kHz is 1.5x 120Hz. 

    And for the current, we assume the 3 capacitors were balanced. so Ic = 1/3*Icout. After that, you can calculate the total PD. 

    B.R

    Hawken

  • 0 in reply to Hawken Li
    Expert 1735 points

    Hi Hawken,

    Thanks for your feedback. I have calculated both high frequency and low frequency losses separately as below.

    Icout_HF=2.193A and Icout_2fline=1.634A 

    So for each capacitor Icout_HF=2.193A/3 =0.731A and Icout_2fline=1.634A /3 =0.5446A

    ESR for each capacitor at low frequency equals ESR low freq= 0.2/(2*3.14*120*220uF)

    ESR low freq=1.203 ohm

    ESR for each capacitor at 100K frequency equals ESR high freq=1.5*1.203 =1.8045 ohm

    Power dissipation low freq= 0.5446*0.5446*1.203 = 0.356W

    Power dissipation high freq= 0.731*0.731*1.805= 0.964W

    Power dissipation of single cap=1.321W

    Total power dissipation of three capacitor =3*1.321=3.963W

    Is the above calculation correct? 

    Regards

    Aneesh

  • 0 in reply to Aneesh TS
    TI__Intellectual 2585 points

    Hi Aneesh,

    The calculation is correct. 

    B.R