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    Common heatsink Calculation

    I want to use the common heatsink for the Bridge rectifier,IGBT and Boost Diode.

    I have calculated the Each of the Dissipation

    P_DIS_Bridge=18w

    P_Dis_igbt=24w

    P_boost_diode=6w

    RJC_BRIDGE=0.6DEGREE/W
    RJA_BRIDGE=1.63 DEGREE/W

    RJC_IGBT=0.58 DEGREE/W
    RJA_IGBT=1.66 DEGREE/W

    RJC_Diode=0.85 DEGREE/W
    RJA_Diode=6.66 DEGREE/W
    TJ=90 DEGREE
    TA=50 DEGREE

    How to calculate the common heatsink for all 3 power components...??

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    Re: Common heatsink Calculation

    Hi,

    Any heatsink calculaton document will give this information. Read through them.

    RJA is not valid for your situation, because you use a heatsink.
    (RJA is for use without heatsink)

    RJC is for use with heatsink.

    RJC x power_dissipation gives the difference temperature between junction and case.
    Calculate this for each device.
    Take the max value of those three.

    Take TJ - max_vlaue to get max_heatsink_temp at full load. (add some margin for difference temperature between device_temp and heatsink_temp)

    Then calculate the difference between TA and max_heatsink_temp = allowed heatsink_temperature_rise.

    Heatsink value = allowed heatsink_temperature_rise / total power dissipation.

    Klaus



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    Re: Common heatsink Calculation

    Hello KlauuST

    I have calculated a per your suggestions.

    Normally all datasheet have provided data of R(J-C) IN degree/w but the attached ipm provided it in kelvin/w.

    Now it hard to handle.
    Can you pls advice how to convert the same in degree/W

    I google 3k/w in kelvin to degree Calculator and it is coming -270degree/w and whole result is getting wrong.

    Pls advice on the same

    - - - Updated - - -

    Here is the attached image

    Click image for larger version. 

Name:	KELVIN TO DEGREE.jpg 
Views:	3 
Size:	46.8 KB 
ID:	140695



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  4. #4
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    Re: Common heatsink Calculation

    Hi,

    For temperature rise, which is a relative change in temperature K and C is the same.

    Lets say the temperature rises from 25C to 60C.
    The temperature rise in C is: (60C - 25C) = 35C
    25C = (25 + 273)K = 298K
    60C = (60 + 273)K = 333K
    The temperature rise in K is: (333K - 298K) = 35K

    For all relative temperature calculations you may use the same value in K as in C.

    5K/W for relative calculations is the same as 5C/W.

    Klaus



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    Re: Common heatsink Calculation

    No need to convert between degree C and K for a linear heat dissipation problem.

    It's the simple point that thermal resistance has the commonly agreed unit K/W, although degree C/W is the same number because you are measuring temperature differences.



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    Re: Common heatsink Calculation

    Hello Guys..

    Understand..

    Now what problem i am facing here is.
    Power dissipation per igbt =15.68 (There are 6 igbt inside the ipm module)

    TJ=90 Degree
    TA=60 Degree
    Junction-to-Ambient Thermal Resistance=(TJ-TA)/Power dissipation across single igbt)=(90-60)/15.68=1.97degree/Watt

    Now,
    R(heatsink to ambient)=J-A-(J-C+C-H)=1.97-(3K/W+0.2)=-0.8

    This is the problem i am facing..?

    - - - Updated - - -

    For The final calculation
    RSA_IPM=(TJ1-TA)-P_IPM(RJC4+RCS4)/(Total heat dissipated)

    TJ1=90
    TA=60
    P_IPM=Heat dissipated in ipm=15w
    RJC4=3K/W
    RCS4=0.2D/W (For silpad)

    RSA_IPM=((90-60)-15(3+0.2))/140=-363degree/w



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  7. #7
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    Re: Common heatsink Calculation

    Hi,

    This is the problem i am facing..?
    --> reread post#2

    RJC4=3K/W
    I doubt this value. It should be much smaller. Although you showed the datasheet picture... could you give the link to the complete datasheet?
    * maybe there is additional information or there is an errata...

    And there is a mistake in your calcualtion.
    The result of your formula should be -0,129K/W
    And were do the 140W come from?

    Klaus


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    Re: Common heatsink Calculation

    https://www.mitsubishielectric-mesh....S92F6-AG_N.pdf

    The Addition of all heat dissipated.

    1) Bridge Rectifier:18w
    2) IGBT_PFC=24W
    3)Boost=6W
    4) IPM=15*6=90W

    TJ1-TA-P_IPM*6*(RJC4+RCS4)/(Total heat dissipated)

    YES IT IS 0.129K/W



  9. #9
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    Re: Common heatsink Calculation

    Hi,

    according datasheet the 3K/W is true.
    So with a disspated power of 15W per IGBT you already get a temperature difference of 15W * 3K/W = 45K between junction and IBGT case.
    This means if you want to limit junction temperature to 90C (why that low? datasheet says 150C) then the IGBT_case temparature needs to be less than 45C.
    This is impossible with 60C ambient temperature.

    Klaus


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  10. #10
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    Re: Common heatsink Calculation

    Yes.. now by the calculation

    Thermal resistance of the Heatsink is 0.133C/W

    How heatsink area calculation works..??

    How to design customised heatsink for Aluminium type.

    Regards
    Marx

    - - - Updated - - -

    Yes.. now by the calculation

    Thermal resistance of the Heatsink is 0.133C/W

    How heatsink area calculation works..??

    How to design customised heatsink for Aluminium type.

    Regards
    Marx



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