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WEBENCH® Tools/UCC28C42: Calculations for Design Generated by Webench

Vishal Kakade
Intellectual 930 points
Part Number: UCC28C42

Tool/software: WEBENCH® Design Tools

Hi,

I have designed a power supply for below specifications.

AC_DC

Vin (Min) (V): 165
Vin (Max) (V): 260

frequency: 50hz

Vout (Nom) (V): 12
Iout (Max) (A): 5
Output Power (W): 60

DC_DC

Vin (Min) (V): 44
Vin (Max) (V): 55.2
Vout (Nom) (V): 12
Iout (Max) (A): 5
Output Power (W): 60
Isolated/Non-Isolated: Isolated

Now when I match this design with the calculations given in datasheet they don't match. I want the calculations done by webench for each and every component to get the desired output results. As I have to give the TOT for my design and can't say I have used webench.

please find the publik link for my design below

ac-dc

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=9314612C8D52DBDB

dc-dc

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=398595656EA35102

  • 0
    TI__Mastermind 31580 points
    Hi Vishal

    I am not aware of any mechanism to export the calculations from the webench tool. The webench design is intended as a starting point for the power stage design and then the engineer can further optimise it based on their design methodology such as available components within their company's part numbering system and component derating requirements.

    I suggest you put together an excel file and work through the calculations in the datasheet and update the values in the webench schematic where you find differences.

    In the meantime I will ask the webench team if there is anyway to export the calculations.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    Intellectual 930 points

    Hello Sir,

    Can you write the calculations for one design with formulas? I can later relate them to my other design.

    Regards

    Vishal kakade

  • 0 in reply to Peter Meaney
    Intellectual 930 points

    Hello Peter,

    I have Calculated transformer winding and inductance and other parameters like output capacitance from the datasheet. They are not matching with my webench design. 

    Regards

    Vishal kakade

  • 0 in reply to Vishal Kakade
    TI__Mastermind 31580 points

    Hi Vishal,

    What values did you get from your calculations using the datasheet compared to the webench design?

    Regards

    Peter

  • 0 in reply to Peter Meaney
    Intellectual 930 points

    Hello Peter,

    15

    Please note the values below for AC-DC design.

    Webench design: 

    Cin: 15uFx4

    Cout: 330uFx2 - 1.5uH - 270uFx3 (Pi Filter).

    Transformer: Np:Ns: 86:5,  Np:Na: 86:6

    Lpri: 871uH

     

    As per datasheet valculations: 

    Cin: 57uF

    Cout: 2280uF

    Transformer: Np:Ns: 21:1,  Np:Na: 21.35:1

    Lpri: 10mH

    Regards

    Vishal kakade

  • 0 in reply to Vishal Kakade
    TI__Mastermind 31580 points

    UCC38C4x flyback calculator.xlsxHi Vishal,

    The webench values may be slightly different depending on the assumptions they made on minimum bulk voltage etc.

    I ran through the the datasheet and put the formulas into a basic excel file and they match pretty closely to the datasheet values for the example application. You can change the values in the excel sheet to match your application and use this values for your design.

    Regards

    Peter

  • 0 in reply to Peter Meaney
    Intellectual 930 points

    Hello Peter,

    Lpri in Webench design is 876uH, whereas in your excel sheet and datasheet calculations, it is 3.3mH. and it's a huge difference. 

    Can you explain the complete design of flyback to me? One complete circuit explanation.

    Regards

    Vishal

  • 0 in reply to Vishal Kakade
    TI__Mastermind 31580 points
    Hi Vishal,

    The Webench tool has a slide bar, on the left, to set the pk-pk primary ripple current as a percentage of the average current. by adjusting the value between 60% and 160% you can vary the load at which the power stage transitions from DCM to CCM operation, this varies the value of the primary inductance. The datasheet specifies this DCM/CCM transition point as a percentage of output load, in the UCC28C4x datasheet the application uses 10% load as the value. I must admit its not easy to reconcile the two approaches and I need to talk to the Webench team to ask why they implemented the feature in this way.

    Unfortunately its not feasible to provide the level of support to outline the complete circuit explanation but TI does have a library of power supply design papers which cover flyback designs in detail. You can find these using this link www.ti.com/ww/en/power-training/login.shtml?DCMP=pwr-psds-archive&HQS=pwr-psds-archive-psds

    Regards

    Peter