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Original question:

LM5023: NOT GET OUTPUT PWM PULSE IN PIn 7 LM5023 IC

LM5023: SMPS design verification or transformer pin configuration

GS Lodhi
Prodigy 15 points

Part Number: LM5023

 

 

Suggest pin configuration for transformer design of this design 

Verify his schematic for input 85-265 Vac input , output 12v @2.5amp 

find design link : Power Designer 
i created this design using web bench tool. 

need to help for transformer design strat and finish winding

Core Type: E25/13/7  Core Material: N87  Turns Ratio(Nps): 85:9  
Coil former B66208B1110T1
 
Core :-B66317G0000X187

Screenshot 2025-12-17 113709.png

  • 0
    TI__Intellectual 1160 points

    Hello

    Assuming suggestion is asked for which pins can be assigned to primary, secondary, auxiliary winding in coil former. Correct me if i am wrong.

    Suggestion: While making layout of PCB, depending on position of coil former, assigning primary winding pins which will be near to FET drain terminal and also snubber is kept near to it will be good.

    Aux winding pins can also be assigned to same side of primary if the components attached to aux are kept in same side of primary winding components and components are near to IC pins.

    similarly for secondary winding pins assignment to coil former.

    So depending on positioning of coil former, pin assignment can be decided to make loops connecting to its components and also IC pin to be small.

    Regards

    Rohan

  • 0 in reply to ROHAN SHAH
    Prodigy 15 points

    Sorry you are assuming wrong 
    My concern suggests pin configuration for transformer design?  

    like in transformer design whether the start and finish winding?

    for coil former:  B66208B1110T1

    Side A (Primary + Auxiliary):

    • Pin 1: Primary START (dot) → MOSFET drain + snubber 
    • Pin 2: X(float)
    • Pin 3: Primary FINISH → Vin (rectified input Vin)
    • Pin 4: Auxiliary START (dot) → RC + diode to controller VCC
    • Pin 5: Auxiliary FINISH → PGND

    Side B (Secondary outputs):

    • Pin 6-7: Secondary START (dot) → Rectifier input (anode or cathode depending on polarity)
    • Pin 8:  x (float)
    • Pin 9-10: Secondary FINISH → Output ground

    Above pin configuration is correct for transformer design according to the coil former B66208B1110T1 or above schematic.
    kindly check SMPS schematic and please suggest the transformer design pin configuration?

  • 0 in reply to GS Lodhi
    TI__Intellectual 1160 points

    Hello

    Pin 1: Primary START (Vin)--rectified input

    Pin 3: Primary FINISH (dot)---MOSFET drain

    Pin 4: Auxiliary START (dot) → RC + diode to controller VCC

    Pin 5: Auxiliary FINISH → PGND

     (Secondary outputs):

    Pin 6-7: Secondary START (dot) → Rectifier input (anode or cathode depending on polarity)

    Pin 8:  x (float)

    Pin 9-10: Secondary FINISH → Output ground

    Regards

    Rohan

  • 0 in reply to ROHAN SHAH
    Prodigy 15 points

    thankyou I will check the schematic with this transformer pin configuration.

  • 0 in reply to GS Lodhi
    TI__Intellectual 1160 points

    Hello

    Since flyback transformer primary and secondary winding have opposite polarity, have suggested changes stated above.

    Thank you

    Rohan

  • 0 in reply to ROHAN SHAH
    Prodigy 15 points

    Please check pin configuration is correct for transformer design?

    I am little bit confuse on secondary side on rectifier input 

    • When the MOSFET turns OFF, the dot end of the secondary winding goes positive relative to the non-dot end.
    • If the diode anode is at the dot end, the cathode will be at the output rail, so the output will be negative with respect to the other end.

    • can you please check ?

  • 0 in reply to GS Lodhi
    TI__Intellectual 1160 points

    Hello

    Connections are alright. 

    When MOSFET is ON, secondary side DOT end is negative relative to other end, so diode does not conduct.

    When MOSFET turns OFF, secondary side DOT end is positive relative to other end, and so energy transfer takes place to output and output will be positive relative to other end.

    Regards

    Rohan

  • 0 in reply to ROHAN SHAH
    Prodigy 15 points

    thank you for your confirmation i will be going with this pin configuration for transformer and as well as with schematic design 

  • 0 in reply to GS Lodhi
    TI__Intellectual 1160 points

    Hello

    alright.

    Thank you

    Rohan

  • 0 in reply to ROHAN SHAH
    Prodigy 15 points



    Transformer design specification suggest by web bench 
    primary and secondary wire i think thin according to current (peak and rms current ).
    can you please confirm ?

  • 0 in reply to GS Lodhi
    Prodigy 15 points

    Hi Sir can i get your mail?  

  • 0 in reply to GS Lodhi
    TI__Intellectual 1160 points

    Hello

    For deciding AWG for primary and secondary side, depends on current density one assumes to find the diameter of wire to be used. So you can assume higher current density for using thinner wires, no worries, but make sure the number of layers of all winding would get fit in former size.

    You can send friend request in e2e forum to message personally. 

    Regards

    Rohan

  • 0 in reply to ROHAN SHAH
    Prodigy 15 points

    Hello ,

    As per web bench suggestion transformer winding too thin for current density as suggest by web bench 

    primary peak   813.71 mA    wire awg 29
    secondary peak 7.6 A   Sec AWG 25 

    I have send you the friend request on E2E forum.

    Regards

    GS Lodhi

  • 0 in reply to GS Lodhi
    TI__Intellectual 1160 points

    Hello

    wire AWG 25 is thicker than AWG 29, so secondary winding is suggested to be AWG 25.

    Regards

    Rohan