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Original question:

LM5022: LM5022 transformer design calculation sheet

LM5022: LM5022 transformer design calculation sheet

Jack Deng
Expert 1090 points
Part Number: LM5022

Hi TI Guys：

I have a project as below:

input: 30VDC or 90~264Vac

output: 24V1.6A

PMP7760 is 30V~800V input, it is similar to my project parameter,

 all design is follow the PMP7760, but when i set the input=30V,
the output only can load CC=500mA, if CC>500mA, Vout will drop to below 20V soon,
i check the PMP7760 test report, it seem PMP7760 load CC=500mA when 30V input,


I have adjust the transformer to Lp = 5.8mH  Np:Ns = 1:8   Np:Naux = 1:8， but the problem still exists.
I reduced the sense resistor by 3 times, but there’s no noticeable improvement.
i need CC1.5A when 30V and 90~264Vac input, do you have any suggest, thx

  • 0
    TI__Mastermind 31165 points
    Hi Jack,

    Thanks for using the LM5022. Are you using the same transformer specified in the BOM, the G094215LF? Can you also send scope shots of COMP and SW?

    BR,
    Richard
  • 0 in reply to Richard Fu22
    TI__Mastermind 21720 points
    Jack,

    I see that you have posted about this in the past.
    e2e.ti.com/.../704064

    Does the schematic still match the one provided previously? The best way to check if it is current limit is measuring the CS pin voltage with a short ground lead. This will allow you to see if the device is entering current limit.

    Please also check the LO pin voltage to ensure the gate driver duty cycle is not exceeding the maximum duty cycle of 90%. I think this might be happening with the selected turns ratio of the transformer.

    Pleat let me know if you have any questions.

    Thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Expert 1090 points
    thanks Garrett, i will try again under changing the turns ratio.
  • 0 in reply to Jack Deng
    Expert 1090 points

    Hi Garrett,

    Sorry to bother you again,  the problem remains unresolved.

    Could you please help to provide the LM5022 Design Tool. thx

  • 0 in reply to Jack Deng
    TI__Guru* 78240 points
    Hi Jack,

    We currently do not have the design tool for LM5022. Our team will create one in the future.

    I read this trail and it seems our transformer turns ratio is not correct. Do you mean Np:Ns=1:8? Or it is actually 8:1? Yes you copied the PMP7760, but it seemed you changed to a different transformer (by saying you increased the inductance to 5mH). Could you double check your transformer polarity? If one winding polarity is reversed, you basically changed the circuit to a forward converter and it will not hit current limit even you reduce the current sense resistor by many times.

    Thanks,
    Youhao Xi, Applications Engineering.