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LM5160A: flybuck converter

Part Number: LM5160A

Hi,

    I  getting the issue with the voltage drop in output when increasing load. 

    VIN  :--    20 V to 60V 

     VOUT :-  12V

    Iout :-   1.5 A

I have used web bench for designing circuit.   

When increasing load, Output voltage drop to 8.7 volts.

  • Deepak,

    Fly-Bucks don't have the ability to regulate the isolated output directly so I'm not surprised by some drop, but this is too much.

    1. Please share schematic and layout.

    2. Is the primary output also dropping with load?

    3. Is the switch waveform a constant frequency/duty cycle rectangular wave?

    4. What else have you found from your debugging?

    -Sam

  • webench_design_5321215_8_978674703.pdfHi Samuel Jaffe,

       1.  There is no drop in primary voltage.

            It is around 8.8V before and after Load 

       

       2.  But without load output is 20 volt.

           after connecting the 50mA load. it drops to the 12.3.

       3.  when connecting 1.2A load it drops to 8.8 volt

            I am using  VPH2-0083 transformer      Np to Ns   is 1.5 

            Mean if the primary voltage is 8.8v, secondary should be 12.3 approx.

      Is a problem with the Transformer?

  • 4024.webench_design_5321215_8_978674703.pdfHi Samuel Jaffe,

       1.  There is no drop in primary voltage.

            It is around 8.8V before and after Load 

       

       2.  But without load output is 20 volt.

           after connecting the 50mA load. it drops to the 12.3.

       3.  when connecting 1.2A load it drops to 8.8 volt

            I am using  VPH2-0083 transformer      Np to Ns   is 1.5 

            Mean if the primary voltage is 8.8v, secondary should be 12.3 approx.

      Is a problem with the Transformer?

     what is a solution for regulating output voltage in the Flyback mode with feedback?

  • Hi,

    Do you have oscilloscope waveform of the SW node when the output drops? Also can you confirm that the FPWM pin is connected to VCC so that it operates in FPWM mode? 

    Is this drop also when you are operating with 20V input? Have you try to operate at higher voltage?

    Have you try to load the primary and see if the primary regulates?

    Thanks

    -Arief