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LM5119 output incorrect by order of magnitude

Sean Bigley
Genius 17175 points
Other Parts Discussed in Thread: LM5119

Team,


In an LM5119 simulation, one of the transformer outputs is showing to be 25V instead of 2.5V. The voltage across R17 is 2.5V when I build this schematic on a board and test probe it, but in Webench, the voltage is off by an order of 10. Can you please help me figure out what is incorrect, if anything?

http://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=7090C1060C94B1E4

Thanks,

Sean

  • 0
    TI__Mastermind 41310 points

    Sean,

    I have taken a quick look at the simulation and I believe that the 25V is correct. The transformer characteristics being used (turns ratio) from primary to the two secondary coils are:

    The primary is seeing swings of 50V, so the two output coils should see 150V (negative because of the configuration) and 25V. If you needed 2.5V, you would need to change the turns ratio to 0.05 to get from 50V on the primary to 2.5V on the second secondary coil.

    Let me know if this makes sense. I am not sure how the schematic design was made since this is in the schematic editor. Was the topology changed or the transformer added or modified from an original WEBENCH® design?