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LM5160A: Flybuck Primary Output Voltage

Part Number: LM5160A

Hi Expert,

I have some questions to the design example in datasheet 9.2.2 18-32Vin to 9Vpri and 12Viso following from below thread.

1. 12V is isolated output and 8V is primary output. So for primary output that cannot be no more than one half of the minimum input voltage is still a hard restriction or a just recommendation?

2. Is LM5160A good for customer's use case, 10-28Vin to 5.5Vpri and 15Viso? It looks it breaks the 50% duty rule however it can still run simulation on Webench. Please clarify.




  • Hi Allan,

    The 50% duty cycle is a recommendation and it is not a hard restriction on the flybuck design as Arief mentioned in that thread.

    The secondary side is conducting during the off-time, so a larger duty cycle on the primary means lower conduction time on the secondary. 

    With lower conduction time, the secondary side will have larger peak currents. Larger peak currents lead to poor regulation and more transformer losses.

    Thats why less than 50% duty cycle is recommended. 

    For 10-28Vin to 5.5Vpri and 15Viso, what are your output currents?

    The converter should work fine as long as your 15Viso is not large current.

    Just be sure your secondary rectifier diode is rated at enough voltage.

    From the paper linked here:  Vd ≈ n*Vin.

    Please let us know if you have any other questions,

    -Orlando Murray