• Resolved

LM5145EVM-HD-20A: Trying to convert LM5145-EVM non isolated converter to fly buck

Prodigy 200 points

Replies: 4

Views: 51

Part Number: LM5145EVM-HD-20A


I am trying to convert LM5145-EVM to a fly buck converter. I have replaced its inductor with a toroid. I measured the efficiency on the secondary side without loading the primary and its not good, is in the range of 60%-70%. Is it because my toroid has a single turn and is incurring a lot of core loss??

I have used diodes on the secondary side for rectification. I am thinking of driving Mosfet on the secondary side by using the low side gate drive pulse coming from LM5145 and isolating it from the primary by using a small transformer. Is it a good idea??

Any suggestions??


Nayana Soni

  • Hi Nayana,

    The LM5145 is generally not suitable for operation with a Fly-Buck configuration. Typically, the Fly-Buck needs a negative current limit and a current limit off timer.

    Please consider the LM5160 and LM5161 converters to implement a Fly-Buck.

  • In reply to Timothy Hegarty:

    Hi Tim,

    Thank you for the suggestion.

    In general does using a toroid for single turn incurs lot of core loss or it works fine?

    Thanks and Regards,


  • In reply to Nayana Soni:

    Hi Nayana,

    A conventional inductor will likely provide better efficiency and more predictable performance. I doubt you will get enough inductance with a single turn implementation.



  • In reply to Timothy Hegarty:

    Thank you Tim!!