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

Nayana Soni

Part Number: LM5145EVM-HD-20A
Other Parts Discussed in Thread: LM5145, LM5161, LM5160

Hello,

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??

Regards,

Nayana Soni

over 4 years ago

0 Timothy Hegarty over 4 years ago

TI__Mastermind 49647 points

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.

Regards,
Tim

0 Nayana Soni over 4 years ago in reply to Timothy Hegarty

TI__Prodigy 200 points

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,

Nayana

0 Timothy Hegarty over 4 years ago in reply to Nayana Soni

TI__Mastermind 49647 points

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.

Regards,

Tim

0 Nayana Soni over 4 years ago in reply to Timothy Hegarty

TI__Prodigy 200 points

Thank you Tim!!

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