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LM5041: LM5041

arif anwar
Prodigy 90 points
Part Number: LM5041
Other Parts Discussed in Thread: UCC2897A

Hi Team

We have been tasked to design a new DC-DC converter for rail applications specifications as follows

1)  Vin: 14.4 - 137Vdc

2)  Vout: 24Vdc

3)  Iout: 2A

 

We would like to use the LM5041 in a buck current fed push pull configuration for this converter.

1)  Would this be possible with the LM5041, being that the input maybe lower than the output?

2)  Are there any worked examples/application notes/design notes for this?

3)  Is there another topology you can suggest?

Any suggestions/help would be greatly appreciated.

Greetings from Sydney Australia

Arif 

  • 0
    TI__Mastermind 27105 points

    Hi Arif,

    Thanks for your interest in TI. One potential issue I could see with using LM5041 is the VIN pin has a range of 15V to 100V so some external circuitry would be needed to limit the maximum voltage on the VIN pin. I was unable to find any current fed push pull reference designs based on LM5041 similar to these design requirements unfortunately.

    Based on the wider input voltage range and the output power level, a flyback topology could be a good fit.  Flyback is well equipped to handle wider input voltage ranges such as this and requires only 1 MOSFET on the primary side instead of 4 MOSFETs for the current fed push pull. I didn't find a reference design that is an exact match for these input/output requirements but here is a webench schematic I generated based on your design spec. This could serve as a good starting point:webench_design_4369191_37_822481690.pdf

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    Prodigy 90 points

    Hi Ben

    Thank you for the detailed and quick response. I realise that external circuitry will be needed for the LM5041, and even though the design requires 4 FET's, it should be a lot more

    efficient across the voltage range. I have considered flyback as a topology, but the peak secondary currents and the requirement for

    lots of output capacitance are a bit of a concern for the Rail environment. Also from  an efficiency point of view, the flyback designs that Ive simulated on 

    Webench have been pretty poor (60% and less) over the voltage range.

    Any other suggestions you might have would be appreciated. Thank you once again

  • 0 in reply to arif anwar
    TI__Mastermind 27105 points
    Hi Arif,

    Thank you for the clarification. One option for using LM5041 with this input voltage range is to use an emitter follower to feed the VIN pin and clamp the base of the NPN with a high voltage zener. This will clamp the max voltage on the VIN pin to below the 100V rating of the pin. For reference, here is a 220V -400V input active clamp forward that uses this strategy to limit the max input voltage of the VIN pin of UCC2897A to 91V:www.ti.com/.../slur901.pdf.

    Best Regards,
    Ben Lough