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LM5020: Most Powerfull Isolated Flyback DC/DC controller

Part Number: LM5020
Other Parts Discussed in Thread: PMP20777, LM5185, , LM5155, LM5156, LM51561, LM51551

Good morning,

I'm looking for find the best Actually TI controller for develop an Isolated Flyback DC/DC controller most powerfull possible.

I use a PoE++ Transformer like 750319032 Or 750319021    

I have see the isolated CCM DC/DC like PMP20777. My design need similar I/O parameters:  Input About 30 to 60 Volt  <> Output about 24 to 28 Volt 3/4 Ampere as large as possible... >80 to 90 Watt Max output Power

I have tested the new LM5185 but with it, there isn't the possible of external frequency regulation, and the PSR mode sometimes goes in fault with low output voltage conditions. I preferr the Optocoupler voltage regulation, because with the PSR mode I think I will hardly be able to exceed 70 Watts in output.

So the older LM5020MM-1/NOPB may be the best for my purposes, Can you suggest me if there are newer and better controllers than the LM5020??

NB: My important degree of freedom of mine; my Vout voltage does not have to be perfectly regulated and stabilized, it can also have a high ripple, and also my vary from 22 V to 35 Volt 

  • Hello Michele,

    Thanks for reaching out to us via e2e.

    Please have a look at the LM5155 / LM5156 for a more modern controller for asynchronous topologies.

    Best regards

  • Thank you Harry for suggest,

    Today i see this two controller and I'll make a comparison, see you soon!

  • Good Morning Harry, 

    I have see your suggest thank you, but I'm undecided;   LM5156 - LM51561  Could be the only alternative to the classic but reliable LM5020, because i Have 60 Volt Maximum Input voltage.

    I have use in the past the similar LM51551 (with 12 V input) but I had a lot of problems with HICCUP MODE protection, with start-up pre-post soft start etc.. 

    I had to work with shunt resistances much lower than the reference and make the CS current sense stage less sensitive. So I have the impression that the old LM5020 is simpler and more stable, I don't need precision and I can accept high ripple, the priority for me is to obtain the maximum output power of 90 Watts with the Wurth transformer. 

    The LM5156x device use PCM peak current mode control, while the 750319032 transformer is optimized for CCM Flyback like LM5020 controller that is CCM Continuous Current Mode  Correct ??

    The doubt is that the LM51561 contains better technology, more modern and stable, but more difficult to fine-tune !?!?

    Thank you for your opinions and advice


  • Hello Michele,

    I don't want to force you in one or the other direction.
    You had asked for alternatives, and I gave you a part number.
    Please select the part that you can handle best.

    Just as an explanation on your question:

    Both device families are using peak current mode control as the inner control loop.

    It depends on the selection of the external components if the energy that was stored in the inductor/transformer has been consumed before the cycle is over (DCM)
    or if there is still some energy left when the cycle ends (CCM).
    These are no different "modes" of our controllers.
    And this is independent of the peak current mode control that is used as the inner control loop.

    Best regards

  • Good Morning Harry, 

    all clear for now, thank you,
    Ok so both modes are well supported. It certainly also depends on the calibration of the external components. 
    Then I will check which of the two gives me the most flexibility and confidence.

    Thank you