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Original question:

Looking for a step down converter for my power supply

Looking for a step down converter for my power supply

Mateusz Kaluzny17
Expert 1065 points
Other Parts Discussed in Thread: LM2676, LM2596, LMR23615, LM317

Hi dear Ti community.

At this moment I'm working on my PSU and I've got few concerns about it - details below :
I'm going to use MeanWell MPM-30-24 module (or IRM-30-24) as my main PSU, but I'm looking for good solution to lower it output voltage via step down IC (because this PSU couldn't be regulated).

So PSU is 1.3A - 24VDC, switching freq is ~ 65kHz.
What I want to achieve? Good and stable 18-20V output with ability to use all available current from this PSU.

There is a plenty of IC (according to Ti Power Designer) and I know some older types like LM2676.

My questions are :

- which one should I pick? Costs are my second concern here, my frist priority is to get stable and reliable output - I'm want to stick with converters or whole module instead of controllers,

- CLC input filter - should I use it? If yes how to calculate parts according to MeanWell PSU spec (if this is somehow important),

- LC output filter (post filter) does it really matter if I'm going to use hi-PSRR voltage regulators right after those DC-DC?

- I assume if I pick buck IC with swithing freq in range of best PSRR performance of my LDO I'll make best deal?

Thank you for your time ;)

If you need more info or clarification just tell me what you need, I'll try to answer best I could.

  • 0
    TI__Mastermind 23845 points
    Hi,

    Yes there is plenty of integrated switch buck converter that you can use.
    From LM2596 to the newer ones that we have.
    Here is one example design using LMR23615. You can always use webench to get general idea of the initial component selection
    webench.ti.com/.../SDP.cgi

    - As for CLC input filter, i dont think you need to use it. The front end of your supply is the meanwell supply, therefore it has the filter internally i presume from the power supply

    - LC output filter, in general you don't need it because the buck converter output is generally clean due to LC filter inherited on the output stage of a buck..

    - Yes, if you have an LDO after this buck converter, you can pick switching frequency in the range of the LDO PSRR, but again generally in buck converter you have already an LC filter in the output stage. The PSRR of the LDO will help also attenuating the higher frequency spikes.

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Expert 1065 points

    Seems logic ;)

    But I've got other question, how about making negative buck converter to handle and work directly with negative input voltage?
    Let's assume that I want to make bipolar power supply with common ground when both voltage will be 24VDC.

    There is an easy way to produce lower voltage from positive rail, but how about negative one?
    I know that there is a way to produce negative voltage from positive rail (inverter) but they're often not sufficient in term of current capability.

    Is there exist any good way to directly handle negative potential?
    Or my only way is to build two identical PSU's and tie them to create "virtual ground"?

    I could use LM317/337 pair to drop some voltage from 24V to 18-20V but I assume that will be not effective solution even if it's cheap somehow and bullet proof.

  • 0 in reply to Mateusz Kaluzny17
    TI__Mastermind 23845 points

    Hi Mateusz,

    If i understand you correctly, seems like you want to create a dual rail of positive and negative rail?

    If thats correct, here is one design that you might be able to take a look and see if it suit your needs

    http://www.ti.com/tool/PMP9379

    Thanks

    -Arief