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  1. #1
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    variable smps

    Hi,I need to make a Variable Power Supply that is very light and compact with moderate cost.I am currently using a 31V SMPS Output and a Linear Regulator at 2A. But Using a linear Power Supply is old and is very inefficient.I came across this Variable SMPS circuit and was wondering if It really works.Although it is a Buck Converter it is too complicated for me to understand.Please tell me your thoughts
    http://<br /> http://www.elecfree.c...tl494-mj15004/

    Also appreciate it if you could point me in the direction of similar Circuits or the author of the one above

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  2. #2
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    variable output smps

    Hi,
    The PSU that you reference is a standard PSU with a switching buck regulator on the output, it will be a bit more efficient than a linear regulated PSU with the same power output but will not be very much lighter physically as it still uses a 50Hz transformer to produce the raw DC, which is the heaviest component. OK, it will only need a 50V input, a linear one will need a bit higher raw DC input voltage but that transformer will not be much different in size as the current requirement will be similar.

    If you use an isolated topology 50V SWMP to generate the raw 50V input the overall package will probably be about the same size, it may be a bit lighter but will more complicated to design.

    I have not built the circuit or analysed it in detail, so cannot comment on whether it has any inherrent snags, the principle on which it is based seems to be sound.
    Regards
    Bob.



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  3. #3
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    variable output buck converter

    I want to use a 48VDC SMPS For the Input but can you please tell me the Topology of the Power Supply as I would like to design my own variable Regulator also what will be the efficiency of the Output Section.



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  4. #4
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    variable output buck smps

    Hi,
    Do you already have a bulk 48V power supply that you intend to use, or do you want to design that part as well? A flyback design will cope easily with the 60 to 70W that you require for your regulator input, these are isolated and a number of reference designs exist for offline PSUs, the efficiency is usually about 70%. This bulk supply PSU MUST use an isolated topology if you are using a non-isolated low voltage regulator such as the buck.

    For the regulator the buck design as per your reference design is probably OK, they can be made quite efficient, usually around 80 to 85%. The 555 / 741 at the top is only used as an out of regulation indicator, the Buck part is handled by the TL494 and its associated pass transistors, which handle the voltage regulation and over current limiting. VR1 sets the output voltage and R24 is the current sense resistor as you probably already know.
    Regards,
    Bob.



  5. #5
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    variable power supply smps

    I have a 48V Input Circuit.But I have found something simpler.I'll give it as a Image.Its really good based on a L4970.




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  6. #6
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    variable current smps

    Hi,
    Looks like you have found an excellent solution to your problem, that device is a fully integrated buck regulator device complete with the power transistors built in, I had not seen it before, it may be useful to me someday too. You will need to recalculate the values of R1, R2, & R3 for your 48V input and for whatever output you want, otherwise the circuit looks fine as it is. Here is a url of an application note that may be useful if you have not already found it.
    http://www.selectronic.fr/includes_s...son/L4970A.pdf

    Incidentally I understand from the datasheet that the output of that device can only be adjusted from 5.1V to 40V, I hope that will be sufficient for your needs.

    Good luck with your project.
    Regards
    Bob.



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