ps problem

Discussion in 'General Electronics Chat' started by cgha20@yahoo.com, May 15, 2014.

  1. cgha20@yahoo.com

    Thread Starter Active Member

    Oct 21, 2009
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    0
    So I have the following specification and am having trouble finding where to start. I am thinking of using TPS four zero two zero zero from TI in flyback topology. Is it even feasible to build something like this with this physical size requirement? How do I make sure both outputs are isolated? Is this efficiency possible?

    Input: +15V to 50V
    Output: +5V, +45V
    power: 10W
    dimension: 0.86" x 1.29" x 0.31"
    Efficiency: 85% or better
    outputs are to be isolated
     
  2. cgha20@yahoo.com

    Thread Starter Active Member

    Oct 21, 2009
    61
    0
    sorry for the brief title, but I have been trying to post this since yesterday and it would not let me post even on different machines. When I shortened the title to almost nothing, it seemed to work.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    You don't say what the output current is for each output, but if the total power is only 10 watts then here are some thoughts.

    The TPS40200 will work for the 5V output only. It is a buck regulator, so it is designed to step down from a higher input voltage to a lower output voltage.

    The 45V output will be more difficult because it can be either stepping up from 15V or stepping down from 50 V. This sometimes called a buck-boost configuration. Linear Technology has a line of chips specifically for this situation.

    The bad news is that the standard form of these circuits is non-isolated. For isolated outputs you will need at least one transformer. That is a much more difficult design problem.

    The efficiency is possible, but the size would be difficult to meet with non-isolated circuits. I don't see any say to get there with transformer isolation. What is this for? Is this classwork, or product design?

    ak
     
  4. cgha20@yahoo.com

    Thread Starter Active Member

    Oct 21, 2009
    61
    0
    The total power is 10W. Yes I would need to use a transformer. Can I use the 5V to step up to the 45V? It is a real application. Just looking to see how feasible this will be and how complex as well.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Stepping 5V up to 45V is easier with a transformer than with a more simple boost converter. Lotsa vendors and chips to do this. But dual conversion (15to50V to 5V, then 5V to 45V) will be, well, twice as inefficient. Two 90% stages would yield 81% efficiency.

    Why do you need galvanic isolation? What is the application and what are the isolation requirements?

    ak
     
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