Optimum switching frequency for power transfer in non-inverting buck-boost

Discussion in 'General Electronics Chat' started by anhnha, Feb 17, 2016.

  1. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    This is a buck-boost non-inverting converter.
    How would you calculator optimum switching frequency for maximum power transfer to inductor here?
    With each individual buck or boost it is OK but I couldn't find a way to do that for the buck-boost converter?

    Four switch non-inverting buck-boost converter.PNG
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Depends on the magnetic properties of the inductor core.

    ak
     
  3. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Thanks. I think I figured it out. Let's assume that the inductor is ideal and this discussion is only in theory. So the optimum switching frequency for buck, boost and buck-boost are the same.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    If you are not talking about real-world components, there is no optimum switching frequency for any topology. 1 Hz, 1 kHz, 1 MHz, 1 GHz, whatever. With perfect inductors, capacitors, and transistors, they're all the same. I don't understand the question.

    "In theory there is no difference between theory and practice. In practice there is."
    - Yogi Berra

    ak
     
  5. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Well, there is only one frequency where energy transferred from source to load is maximum. This is what I am referring to:

    Maximum power transfer boost converter.PNG
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Skip the first few pages to get to the section covering the various loss mechanisms in buck converter
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    No, there isn't.

    There is an optimum frequency for a particular set of component values, but that is not what you originally asked about. In your graphic, Fs is not equal to a value, like 157.0796 kHz. It is dependent on the components, specifically the output impedance of the energy source and the value of the inductor. In real life it is dependent on many more things than that, like the inductor's resistance, self-resonant frequency, the permeability of its core, the resistance of the switch, etc.

    ak
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    Does it matter? Switching frequency will vary according to load requirements.
     
  9. hp1729

    Well-Known Member

    Nov 23, 2015
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    Does something like this show up in a simulation? Or is the solution to build it and see?
     
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    LTSpice was originally designed to help build switching power supplies by simulating circuit operations. It is very good at simulation of many circuits and is worth getting and spending a week or two learning.
    Ultimately, you will have to build it to see how it really works. SMPS design is an art almost as much fun as high frequency RF circuit design.
     
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