# 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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48
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?

2. ### AnalogKid Distinguished Member

Aug 1, 2013
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1,297
Depends on the magnetic properties of the inductor core.

ak

3. ### anhnha Thread Starter Active Member

Apr 19, 2012
776
48
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
4,685
1,297
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
776
48
Well, there is only one frequency where energy transferred from source to load is maximum. This is what I am referring to:

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

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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.