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

#### anhnha

Joined Apr 19, 2012
905
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?

#### AnalogKid

Joined Aug 1, 2013
10,799
Depends on the magnetic properties of the inductor core.

ak

#### anhnha

Joined Apr 19, 2012
905
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.

#### AnalogKid

Joined Aug 1, 2013
10,799
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

#### anhnha

Joined Apr 19, 2012
905
Well, there is only one frequency where energy transferred from source to load is maximum. This is what I am referring to:

#### Kermit2

Joined Feb 5, 2010
4,162
Skip the first few pages to get to the section covering the various loss mechanisms in buck converter

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#### AnalogKid

Joined Aug 1, 2013
10,799
Well, there is only one frequency where energy transferred from source to load is maximum.
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

#### dl324

Joined Mar 30, 2015
16,206
Well, there is only one frequency where energy transferred from source to load is maximum.
Does it matter? Switching frequency will vary according to load requirements.

#### hp1729

Joined Nov 23, 2015
2,304
Does something like this show up in a simulation? Or is the solution to build it and see?

#### Kermit2

Joined Feb 5, 2010
4,162
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.