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I am looking at various DC/DC converter topologies for a power system I am designing. The most suitable topology for me is one that can perform both step-up and step-down functions, so I am looking into buck-boost and similar topologies like Cuk, SEPIC and Zeta.

While selecting the candidate ICs for the switching controller, I noticed a curios thing. On Digikey, where it is possible to filter by topology, the buck-boost & four-switch buck-boost topology occupies a large majority of the market. For instance, Digikey's catalog lists 471 active switching controller designs for a buck-boost topology, whereas for Cuk/SEPIC topologies there are only a handful of chips available (in the range of 15-20 chips).

Why is there such a preference for buck-boost topologies over Cuk and Sepic? Or is this just a shortcoming of Digikey's catalog?

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    \$\begingroup\$ Buck boost usually only needs one inductor. \$\endgroup\$
    – Andy aka
    Mar 18, 2021 at 10:26
  • \$\begingroup\$ @Andyaka Does this mean that buck-boost is more popular due to component count, and therefore price? So there is no technical motivation behind this, only financial? \$\endgroup\$
    – Mu3
    Mar 18, 2021 at 10:36
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    \$\begingroup\$ Given that the inductor in any switching converter is usually the most inefficient in terms of losses, there is a good technical reason to choose a design that only has one inductor. \$\endgroup\$
    – Andy aka
    Mar 18, 2021 at 10:42
  • \$\begingroup\$ 1) with some buck converter ICs, it is also possible to make other architectures as well, they might still be listed only as a "buck converter IC". 2) The number of components that is available doesn't tell you anything about preference, suppose there's one "does it all" IC that is cheap and no other manufacturer can provide an alternative, then there could only be that one IC for sale as the rest is made redundant by it. 3) The market and demand for buck converters is larger resulting in more ICs being available for that to cover all demands. \$\endgroup\$ Mar 18, 2021 at 12:04
  • \$\begingroup\$ "Designing DC/DC converters based on ZETA topology" seems to say that a Zeta converter can be built from a buck controller, and a SEPIC converter can be built from a boost converter. \$\endgroup\$
    – davidcary
    Sep 5, 2021 at 1:03

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The Ćuk converter has an inherent inverting topology. This means if you feed a Ćuk converter with a positive input supply voltage it will produce a negative output voltage. This is a minority application hence it attracts fewer offerings in Digikey. However, the Ćuk converter has continuous input and output current capability hence it has an attraction (fewer emissions and output ripple) but, still it is "inverting" and uses two magnetic components (or one more complex coupled inductor).

If you swap the input inductor and MOSFET around, you can convert the Ćuk circuit into a Zeta circuit with the benefit that you get positive out for positive in but the input current is now going to be discontinuous in many applications. Compared against regular converters like buck and boost which can be operated with continuous input current (and use only one magnetic winding), the preference is to choose those devices.

As for the SEPIC, it also uses two wound components and, as pointed out for the other two types (Ćuk and Zeta) it uses two wound components. It also has a discontinuous output current and can be noisy when feeding poor output capacitors. The same can be said of boost converters but these only use one inductor.

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