Comments on Why do DC/DC switching controllers seem to favour the buck-boost topology over similar ones like Cuk, SEPIC and Zeta?
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Why do DC/DC switching controllers seem to favour the buck-boost topology over similar ones like Cuk, SEPIC and Zeta?
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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I think the point is simply that there are much more demand on the buck-boost topology than on the Cuk/Sepic ones. And there are GOOD reasons for that:
Several years ago, I asked a question on the SE forum: "where are Cuk converters". You can read the excellent answer there. The main point is that the Cuk/Sepic converters are of fourth order nature, which means that they regulate voltage much slower than 3d order regulators. What most of the people want is VOLTAGE REGULATION in addition to the buck/boost property. That's probably why there are fewer controllers of this type. I quote here the disadvantages of the SEPIC topology from Wikipedia:
- Like the buck–boost converter, the SEPIC has a pulsating output current. The similar Ćuk converter does not have this disadvantage, but it can only have negative output polarity, unless the isolated Ćuk converter is used.
- Since the SEPIC converter transfers all its energy via the series capacitor, a capacitor with high capacitance and current handling capability is required.
- The fourth-order nature of the converter also makes the SEPIC converter difficult to control, making it only suitable for very slow varying applications.
My opinion is that the Cuk converter, with its remarkable property of "zero ripple" can still be useful if you only want to increase or decrease the voltage, and then REGULATE the voltage with a standard (non switching) voltage regulator. Then it should be possible to obtain a higher or lower regulated voltage, free of the usually important (and very difficult to filter) noise produced by switching converters.
This may be interesting for very low noise demanding applications.
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