Is it a cuk converter? - Page 1
Forum section: electronics / beginners

author: kostasb
author_rank: Newbie
timestamp: January 09, 2018, 05:42:37 pm
content: Hello,I made the schematic (only the power part) of a circuit for e-cig mod.It looks like cuk converter, but the reversed polarity in the input confused me.Is it a cuk converter and how does it work?Any help will be appreciated!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 09, 2018, 06:10:03 pm
content: Close, at least: SEPIC, Cuk and Zeta converters are related by which way the supply/load is connected.Cuk has the unique distinction of continuous current on both nodes, and the disadvantage that the input and output are opposite polarity.As you probably guess (and have neatly drawn, as if to suggest this very point..!), this does not have continuous current at the supply; rather, it is pulsed, so that the bypass capacitor is required, not just nice-to-have. This is an example of the (drumroll please) Zeta converter.Tim

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 09, 2018, 08:10:59 pm
content: That's a real thing? Whoever came up with that term should be fired. I mean it's just one C away from...Why would you want a voltage converter in an E-cig, wouldn't that just use up the battery faster?

author: kostasb
author_rank: Newbie
timestamp: January 09, 2018, 09:21:38 pm
content: Yes it is a real thing.We want voltage converter because of the many differences in equipment we use.In some cases (vaping with temperature control) we need very precise voltage converters.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 10, 2018, 02:04:28 am
content: Quote from: Cyberdragon on January 09, 2018, 08:10:59 pmThe C has an accent, it's pronounced "chook". Named for its Serbian inventor. Due to limitations on this forum (lack of Unicode support, laziness) I didn't try accenting it.Tim

author: RoGeorge
author_rank: Super Contributor
timestamp: January 10, 2018, 02:45:13 am
content: Power topologies poster:http://www.ti.com/lit/sg/sluw001f/sluw001f.pdfPower Topologies Handbook:https://www.ti.com/seclit/ug/slyu036/slyu036.pdf

author: David Hess
author_rank: Super Contributor
timestamp: January 10, 2018, 01:41:55 pm
content: Patent licensing issues with Cuk converters prevented me from using them. There were dire warnings in application notes about it. I assume this would not be a problem now.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 10, 2018, 02:09:14 pm
content: Quote from: David Hess on January 10, 2018, 01:41:55 pmMust've been terribly old appnotes then:https://www.google.com/patents/US4184197Sept 1977!Tim

author: David Hess
author_rank: Super Contributor
timestamp: January 11, 2018, 02:56:58 am
content: Quote from: T3sl4co1l on January 10, 2018, 02:09:14 pmAnd a shelf full of books dedicated to switching power supply design.I know how old the patent is but it is not like old application notes and books become obsolete easily. In any event, the patent did not expire until years after I had an interest in the subject.

author: BravoV
author_rank: Super Contributor
timestamp: January 11, 2018, 03:00:00 am
content: Quote from: T3sl4co1l on January 09, 2018, 06:10:03 pmWhat is the example case/scenario that a reversed output can be a problem ? Enlighten me please.

author: David Hess
author_rank: Super Contributor
timestamp: January 11, 2018, 03:59:39 am
content: Quote from: BravoV on January 11, 2018, 03:00:00 amIt is the same with a non-isolated inverting switching regulator; if you have to share a common ground then either one side has to be floating or you have to live with the positive to negative inversion. LCD bias supplies are an example where this is an advantage but they do not require the high current that a Cuk converter would be used for.They also tend to have lower efficiency which I assume is due to increased charge pumping through the parasitic capacitances.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 11, 2018, 08:31:50 am
content: Quote from: BravoV on January 11, 2018, 03:00:00 amUh, well... every single POL converter, e.g. the 4V to 1.2V converter in your phone, the 18V to (1.2, 2.5, 3.3, etc.) converters in a laptop, etc.It's a matter of suitability. Very few converters need to be negative output, so Cuk (and inverting buck boost, and an isolated converter with the input negative and output positive linked for an inverting output) are encountered infrequently. For those few times when you DO need it, it's a fantastic option -- low input AND output ripple! It's just not an option you get to exercise very often.Tim