Reply by John Larkin July 24, 20132013-07-24

I disagree with this part:

It's impractical to do things like efficiency estimates by hand, what with
variable frequency, ohmic losses, switching losses, diode and ESR losses,
snubbers, all that. Instinct and Spice can optimize a circuit fast.

>Read a little about isolated Cuk converters. Why are they not used >instead of Buck, boost, Buck-boost converters?
They use more expensive magnetics, for one. -- John Larkin Highland Technology Inc jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Reply by Glenn July 24, 20132013-07-24
Read a little about isolated Cuk converters. Why are they not used 
instead of Buck, boost, Buck-boost converters? They work best with CCM 
but can of cause also use DCM. The original patents are expired:
The 1:1 transformer is gapless. The input/output-transformer must have a 

Cuk topology is current loading/dumping, which means both input and 
output ripple is a lot easier to tame. Hey there is an inductor for 
"free" in series with the input and output.

( Here only the basic unisolated Cuk is described: )

I have only found one (non-isolated) Cuk chip:


It is even possible couple the input/output inductor to (almost) zero 
input ripple.


The "worst"/"impossible" Cuk to design seems to be the Integrated 
Magnetics Cuk Converter (IMCC, "DC transformer") because of "the two RHP 
zeros". Why is that a problem? Can the control be some AI? In DCM a each 
cycle can be done separately so you have full control? Note: The IMCC is 
the 1:1 transformer and input/output-transformer integrated.

It is called a DC transformer because of (almost) zero input and output 

- Easy Design of the Boostbuck Family of Converters: Beef:
Quote: "...Gus: I visited Dr. Cuk at his Irvine laboratories not long 
ago--he is an old mentor and friend of mine. He told me himself that the 
original patents on his converter had expired. His company has patents 
on further mods to the topology still in effect, but the original 
topology is no longer patented. It is this original that I deal with on 
my site...Gus: Nothing on my website is patented..." Cuk converter:
Citat: "...The Cuk converter is a new SMPS topology at this moment. It 
include higher efficiency, low input and output current ripple, minimal 
RFI, small size and weight..."

T.S. Finnegan (January, 1991). "Cúk: the best SMPS" (på English). 
Electronics World & Wireless World ISSN: 0959-8332 Discontinued in 1995. 
Continued by Electronics World (ISSN: 1365-4675).: pp.69--72. Look at 
table at page 71. Quote: "...
The table below gives the effective primary and secondary copper losses, 
and the transistor and diode stress levels for the three types of 
converter, operating under identical conditions, for three different 
output voltages. The Cúk converter is more efficient and has lower 
stress levels in almost every respect

Terrence Finnegan (July, 1991). "Design brief: 60W Cuk converter". 
Electronics World & Wireless World ISSN: 0959-8332 Continued by 
Electronics World (ISSN: 1365-4675).: pp.596--600.

Ćuk, Slobodan; Middlebrook, R. D. (June 8, 1976). "A General Unified 
Approach to Modelling Switching-Converter Power Stages" (PDF). 
Proceedings of the IEEE Power Electronics Specialists Conference 
(Cleveland, OH.): pp.73-86: