On 8/14/06, Russell McMahon wrote: > >> Did anyone find this interesting? I spent a while photocopying it > >> in the > >> library, scanning it, converting it to PDF.. :-) > > > Sure, but cuk is quite known, I'm using it because could be quiet. > > The circuit that Martin referenced seemed to cover a little more than > basic CUK. > > Not having played with CUK in practice I may be missing something > that's in most CUK implementations BUT these circuits had a polynomial > relationship between duty-cycle and voltage ratio allowing a much > wider than usual input:output voltage ratio and/or a much wider > control range. > > They are effectively two buck converters in series with the first > being "passive" and being driven by the current pulses from the second > active stage > > The author also makes the point that any buck converter with pulsating > current input can be preceded by a passive buck stage and thereby > achieve an N^2 voltage transformation ratio. Which would often be > useful. > > Having an eg N^2 ratio for a say 300 volt to 12 volt converter would > allow each stage to have sqrt(300/12) ~= 5:1 conversion. eg 1st stage > is 300V:60 Volt and second 60V:12V. This could have substantial > advantages in inductor design over a single stage system. I didn't read carefully that datasheet, I'm in holiday and I don't want to "waste" my time. However just notice that a 300V single stage having a coil as load will require at least an 1200V transistor which already is not so funny... Fo me as a cuk user, there isn't any benefit in the cuk structure except maybe the ripple which may be minimised quite low. The efficiency isn't very high and the problems are everywhere. greetings, Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist