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[Reads from bottom up...] Gus: Maybe Dr. Cuk himself can shed some light on the exact status of the patents on the "Cukonverter!" As for the PEG, it no longer exists at Caltech since Dr. Middlebrook's retirement, and Dr. Cuk's resignation from the faculty there. It may take a while for him, or his secretary, to respond, as he travels regularly in connection with his business! Best regards, W. I. Behen ----- Original Message ----- From: Gus Bangerskis Sent: Friday, July 25, 2003 2:47 PM To: WILLIAM BEHEN Subject: RE: No Patents Bill If you are using the Cuk topology....... this is what the www.teslaco.com web-site has to say: "TESLAco’s proprietary technology is covered with 14 issued U.S. and foreign patents and a number of new patents are in the filing process. In addition, TESLAco has an exclusive license from the California Institute of Technology (Caltech, Pasadena), to the CUKonverter technology patents as well as all other patents generated by Caltech’s Power Electronics Group (PEG) which is headed by Dr. Cuk. Thus, for the rights to use CUKonverter technology, and/or other patents granted to Caltech’s Power Electronics Group, the License Agreement must be concluded with TESLAco." Sounds to me like it's still covered by patents and requires licensing...... unless I'm "missing" something. Gus 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. Since the claim of optimality is topological in nature, one does not need the more recent advances to outperform Bucks, Boosts, Flybacks, etc. Attempts by various academics to "hotrod" those topologies always fail, since it is the topologies themselves that are flawed! In practice, what happens is that any advances in the way of soft switching, synchronous rectification, or resonant or high frequency switching are a) just as easily applied to the Cuk Converter and, more importantly b) futile, due to the inherent shortcomings of the other topologies. Bill Bill Is that to say the patents on the Cuk converter have expired?? Years ago it was a "no-no" for commercial sale of supplies utilizing the Cuk topology with out licensing. Gus Gus: Nothing on my website is patented. If you go to the home page www.boostbuck.com, and click on the Greek column icon, you will land on my old original website. There is plenty of discussion there about the relative merits of coupled, uncoupled, integrated, and cascaded Boostbuck (Cuk) topologies! Best regards, W. I. Behen I haven't had any personnel experience with the Cuk converter outside of textbooks. I found the concept of a zero-ripple converter interesting. To tell the truth, I'm not even sure of the current "patent/licensing" status for commercially producing converters that use the topology. Gus -----Original Message----- From: WILLIAM BEHEN [mailto:billbehen@msn.com] Sent: Sunday, July 20, 2003 1:41 AM To: Gus Bangerskis Subject: Re: Web site Thanks for the clarification. What would you say is the main reason you don't like the Cuk converter? Have you had a bad experience with it? My reasons for favoring the boostbuck topologies are mostly theoretical, but with some practical design experience as well. Most engineers these days either swear by the converter, or at it! Any input would appreciated. Bill Depending on the product line.... non-isolated point-of-load supplies are buck (starting to tinker with multi-phase), low power (<10W) are flyback, resonant reset single ended forward, push-pull or push-pull with current doubler depending on Vout and full bridge. Of course synchronous rectification is used in all of these with the exception of the flyback, which is discontinuous. All are current mode except the flyback. No active clamp stuff or anything where patent licensing would be involved. Also a lot of custom, multi-output supplies that may mix topologies depending on the customers isolation and power requirements. All are DC-DC's. Gus -----Original Message-----From: WILLIAM BEHEN [mailto:billbehen@msn.com]Sent: Tuesday, July 15, 2003 11:52 PM To: Gus BangerskisSubject: Re: Web site Gus, What topology do you use? WIB ----- Original Message -----From: Gus Bangerskis Sent: Monday, July 14, 2003 7:22 AMTo: WILLIAM BEHEN Subject: RE: Web site Bill Thanks for the reply. While I would agree that "...off voltage and pass current..." may loosely represent some figure of merit for a components capability, that's a far cry from defining the "actual stress" it's subjected to in operation. Gus P.S. I notice on your web-site your a BIG fan of the Cuk converter can't say the same for myself, and in regards to "...In practice, any better than several percent transient regulation is unattainable without linear post regulation...", we routinely attain transient's of 2% - 3%, without it (sub 100W levels). If the converters "we" made here were much beyond that, our customers wouldn't buy them. -----Original Message-----From: WILLIAM BEHEN [mailto:billbehen@msn.com]Sent: Saturday, July 12, 2003 1:06 AM To: Gus BangerskisSubject: Re: Web site Gus: My website is just www.boostbuck.com. Though a FET doesn't both stand off voltage and pass current except during the switching interval between D and D', the same part must do both. This makes the product mentioned a good gauge of the stress experienced by a switch transistor. If you browse a MOSFET data book or mfgs. website you will notice that, for a given die size, as the current rating rises the voltage rating falls. Thus, for a given state of the art in transistor (or diode, for that matter) technology, a switcher can be designed to handle only so much power per simple topology. Beyond that, multiple converters must be run in parallel (or series) to process more Watts. It is interesting to note that some isolated topologies (e.g. the "Stress Sharing Buck,") use more than one transistor or diode to achieve power conversion, thus lowering the stress on the individual devices. Whether this is preferable to paralleling or seriesing the devices themselves is an open question. Series connexion of P's and Q's always seemed clumsy to me, while paralleling is recommended by device manufacturers, though I'm not sure it's often done! What is certain is that it takes the same total amount of stress handling capability on the input side of an isolated converter as on the output side--and that this amount is exactly the same for all converter topologies! The total amount is just (Vg + V) x (Ig + I). Vg & Ig are input voltage and current respectively, while V & I are output current and voltage. Best regards, WIB ----- Original Message -----From: Gus Bangerskis Sent: Wednesday, June 25, 2003 8:56 AMTo: billbehen@msn.com Subject: Web site Mr Behen You make references to your web-site, but I cant locate the address anywhere....... what is it?? Also, in the passage below, you define "stress" as "the product of the ON current times the OFF voltage ". What is this?? Under those conditions, which DON NOT happen at the same point in time, NO POWER is being dissipated and as long as the devices have the proper voltage and current ratings, what is the "stress" your referring too?? Thanks Gus Bangerskis Posted by William I. Behen on December 05, 2002 at 00:02:30: In Reply to: Re: 24v dc to 12v dc transformer Cuk converter :-( posted by John Collins on October 24, 2002 at 14:27:18: The total stress on the input transistors (and output diodes) is the same for ALL isolated converters, including your push-pull. By stress, I mean the product of the ON current times the OFF voltage of each device added together. Though a push-pull topology divides the stress between two devices, balancing is always a problem with such converters, especially under the transient load that this application requires. Also, I doubt the chip mentioned will drive such large FETs as will be needed! Further, beware of poor line rejection common to all Buck-based topologies. See my website for a full discussion. | Aussie Beef | Background | Tips | Engineering vs. Science | | Isolation of the Cuk Converter | Historical Perspective | | Return Home | Safety First | Lesson in Ethics | The Consequences of Bad Design | Real World Applications | Deals | e-mail me! | |
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