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'[EE]: Son of simple step-up SMPS challenge'
2002\10\30@230528 by Brendan Moran

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At 01:16 AM 27/10/2002 +1300, you wrote:
>Somewhat over a year ago I proposed a design challenge for a simple circuit
>to step up low voltages to somewhat higher ones for a range of applications.
>I believe there was and is a demand for such capability and that such a
>circuit may even provide functionality not readily achieved with available
>ICs. While there was some initial response to this challenge it died an
>early death, probably due to the events of September 11th.

I have no intention of getting into the logistics of the control system at
this point, but for a converting topology, I suggest the Cuk configuration.

Information could be found at http://www.boostbuck.com until recently (they are
now revamping their website) so google's cache is effective.
http://www.google.ca/search?q=cache:-RkKDi3znT8C:http://www.boostbuck.com/+&hl=en&ie=UTF-8

This topology uses a capacitor as the primary transfer element, and thereby
becomes more efficient than conventional topologies.
One possible disadvantage is that it is an inverting topology.  However,
there appears to be an isolated version.

This design is worth, at least, a small consideration.

--Brendan

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2002\10\31@212157 by Roman Black

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Brendan Moran wrote:
>
> I have no intention of getting into the logistics of the control system at
> this point, but for a converting topology, I suggest the Cuk configuration.
>
> Information could be found at
http://www.boostbuck.com/TheFourTopologies.html

> This topology uses a capacitor as the primary transfer element, and thereby
> becomes more efficient than conventional topologies.


I believe there is a certain amount of hype on
that page, especially the claim that "features
capacitive energy transfer for high efficiency"
which is supposed to reduce the I2R losses from
the inductor.

They seem to have neglected to mention capacitor
ESR, which at switching frequencies of 50kHz etc
is often multiple ohms. Even with a low-ESR cap
the Cuk converter shown has TWO inductors and
the cap in series with the main current path, I
just can't believe that this is ever going to
provide better efficiency that a properly designed
buck converter with a single inductor especially
after the ESR I2R losses are added in.

Just some MENTION of the differences between
inductor resistance I2R losses and capacitor ESR
I2R losses would have given some credibility.
-Roman

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2002\10\31@213351 by Russell McMahon

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> I have no intention of getting into the logistics of the control system at
> this point, but for a converting topology, I suggest the Cuk
configuration.
>
> Information could be found at http://www.boostbuck.com until recently (they are
> now revamping their website) so google's cache is effective.
>
http://www.google.ca/search?q=cache:-RkKDi3znT8C:http://www.boostbuck.com/+&hl=en&i
e=UTF-8
>
> This topology uses a capacitor as the primary transfer element, and
thereby
> becomes more efficient than conventional topologies.
> One possible disadvantage is that it is an inverting topology.  However,
> there appears to be an isolated version.

Also look at SEPIC.
I have been looking at capacitor isolated designs as possible candidates.
One advantage of such is that you can implement a boost-buck capability
where the input voltage does not "flood" the output when you change from
boost to buck mode or when the circuit is off. (Some simple boost designs
provide a direct diode path from battery to output at all times which can be
a significant disadvantage). A number of topologies are useful for only buck
or boost for secondary rather than fundamental reasons. Some of the
advantages of the newer topologies are more relevant in higher power
applications where stress on components or full utilisation of magnetics may
be of greater importance.

       RM

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2002\10\31@215021 by hard Prosser

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I believe that there are significant patent issues with using the Cuk
converter also.
Richard P



Brendan Moran wrote:
>
> I have no intention of getting into the logistics of the control system
at
> this point, but for a converting topology, I suggest the Cuk
configuration.
>
> Information could be found at
http://www.boostbuck.com/TheFourTopologies.html

> This topology uses a capacitor as the primary transfer element, and
thereby
> becomes more efficient than conventional topologies.


I believe there is a certain amount of hype on
that page, especially the claim that "features
capacitive energy transfer for high efficiency"
which is supposed to reduce the I2R losses from
the inductor.

They seem to have neglected to mention capacitor
ESR, which at switching frequencies of 50kHz etc
is often multiple ohms. Even with a low-ESR cap
the Cuk converter shown has TWO inductors and
the cap in series with the main current path, I
just can't believe that this is ever going to
provide better efficiency that a properly designed
buck converter with a single inductor especially
after the ESR I2R losses are added in.

Just some MENTION of the differences between
inductor resistance I2R losses and capacitor ESR
I2R losses would have given some credibility.
-Roman

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2002\10\31@233448 by Brendan Moran

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>I believe there is a certain amount of hype on
>that page, especially the claim that "features
>capacitive energy transfer for high efficiency"
>which is supposed to reduce the I2R losses from
>the inductor.
>
>They seem to have neglected to mention capacitor
>ESR, which at switching frequencies of 50kHz etc
>is often multiple ohms. Even with a low-ESR cap
>the Cuk converter shown has TWO inductors and
>the cap in series with the main current path, I
>just can't believe that this is ever going to
>provide better efficiency that a properly designed
>buck converter with a single inductor especially
>after the ESR I2R losses are added in.

I am not an expert in this area.  I ran across the Cuk converter in a
rather obscure website while trying to teach myself about SMPS last year.

I thought it bared mentioning, because the design is unknown by most, and
seems worth investigating.  It may have benefits you've overlooked.   While
there are multiple inductors, I believe that they can be quite low value,
and the converter will still work well.  Besides, a near perfect inductor
is far more difficult to manufacture than a near perfect capacitor.

I leave the analysis to those with more experience than I.

--Brendan

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2002\10\31@234523 by Brendan Moran

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At 03:50 PM 01/11/2002 +1300, you wrote:
>I believe that there are significant patent issues with using the Cuk
>converter also.
>Richard P

There were.  I *believe* they have been lifted recently.

--Brendan

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