I need to make an isolated DC-DC switching converter with a 9:1 output range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty cycle range looks tricky to make work well. So far I am most tempted to boost to an intermediate rail (which takes up the 5:1 range) and then convert from that over the 9:1 range. The intermediate rail could be useful for other purposes too. However I came across descriptions of quadratic converters. Namely duty cycle variation needed would be SQRT(45), have any of you experience of those? piglet
Quadratic DC-DC converters?
Started by ●November 7, 2021
Reply by ●November 7, 20212021-11-07
On Sun, 7 Nov 2021 14:24:50 +0000, piglet <erichpwagner@hotmail.com> wrote:>I need to make an isolated DC-DC switching converter with a 9:1 output >range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty >cycle range looks tricky to make work well.10 watts over the full range?> >So far I am most tempted to boost to an intermediate rail (which takes >up the 5:1 range) and then convert from that over the 9:1 range. The >intermediate rail could be useful for other purposes too. > >However I came across descriptions of quadratic converters. Namely duty >cycle variation needed would be SQRT(45), have any of you experience of >those? > >pigletMost of the papers are paywalled, but this one https://www.mdpi.com/1996-1073/14/14/4372/pdf looks like a boost feeding a boost. Inefficiently. Output can't go much below input. If an intermediate rail is useful, two separate converters sound sensible. -- Father Brown's figure remained quite dark and still; but in that instant he had lost his head. His head was always most valuable when he had lost it.
Reply by ●November 7, 20212021-11-07
On 11/7/2021 10:05 AM, jlarkin@highlandsniptechnology.com wrote:> On Sun, 7 Nov 2021 14:24:50 +0000, piglet <erichpwagner@hotmail.com> > wrote: > >> I need to make an isolated DC-DC switching converter with a 9:1 output >> range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty >> cycle range looks tricky to make work well. > > 10 watts over the full range? > > >> >> So far I am most tempted to boost to an intermediate rail (which takes >> up the 5:1 range) and then convert from that over the 9:1 range. The >> intermediate rail could be useful for other purposes too. >> >> However I came across descriptions of quadratic converters. Namely duty >> cycle variation needed would be SQRT(45), have any of you experience of >> those? >> >> piglet > > Most of the papers are paywalled, but this one > > https://www.mdpi.com/1996-1073/14/14/4372/pdf > > looks like a boost feeding a boost. Inefficiently. Output can't go > much below input. > > If an intermediate rail is useful, two separate converters sound > sensible. >High-gain Cuk converters can be very efficient by charging up inductors in parallel and discharging in series into the link capacitance, with the usual disadvantage that the output is inverted. The stock isolated Cuk isn't quadratic but can fix the inversion issue and the transformer doesn't have to be 1:1, can step the gain up that way, with further advantage it doesn't have to store energy and can be planar or something if needed. For when it has to be above or below the input this buck/boost looks interesting: <https://www.semanticscholar.org/paper/A-novel-single-switch-transformerless-quadratic-Mostaan-Gorji/b5ca4705bb237350e1fa112cd545e55b4474a074>
Reply by ●November 7, 20212021-11-07
On 11/7/2021 16:24, piglet wrote:> I need to make an isolated DC-DC switching converter with a 9:1 output > range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty > cycle range looks tricky to make work well. > > So far I am most tempted to boost to an intermediate rail (which takes > up the 5:1 range) and then convert from that over the 9:1 range. The > intermediate rail could be useful for other purposes too. > > However I came across descriptions of quadratic converters. Namely duty > cycle variation needed would be SQRT(45), have any of you experience of > those? > > piglet >If you need that 5:1 anyway just do it this way. 45:1 at a fixed frequency won't work without skipping cycles which you probably don't want. Our HV sources are guaranteed between 500 and 5000V, they work much below 500 though - but I would not put out such a spec. If you have to do it with 5:1 input range I would suggest you make the frequency input voltage dependent so the load regulation does not need to cover much more than 10:1.
Reply by ●November 7, 20212021-11-07
On Sun, 7 Nov 2021 10:41:46 -0500, bitrex <user@example.net> wrote:>On 11/7/2021 10:05 AM, jlarkin@highlandsniptechnology.com wrote: >> On Sun, 7 Nov 2021 14:24:50 +0000, piglet <erichpwagner@hotmail.com> >> wrote: >> >>> I need to make an isolated DC-DC switching converter with a 9:1 output >>> range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty >>> cycle range looks tricky to make work well. >> >> 10 watts over the full range? >> >> >>> >>> So far I am most tempted to boost to an intermediate rail (which takes >>> up the 5:1 range) and then convert from that over the 9:1 range. The >>> intermediate rail could be useful for other purposes too. >>> >>> However I came across descriptions of quadratic converters. Namely duty >>> cycle variation needed would be SQRT(45), have any of you experience of >>> those? >>> >>> piglet >> >> Most of the papers are paywalled, but this one >> >> https://www.mdpi.com/1996-1073/14/14/4372/pdf >> >> looks like a boost feeding a boost. Inefficiently. Output can't go >> much below input. >> >> If an intermediate rail is useful, two separate converters sound >> sensible. >> > >High-gain Cuk converters can be very efficient by charging up inductors >in parallel and discharging in series into the link capacitance, with >the usual disadvantage that the output is inverted. The stock isolated >Cuk isn't quadratic but can fix the inversion issue and the transformer >doesn't have to be 1:1, can step the gain up that way, with further >advantage it doesn't have to store energy and can be planar or something >if needed.Sepic is the non-inverting equivalent buck-boost. That might do what the OP wants. It's easy to Spice. https://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter> >For when it has to be above or below the input this buck/boost looks >interesting: > ><https://www.semanticscholar.org/paper/A-novel-single-switch-transformerless-quadratic-Mostaan-Gorji/b5ca4705bb237350e1fa112cd545e55b4474a074> >The trend seems to be to brag about needing one mosfet, with no limit on how many diodes that costs. -- Father Brown's figure remained quite dark and still; but in that instant he had lost his head. His head was always most valuable when he had lost it.
Reply by ●November 7, 20212021-11-07
On 07/11/2021 15.24, piglet wrote:> I need to make an isolated DC-DC switching converter with a 9:1 output > range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty > cycle range looks tricky to make work well. > > So far I am most tempted to boost to an intermediate rail (which takes > up the 5:1 range) and then convert from that over the 9:1 range. The > intermediate rail could be useful for other purposes too. > > However I came across descriptions of quadratic converters. Namely duty > cycle variation needed would be SQRT(45), have any of you experience of > those? > > piglet >You could do it with a standard converter, then handling the wide range with oversized output capacitor and (you probably need that anyway due to feedback stability at worst case point) A little wiggle on the dutycycle is ok as long as the overall stability is ok Regards Klaus
Reply by ●November 7, 20212021-11-07
On 11/7/2021 11:49 AM, jlarkin@highlandsniptechnology.com wrote:> On Sun, 7 Nov 2021 10:41:46 -0500, bitrex <user@example.net> wrote: > >> On 11/7/2021 10:05 AM, jlarkin@highlandsniptechnology.com wrote: >>> On Sun, 7 Nov 2021 14:24:50 +0000, piglet <erichpwagner@hotmail.com> >>> wrote: >>> >>>> I need to make an isolated DC-DC switching converter with a 9:1 output >>>> range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty >>>> cycle range looks tricky to make work well. >>> >>> 10 watts over the full range? >>> >>> >>>> >>>> So far I am most tempted to boost to an intermediate rail (which takes >>>> up the 5:1 range) and then convert from that over the 9:1 range. The >>>> intermediate rail could be useful for other purposes too. >>>> >>>> However I came across descriptions of quadratic converters. Namely duty >>>> cycle variation needed would be SQRT(45), have any of you experience of >>>> those? >>>> >>>> piglet >>> >>> Most of the papers are paywalled, but this one >>> >>> https://www.mdpi.com/1996-1073/14/14/4372/pdf >>> >>> looks like a boost feeding a boost. Inefficiently. Output can't go >>> much below input. >>> >>> If an intermediate rail is useful, two separate converters sound >>> sensible. >>> >> >> High-gain Cuk converters can be very efficient by charging up inductors >> in parallel and discharging in series into the link capacitance, with >> the usual disadvantage that the output is inverted. The stock isolated >> Cuk isn't quadratic but can fix the inversion issue and the transformer >> doesn't have to be 1:1, can step the gain up that way, with further >> advantage it doesn't have to store energy and can be planar or something >> if needed. > > Sepic is the non-inverting equivalent buck-boost. That might do what > the OP wants. It's easy to Spice. > > https://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter > >> >> For when it has to be above or below the input this buck/boost looks >> interesting: >> >> <https://www.semanticscholar.org/paper/A-novel-single-switch-transformerless-quadratic-Mostaan-Gorji/b5ca4705bb237350e1fa112cd545e55b4474a074> >> > > The trend seems to be to brag about needing one mosfet, with no limit > on how many diodes that costs. >The general idea of the high-ratio converters is to get the duty cycle away from the extremes of the range where unless the comparator, switch, and diodes very fast the nice output gain and control loop equations become less valid as they're struggling to keep up. A forward or flyback can do this too but at high turns ratio the primary side switch gets pummeled. Some extra diodes is OK if they can slum it thanks to the extra gain, but the high-side switch in that particular one doesn't enthuse me. There are lots of variations on this stuff this high-gain Sepic uses two low-side switches, one diode, one L, one coupled L, cool: <https://www.irjet.net/archives/V7/i3/IRJET-V7I3156.pdf> But as usual it's not documented particularly well, they fudge a control loop in Simulink who knows what the transfer function of that structure is.
Reply by ●November 8, 20212021-11-08
On 07/11/2021 15:41, bitrex wrote:> On 11/7/2021 10:05 AM, jlarkin@highlandsniptechnology.com wrote: >> On Sun, 7 Nov 2021 14:24:50 +0000, piglet <erichpwagner@hotmail.com> >> wrote: >> >>> I need to make an isolated DC-DC switching converter with a 9:1 output >>> range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty >>> cycle range looks tricky to make work well. >> >> 10 watts over the full range? >> >> >>> >>> So far I am most tempted to boost to an intermediate rail (which takes >>> up the 5:1 range) and then convert from that over the 9:1 range. The >>> intermediate rail could be useful for other purposes too. >>> >>> However I came across descriptions of quadratic converters. Namely duty >>> cycle variation needed would be SQRT(45), have any of you experience of >>> those? >>> >>> piglet >> >> Most of the papers are paywalled, but this one >> >> https://www.mdpi.com/1996-1073/14/14/4372/pdf >> >> looks like a boost feeding a boost. Inefficiently. Output can't go >> much below input. >> >> If an intermediate rail is useful, two separate converters sound >> sensible. >> > > High-gain Cuk converters can be very efficient by charging up inductors > in parallel and discharging in series into the link capacitance, with > the usual disadvantage that the output is inverted. The stock isolated > Cuk isn't quadratic but can fix the inversion issue and the transformer > doesn't have to be 1:1, can step the gain up that way, with further > advantage it doesn't have to store energy and can be planar or something > if needed. > > For when it has to be above or below the input this buck/boost looks > interesting: > > <https://www.semanticscholar.org/paper/A-novel-single-switch-transformerless-quadratic-Mostaan-Gorji/b5ca4705bb237350e1fa112cd545e55b4474a074> > > >Thanks. I simulated some by Maksimovic and Cuk and although they worked I was not too impressed. piglet
Reply by ●November 8, 20212021-11-08
On 07/11/2021 16:49, jlarkin@highlandsniptechnology.com wrote:> On Sun, 7 Nov 2021 10:41:46 -0500, bitrex <user@example.net> wrote: > >> On 11/7/2021 10:05 AM, jlarkin@highlandsniptechnology.com wrote: >>> On Sun, 7 Nov 2021 14:24:50 +0000, piglet <erichpwagner@hotmail.com> >>> wrote: >>> >>>> I need to make an isolated DC-DC switching converter with a 9:1 output >>>> range and 5:1 input range. Power is about ten watt. Resulting 45:1 duty >>>> cycle range looks tricky to make work well. >>> >>> 10 watts over the full range? >>> >>> >>>> >>>> So far I am most tempted to boost to an intermediate rail (which takes >>>> up the 5:1 range) and then convert from that over the 9:1 range. The >>>> intermediate rail could be useful for other purposes too. >>>> >>>> However I came across descriptions of quadratic converters. Namely duty >>>> cycle variation needed would be SQRT(45), have any of you experience of >>>> those? >>>> >>>> piglet >>> >>> Most of the papers are paywalled, but this one >>> >>> https://www.mdpi.com/1996-1073/14/14/4372/pdf >>> >>> looks like a boost feeding a boost. Inefficiently. Output can't go >>> much below input. >>> >>> If an intermediate rail is useful, two separate converters sound >>> sensible. >>> >> >> High-gain Cuk converters can be very efficient by charging up inductors >> in parallel and discharging in series into the link capacitance, with >> the usual disadvantage that the output is inverted. The stock isolated >> Cuk isn't quadratic but can fix the inversion issue and the transformer >> doesn't have to be 1:1, can step the gain up that way, with further >> advantage it doesn't have to store energy and can be planar or something >> if needed. > > Sepic is the non-inverting equivalent buck-boost. That might do what > the OP wants. It's easy to Spice. > > https://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter > >> >> For when it has to be above or below the input this buck/boost looks >> interesting: >> >> <https://www.semanticscholar.org/paper/A-novel-single-switch-transformerless-quadratic-Mostaan-Gorji/b5ca4705bb237350e1fa112cd545e55b4474a074> >> > > The trend seems to be to brag about needing one mosfet, with no limit > on how many diodes that costs. > > >Yeah, many times multiple mosfets all switched from same gate signal is going to be more efficient and cost only cents more. piglet
Reply by ●November 8, 20212021-11-08
On 07/11/2021 20:00, Klaus Vestergaard Kragelund wrote:> On 07/11/2021 15.24, piglet wrote: >> I need to make an isolated DC-DC switching converter with a 9:1 output >> range and 5:1 input range. Power is about ten watt. Resulting 45:1 >> duty cycle range looks tricky to make work well. >> >> So far I am most tempted to boost to an intermediate rail (which takes >> up the 5:1 range) and then convert from that over the 9:1 range. The >> intermediate rail could be useful for other purposes too. >> >> However I came across descriptions of quadratic converters. Namely >> duty cycle variation needed would be SQRT(45), have any of you >> experience of those? >> >> piglet >> > You could do it with a standard converter, then handling the wide range > with oversized output capacitor and (you probably need that anyway due > to feedback stability at worst case point) > > A little wiggle on the dutycycle is ok as long as the overall stability > is ok > > Regards > > KlausThanks, I'd like to keep it agile if possible so a very large cap is lower down my list of options :) piglet
