On 07/11/2021 16:16, Dimiter_Popoff wrote:> 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.Thanks, good tip. piglet
Quadratic DC-DC converters?
Started by ●November 7, 2021
Reply by ●November 8, 20212021-11-08
Reply by ●November 8, 20212021-11-08
On Mon, 8 Nov 2021 21:30:30 +0000, piglet <erichpwagner@hotmail.com> wrote:>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 > >Right, diodes have a lot more voltage drop than saturated mosfets. SEPIC might work for you. -- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end in certainties. Francis Bacon
Reply by ●November 8, 20212021-11-08
On 11/8/2021 23:36, piglet wrote:> On 07/11/2021 16:16, Dimiter_Popoff wrote: >> 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. > > Thanks, good tip. > > piglet >On a second thought I may be overcomplicating things suggesting to vary the frequency. You will still need filtering for the lowest frequency, so may be just go as low as it takes so you can do the 1:45 PW variation. 10W is not much, we have mosfets and drivers nowadays which can switch really fast... unlike during the 80-s when we had to deal with storage times of a few microseconds etc.
Reply by ●November 8, 20212021-11-08
On 11/8/2021 4:25 PM, piglet wrote:> 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 >Seems like it would be hard to get worse than cascading converters for appreciable power outputs tho
