Baxandall class D oscillator, can it produce a triangle like waveform?
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From: John Devereux on 23 Jul 2010 13:42 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > On Thu, 22 Jul 2010 15:04:46 +0100, "markp" <map.nospam(a)f2s.com> > wrote: > >>Hi All, >> >>If I had a Baxandall class D resonant oscillator, would it be possible by >>modulating the current input to the drive circuit to produce a rounded off >>triangle like waveform? >> >>Bill Sloman's excellent work >>http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class-D%20oscillator1.htm >>found that the odd harmonic distortion was caused mainly by the AC ripple >>current flowing through the source inductor (and hence the driving >>windings). This presumably causes a perturbation in the dB/dt of the flux >>which modifies the output waveform. >> >>So would it be possible (in theory) by controlling this drive current more >>accurately to produce a rounded off triangle waveform without losing all the >>efficiencies and advantages of a resonant class D oscillator? >> >>Mark. >> > > Doesn't this work? > > ftp://jjlarkin.lmi.net/Triangle_Cap.JPG > > What's interesting is that, once it's all going, the power supply can > be cranked down to zero and you can make the triangle forever, for > free, since the ideal circuit is lossless. The slopes are technically > segments of sine waves, not linear bits, so there will be some small > curvature, less as L gets bigger. Given a real inductor, simple tweaks > could make the slopes straight. Nice! Though why you would want to put a triangle across a cap in the first place is a bit of a mystery :) -- John Devereux
From: John Fields on 23 Jul 2010 14:22 On Fri, 23 Jul 2010 12:31:33 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Fri, 23 Jul 2010 08:53:46 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Thu, 22 Jul 2010 15:04:46 +0100, "markp" <map.nospam(a)f2s.com> >>wrote: >> >>>Hi All, >>> >>>If I had a Baxandall class D resonant oscillator, would it be possible by >>>modulating the current input to the drive circuit to produce a rounded off >>>triangle like waveform? >>> >>>Bill Sloman's excellent work >>>http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class-D%20oscillator1.htm >>>found that the odd harmonic distortion was caused mainly by the AC ripple >>>current flowing through the source inductor (and hence the driving >>>windings). This presumably causes a perturbation in the dB/dt of the flux >>>which modifies the output waveform. >>> >>>So would it be possible (in theory) by controlling this drive current more >>>accurately to produce a rounded off triangle waveform without losing all the >>>efficiencies and advantages of a resonant class D oscillator? >>> >>>Mark. >>> >> >>Doesn't this work? >> >>ftp://jjlarkin.lmi.net/Triangle_Cap.JPG > >--- >Sorry, not even close. > >Not at Mark's frequency and cap spec, at any rate. > > >Version 4 >SHEET 1 880 680 >WIRE 96 -16 -48 -16 >WIRE 336 -16 176 -16 >WIRE 576 -16 336 -16 >WIRE 336 48 336 -16 >WIRE 576 48 576 -16 >WIRE 288 64 272 64 >WIRE 640 64 624 64 >WIRE 288 112 240 112 >WIRE 672 112 624 112 >WIRE -48 160 -48 -16 >WIRE 336 192 336 128 >WIRE 416 192 336 192 >WIRE 576 192 576 128 >WIRE 576 192 480 192 >WIRE 336 272 336 192 >WIRE 576 272 576 192 >WIRE 288 288 272 288 >WIRE 640 288 624 288 >WIRE 64 336 64 304 >WIRE 176 336 176 304 >WIRE -48 432 -48 240 >WIRE 64 432 64 416 >WIRE 64 432 -48 432 >WIRE 176 432 176 416 >WIRE 176 432 64 432 >WIRE 240 432 240 112 >WIRE 240 432 176 432 >WIRE 288 432 288 336 >WIRE 288 432 240 432 >WIRE 336 432 336 352 >WIRE 336 432 288 432 >WIRE 576 432 576 352 >WIRE 576 432 336 432 >WIRE 624 432 624 336 >WIRE 624 432 576 432 >WIRE 672 432 672 112 >WIRE 672 432 624 432 >WIRE -48 512 -48 432 >FLAG -48 512 0 >FLAG 64 304 A >FLAG 272 64 A >FLAG 640 288 A >FLAG 176 304 B >FLAG 272 288 B >FLAG 640 64 B >SYMBOL voltage -48 144 R0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V2 >SYMATTR Value 12 >SYMBOL sw 336 368 M180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S1 >SYMBOL sw 336 144 M180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S2 >SYMBOL voltage 64 320 R0 >WINDOW 0 -53 5 Left 0 >WINDOW 3 -242 110 Invisible 0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V1 >SYMATTR Value PULSE(1 0 0 1E-6 1E-6 .005 .01) >SYMBOL sw 576 144 R180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S3 >SYMBOL sw 576 368 R180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S4 >SYMBOL cap 416 208 R270 >WINDOW 0 32 32 VTop 0 >WINDOW 3 0 32 VBottom 0 >SYMATTR InstName C2 >SYMATTR Value 3e-6 >SYMBOL ind 80 0 R270 >WINDOW 0 32 56 VTop 0 >WINDOW 3 5 56 VBottom 0 >SYMATTR InstName L2 >SYMATTR Value .845 >SYMBOL voltage 176 320 R0 >WINDOW 0 -53 5 Left 0 >WINDOW 3 -242 110 Invisible 0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V3 >SYMATTR Value PULSE(0 1 0 1E-6 1E-6 .005 .01) >TEXT -40 480 Left 0 !.model SW SW(Ron=1 Roff=1E8 Vt=0.5 Vh=0) >TEXT -32 456 Left 0 !.tran .1 > >--- > >>What's interesting is that, once it's all going, the power supply can >>be cranked down to zero and you can make the triangle forever, for >>free, since the ideal circuit is lossless. > >--- >Sorry, but no. --- Snipped circuit list. 0ops... With zero ohm switches you're right. --- >>The slopes are technically >>segments of sine waves, not linear bits, so there will be some small >>curvature, less as L gets bigger. Given a real inductor, simple tweaks >>could make the slopes straight. > >--- >Blah, blah, blah, coulda, shoulda, woulda. > >"It's all just words..." --- What kind of "tweaks" are you talking about?
From: John Fields on 23 Jul 2010 15:28 On Fri, 23 Jul 2010 21:00:45 +0200, Fred Bartoli <" "> wrote: >John Fields a �crit : >> On Fri, 23 Jul 2010 08:53:46 -0700, John Larkin >> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> On Thu, 22 Jul 2010 15:04:46 +0100, "markp" <map.nospam(a)f2s.com> >>> wrote: >>> >>>> Hi All, >>>> >>>> If I had a Baxandall class D resonant oscillator, would it be possible by >>>> modulating the current input to the drive circuit to produce a rounded off >>>> triangle like waveform? >>>> >>>> Bill Sloman's excellent work >>>> http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class-D%20oscillator1.htm >>>> found that the odd harmonic distortion was caused mainly by the AC ripple >>>> current flowing through the source inductor (and hence the driving >>>> windings). This presumably causes a perturbation in the dB/dt of the flux >>>> which modifies the output waveform. >>>> >>>> So would it be possible (in theory) by controlling this drive current more >>>> accurately to produce a rounded off triangle waveform without losing all the >>>> efficiencies and advantages of a resonant class D oscillator? >>>> >>>> Mark. >>>> >>> Doesn't this work? >>> >>> ftp://jjlarkin.lmi.net/Triangle_Cap.JPG >> >> --- >> Sorry, not even close. >> >> Not at Mark's frequency and cap spec, at any rate. >> > >But it does. > >Even with real switches and inductor... > > >Version 4 >SHEET 1 1072 680 >WIRE 96 -16 -48 -16 >WIRE 336 -16 176 -16 >WIRE 448 -16 336 -16 >WIRE 576 -16 448 -16 >WIRE 336 48 336 -16 >WIRE 576 48 576 -16 >WIRE 992 48 912 48 >WIRE 288 64 272 64 >WIRE 640 64 624 64 >WIRE 288 112 240 112 >WIRE 672 112 624 112 >WIRE -48 160 -48 -16 >WIRE 912 176 912 48 >WIRE 336 192 336 128 >WIRE 416 192 336 192 >WIRE 576 192 576 128 >WIRE 576 192 480 192 >WIRE 864 192 576 192 >WIRE 336 240 336 192 >WIRE 864 240 336 240 >WIRE 336 272 336 240 >WIRE 576 272 576 192 >WIRE 288 288 272 288 >WIRE 640 288 624 288 >WIRE 64 336 64 304 >WIRE 176 336 176 304 >WIRE -48 432 -48 240 >WIRE 64 432 64 416 >WIRE 64 432 -48 432 >WIRE 176 432 176 416 >WIRE 176 432 64 432 >WIRE 240 432 240 112 >WIRE 240 432 176 432 >WIRE 288 432 288 336 >WIRE 288 432 240 432 >WIRE 336 432 336 352 >WIRE 336 432 288 432 >WIRE 576 432 576 352 >WIRE 576 432 336 432 >WIRE 624 432 624 336 >WIRE 624 432 576 432 >WIRE 672 432 672 112 >WIRE 672 432 624 432 >WIRE 912 432 912 256 >WIRE 912 432 672 432 >WIRE -48 512 -48 432 >FLAG -48 512 0 >FLAG 64 304 A >FLAG 272 64 A >FLAG 640 288 A >FLAG 176 304 B >FLAG 272 288 B >FLAG 640 64 B >FLAG 992 48 Vcap >FLAG 448 -16 Sup >SYMBOL voltage -48 144 R0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V2 >SYMATTR Value 0.022 >SYMBOL sw 336 368 M180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S1 >SYMBOL sw 336 144 M180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S2 >SYMBOL voltage 64 320 R0 >WINDOW 0 -53 5 Left 0 >WINDOW 3 -242 110 Invisible 0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V1 >SYMATTR Value PULSE(1 0 0 1E-6 1E-6 .004999 .01) >SYMBOL sw 576 144 R180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S3 >SYMBOL sw 576 368 R180 >WINDOW 0 32 15 Left 0 >WINDOW 3 32 44 Left 0 >SYMATTR InstName S4 >SYMBOL cap 416 208 R270 >WINDOW 0 32 32 VTop 0 >WINDOW 3 0 32 VBottom 0 >SYMATTR InstName C2 >SYMATTR Value 3e-6 >SYMBOL ind 80 0 R270 >WINDOW 0 32 56 VTop 0 >WINDOW 3 5 56 VBottom 0 >SYMATTR InstName L2 >SYMATTR Value 10 >SYMATTR SpiceLine Ipk=12m Rser=1 >SYMBOL voltage 176 320 R0 >WINDOW 0 -53 5 Left 0 >WINDOW 3 -242 110 Invisible 0 >WINDOW 123 0 0 Left 0 >WINDOW 39 0 0 Left 0 >SYMATTR InstName V3 >SYMATTR Value PULSE(0 1 0 1E-6 1E-6 .004999 .01) >SYMBOL e 912 160 R0 >SYMATTR InstName E1 >SYMATTR Value 1 >TEXT -40 480 Left 0 !.model SW SW(Ron=0.1 Roff=1E6 Vt=0.5 Vh=0) >TEXT -32 456 Left 0 !.tran 0 25 24.9 1m --- Can't argue with that! :-) Thanks, JF
From: John Larkin on 23 Jul 2010 16:34 On Fri, 23 Jul 2010 13:22:37 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Fri, 23 Jul 2010 12:31:33 -0500, John Fields ><jfields(a)austininstruments.com> wrote: > >>On Fri, 23 Jul 2010 08:53:46 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>>On Thu, 22 Jul 2010 15:04:46 +0100, "markp" <map.nospam(a)f2s.com> >>>wrote: >>> >>>>Hi All, >>>> >>>>If I had a Baxandall class D resonant oscillator, would it be possible by >>>>modulating the current input to the drive circuit to produce a rounded off >>>>triangle like waveform? >>>> >>>>Bill Sloman's excellent work >>>>http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class-D%20oscillator1.htm >>>>found that the odd harmonic distortion was caused mainly by the AC ripple >>>>current flowing through the source inductor (and hence the driving >>>>windings). This presumably causes a perturbation in the dB/dt of the flux >>>>which modifies the output waveform. >>>> >>>>So would it be possible (in theory) by controlling this drive current more >>>>accurately to produce a rounded off triangle waveform without losing all the >>>>efficiencies and advantages of a resonant class D oscillator? >>>> >>>>Mark. >>>> >>> >>>Doesn't this work? >>> >>>ftp://jjlarkin.lmi.net/Triangle_Cap.JPG >> >>--- >>Sorry, not even close. >> >>Not at Mark's frequency and cap spec, at any rate. >> >> >>Version 4 >>SHEET 1 880 680 >>WIRE 96 -16 -48 -16 >>WIRE 336 -16 176 -16 >>WIRE 576 -16 336 -16 >>WIRE 336 48 336 -16 >>WIRE 576 48 576 -16 >>WIRE 288 64 272 64 >>WIRE 640 64 624 64 >>WIRE 288 112 240 112 >>WIRE 672 112 624 112 >>WIRE -48 160 -48 -16 >>WIRE 336 192 336 128 >>WIRE 416 192 336 192 >>WIRE 576 192 576 128 >>WIRE 576 192 480 192 >>WIRE 336 272 336 192 >>WIRE 576 272 576 192 >>WIRE 288 288 272 288 >>WIRE 640 288 624 288 >>WIRE 64 336 64 304 >>WIRE 176 336 176 304 >>WIRE -48 432 -48 240 >>WIRE 64 432 64 416 >>WIRE 64 432 -48 432 >>WIRE 176 432 176 416 >>WIRE 176 432 64 432 >>WIRE 240 432 240 112 >>WIRE 240 432 176 432 >>WIRE 288 432 288 336 >>WIRE 288 432 240 432 >>WIRE 336 432 336 352 >>WIRE 336 432 288 432 >>WIRE 576 432 576 352 >>WIRE 576 432 336 432 >>WIRE 624 432 624 336 >>WIRE 624 432 576 432 >>WIRE 672 432 672 112 >>WIRE 672 432 624 432 >>WIRE -48 512 -48 432 >>FLAG -48 512 0 >>FLAG 64 304 A >>FLAG 272 64 A >>FLAG 640 288 A >>FLAG 176 304 B >>FLAG 272 288 B >>FLAG 640 64 B >>SYMBOL voltage -48 144 R0 >>WINDOW 123 0 0 Left 0 >>WINDOW 39 0 0 Left 0 >>SYMATTR InstName V2 >>SYMATTR Value 12 >>SYMBOL sw 336 368 M180 >>WINDOW 0 32 15 Left 0 >>WINDOW 3 32 44 Left 0 >>SYMATTR InstName S1 >>SYMBOL sw 336 144 M180 >>WINDOW 0 32 15 Left 0 >>WINDOW 3 32 44 Left 0 >>SYMATTR InstName S2 >>SYMBOL voltage 64 320 R0 >>WINDOW 0 -53 5 Left 0 >>WINDOW 3 -242 110 Invisible 0 >>WINDOW 123 0 0 Left 0 >>WINDOW 39 0 0 Left 0 >>SYMATTR InstName V1 >>SYMATTR Value PULSE(1 0 0 1E-6 1E-6 .005 .01) >>SYMBOL sw 576 144 R180 >>WINDOW 0 32 15 Left 0 >>WINDOW 3 32 44 Left 0 >>SYMATTR InstName S3 >>SYMBOL sw 576 368 R180 >>WINDOW 0 32 15 Left 0 >>WINDOW 3 32 44 Left 0 >>SYMATTR InstName S4 >>SYMBOL cap 416 208 R270 >>WINDOW 0 32 32 VTop 0 >>WINDOW 3 0 32 VBottom 0 >>SYMATTR InstName C2 >>SYMATTR Value 3e-6 >>SYMBOL ind 80 0 R270 >>WINDOW 0 32 56 VTop 0 >>WINDOW 3 5 56 VBottom 0 >>SYMATTR InstName L2 >>SYMATTR Value .845 >>SYMBOL voltage 176 320 R0 >>WINDOW 0 -53 5 Left 0 >>WINDOW 3 -242 110 Invisible 0 >>WINDOW 123 0 0 Left 0 >>WINDOW 39 0 0 Left 0 >>SYMATTR InstName V3 >>SYMATTR Value PULSE(0 1 0 1E-6 1E-6 .005 .01) >>TEXT -40 480 Left 0 !.model SW SW(Ron=1 Roff=1E8 Vt=0.5 Vh=0) >>TEXT -32 456 Left 0 !.tran .1 >> >>--- >> >>>What's interesting is that, once it's all going, the power supply can >>>be cranked down to zero and you can make the triangle forever, for >>>free, since the ideal circuit is lossless. >> >>--- >>Sorry, but no. > >--- >Snipped circuit list. > >0ops... > >With zero ohm switches you're right. Thanks for the correction. That saved me some time. >--- > >>>The slopes are technically >>>segments of sine waves, not linear bits, so there will be some small >>>curvature, less as L gets bigger. Given a real inductor, simple tweaks >>>could make the slopes straight. >> >>--- >>Blah, blah, blah, coulda, shoulda, woulda. I like to leave some of the details to peoples' imaginations. A few people actually do have imaginations; I most always get along with them. >> >>"It's all just words..." > >--- >What kind of "tweaks" are you talking about? Maybe a controlled current source to add a compensating curvature, for a small added power dissipation. Or kick in some smaller inductors here and there on the curve, to pick up the droop. We don't really know the requirements, which is nice, because it allows for more ideas. Switching inductor taps is always interesting. If you switch to an intermediate tap, current jumps up... just what you need to keep the triangle slope up, in a bang-bang sort of way. I once did a buck switcher that converted +24 to +5, for a control system on some Navy ships. Schottky rectifier dides were fairly new, and none I could get were good for 24 volts reverse. I connected the catch diode to the center-tap of the buck inductor, which reduced the peak reverse voltage to about 15, good enough. But the consequence of, essentially, tap switching was that the ripple current into the +5 filter cap went way, way up. Had to use a big wet-slug tantalum. So, puzzle of the day: Take a 2 henry inductor that has a center-tap. Run 1 amp through the whole thing, steady-state. Then short one end of the inductor to the CT, and remove the current source. What happens when you do that? Is anything conserved? Energy? N*I? John
From: John Larkin on 23 Jul 2010 16:35
On Fri, 23 Jul 2010 18:42:55 +0100, John Devereux <john(a)devereux.me.uk> wrote: >John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> writes: > >> On Thu, 22 Jul 2010 15:04:46 +0100, "markp" <map.nospam(a)f2s.com> >> wrote: >> >>>Hi All, >>> >>>If I had a Baxandall class D resonant oscillator, would it be possible by >>>modulating the current input to the drive circuit to produce a rounded off >>>triangle like waveform? >>> >>>Bill Sloman's excellent work >>>http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class-D%20oscillator1.htm >>>found that the odd harmonic distortion was caused mainly by the AC ripple >>>current flowing through the source inductor (and hence the driving >>>windings). This presumably causes a perturbation in the dB/dt of the flux >>>which modifies the output waveform. >>> >>>So would it be possible (in theory) by controlling this drive current more >>>accurately to produce a rounded off triangle waveform without losing all the >>>efficiencies and advantages of a resonant class D oscillator? >>> >>>Mark. >>> >> >> Doesn't this work? >> >> ftp://jjlarkin.lmi.net/Triangle_Cap.JPG >> >> What's interesting is that, once it's all going, the power supply can >> be cranked down to zero and you can make the triangle forever, for >> free, since the ideal circuit is lossless. The slopes are technically >> segments of sine waves, not linear bits, so there will be some small >> curvature, less as L gets bigger. Given a real inductor, simple tweaks >> could make the slopes straight. > >Nice! > >Though why you would want to put a triangle across a cap in the first >place is a bit of a mystery :) Umm, good point. John |