Baxandall class D oscillator, can it produce a triangle like waveform?
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From: John Fields on 23 Jul 2010 17:17 On Fri, 23 Jul 2010 13:34:03 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 23 Jul 2010 13:22:37 -0500, John Fields ><jfields(a)austininstruments.com> wrote: >>>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. --- There _are_ a few notable exceptions. --- >>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: --- Decline...
From: John Larkin on 23 Jul 2010 17:37 On Fri, 23 Jul 2010 16:17:48 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Fri, 23 Jul 2010 13:34:03 -0700, John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > >>On Fri, 23 Jul 2010 13:22:37 -0500, John Fields >><jfields(a)austininstruments.com> wrote: > >>>>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. > >--- >There _are_ a few notable exceptions. >--- > >>>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: > >--- >Decline... Right. John
From: John Larkin on 24 Jul 2010 00:15 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 Cool. It looks just like my sketch! The triangle is visually almost perfect, and the waveforms on the ends of the cap are especially nice. John
From: Bill Sloman on 24 Jul 2010 01:27 On Jul 24, 1:53 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 22 Jul 2010 15:04:46 +0100, "markp" <map.nos...(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? > > >BillSloman'sexcellent work > >http://home.planet.nl/~sloma000/Baxandall%20parallel-resonant%20Class... > >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 - and a much neater solution than mine. I am fixated on the Baxandall circuit, which lead me to a much more complicated (and less good) solution. I'm wondering if you could get away with putting a second winding on your inductor, return one end to Vcc/2, and drive the second winding with the buffered (and offset by Vcc/2) voltage appearing at the switch end of the inductor, thus making up the voltage drive lost as the capacitor charges up That wouldn't work with a single supply rail, but tapping the inductor say one third of the way down from Vcc and buffering that voltage into three times as many turns of over-winding might be persuaded to work. It's feedback, and could well oscillate, but you are driving a capacitor, which would kill the high frequency gain - which is where oscillations like to happen - so it might be worth a try. -- Bill Sloman, Nijmegen
From: John Larkin on 24 Jul 2010 12:20
On Sat, 24 Jul 2010 12:01:20 -0400, ehsjr <ehsjr(a)nospamverizon.net> wrote: >John Devereux 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 :) >> > >It's the schematic symbol for a new chip they're developing for >Robocop, called the COPAmp > > |\ > | \ > | \ > ---| \ > | \ > | | \ > | --- \____ > | --- / > | | / > | / > ---| / > | / > | / > |/ Beer factory control systems use hopamps. SGS, the Italian semiconductor company, makes wopamps. John |