C-multiplier again
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From: dagmargoodboat on 26 May 2010 12:21 On May 26, 12:07 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Wed, 26 May 2010 15:57:09 GMT, Mike <s...(a)me.not> wrote: > >Winfield Hill <Winfield_mem...(a)newsguy.com> wrote: > > >[...] > > >> I see your idea, not bad. It's a nice simplification of this, > >> incorporating the current-sinking transistor into the opamp. > > >> +15V >--+--------+--------+----/\/\--+-----> Vout 14.8v > >> | | | 4.7R | > >> | R3 | | > >> | 2.7M | | > >> } | _| | > >> | C1 +------| \ |/ > >> '---||---+ | >------| > >> 10uF | ,--|__/ |\V > >> | | | | > >> R7 '--- |----------+ > >> TBD | | > >> 27k | R4 > >> | | 4.7R > >> | | | > >> --+--------+----------+---- > > >> This scheme is DC regulating as well. The class-A current > >> is set by R3 and R7, so the dc voltage drop is fixed. > > >Cancellation schemes give a 6dB/octave drop to a notch frequency, then a > >6dB/octave rise. The depth of the notch is extremely sensitive to the > >emitter resistance and probably the temperature of the transistor. Some > >examples may show large amounts of second harmonic distortion on the > >output. This does not appear on the frequency analysis plot. > > >In this example, the notch frequency is about 2KHz with a depth of -92dB.. > >Try changing the emitter resistance to get an idea of how critical it is.. > > >I don't think you want to rely on this method for any more than a minor > >amount of cancellation, say 20 dB or thereabouts. > > You'd need a trimpot to make up for the tolerance of the 4.7r > resistors. And yes, the dynamics are terrible here. And it's a power > hog. > > Feedforward is great when you want a 3:1, or even sometimes 10:1, fix > to some problem. Like for temperature compensation or some other > situation when negative feedback isn't available. Well, apart from THAT, Mrs. Lincoln, how'd you enjoy the play? -- Cheers, James Arthur
From: Mike on 26 May 2010 13:53 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > You'd need a trimpot to make up for the tolerance of the 4.7r > resistors. And yes, the dynamics are terrible here. And it's a power > hog. > > Feedforward is great when you want a 3:1, or even sometimes 10:1, fix > to some problem. Like for temperature compensation or some other > situation when negative feedback isn't available. > > John I'd stay away from a trimpot. If you try to get exact balance, it may work in the lab. But if you ship it to the customer and there is some noise problem, it may work one day and not work the next. That would be impossible to troubleshoot. Also, it is impossible to do a worst-case tolerance analysis on this method. If you cannot guarantee that you know how it will work under all conditions, give it to Joerg and let him fix it:) Anyway, I have solved your problem. This approach gives -180dB at 1KHz, with a -200dB notch at 1MHz. The IR drop is 18.8 * ImA, so if you have a 10mA drain, you end up with 14.8V. An additional benefit is very good brownout protection. It will keep your lamps lit for a long time! I left the cancellation method in for comparison. Mike Version 4 SHEET 1 1140 1108 WIRE -1072 -432 -1088 -432 WIRE -944 -432 -992 -432 WIRE -896 -432 -944 -432 WIRE -832 -432 -896 -432 WIRE -720 -432 -832 -432 WIRE -656 -432 -720 -432 WIRE -496 -432 -576 -432 WIRE -480 -432 -496 -432 WIRE -320 -432 -336 -432 WIRE -224 -432 -240 -432 WIRE -160 -432 -224 -432 WIRE -48 -432 -80 -432 WIRE -832 -416 -832 -432 WIRE -944 -400 -944 -432 WIRE -224 -400 -224 -432 WIRE -48 -400 -48 -432 WIRE -1088 -352 -1088 -432 WIRE -480 -320 -480 -432 WIRE -224 -320 -224 -336 WIRE -48 -320 -48 -336 WIRE -944 -304 -944 -336 WIRE -832 -304 -832 -336 WIRE -832 -304 -944 -304 WIRE -720 -304 -720 -432 WIRE -752 -288 -768 -288 WIRE -624 -272 -688 -272 WIRE -544 -272 -624 -272 WIRE -1088 -256 -1088 -272 WIRE -832 -256 -832 -304 WIRE -800 -256 -832 -256 WIRE -752 -256 -800 -256 WIRE -320 -240 -336 -240 WIRE -224 -240 -240 -240 WIRE -160 -240 -224 -240 WIRE -48 -240 -80 -240 WIRE 0 -240 -48 -240 WIRE 48 -240 0 -240 WIRE -832 -224 -832 -256 WIRE -720 -224 -720 -240 WIRE -224 -208 -224 -240 WIRE -48 -208 -48 -240 WIRE 48 -208 48 -240 WIRE -768 -176 -768 -288 WIRE -736 -176 -768 -176 WIRE -480 -176 -480 -224 WIRE -480 -176 -736 -176 WIRE -480 -160 -480 -176 WIRE -832 -128 -832 -144 WIRE -224 -128 -224 -144 WIRE -48 -128 -48 -144 WIRE 48 -128 48 -144 WIRE -480 -64 -480 -80 FLAG -1088 -256 0 FLAG -896 -432 Vin FLAG -496 -432 Vout FLAG -480 -64 0 FLAG -720 -224 0 FLAG -832 -128 0 FLAG -800 -256 U1P FLAG -736 -176 U1N FLAG -624 -272 U1O FLAG -336 -432 Vin FLAG -224 -320 0 FLAG -224 -432 Vout2 FLAG -48 -320 0 FLAG -48 -432 Vout3 FLAG -224 -128 0 FLAG -224 -240 Vout4 FLAG -48 -128 0 FLAG 0 -240 Vout5 FLAG -336 -240 Vout3 FLAG 48 -128 0 SYMBOL npn -544 -320 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL voltage -1088 -368 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL voltage -976 -432 R90 WINDOW 0 49 39 VRight 0 WINDOW 123 -48 40 VRight 0 WINDOW 39 0 0 Left 0 WINDOW 3 -2 123 VRight 0 SYMATTR InstName V2 SYMATTR Value2 AC 1 SYMATTR Value SINE(0 0.1 2.111e3) SYMBOL res -496 -176 R0 SYMATTR InstName R1 SYMATTR Value 4.681 SYMBOL res -672 -448 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 4.7 SYMBOL opamps\\1pole -720 -272 R0 SYMATTR InstName U1 SYMBOL res -848 -432 R0 SYMATTR InstName R3 SYMATTR Value 2.7e6 SYMBOL res -848 -240 R0 SYMATTR InstName R4 SYMATTR Value 27k SYMBOL cap -960 -400 R0 SYMATTR InstName C1 SYMATTR Value 10�f SYMBOL cap -240 -400 R0 SYMATTR InstName C2 SYMATTR Value 10000�f SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -336 -448 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R5 SYMATTR Value 4.7 SYMBOL cap -64 -400 R0 SYMATTR InstName C3 SYMATTR Value 10000�f SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -176 -448 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R6 SYMATTR Value 4.7 SYMBOL cap -240 -208 R0 SYMATTR InstName C4 SYMATTR Value 10000�f SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -336 -256 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R7 SYMATTR Value 4.7 SYMBOL cap -64 -208 R0 SYMATTR InstName C5 SYMATTR Value 10000�f SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -176 -256 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R8 SYMATTR Value 4.7 SYMBOL cap 32 -208 R0 SYMATTR InstName C6 SYMATTR Value 10�f SYMATTR SpiceLine Rser=2m Lser=2.5nh TEXT -824 -528 Left 0 ;'Op Amp Ripple Cancellation TEXT -832 -488 Left 0 !.ac oct 100 0.1 4e6
From: John Larkin on 26 May 2010 14:39 On Wed, 26 May 2010 17:53:56 GMT, Mike <spam(a)me.not> wrote: >John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > > >> You'd need a trimpot to make up for the tolerance of the 4.7r >> resistors. And yes, the dynamics are terrible here. And it's a power >> hog. >> >> Feedforward is great when you want a 3:1, or even sometimes 10:1, fix >> to some problem. Like for temperature compensation or some other >> situation when negative feedback isn't available. >> >> John > >I'd stay away from a trimpot. If you try to get exact balance, it may >work in the lab. But if you ship it to the customer and there is some >noise problem, it may work one day and not work the next. That would be >impossible to troubleshoot. > >Also, it is impossible to do a worst-case tolerance analysis on this >method. If you cannot guarantee that you know how it will work under all >conditions, give it to Joerg and let him fix it:) > >Anyway, I have solved your problem. This approach gives -180dB at 1KHz, >with a -200dB notch at 1MHz. The IR drop is 18.8 * ImA, so if you have a >10mA drain, you end up with 14.8V. An additional benefit is very good >brownout protection. It will keep your lamps lit for a long time! > >I left the cancellation method in for comparison. > >Mike It's a shame that supercaps have such high ESRs. John
From: dagmargoodboat on 26 May 2010 15:08 On May 26, 1:39 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Wed, 26 May 2010 17:53:56 GMT, Mike <s...(a)me.not> wrote: > >John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > > >> You'd need a trimpot to make up for the tolerance of the 4.7r > >> resistors. And yes, the dynamics are terrible here. And it's a power > >> hog. > > >> Feedforward is great when you want a 3:1, or even sometimes 10:1, fix > >> to some problem. Like for temperature compensation or some other > >> situation when negative feedback isn't available. > > >> John > > >I'd stay away from a trimpot. If you try to get exact balance, it may > >work in the lab. But if you ship it to the customer and there is some > >noise problem, it may work one day and not work the next. That would be > >impossible to troubleshoot. > > >Also, it is impossible to do a worst-case tolerance analysis on this > >method. If you cannot guarantee that you know how it will work under all > >conditions, give it to Joerg and let him fix it:) > > >Anyway, I have solved your problem. This approach gives -180dB at 1KHz, > >with a -200dB notch at 1MHz. The IR drop is 18.8 * ImA, so if you have a > >10mA drain, you end up with 14.8V. An additional benefit is very good > >brownout protection. It will keep your lamps lit for a long time! > > >I left the cancellation method in for comparison. > > >Mike > > It's a shame that supercaps have such high ESRs. > > John I was thinking about that. Maxwell Technology makes unit with milliohm ESRs, but I wasn't sure there wasn't some funky noise problem, like electrolyte convection or who knows what. Oh, and they're a few cubic inches--not surface mountable. But as for leakage, I've seen a *really* clever dodge around that. Walt Jung, I think, in a low-noise reference IIRC. -- Cheers, James Arthur
From: dagmargoodboat on 26 May 2010 16:03
On May 26, 10:57 am, Mike <s...(a)me.not> wrote: > Winfield Hill <Winfield_mem...(a)newsguy.com> wrote: > > [...] > > > > > I see your idea, not bad. It's a nice simplification of this, > > incorporating the current-sinking transistor into the opamp. > > > +15V >--+--------+--------+----/\/\--+-----> Vout 14.8v > > | | | 4.7R | > > | R3 | | > > | 2.7M | | > > } | _| | > > | C1 +------| \ |/ > > '---||---+ | >------| > > 10uF | ,--|__/ |\V > > | | | | > > R7 '--- |----------+ > > TBD | | > > 27k | R4 > > | | 4.7R > > | | | > > --+--------+----------+---- > > > This scheme is DC regulating as well. The class-A current > > is set by R3 and R7, so the dc voltage drop is fixed. > > Cancellation schemes give a 6dB/octave drop to a notch frequency, then a > 6dB/octave rise. The depth of the notch is extremely sensitive to the > emitter resistance and probably the temperature of the transistor. Some > examples may show large amounts of second harmonic distortion on the > output. This does not appear on the frequency analysis plot. > > In this example, the notch frequency is about 2KHz with a depth of -92dB. > Try changing the emitter resistance to get an idea of how critical it is. > > I don't think you want to rely on this method for any more than a minor > amount of cancellation, say 20 dB or thereabouts. > > Mike <snip LTSpice model> 20dB sounds about right. The advantages of this approach are low drop- out voltage and superior low-frequency noise cancellation (compared to practical passive equivalents). A big part of the dynamic limitation is the f.f. network rolling off. If you change C1 to 100uF, and tack 100uF on the output to cover the high-end, overall performance is much improved--nearly as good as a passive version using 10,000uF caps, and a lot smaller. For super massive attenuation of input noise and ripple, other approaches are better. If John could knock down that 50mV switcher ripple with an LC at the input, that's a bonus. But he won't--The Brat would kill him. -- Cheers, James Arthur |