C-multiplier again
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From: Joerg on 26 May 2010 21:24 John Larkin wrote: > On Wed, 26 May 2010 17:17:32 -0400, Spehro Pefhany > <speffSNIP(a)interlogDOTyou.knowwhat> wrote: > >> On Wed, 26 May 2010 13:53:55 -0700, John Larkin >> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> On Wed, 26 May 2010 13:03:33 -0700 (PDT), dagmargoodboat(a)yahoo.com >>> wrote: >>> >>>> 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. >>> No, I survived. The Gerbered board had... >>> >>> Wall wart connector >>> >>> Polyfuse >>> >>> Transzorb >>> >>> 10 uF ceramic >>> >>> 47 uH inductor >>> >>> two 10 uF ceramics and one 120 uF polymer aluminum to make "+15 >>> volts." That's 12 dB/octave starting at about 2 KHz. >>> >>> Then the LM8261 low-noise LDO reg, which has its own 15 ohms + 2x10uF >>> + 120uF at its output. >> Using an LM8261 op-amp to make an LDO? > > Yup, it's this one: > > ftp://jjlarkin.lmi.net/P14_reg.gif > > (hope you can see it; some people are reporting trouble accessing my > FTP files) > Never had any problems. In fact, I like it that you store them in an economic and compact file format. It irks me when a schematic turns out to be some several megabyte download where a GIF or PNG containing the same information would have been 50k. > The LM8261 is a great part. Pretty good RRIO opamp, 32 volts, 21 MHz, > tons of current drive, stable into any capacitive load. > Just keep in mind that the output RR capability really falls off the cliff at around 20mA. So with your 15mA you are "dang close" :-) So, is your circuit good enough now for its purpose? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Mike on 26 May 2010 21:27 dagmargoodboat(a)yahoo.com wrote: > 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 Here's Walt's article: http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf Here's some data on leakage in electrolytics. I = K * C * V ; leakage current where I, C, and V are standard values. Here's some values for K: K = 0.002 ; low leakage electrolytic spec K = 0.02 ; typical electrolytic spec K = 1.89e-5 ; AVX Bestcap spec K = 3.86e-5 ; HiTeck supercap spec K = 5e-7 ; measured 1 Farad supercap K = 7e-7 ; measured supercap K = 8.5e-5 ; 470uf electrolytic caps measured by Win Supercaps can be two orders of magnitude better than the best electrolytic. Pity the working voltage is so low. Mike
From: Mike on 26 May 2010 21:42 dagmargoodboat(a)yahoo.com wrote: > 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. I was playing with that. Still quite fiddly. If you don't get the balance exactly right you end up with two attenuation plateaus. It would be difficult to tell when it is adjusted correctly and to keep it there. See the asc file for example. > For super massive attenuation of input noise and ripple, other > approaches are better. Any examples or links? > 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 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 -416 -432 -480 -432 WIRE -832 -416 -832 -432 WIRE -416 -416 -416 -432 WIRE -944 -400 -944 -432 WIRE -1088 -352 -1088 -432 WIRE -416 -336 -416 -352 WIRE -480 -320 -480 -432 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 -832 -224 -832 -256 WIRE -720 -224 -720 -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 -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 -416 -336 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 4.7 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 1000�f SYMBOL cap -432 -416 R0 SYMATTR InstName C2 SYMATTR Value 100�f 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 22:23 On Wed, 26 May 2010 18:06:20 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On May 26, 7:02�am, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodb...(a)yahoo.com >> wrote: >> >> >> >> >On May 26, 8:26�am, Winfield Hill �<Winfield_mem...(a)newsguy.com> >> >wrote: >> >> John Larkin wrote... >> >> ><snip> >> >> >> > How about an opamp powered from Vout, with a resistor from the opamp >> >> > output to ground? Let the opamp supply current fight the output >> >> > ripple. That's thermally stable, simple, high gain, and tunable. >> >> >> > (except I need regulation, too) >> >> >> �+15V >--+--------+--/\/\--+-----> Vout 14.8v >> >> � � � � �| � � � �| �4.7R �| >> >> � � � � �| � � � R3 � � � �| >> >> � � � � �| � � �2.7M � � � | >> >> � � � � �} � � � �| � � � _| >> >> � � � � �| � C1 � +------| �\ � � � >> >> � � � � �'---||---+ � � �| � >--+---, >> >> � � � � � � 10uF �| � ,--|__/ � | � | >> >> � � � � � � � � � | � | � �| � �| � | >> >> � � � � � � � � �R7 � '--- |----' �R4 >> >> � � � � � � � �TBD 27k � � | � � � 4.7R >> >> � � � � � � � � � | � � � �| � � � �| >> >> � � � � � � � � --+--------+--------+---- >> >> >> �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. >> >> >Both give line regulation, true. �John's problem seems to be that he >> >needs(?) load regulation too. >> >> If there's no voltage reference, there's no regulation. >> >> >> >> >> >> >The multi-pole BJT C-mult looks great for feather-weight and constant >> >loads. �If the ultra-clean part of the load is separable, I'd do that. >> >> >If John really needs low-dropout, 15mA, tight load regulation, and low >> >noise, my best shot so far is to bootstrap the op-amp's supplies on >> >the Gerber'd "filtered-reference feeding a R-R op-amp" thing he linked >> >to, to circumvent the op amp's CMRR / PSRR feeding thru. >> >> >Or, I guess, feed the op amp with a steady voltage, e.g., to make an >> >ultra-clean supply, start with an ultra-clean supply... >> >> >Or cascade a couple such op-amp stages, each feeding the next, each >> >stage improving PSRR by whatever it can muster. 50-60dB? �(I don't >> >really trust op amps to have low noise and amazing PSRRs and CMRRs >> >over frequency, but then I've not looked at all the latest and >> >greatest.) >> >> All I want is a SOT-23 LDO regulator with 1 nv/rthz noise, 140 dB PSRR >> to 1 MHz, and not made by Maxim. > >I have an interesting idea. How about a blue LED as the reference. >It >is a forward biased diode so it may be low noise. > >> >> John That sounds familiar. Its dynamic impedance (hence Johnson noise) is low. I recently did the math to compare shot noise (which a diode has) to the Johnson noise. If I did it right, the shot noise current dumped into the dynamic impedance is somewhat less than the Johnson noise, so the sum isn't a lot higher than the Johnson noise alone. I just used two diodes in series to make a low-noise -1.5 volt shunt-type supply. I could have used an LED, which would be cool - they light up! - but I didn't want any stray light inside our box. John
From: John Larkin on 26 May 2010 22:34
On Thu, 27 May 2010 01:27:03 GMT, Mike <spam(a)me.not> wrote: >dagmargoodboat(a)yahoo.com wrote: > > >> 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 > > Here's Walt's article: > > http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf > > Here's some data on leakage in electrolytics. > > I = K * C * V ; leakage current > > where I, C, and V are standard values. > > Here's some values for K: > > K = 0.002 ; low leakage electrolytic spec > K = 0.02 ; typical electrolytic spec > K = 1.89e-5 ; AVX Bestcap spec > K = 3.86e-5 ; HiTeck supercap spec > K = 5e-7 ; measured 1 Farad supercap > K = 7e-7 ; measured supercap > K = 8.5e-5 ; 470uf electrolytic caps measured by Win > > Supercaps can be two orders of magnitude better than the best > electrolytic. Pity the working voltage is so low. > > Mike The polymer aluminums are pretty spiffy. The 120 uF 16V one I'm using is 24 milliohms typ. And it's an affordable surface-mount thing. John |