C-multiplier again
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From: George Herold on 26 May 2010 10:59 On May 26, 10:02 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. > > John- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text - If Maxim made such a beast I'd buy it.... Buy a boat load and be done with it. George H.
From: John Larkin on 26 May 2010 11:17 On Wed, 26 May 2010 07:30:39 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >On May 26, 10:02�am, John Larkin 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 +15v is the reference. So, maybe more accurately, these circuits >don't regulate, but they preserve the +15v input's line regulation. >rOut = 5 ohms, load regulation = zip. > > >> >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. > >Heathen. If you don't mind, I prefer "barbarian." John
From: Fred Bartoli on 26 May 2010 11:43 John Larkin a �crit : > On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodboat(a)yahoo.com > wrote: > .... > 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. > And a gmail account? -- Thanks, Fred.
From: Mike on 26 May 2010 11:57 Winfield Hill <Winfield_member(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 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 -832 -416 -832 -432 WIRE -944 -400 -944 -432 WIRE -1088 -352 -1088 -432 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 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 1200) 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 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 12:07
On Wed, 26 May 2010 15:57:09 GMT, Mike <spam(a)me.not> wrote: >Winfield Hill <Winfield_member(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. John |