C-multiplier again
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From: Mike on 26 May 2010 06:38 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > On Tue, 25 May 2010 21:48:13 GMT, Mike <spam(a)me.not> wrote: > >>> I did about the same, similar results. >>> >>> ftp://jjlarkin.lmi.net/C-multiplier.gif >> >>Phil mentioned many spice programs don't handle this very well. Using >>the data from his later post showed the results with LTspice are not >>usable. >> >>Mike > > The question is whether the Early voltage slope is realistic. I don't > know. I suppose I should breadboard some parts but... the Gerbers are > gone! > John You could do a quick test. Use the grounded base circuit you just posted, with the base lead soldered to copperclad. Apply appropriate bias and signal, and measure the result. I modeled the MPSA14. It took a 20MEG in parallel with 5nF, in series with 800pF in parallel with 100k. I then compared a single 2N4401 with the P. Hobbs model. The results with LTspice are completely unrealistic. The files are archived in 3CBA32DC.ZIP, posted to abse with the title "More E-F Ripple Filter Simulations". Mike
From: Winfield Hill on 26 May 2010 08:26 John Larkin wrote... > >On 23 May 2010 16:54:54 -0700, Winfield Hill ><Winfield_member(a)newsguy.com> wrote: > >>dagmargoodboat(a)yahoo.com wrote... >>> >>> This shunt filter only needs 200mV headroom: >>> >>> FIG. 2 >>> R1 >>>+15V >--+------------------/\/\/\--------+--> Vout 14.8v >>> | 5 | >>> | | >>> | .-------+------+--------+ >>> | | | | | >>> | | | R6 | >>> | | | 1k | >>> | R3 R5 | |<' Q3 >>> | 2.7M 10K +------| 2n3906 >>> | | | | |\ >>> | | | |/ Q2 | >>> | | +----| 2n3904 | >>> | | | |>. | >>> | C1 | |<' | | >>> '---||---+----| Q1 '--------+ >>> 10uF |\ 2n3906 | >>> | R4 >>> | 4.7R >>> | | >>> ------+----------------+---- >> >> Nice ASCII art. Is fig 2 from your feverish brain? >> >> I see your idea, invert the ripple and subtract it out. >> Good. To do that the cancellation amplifier needs to >> be biased class A, so it can work over the entire ripple >> range. It should continuously draw current from the >> supply through R1, and superimpose the inverted ripple >> signal on top of that. R4 can be trimmed to optimize. >> The new R7 should be sized to handle the p-p ripple. >> >> Then John's delicate C-multiplier filter can follower, >> with all the heavy lifting having been done. >> >> +15V >--+-----------------/\/\/\--------+--> Vout 14.8v >> | 5 | >> | | >> | .------+------+--------+ >> | | | | | >> | | | R6 | >> | | | 1k | >> | R3 R5 | |<' Q3 >> | 2.7M 10K +------| 2n4403 >> | | | | |\ >> | | | |/ Q2 | >> | C1 | +----| 2n3904 | >> '---||---+ | |>. | >> 10uF | |<' | | >> +----| Q1 '--------+ >> | |\ 2n3906 | >> R7 | R4 >> TBD 27k | 4.7R >> | | | >> --+------+---------------+---- > > > 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. -- Thanks, - Win
From: dagmargoodboat on 26 May 2010 09:56 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. 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.) -- Cheers, James Arthur
From: John Larkin on 26 May 2010 10:02 On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodboat(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
From: dagmargoodboat on 26 May 2010 10:30
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. -- Cheers, James Arthur |