On Wed, 26 May 2010 17:17:32 -0400, Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:>On Wed, 26 May 2010 13:53:55 -0700, John Larkin ><jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: > >>On Wed, 26 May 2010 13:03:33 -0700 (PDT), dagmargoodboat@yahoo.com >>wrote: >> >>>On May 26, 10:57�am, Mike <s...@me.not> wrote: >>>> Winfield Hill �<Winfield_mem...@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) The LM8261 is a great part. Pretty good RRIO opamp, 32 volts, 21 MHz, tons of current drive, stable into any capacitive load. John
C-multiplier again
Started by ●May 22, 2010
Reply by ●May 26, 20102010-05-26
Reply by ●May 26, 20102010-05-26
John Larkin wrote:> > On Wed, 26 May 2010 07:30:39 -0700 (PDT), dagmargoodboat@yahoo.com > wrote: > > >On May 26, 10:02 am, John Larkin wrote: > >> On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodb...@yahoo.com > >> wrote: > >> > >> > >> > >> >On May 26, 8:26�am, Winfield Hill <Winfield_mem...@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."I thought you preferred 'Mary'? :) -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
Reply by ●May 26, 20102010-05-26
On May 26, 7:02=A0am, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodb...@yahoo.com > wrote: > > > > >On May 26, 8:26=A0am, Winfield Hill =A0<Winfield_mem...@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) > > >> =A0+15V >--+--------+--/\/\--+-----> Vout 14.8v > >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A04.7R =A0| > >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 R3 =A0 =A0 =A0 =A0| > >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A02.7M =A0 =A0 =A0 | > >> =A0 =A0 =A0 =A0 =A0} =A0 =A0 =A0 =A0| =A0 =A0 =A0 _| > >> =A0 =A0 =A0 =A0 =A0| =A0 C1 =A0 +------| =A0\ =A0 =A0 =A0 > >> =A0 =A0 =A0 =A0 =A0'---||---+ =A0 =A0 =A0| =A0 >--+---, > >> =A0 =A0 =A0 =A0 =A0 =A0 10uF =A0| =A0 ,--|__/ =A0 | =A0 | > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 | =A0 =A0| =A0 =A0| =A0 | > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0R7 =A0 '--- |----' =A0R4 > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0TBD 27k =A0 =A0 | =A0 =A0 =A0 4.7R > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0=|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 --+--------+--------+---- > > >> =A0I see your idea, not bad. =A0It's a nice simplification of this, > >> =A0incorporating the current-sinking transistor into the opamp. > > >> =A0+15V >--+--------+--------+----/\/\--+-----> Vout 14.8v > >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0| =A0 =A04.7R =A0=|> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 R3 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 ==A0|> >> =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A02.7M =A0 =A0 =A0 | =A0 =A0 =A0 =A0 =A0=|> >> =A0 =A0 =A0 =A0 =A0} =A0 =A0 =A0 =A0| =A0 =A0 =A0 _| =A0 =A0 =A0 =A0 ==A0|> >> =A0 =A0 =A0 =A0 =A0| =A0 C1 =A0 +------| =A0\ =A0 =A0 =A0 |/ > >> =A0 =A0 =A0 =A0 =A0'---||---+ =A0 =A0 =A0| =A0 >------| > >> =A0 =A0 =A0 =A0 =A0 =A0 10uF =A0| =A0 ,--|__/ =A0 =A0 =A0 |\V > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 | =A0 =A0| =A0 =A0 =A0 =A0 ==A0|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0R7 =A0 '--- |----------+ > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 TBD =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 ==A0|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A027k =A0 =A0 =A0 | =A0 =A0 =A0 =A0 R=4> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0=4.7R> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0==A0|> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 --+--------+----------+---- > > >> =A0This scheme is DC regulating as well. =A0The class-A current > >> =A0is set by R3 and R7, so the dc voltage drop is fixed. > > >Both give line regulation, true. =A0John'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. =A0If 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? =A0(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
Reply by ●May 26, 20102010-05-26
John Larkin wrote:> On Wed, 26 May 2010 17:17:32 -0400, Spehro Pefhany > <speffSNIP@interlogDOTyou.knowwhat> wrote: > >> On Wed, 26 May 2010 13:53:55 -0700, John Larkin >> <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote: >> >>> On Wed, 26 May 2010 13:03:33 -0700 (PDT), dagmargoodboat@yahoo.com >>> wrote: >>> >>>> On May 26, 10:57 am, Mike <s...@me.not> wrote: >>>>> Winfield Hill <Winfield_mem...@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.
Reply by ●May 26, 20102010-05-26
dagmargoodboat@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 ArthurHere'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
Reply by ●May 26, 20102010-05-26
dagmargoodboat@yahoo.com wrote:> On May 24, 3:57 pm, David Eather <eat...@tpg.com.au> wrote: >> On 24/05/2010 12:11 PM, dagmargoodb...@yahoo.com wrote: >> >> >> >>> On May 23, 6:56 pm, David Eather<eat...@tpg.com.au> wrote: >>>> On 24/05/2010 8:45 AM, John Larkin wrote: >>>>> On Mon, 24 May 2010 08:28:03 +1000, David Eather<eat...@tpg.com.au> >>>>> wrote: >>>>>> On 24/05/2010 8:07 AM, John Larkin wrote: >>>>>>> On Sun, 23 May 2010 13:26:26 -0700 (PDT), dagmargoodb...@yahoo.com >>>>>>> wrote: >>>>>>>> On May 23, 11:29 am, John Larkin >>>>>>>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>>> On 23 May 2010 04:28:01 -0700, Winfield Hill >>>>>>>>> <Winfield_mem...@newsguy.com> wrote: >>>>>>>>>> John Larkin wrote... >>>>>>>>>>> I need a super-low noise power supply. I have a 15 volt switching >>>>>>>>>>> wall-wart input and want as close to 15 volts, regulated, as I can >>>>>>>>>>> get; 14 would be nice, 13.5 is OK. >>>>>>>>>>> The LDOs that I can find are all pretty noisy and have mediocre PSRR. >>>>>>>>>>> So I thought about using a Phil Hobbs-ian c-multiplier transistor, an >>>>>>>>>>> R-C lowpass and an emitter follower, with a slow opamp loop wrapped >>>>>>>>>>> around it for DC regulation. It looks fine on paper, simple loop to >>>>>>>>>>> stabilize, but I figured I may as well Spice it and be sure. >>>>>>>>>>> What I'm seeing is mediocre PSRR. Stripping out the opamp and such, I >>>>>>>>>>> have... ftp://jjlarkin.lmi.net/C-multiplier.gif >>>>>>>>>>> which has psrr of about 70 dB at low frequencies, improving as the >>>>>>>>>>> output cap finally kicks in at around 5 KHz. The transistor equivalent >>>>>>>>>>> seems to look like the expected dynamic Re of about 2 ohms, with a C-E >>>>>>>>>>> resistor of around 6.6K. Reducing Vb (and Vout) doesn't help much. >>>>>>>>>> You're complaining about a 70dB improvement? There is a simple >>>>>>>>>> way to use your 0.7 volts, well maybe 0.8 volts, to get even >>>>>>>>>> more rejection: change your simple NPN follower into a Sziklai >>>>>>>>>> connection (AoE page 95). The base resistor across the added >>>>>>>>>> PNP creates a relatively-fixed collector current for your NPN, >>>>>>>>>> which means a fixed Vbe, for improved AC ripple rejection. >>>>>>>>> Since the problem is the Early effect, namely the effective C-E >>>>>>>>> resistance bleeding ripple through, it didn't seem to me like the >>>>>>>>> Sziklai thing would help. The PNP doesn't insulate the NPN from the >>>>>>>>> ripple. So I spiced it. If the LT Spice transistor models are to be >>>>>>>>> trusted, it's actually worse. The optimum value for the PNP's b-e >>>>>>>>> resistor is zero. >>>>>>>>> John >>>>>>>> Win's idea looks pretty decent to me, IIUIC: >>>>>>>> FIG. 1 (View in fixed font) >>>>>>>> ====== >>>>>>>> Q1 >>>>>>>> 2n3906 >>>>>>>> Vin>--+----. .-------+---+------+--> +13.3v >>>>>>>> | V / | | | >>>>>>>> R1 ------ | R2 --- C1 >>>>>>>> 470 | Q2 | 1k --- 15uF >>>>>>>> | | 2n3904 | | | >>>>>>>> '------+---. / === === >>>>>>>> \ ^ >>>>>>>> ----- >>>>>>>> | >>>>>>>> R3 >>>>>>>> 33 >>>>>>>> | >>>>>>>> +14v>---' >>>>>>>> LT Spice says 31uV of the 50mV 1KHz ripple gets through (32dBv), >>>>>>>> and the load step is 340uV. That's a lot stiffer than the original, >>>>>>>> which >>>>>>>> had a 4.5mV load step (d(i) = 2mA for both). >>>>>>>> The Sziklai version has the same ripple; I don't quite understand >>>>>>>> how Early explains that--Early should wreck the load step response >>>>>>>> too, shouldn't it? >>>>>>>> FIG 1's load step is only 60uV if you replace R1 with a 5mA current >>>>>>>> source, >>>>>>>> the 1KHz ripple stays the same. >>>>>>>> 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 | >>>>>>>> R2 | R4 >>>>>>>> 5k | 4.7R >>>>>>>> | | | >>>>>>>> === === === >>>>>>>> LT Spice says 20dBV rejection @ 1KHz, zero @ d.c., natch. >>>>>>> Only 100 dB to go! But I don't understand Q1s biasing. >>>>>> Improved ripple response (but I think a little defective - it only works >>>>>> when Vin drops). >>>>>> When Vin drops Q1 turns on via base current drawn out through C1. Q1 >>>>>> robs base current from Q2 turning it off, which in turn turns off Q3 and >>>>>> reduces the current flow and hence voltage loss through R1. >>>>> So what's the quiescent current of Q1? Of Q3? >>>>> John >>>> R2 is missing - from the base of Q1 to GND - I suggest a value of 18k >>>> but it is a weird circuit I think a ripple reduction of no more than 46db >>> If by 46dB you mean power, i.e. 20log(Vin/Vout) = 46, yes, that's >>> easily possible--that implies 0.5% gain accuracy. >>> If you mean 46dBv, i.e. 10log(Vin/Vout) = 46, i.e. Vout / Vin = 25ppm, >>> no, that ain't happening, not unless you use op amps and some mighty >>> fine resistors. >> Um, I thought power was 10*log(what ever / what ever else) and voltage >> was 20*log(what ever / what ever else) e.g. a reduction in ripple of 46 >> db = a factor of 200, no? > > My description was crap--it was a question of notation. I'm not sure > of the dB convention as applied to these circuit--some R.F. work a > ways back ruined me. > > In R.F., 'dB' in our shop meant a ratio of powers unless otherwise > specified. So, if you said '40dB' I'd assume you meant a ratio of > 10,000 in power, or, equivalently--power being V^2/R--that you meant a > factor of merely 100, voltage. > > I vaguely recall, but I don't remember clearly, that we used to used > the symbol 'dBv' to designate when a ratio of voltages was being > reported. To convert that to power comparison, we'd have to multiply > those dB by 2. > > Anyway, the other posts have cleared it all up. Thanks. > > -- > Cheers, > James ArthurDecibels are always a power ratio. That formula with a 20 in it is a convenience for when you're measuring everything at the same impedance level, or when impedance isn't particularly relevant, e.g. at an op amp output. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 26, 20102010-05-26
dagmargoodboat@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 ArthurMike 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
Reply by ●May 26, 20102010-05-26
On Wed, 26 May 2010 18:06:20 -0700 (PDT), MooseFET <kensmith@rahul.net> wrote:>On May 26, 7:02�am, John Larkin ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodb...@yahoo.com >> wrote: >> >> >> >> >On May 26, 8:26�am, Winfield Hill �<Winfield_mem...@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. > >> >> JohnThat 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
Reply by ●May 26, 20102010-05-26
Mike <spam@me.not> wrote:> dagmargoodboat@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.The included asc file might be interesting. Part of the problem is the gain depends on the bjt Re, which changes with current, temperature, device, and phase of the moon. If the bjt is replaced by a MOSFET, the gain appears to be much better controlled. Indeed, the correct source resistance for perfect match is now the same value as the VCC series resistor. So this approach might be ideal when two matched resistors in the same case are used. 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 -640 -272 -688 -272 WIRE -624 -272 -640 -272 WIRE -1088 -256 -1088 -272 WIRE -832 -256 -832 -304 WIRE -800 -256 -832 -256 WIRE -752 -256 -800 -256 WIRE -624 -240 -624 -272 WIRE -528 -240 -624 -240 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 -640 -272 U1O FLAG -416 -336 0 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 22k SYMBOL cap -960 -400 R0 SYMATTR InstName C1 SYMATTR Value 1000�f SYMBOL nmos -528 -320 R0 SYMATTR InstName M1 SYMATTR Value IRF530 SYMBOL cap -432 -416 R0 SYMATTR InstName C2 SYMATTR Value 1000�f TEXT -888 -528 Left 0 ;'Op Amp MOSFET Ripple Cancellation TEXT -832 -488 Left 0 !.ac oct 100 0.1 4e6
Reply by ●May 26, 20102010-05-26
John Larkin wrote:> On Wed, 26 May 2010 18:06:20 -0700 (PDT), MooseFET > <kensmith@rahul.net> wrote: > >> On May 26, 7:02 am, John Larkin >> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >>> On Wed, 26 May 2010 06:56:18 -0700 (PDT), dagmargoodb...@yahoo.com >>> wrote: >>> >>> >>> >>>> On May 26, 8:26 am, Winfield Hill <Winfield_mem...@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 > >If the diode obeys the diode equation (i.e. low level injection assumed) the noise is exactly half what you'd calculate from applying the Johnson noise formula to the differential resistance. IOW, the junction has a noise temperature of T_J/2. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
