c-multiplier, real life
in [Design]
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From: ehsjr on 3 Jun 2010 22:19 John Larkin wrote: > I think I did all this right... I'm not so sure. Looks like you took input vs output measurements. It may be more informative in terms of characterizing the filter circuit performance to take unfiltered output versus filtered output measurements, at the load. function gen====>load function gen====>circuit===>load Ed > > ftp://jjlarkin.lmi.net/C-mult_bb.JPG > > ftp://jjlarkin.lmi.net/C-mult_BCX70.JPG > > > John >
From: Jan Panteltje on 4 Jun 2010 05:10 On a sunny day (Thu, 03 Jun 2010 18:37:42 -0400) it happened Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in <S4WNn.36246$rU6.2337(a)newsfe10.iad>: >Jan Panteltje wrote: > >> On a sunny day (Wed, 02 Jun 2010 17:02:45 -0700) it happened John Larkin >> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >> <tjrd06hpdgiafmof0hq05devdqebcecd06(a)4ax.com>: >> >> >>>I think I did all this right... >>> >>>ftp://jjlarkin.lmi.net/C-mult_bb.JPG >>> >>>ftp://jjlarkin.lmi.net/C-mult_BCX70.JPG >>> >>> >>>John >>> >> >> >> LM317 has > 60 Db ripple rejection? >> Why bother with all this? >> >Head room ? Yes head room is better with an emittor follower, but I think he had free choice of input voltage (a wallwart). >
From: John Larkin on 4 Jun 2010 11:11 On Fri, 04 Jun 2010 09:10:03 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Thu, 03 Jun 2010 18:37:42 -0400) it happened Jamie ><jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in ><S4WNn.36246$rU6.2337(a)newsfe10.iad>: > >>Jan Panteltje wrote: >> >>> On a sunny day (Wed, 02 Jun 2010 17:02:45 -0700) it happened John Larkin >>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>> <tjrd06hpdgiafmof0hq05devdqebcecd06(a)4ax.com>: >>> >>> >>>>I think I did all this right... >>>> >>>>ftp://jjlarkin.lmi.net/C-mult_bb.JPG >>>> >>>>ftp://jjlarkin.lmi.net/C-mult_BCX70.JPG >>>> >>>> >>>>John >>>> >>> >>> >>> LM317 has > 60 Db ripple rejection? >>> Why bother with all this? >>> >>Head room ? > >Yes head room is better with an emittor follower, >but I think he had free choice of input voltage (a wallwart). > I'm using a 15-volt wart that we stock, and going to a 24-volt one would push up the dissipation on other regulators. So I want a super-low-noise, low-power LDO. This is what I did: ftp://jjlarkin.lmi.net/P14_reg.gif which is maybe not too bad. The opamp has PSRR rejection better than the Early feedthrough of an NPN, and the 15 ohm resistor makes a lower corner with the output caps than would 2 ohms of Re. And it regulates and current limits. A 2-stage c-mult might be better in other situations, or maybe an LDO followed by one c-mult. John
From: Winfield Hill on 4 Jun 2010 12:35 John Larkin wrote... > > I think I did all this right... > ftp://jjlarkin.lmi.net/C-mult_bb.JPG > ftp://jjlarkin.lmi.net/C-mult_BCX70.JPG OK, let's explore this a bit. Here's an ASCII drawing of a simplified version of your circuit: .. ,------------ c e ----+--- amp + scope .. | b | .. Vac | 1k0 .. | 33R | .. Vc | gnd .. | Vb .. gnd | .. gnd I ignored 2k base resistance that's isolated behind a BFC. And here's your test data, which is all with Vc = 10 Vdc and Vac = 200 mVpp. Vbe = 0.65 V. Vb Ve p-p dB spice --- ------ ---- ----- +5 98uV -66 53.3uV +8 144 -63 54.4 +9 170 -61 55.5 +9.9 2800 -37 56.1 +10.25 56.3 +10.5 138 This data looks very suspect to me. You observe the emitter follower failing its job when it still has Vce = 0.75 volts, which makes no sense to me, unless perhaps your Vac voltage is really much higher than you thought it was. I ran a spice model of the above circuit. Intusoft's BCX70 library has the BCX70's Early voltage VAF = 120 volts, which seemed a bit conservative to me, but OK. We calculate mu = VT/VA = 2.1 x 10^-4. For 200mV on the collector, that's 42uV of Early effect at the base, and arguably the same at the emitter. Nonetheless, the spice engine reports 53 to 56uV, which I'm happy to accept. But it's much less than you report. The spice model also has the BJT continuing to function well until Vce is under 200mV, which it should do. I'll say this, narrow base-width high-beta transistors have a much worse VA than ordinary parts. I see you reported beta = 670, maybe that's an issue here. My spice part was a BCX70G, with BF = 234. NXP's BCX70 datasheet says the 70G parts have beta from 120 to 220, and K parts from 380 to 630. My spice library has a BCX70J with BF = 400 and VAF = 80 volts. Maybe that's what's going on here. Super-beta parts need not apply. -- Thanks, - Win
From: Grant on 4 Jun 2010 16:46
On Fri, 04 Jun 2010 08:11:34 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Fri, 04 Jun 2010 09:10:03 GMT, Jan Panteltje ><pNaonStpealmtje(a)yahoo.com> wrote: > >>On a sunny day (Thu, 03 Jun 2010 18:37:42 -0400) it happened Jamie >><jamie_ka1lpa_not_valid_after_ka1lpa_(a)charter.net> wrote in >><S4WNn.36246$rU6.2337(a)newsfe10.iad>: >> >>>Jan Panteltje wrote: >>> >>>> On a sunny day (Wed, 02 Jun 2010 17:02:45 -0700) it happened John Larkin >>>> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in >>>> <tjrd06hpdgiafmof0hq05devdqebcecd06(a)4ax.com>: >>>> >>>> >>>>>I think I did all this right... >>>>> >>>>>ftp://jjlarkin.lmi.net/C-mult_bb.JPG >>>>> >>>>>ftp://jjlarkin.lmi.net/C-mult_BCX70.JPG >>>>> >>>>> >>>>>John >>>>> >>>> >>>> >>>> LM317 has > 60 Db ripple rejection? >>>> Why bother with all this? >>>> >>>Head room ? >> >>Yes head room is better with an emittor follower, >>but I think he had free choice of input voltage (a wallwart). >> > >I'm using a 15-volt wart that we stock, and going to a 24-volt one >would push up the dissipation on other regulators. So I want a >super-low-noise, low-power LDO. > >This is what I did: > >ftp://jjlarkin.lmi.net/P14_reg.gif > >which is maybe not too bad. The opamp has PSRR rejection better than >the Early feedthrough of an NPN, and the 15 ohm resistor makes a lower >corner with the output caps than would 2 ohms of Re. And it regulates >and current limits. > >A 2-stage c-mult might be better in other situations, or maybe an LDO >followed by one c-mult. My eyes would burn, trying to work with that colour set ;) Especially the black background, the stuff would be floating, drifting in space for me after a while. Grant. -- http://bugs.id.au/ |