C-multiplier again
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From: MooseFET on 27 May 2010 09:19 On May 27, 3:02 am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Wed, 26 May 2010 19:23:49 -0700) it happened John Larkin > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in > <iilrv5l0t83k7mkmv4hdbr0105hd5o0...(a)4ax.com>: > > >I could have used an LED, which would be cool - > >they light up! - but I didn't want any stray light inside our box. > > Stick it outside then :-) > http://panteltje.com/panteltje/mvp/mpv-0.2-pcb.jpg > > Here used as power indicator, and 1.5V reference (old LED). You don't want light hitting your "low noise reference diode" I suggested a blue LED under the assumption that the higher forward voltage would make the "SNR" better by making the "signal" bigger. Since then, I have had a reason to rethink that. I think that the impedance of the so called "super bright" RED is lower than that of the BLUE. BTW: There is no such thing as a superbright LED. LEDs come in 3 brightness classes: (1) Are you sure this is on (2) Way to dim (3) I guess this will do I use LEDs in full sunlight.
From: MooseFET on 27 May 2010 09:22 On May 26, 7:34 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 27 May 2010 01:27:03 GMT, Mike <s...(a)me.not> wrote: > >dagmargoodb...(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. Is the leakage current in them very noisy? I have always assumed that the noise current part of the leakage current was equal to the shot noise of a semiconductor device. If it is like a resistor, the noise would be less. > > John
From: MooseFET on 27 May 2010 09:37 On May 26, 6:27 pm, Mike <s...(a)me.not> wrote: [....] > http://waltjung.org/PDFs/Build_Ultra_Low_Noise_Voltage_Reference.pdf I have a slightly improved version: !\U1 Ref ------[R]--+------------! >-----+- Low noise version ! !/ ! ! ! C1[C] ---[R]---+---[R]-+ ! ! ! ! ! ! /-!-- [R] ---+--< ! ! \+!----------+ U2 ! [C]C2 ! GND The time constant at C2 can be huge because the leakage of C2 doesn't cause your reference to be low. The gain of U2 makes C1 look larger than it is. The circuit is second order so it does have a noise peak at the corner but that can be at a very low frequency. The resistors on U2 are low value ones because they add directly to the noise.
From: John Larkin on 27 May 2010 09:56 On Thu, 27 May 2010 10:02:58 GMT, Jan Panteltje <pNaonStpealmtje(a)yahoo.com> wrote: >On a sunny day (Wed, 26 May 2010 19:23:49 -0700) it happened John Larkin ><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in ><iilrv5l0t83k7mkmv4hdbr0105hd5o0974(a)4ax.com>: > >>I could have used an LED, which would be cool - >>they light up! - but I didn't want any stray light inside our box. > >Stick it outside then :-) > http://panteltje.com/panteltje/mvp/mpv-0.2-pcb.jpg > >Here used as power indicator, and 1.5V reference (old LED). > Beatcha to it. My green power LED is already the +2 reference for some opamps used as TTL-input level shifters. John
From: John Larkin on 27 May 2010 10:00
On Thu, 27 May 2010 06:19:51 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote: >On May 27, 3:02�am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: >> On a sunny day (Wed, 26 May 2010 19:23:49 -0700) it happened John Larkin >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote in >> <iilrv5l0t83k7mkmv4hdbr0105hd5o0...(a)4ax.com>: >> >> >I could have used an LED, which would be cool - >> >they light up! - but I didn't want any stray light inside our box. >> >> Stick it outside then :-) >> �http://panteltje.com/panteltje/mvp/mpv-0.2-pcb.jpg >> >> Here used as power indicator, and 1.5V reference (old LED). > >You don't want light hitting your "low noise reference diode" > >I suggested a blue LED under the assumption that the higher >forward voltage would make the "SNR" better by making the >"signal" bigger. Since then, I have had a reason to rethink >that. I think that the impedance of the so called "super >bright" RED is lower than that of the BLUE. > >BTW: There is no such thing as a superbright LED. LEDs come >in 3 brightness classes: >(1) Are you sure this is on >(2) Way to dim >(3) I guess this will do > >I use LEDs in full sunlight. I have a friend who manages the LED lighting division for a big electrical products company... you buy their stuff at Home Depot. He snuck me a developmental white LED that, at 14 volts and 0.7 amps, looks like a welding arc. It will literally blind you for a minute if you look straight at it. Their initial target market is street lights. John |