C-multiplier again
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From: Mike on 28 May 2010 04:55 John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > On Fri, 28 May 2010 02:11:32 GMT, Mike <spam(a)me.not> wrote: [...] > That opamp has back-to-back diodes across its inputs and no > current limiting resistors. The problem is too much current from > charging those big caps. So you now agree that a 49.9 ohm resistor is not enough to prevent damage, as I have claimed from the beginning. >> Zero volts across them. Zero current. Probably high capacitance, >> maybe 1nF. In parallel with large electrolytics. What's to add >> noise? > Leakage resistance maybe, and capacitance adding a pole to the > feedback loop. I did say "probably." There are large electrolytics at both inputs. These would swamp any extra capacitance from the diodes. There are 10k and 1k resistors at the inputs. These resistors, plus the electrolytics, would swamp any noise from diode leakage. Since I may need to use a similar approach, I modeled this circuit in LTspice and uploaded the archive 3CBC2208.ZIP to abse. The Transient Analysis is shown in 3CBBA0E7.ASC. I modeled the AD797 as a single pole op amp with Avol=15Meg, GBW=110Meg, Slew=110Meg. I added RX=7.5K across the input pins to match the AD797 datasheet, and also added CX=1nF across the input pins to account for any stray capacitance from the schottky diodes. I evaluated the response with CX and RX both included and excluded in the feedback from the pertubation source V2. As shown in the Transient Analysis, there is considerable ringing at the output of the op amp after a step change at the input. This appears to be caused by driving the large electrolytic cap C5 at the output. Reducing the value of C5 causes the ringing to increase. Increasing the value causes the slew rate limiting to increase. Changing the value of CX from 1pF to 10nF has little or no effect on the response. Changing the value of the series input resistor, R3, from 2 ohms to 49.9 ohms has little or no effect on the response. Thus any extra capacitance from adding schottky protection diodes at the input will not change the loop characteristics. The Open Loop Gain is shown in 3CBC2036.ASC. The response chages considerably depending on how CX and RX are located at the input. However, in either case, the value of CX either has no effect on the open loop response, or improves it. >> Little ones may be fine. The 11DQ05 will take 150 Amp surge, so >> all it needs is a high enough value resistor in series to keep >> the voltage drop under the AD797 spec: >>http://www.datasheetcatalog.org/datasheet/irf/11dq05.pdf > Might work. 100 pF, maybe more, at 0 volts. That was just a quick pass in google. There are probably much better choices. > John Mike
From: Mike on 28 May 2010 06:03 George Herold <gherold(a)teachspin.com> wrote: [...] > Well that figures, It's my first attempt to post a ltspice circuit. > > Not much to it. a two pole low pass RC filter (R-C to ground. feeds R- > C to ground) and this feeds the base of a npn. the output has a > minimum 1 k ohm to ground with anoter C. R is 1k and C is 100uF Al > electro. There's also 10 ohms between the final R-C cap node and the > base, but this is only to stop oscilations and doesn't change the > spice sim much. I'm going to play hookey (sp) from work tomorrow and > get the homestead ready for our annual Memorial Day party. (Else I'd > try and repost) Summer's here early in Buf. NY. If you're in the > area I grill up some great Polish sausage with Walt's mustard. (Walt > lives down the road.) > > George H. Thanks. When you get some time, I'd like to see your circuit. I do love Polish sausage, but I'm up in Ontario near the Great Lakes. A bit too far for a weekend trip. If I still had my plane it would be trivial. But I gave that up after an engine failure at 25,000 ft at midnight over the Sierras. After my copilot declared an emergency, she amended her message to ATC with the words, "And We Only Have One Engine!" Walt who? There has to be some reason you would mention this name. Can I guess? I hope it's who I think. If so, please tell him I think he is one of the finest engineers I have had the pleasure to study. And decades later, his papers are still among the most valuable on the web. Thanks, Mike
From: John Larkin on 28 May 2010 10:01 On Thu, 27 May 2010 22:04:34 -0700 (PDT), whit3rd <whit3rd(a)gmail.com> wrote: > >> >I have an interesting idea. �How about a blue LED as the reference. > >> 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. > >GAAA! If you want low noise from AN OPTICALLY OPEN DIODE >you need to shield from light. Incandescent will cause 120 Hz >input, fluorescent 60 Hz and 120 Hz, electronic ballasts and >CCFL can go from kilohertz to megahertz. GAAA? I said I didn't do it. > >Use a 1.25V bandgap reference like real folk do. Bandgaps are really noisy. The amplify the small difference between two junction drops. That's a lot noisier than the unamplified drop of two junctions in series. John
From: George Herold on 28 May 2010 10:09 On May 28, 6:03 am, Mike <s...(a)me.not> wrote: > George Herold <gher...(a)teachspin.com> wrote: > > [...] > > > Well that figures, It's my first attempt to post a ltspice circuit. > > > Not much to it. a two pole low pass RC filter (R-C to ground. feeds R- > > C to ground) and this feeds the base of a npn. the output has a > > minimum 1 k ohm to ground with anoter C. R is 1k and C is 100uF Al > > electro. There's also 10 ohms between the final R-C cap node and the > > base, but this is only to stop oscilations and doesn't change the > > spice sim much. I'm going to play hookey (sp) from work tomorrow and > > get the homestead ready for our annual Memorial Day party. (Else I'd > > try and repost) Summer's here early in Buf. NY. If you're in the > > area I grill up some great Polish sausage with Walt's mustard. (Walt > > lives down the road.) > > > George H. > > Thanks. When you get some time, I'd like to see your circuit. > > I do love Polish sausage, but I'm up in Ontario near the Great Lakes. A > bit too far for a weekend trip. If I still had my plane it would be > trivial. But I gave that up after an engine failure at 25,000 ft at > midnight over the Sierras. After my copilot declared an emergency, she > amended her message to ATC with the words, "And We Only Have One Engine!" > > Walt who? There has to be some reason you would mention this name. Can I > guess? I hope it's who I think. If so, please tell him I think he is one > of the finest engineers I have had the pleasure to study. And decades > later, his papers are still among the most valuable on the web. > > Thanks, > > Mike Hi Mike, I realized this morning I can just reproduce it a home.... silly me. I live about 30 miles SE of Buffalo NY. (not too far from some parts of Ontario... ) Walt is my neighbor. An older famer, he makes a nice mustard that is just part of our party tradition. You can also get his mustard on sandwiches from the 'hole in the wall' deli/ store at the bottom of our road. Any way I'll try again posting the circuit. (This is far from my circit, I found it first in Phil Hobbs' book.) If it doesn't work this time I can always try again. Oh I also stick a ferrite bead on the base lead of the transistor. This doesn't do much either.. part of trying to stop oscillations. George H. Version 4 SHEET 1 1140 1108 WIRE -688 -448 -768 -448 WIRE -560 -448 -608 -448 WIRE -160 -448 -560 -448 WIRE -128 -448 -160 -448 WIRE -128 -400 -128 -448 WIRE -560 -352 -560 -368 WIRE -560 -352 -624 -352 WIRE -496 -352 -560 -352 WIRE -384 -352 -416 -352 WIRE -304 -352 -384 -352 WIRE -272 -352 -304 -352 WIRE -768 -320 -768 -448 WIRE -624 -320 -624 -352 WIRE -560 -320 -560 -352 WIRE -384 -320 -384 -352 WIRE -304 -320 -304 -352 WIRE -128 -288 -128 -304 WIRE -48 -288 -128 -288 WIRE 16 -288 -48 -288 WIRE -128 -256 -128 -288 WIRE -48 -256 -48 -288 WIRE -768 -224 -768 -240 WIRE -624 -224 -624 -256 WIRE -560 -224 -560 -256 WIRE -560 -224 -624 -224 WIRE -528 -224 -560 -224 WIRE -384 -224 -384 -256 WIRE -384 -224 -528 -224 WIRE -304 -224 -304 -256 WIRE -304 -224 -384 -224 WIRE -528 -208 -528 -224 WIRE -128 -160 -128 -176 WIRE -48 -160 -48 -192 FLAG -528 -208 0 FLAG -768 -224 0 FLAG -128 -160 0 FLAG -160 -448 Vin FLAG 16 -288 Vout FLAG -48 -160 0 SYMBOL npn -192 -400 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL voltage -768 -336 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL voltage -592 -448 R90 WINDOW 0 49 39 VRight 0 WINDOW 123 -48 40 VRight 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value2 AC 1 SYMATTR Value "" SYMBOL res -576 -464 R0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res -400 -368 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 42 49 VTop 0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res -176 -368 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 10 SYMBOL polcap -576 -320 R0 WINDOW 3 24 64 Left 0 SYMATTR InstName C1 SYMATTR Value 100µ SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=50 Irms=600m Rser=0.13 Lser=0 mfg="Nichicon" pn="UPH1H101MRH" type="Al electrolytic" SYMBOL polcap -400 -320 R0 WINDOW 3 24 64 Left 0 SYMATTR InstName C2 SYMATTR Value 100µ SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=50 Irms=600m Rser=0.13 Lser=0 mfg="Nichicon" pn="UPH1H101MRH" type="Al electrolytic" SYMBOL polcap -64 -256 R0 WINDOW 3 24 64 Left 0 SYMATTR InstName C3 SYMATTR Value 100µ SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=50 Irms=600m Rser=0.13 Lser=0 mfg="Nichicon" pn="UPH1H101MRH" type="Al electrolytic" SYMBOL res -144 -272 R0 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL cap -640 -320 R0 SYMATTR InstName C4 SYMATTR Value 1µ SYMATTR SpiceLine V=25 Irms=7.25 Rser=0.004 Lser=0 mfg="KEMET" pn="C1206C105K3PAC" type="X5R" SYMBOL cap -320 -320 R0 SYMATTR InstName C5 SYMATTR Value 1µ SYMATTR SpiceLine V=25 Irms=7.25 Rser=0.004 Lser=0 mfg="KEMET" pn="C1206C105K3PAC" type="X5R" TEXT -216 -536 Left 0 ;Cap multiplier (Hobbs fillter) TEXT -224 -504 Left 0 !.ac oct 100 1 1e7
From: George Herold on 28 May 2010 10:13
On May 28, 10:09 am, George Herold <gher...(a)teachspin.com> wrote: > On May 28, 6:03 am, Mike <s...(a)me.not> wrote: > > > > > > > George Herold <gher...(a)teachspin.com> wrote: > > > [...] > > > > Well that figures, It's my first attempt to post a ltspice circuit. > > > > Not much to it. a two pole low pass RC filter (R-C to ground. feeds R- > > > C to ground) and this feeds the base of a npn. the output has a > > > minimum 1 k ohm to ground with anoter C. R is 1k and C is 100uF Al > > > electro. There's also 10 ohms between the final R-C cap node and the > > > base, but this is only to stop oscilations and doesn't change the > > > spice sim much. I'm going to play hookey (sp) from work tomorrow and > > > get the homestead ready for our annual Memorial Day party. (Else I'd > > > try and repost) Summer's here early in Buf. NY. If you're in the > > > area I grill up some great Polish sausage with Walt's mustard. (Walt > > > lives down the road.) > > > > George H. > > > Thanks. When you get some time, I'd like to see your circuit. > > > I do love Polish sausage, but I'm up in Ontario near the Great Lakes. A > > bit too far for a weekend trip. If I still had my plane it would be > > trivial. But I gave that up after an engine failure at 25,000 ft at > > midnight over the Sierras. After my copilot declared an emergency, she > > amended her message to ATC with the words, "And We Only Have One Engine!" > > > Walt who? There has to be some reason you would mention this name. Can I > > guess? I hope it's who I think. If so, please tell him I think he is one > > of the finest engineers I have had the pleasure to study. And decades > > later, his papers are still among the most valuable on the web. > > > Thanks, > > > Mike > > Hi Mike, I realized this morning I can just reproduce it a home.... > silly me. > > I live about 30 miles SE of Buffalo NY. (not too far from some parts > of Ontario... ) > Walt is my neighbor. An older famer, he makes a nice mustard that is > just part of our party tradition. You can also get his mustard on > sandwiches from the 'hole in the wall' deli/ store at the bottom of > our road. > > Any way I'll try again posting the circuit. (This is far from my > circit, I found it first in Phil Hobbs' book.) > If it doesn't work this time I can always try again. Oh I also stick > a ferrite bead on the base lead of the transistor. This doesn't do > much either.. part of trying to stop oscillations. > > George H. > > Version 4 > SHEET 1 1140 1108 > WIRE -688 -448 -768 -448 > WIRE -560 -448 -608 -448 > WIRE -160 -448 -560 -448 > WIRE -128 -448 -160 -448 > WIRE -128 -400 -128 -448 > WIRE -560 -352 -560 -368 > WIRE -560 -352 -624 -352 > WIRE -496 -352 -560 -352 > WIRE -384 -352 -416 -352 > WIRE -304 -352 -384 -352 > WIRE -272 -352 -304 -352 > WIRE -768 -320 -768 -448 > WIRE -624 -320 -624 -352 > WIRE -560 -320 -560 -352 > WIRE -384 -320 -384 -352 > WIRE -304 -320 -304 -352 > WIRE -128 -288 -128 -304 > WIRE -48 -288 -128 -288 > WIRE 16 -288 -48 -288 > WIRE -128 -256 -128 -288 > WIRE -48 -256 -48 -288 > WIRE -768 -224 -768 -240 > WIRE -624 -224 -624 -256 > WIRE -560 -224 -560 -256 > WIRE -560 -224 -624 -224 > WIRE -528 -224 -560 -224 > WIRE -384 -224 -384 -256 > WIRE -384 -224 -528 -224 > WIRE -304 -224 -304 -256 > WIRE -304 -224 -384 -224 > WIRE -528 -208 -528 -224 > WIRE -128 -160 -128 -176 > WIRE -48 -160 -48 -192 > FLAG -528 -208 0 > FLAG -768 -224 0 > FLAG -128 -160 0 > FLAG -160 -448 Vin > FLAG 16 -288 Vout > FLAG -48 -160 0 > SYMBOL npn -192 -400 R0 > SYMATTR InstName Q1 > SYMATTR Value 2N4401 > SYMBOL voltage -768 -336 R0 > WINDOW 123 0 0 Left 0 > WINDOW 39 0 0 Left 0 > SYMATTR InstName V1 > SYMATTR Value 15 > SYMBOL voltage -592 -448 R90 > WINDOW 0 49 39 VRight 0 > WINDOW 123 -48 40 VRight 0 > WINDOW 39 0 0 Left 0 > SYMATTR InstName V3 > SYMATTR Value2 AC 1 > SYMATTR Value "" > SYMBOL res -576 -464 R0 > SYMATTR InstName R1 > SYMATTR Value 1k > SYMBOL res -400 -368 R90 > WINDOW 0 0 56 VBottom 0 > WINDOW 3 42 49 VTop 0 > SYMATTR InstName R2 > SYMATTR Value 1k > SYMBOL res -176 -368 R90 > WINDOW 0 0 56 VBottom 0 > WINDOW 3 32 56 VTop 0 > SYMATTR InstName R3 > SYMATTR Value 10 > SYMBOL polcap -576 -320 R0 > WINDOW 3 24 64 Left 0 > SYMATTR InstName C1 > SYMATTR Value 100µ > SYMATTR Description Capacitor > SYMATTR Type cap > SYMATTR SpiceLine V=50 Irms=600m Rser=0.13 Lser=0 mfg="Nichicon" > pn="UPH1H101MRH" type="Al electrolytic" > SYMBOL polcap -400 -320 R0 > WINDOW 3 24 64 Left 0 > SYMATTR InstName C2 > SYMATTR Value 100µ > SYMATTR Description Capacitor > SYMATTR Type cap > SYMATTR SpiceLine V=50 Irms=600m Rser=0.13 Lser=0 mfg="Nichicon" > pn="UPH1H101MRH" type="Al electrolytic" > SYMBOL polcap -64 -256 R0 > WINDOW 3 24 64 Left 0 > SYMATTR InstName C3 > SYMATTR Value 100µ > SYMATTR Description Capacitor > SYMATTR Type cap > SYMATTR SpiceLine V=50 Irms=600m Rser=0.13 Lser=0 mfg="Nichicon" > pn="UPH1H101MRH" type="Al electrolytic" > SYMBOL res -144 -272 R0 > SYMATTR InstName R4 > SYMATTR Value 1k > SYMBOL cap -640 -320 R0 > SYMATTR InstName C4 > SYMATTR Value 1µ > SYMATTR SpiceLine V=25 Irms=7.25 Rser=0.004 Lser=0 mfg="KEMET" > pn="C1206C105K3PAC" type="X5R" > SYMBOL cap -320 -320 R0 > SYMATTR InstName C5 > SYMATTR Value 1µ > SYMATTR SpiceLine V=25 Irms=7.25 Rser=0.004 Lser=0 mfg="KEMET" > pn="C1206C105K3PAC" type="X5R" > TEXT -216 -536 Left 0 ;Cap multiplier (Hobbs fillter) > TEXT -224 -504 Left 0 !.ac oct 100 1 1e7- Hide quoted text - > > - Show quoted text - That seemed to work OK, I got some error messages about the cap names, but I clikced on ignore and it loaded. George H |