Hi guys (which includes women in my vernacular)
I've got what looks like another two feedback loop thingie. (It's simpler so maybe I can get a result.)
I use this as a low noise voltage source.
Vin-+------------------+ | | +Vref-+ | p |\ | o~Rb-| | +|-/ |> GND ||/ | +---+-R-+--+---+--\ ^---out/load. | +-C-+ R | --- R/4 idle +Rf-+ | | | GND---------+ Cf +-------+
Rb~500, R = 10k, C = 10-100nF, Ridle-10k, Rf = 500, Cf = 100uF(Al)
It's a voltage reference/ opamp/ pass element/ filter.
There's some RC filtering between pot and opamp that is not shown.
So this has some problems. It's got an output impedance of Rf/beta several ohms, and the temperature variations in the uncontrolled cap mult. output filter. So I tried taking the RC feedback from the output. Putting the cap mult in the loop. Worked, but lots more noise at low frequency. (broad peak at ~2kHz.) The now uncontrolled node between pass transistor emitter and cap mult collector/base now had about the same broad
2 kHz. noise peak. So If I could split up the feed back task so everything slower than (say) 100ms was from the output, with the faster stuff via the pass element.... that might be nice.So as I add HF feedback from the pass element node, I've got to subtract it from the DC path. Is that right? (sorry, just thinking out loud at the SED.)
George H.