Floating simulated inductor idea

I'm not sure, (what's the middle resistor value) photo transistors are slow.

George H.

Depends on the phototransistors you want to drive, it sets how much current is put thru the LEDs at the times that pushing or pulling current is what the floating inductor needs to be doing.

For a phototransistor like the dumpy 4N28 about 1/10th the DC load impedance for that R seems to work OK, the simulated inductance is then approximately (R^2*C)/2

This is simulating a ~5mH inductor into a 1k load @ 100kHz 3V p2p input, off +/- 5 volt supplies, using the LTC1253 "Low Cost Dual Video Amplifier" (I guess $5 is low cost these days, can barely get a decent hamburger for that) with 4N28 optos, I think it looks pretty nice!

Using better optos would help, the current waveforms into the LEDs and into and out of the transistors on the output side are wild, as the feedback yanks them all over the place

OK that looks nice. I'll a little to lazy (or slow) to figure out how that works. Does the step response look right?

George H.

Square wave action:

The way it works is, basically with the op amp integrators connected up as shown impress a voltage on the bridged resistor that produces a current waveform which resembles the input current waveform you'd get if you fed an inductor with say a square wave.

That's not particularly useful in itself but the only place that current can come from or go to is the supply rails, so the photo-transistors in line connected appropriately mirror that current to the ports so they behave the same way too. DC feedback linearizes it and gives it unity gain at 0 Hz

Huh? The optos are not providing isolation, can't you just use regular BJTs? PNP at the top and NPN at the bottom.

Sure, I don't see why four current mirrors wouldn't work, it's 8 more transistors tho, and with fast optos I think totem-pole drive will perform better

I meant 1:1 replacement. swap opto with sub-unity CTR with a BJT aving a higher beta, but yeah mirrors would be better behaved,