Automatic Gain Control Wien Bridge Oscillator

177

03:00:22

Hurz i think this is it. The maximum gain control is done by the 22kohm resistor. The output is a little more drawn to the positive but i don't think that's a problem. The capacitor should straighten that out. 

published 9 years ago

hurz

9 years ago

So this is your bulb emulation (everything left hand to wien bridge)?

thebugger

9 years ago

No it's not a bulb emulation. It's a different kind of amplotude stabilisation.

hurz

9 years ago

So YES, its a "bulb" or PTC emulation. I said nothing about how close it is to a real bulb :P

thebugger

9 years ago

You can even use a normal transistor to simulate PTC. As they heat up their gain changes which may be exploited for amplitude stabilization. The difference is that more or less every other component works in the more linear part of their characteristics while a diode will work exactly in its most nonlinear part.

thebugger

9 years ago

Well put this way, yes it may be viewed as a bulb, but it's not PTC it's AGC in this case. For it to be PTC it should be controlled by the introduced heat from the rising swing, while this is controlled by the rising voltage itself. A bjt transistor may be used as a PTC feedback

hurz

9 years ago

Can be seens as bulb, and can be seens as PTC. Cause only a bulb with PTC behaviour will work at that point in circuit. A transistor "normal" (guess you talk about BJT) is more a NTC! and wont work at that point.

thebugger

9 years ago

No not there, but Transistor NTC will work as a whole. So there are a few ways to stabilise it. PTC, NTC, semiconductors, AGC as far as I'm concerned. It doesn't matter where in the circuit they'll be. This circuit may work the same way as a PTC bulb does, but it doesn't rely on PTC per se, because it's not driven by the increasing heat generated by the circuit. It's more like a voltage controlled negative feedback or something.

hurz

9 years ago

Nobody said it is a PTC! I talked about emulation! And the POINT in circuit were to put a PTC behaviour is VERY important. And its totally different were you would place a NTC behaviour. e.g. NTC would be placed at yur 10k feedback resistor. So dont say its unimportant were to put it. At least you see now the bulb emulation. Try to separate it and make a 150W bulb with it. Cold resistance ~25Ohm hot resistance 354Ohm. I will also make a math precise model.

thebugger

9 years ago

Yes PTC and PTC like behavior are two different things. Why the 150W bulb?

thebugger

9 years ago

I didn't say the position is unimportant. If anything if you put a PTC at the 10k resistor you'll end up reinforcing the feedback, leading it faster to cut off.

hurz

9 years ago

150W, cuz i have one bulb here and measured it already. And i'm not interested to make another wien oscillator. Our main topic was in general "how to make a varistor".

faceblast

9 years ago

bookmarking this circuit just for the comments

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