Subject:
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Re: LEGO light sensor schematic
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 5 May 1999 13:11:13 GMT
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Viewed:
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970 times
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In lugnet.robotics, Dennis Clark writes:
> Could it be that transistor 15 (I think), the one that is configured as a
> diode whose emitter is tied to the emitter on the output of the OpAmp
> potentially be some kind of non-linear negative feedback loop? Maybe to
> prevent oscillation of the circuit?
Transistor 15 only has about .4V across it, so it is not operating in a
very linear region. My best guess is that it helps make up for the drop in the
follower 14 and provides some nonlinear gain. It tends to lower the gain for
larger signals which allows the sensor to operate over a wider range.
Transistor 17 looks like it does the same thing.
I think using transistors as diodes in this case is a surface mount trick.
Because a transistor is in a three leg package it can't be put in backwards
unlike a diode. I would think you could get a real diode with the same VI as
the transistor hooked up this way.
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Message is in Reply To:
 | | Re: LEGO light sensor schematic
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| (...) Mike, Could it be that transistor 15 (I think), the one that is configured as a diode whose emitter is tied to the emitter on the output of the OpAmp potentially be some kind of non-linear negative feedback loop? Maybe to prevent oscillation (...) (25 years ago, 5-May-99, to lugnet.robotics)
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