Although we ended this class session with an introduction to motors, I want to dedicate this blog to class discussion in the first half. We discussed "trick number four" in engineering, feedback.
Positive feedback is when you connect the output of an op amp to the (+) input . Negative feedback is connecting the output to the (-) input which is feeding back the voltage. With negative feedback in an op amp, Vout varies so that the difference between the inputs (V+ - V-) is close to zero. In other words V+ = V- since their difference is "0" only when -12V <Vout<12V. This is true because V- = Vout/2= V+. An interesting thing about the graph of negative feedback is that, unlike positive feedback, there is a slant connecting (-6V, -12V) to (6V,12V).
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Using LT Spice, we made a circuit with an op amp with negative feedback. In the picture above you can see the slant.
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| Hysteresis: Vo (green line) switches between -12V and 12V as V- (red line) switches from 6V to -6V. |
If you are still curious about motors, read my next blog!:)
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