Talk:Circuit Idea/Misleading the Op-amp of a Negative Feedback Circuit
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Here is the building "scenario" that my students (group 64a) and I were using during Lab 4 to transmute negative into positive feedback circuits. Circuit-fantasist (talk) 13:29, 28 April 2008 (UTC)
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[edit] Lab 4: Op-amp circuits with positive feedback
[edit] What negative feedback is
The idea of the negative feedback is to manage to keep the balance. The circuit with negative feedback actually takes the role of active regulating element – never mind what the resistance is it keeps this balance (what do you mean here? Circuit-fantasist (talk) 17:09, 27 April 2008 (UTC)). All that an op-amp tries to do is simply to act as a real thinking human being.
Look at the picture. The difference ∆V between the input voltage Vin and the output voltage Vout is applied to the op-amp differential input. The thing is that the op-amp tries to keep ∆V very close to 0 volts so that the op-amp compensates the difference. However it cannot be more than the voltage on the amplifier itself (what do you mean here? Circuit-fantasist (talk) 17:09, 27 April 2008 (UTC)). Hote that the op-amp does not take energy from the input voltage source to supply the load; instead, it uses its own power supply. The input currents are very low (nano- and pico-ampers); so, we can say they are voltage inputs.
The negative feedback follower just repeats the input value, no matter what the obstacles are. In this way, it acts as a real human being. PavlinPanev 64
[edit] Converting a negative into a positive feedback circuit
[edit] General idea
What happens, if we make a mistake when apply a feedback from the output to the input of the subtractor and, as a result, it becomes a summer? In life this means to fool someone to do things in the wrong direction (for example, to do something bad instead to do something useful and v.v.). He/she "thinks" that he/she reacts in a proper way but actually he/she does exactly the opposite!
We can reproduce this situation in electronics, if we swap (usually, involuntarily) the op-amp's inputs. As a result, the op-amp is "disoriented"; like human beings, it "thinks" that it reacts in a proper way but actually it does exactly the opposite.
In this way, we can introduce the great idea of the positive feedback. It is extremely useful (for example, all the flip-flop RAMs are based on this powerful idea). PavlinPanev 64
[edit] Converting a non-inverting amplifier into an inverting comparator with hysteresis
Similarly, what happens, if we make a mistake when build a non-inverting amplifier swapping the inverting and non-inverting inputs? Let's try.
[edit] How to investigate the circuit
[edit] Investigating the circuit
