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→Applications without using negative feedback: introduce link to voltage comparator, and clarify that positive feedback may still be used, but with side-effects in level detection |
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=== Applications without using negative feedback ===
That is, the op-amp is being used as a [[voltage comparator]]. Note that a device designed primarily as a comparator may be better if, for instance, speed is important or a wide range of input voltages may be found.
====Voltage level detector====
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====Zero voltage level detector====
A zero voltage level detector can convert, for example, the output of a sine-wave from a function generator into a variable-frequency square wave. If E<sub>i</sub> is a sine wave, triangular wave, or wave of any other shape that is symmetrical around zero, the zero-crossing detector's output will be square. Zero-crossing detection may also be useful in triggering [[TRIAC]]s at the best time to reduce mains interference and current spikes.
Because of the wide slew-range and lack of positive feedback, the response of all the level detectors described above will be relatively slow. External overall positive feedback may be applied, to create a [[Schmitt trigger]] but (unlike internal positive feedback that may be applied in the later stages of a purpose-designed comparator) this markedly affects the accuracy of the zero-crossing detection point. Using a general-purpose op-amp, for example, the frequency of E<sub>i</sub> for the sine to square wave converter should probably be below 100 Hz.{{Citation needed|date=February 2011}}
===Negative feedback applications===
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