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university:courses:alm1k:alm-lab-comp [03 Nov 2021 20:23] – [Activity: The Comparator, Positive Feedback and Schmitt Trigger] Doug Merceruniversity:courses:alm1k:alm-lab-comp [16 May 2022 15:21] (current) – [The op-amp as a "comparator":] Doug Mercer
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 <WRAP centeralign>Figure 7, An op-amp used as a comparator</WRAP> <WRAP centeralign>Figure 7, An op-amp used as a comparator</WRAP>
  
-Op Amps and comparators may seem interchangeable at first glance based on their symbols and pinouts. The Analog Parts Kits is supplied with a variety of op-amps and the AD8561 high speed voltage comparator that was used in the earlier activities. Some designers might be tempted to use or substitute readily available op amps as voltage comparators in their projects. There are very important differences however. Comparators are designed to work without negative feedback or open-loop, they are generally designed to drive digital logic circuits from their outputs, and they are designed to work at high speed with minimal instability. Op amps are not generally designed for use as comparators, their input structures may saturate if over-driven which may cause it to respond comparatively slowly. Many have input stages which behave in unexpected ways when driven with large differential voltages or beyond the specified common mode range. In fact, in many cases, the differential input voltage range of an op amp is limited or clamped to prevent damage to the input stage devices.+Op Amps and comparators may seem interchangeable at first glance based on their symbols and pinouts. The Analog Parts Kits is supplied with a variety of op-amps and the AD8561 high speed voltage comparator that was used in the earlier activities. Some designers might be tempted to use or substitute readily available op amps as voltage comparators in their projects. There are very important differences however. Comparators are designed to work without negative feedback or open-loop, they are generally designed to drive digital logic circuits from their outputs, and they are designed to work at high speed with minimal instability. Op amps are not generally designed for use as comparators, their input structures may saturate if over-driven which may cause it to respond comparatively slowly. Many have input stages which behave in unexpected ways when driven with large differential voltages or beyond the specified common mode range. In fact, in many cases, the differential input voltage range of an op amp is limited or clamped to prevent damage to the input stage devices. Note this article on "[[adi>en/analog-dialogue/articles/amplifier-input-protection-friend-or-foe.html|Amplifier Input Protection... Friend or Foe?]]" for more background on this issue.
  
 <note important>Warning: Using op-amps with built-in input clamps as a voltage comparator may damage the IC!</note> <note important>Warning: Using op-amps with built-in input clamps as a voltage comparator may damage the IC!</note>
university/courses/alm1k/alm-lab-comp.txt · Last modified: 16 May 2022 15:21 by Doug Mercer