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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I noticed that there are semiconductors sold labeled COMPARATORS. How are these different than just buying a Norton OpAmp and using it as a comparator?
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
op-amps are used in a linear range for amplifiers and can be used as a comparator. A comparator is an opamp that is designed to have an output that has two states like TTL and used to do voltage or current level threshold detector. I dont know if this will help you . I generaly just read collage text or data sheet if I am interested enough. N.B.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567
I have another OpAmp question for this thread. I hooked up a 741. V- is connected to GND. V+ is connected to 5v. When the OpAmp goes high it goes to 5v. When it goes low it goes to about 1v. Shouldn't it go to zero? The only connections are V+, V-, +IN and -IN.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
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I see that when the two inputs are equal Vout can be above non-zero. I also see that one can connect a pot to the two null offsets and the wiper to V- to balance Vout to zero. Can this be done if the V- supply equals zero? That is, can Vout be equal to zero using the null offsets if the only supply is +5v and GND?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Time for you to learn about input common mode ranges and allowable output swings, grasshopper If you want a short answer: The 741 sucks on a single supply and can't really do much useful, because its output can't get down very near to the V-/ground rail (as you noticed in your earlier post) and it freaks out if you try and pull its inputs down there (as you'll probably find out soonish) Other op-amps can do much more with a single supply.
A related point: No engineer would ever try to trim the output of an op-amp to a stable point like that. Op-amps are only designed to be used with negative feedback around them (or as comparators)
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Op amps and comparators
If you want a short answer: The 741 sucks on a single supply and can't really do much useful, because its output can't get down very near to the V-/ground rail (as you noticed in your earlier post) and it freaks out if you try and pull its inputs down there (as you'll probably find out soonish) Other op-amps can do much more with a single supply.