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Topic: Is JFET same as a FET Op amp? (Read 1 time) previous topic - next topic

limjix

Hey guys,

I am looking for a replacement for the TL082. http://www.ti.com/product/tl082

However I can't seem to tell which will be a good replacement for it from this list.
http://store.aztronics.com/index.php/index.php?route=product/search&keyword=operational%20amplifier&category_id=0

Can someone help me?

Is there a big difference between all these operational amplifiers??

Also, anyone know where I can get a BNC female connector for a project?

Magician

What is the function of the OPA in circuitry?  Selection of IC depends on slew rate, bandwidth, dual/single supply, noise, input impedance. 

limjix

I am using it to amplify a circuit that reads a tiny voltage from a pH probe.

http://www.66pacific.com/ph/simplest_ph.aspx

CrossRoads

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Magician

For such application my choice would be http://www.ti.com/product/opa379
2.56 $ .  And you can use arduino +5V instead of 9V battery ( max voltage of the OPA +7V !).

CrossRoads

@limjix ,
Is surface mount or DIP needed?
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Docedison

My own recommendation would be an LMC662... I've used a lot of them in soil measurement equipment with very good results in Both Dip8 and SO-8.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

SparkysWidgets

Docs suggestion is a good one, you can also check if TLC2262 are available to you. I have actually used all three of these(including the TL0XX series) with good results. Basically you are looking for a rail to rail amp with low offset voltage and extremely low input bias current, after that most modern amps will have better performance then the old TL0XX series.

limjix


You are limited to Malaysia?

"Aztronics Store
MALAYSIA
http://store.aztronics.com"

I'd go with this one
http://www.ti.com/lit/ds/symlink/opa2132.pdf
http://store.aztronics.com/index.php?route=product/product&keyword=operational+amplifier&category_id=0&product_id=59

compare #s to
http://www.ti.com/lit/ds/slos081g/slos081g.pdf




Yes I live in Malaysia. Thanks so much for the recommendation.

Thanks everyone for the suggestions.

But I was wondering how did you guys come to the conclusion of what op amp to use cause it all just looks the same to me?
Is there a difference between JFET and FET?

SparkysWidgets

The type of sensor you are interfacing basically dictates what type of op-amp you are going to need.
pH probes are very high impedance sources that are slow to respond, when you are dealing with 500Mohm input impedance even a tiny current such as a pico amp can change your readings by a very significant amount. This is why we are looking at amps with ultra low input bias current, offset voltage can matter as well, but this can be calibrated out as long as its consistent through the measurement range and so this is also taken into account for which amp we picked out. Since the signals are relatively slow (and mainly DC) we don't care too much about slew rates and bandwidths, and is also why older op-amp designs are still quite effective today especially when cost is factored in.

When they talk about FET, JFET, LINMOS, CMOS they are referring to the physical topology and construction of the transistors which make up the op-amp. While they are all Field Effect Transistors, the methods for construction and materials used are very different and therefor yield the characteristics that we see in all the varying amps(or all ICs) out there. Each company has their own proprietary stuff too which shows up as the strange LINMOS type names, this stuff can get pretty exotic when you start getting down to this level.

limjix

#10
Oct 17, 2012, 08:30 am Last Edit: Oct 17, 2012, 08:38 am by limjix Reason: 1
Hey guys

Which of these are the correct ones to use?

http://my.element14.com/jsp/search/browse.jsp?N=0+110132318&Ntk=gensearch&Ntt=LMC662&Ntx=mode+matchallpartial&suggestions=false&ref=globalsearch&_requestid=1215411&No=0&getResults=true&appliedparametrics=true&locale=en_MY&divisionLocale=en_MY&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=0&mm=1002752||,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D0%26Ntk%3Dgensearch%26Ntt%3DLMC662%26Ntx%3Dmode%2Bmatchallpartial%26suggestions%3Dfalse%26ref%3Dglobalsearch%26_requestid%3D1215411%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_MY%26divisionLocale%3Den_MY%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D0

I also need help to choose a BNC receptacle. I have no idea which to get?

http://my.element14.com/jsp/search/browse.jsp?N=2105+203756&Ntk=gensearch&Ntt=BNC&Ntx=mode+matchallpartial

dhenry

Quote
Which of these are the correct ones to use?


If I were you, I would try to understand your circuit and why TL082 was used. Most of the times, those chips are used not for their jfet input stage but for their low prices. In those cases, pretty much any opamp will do.


MarkT


I am using it to amplify a circuit that reads a tiny voltage from a pH probe.

http://www.66pacific.com/ph/simplest_ph.aspx

Tiny means many things - how tiny?
[ I won't respond to messages, use the forum please ]

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