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looking for a quad op-amp chip

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AXmichigan

New Member
hey guys
thank you so much for the help so far :D

so i am looking for a good comparator chip that has ~4 op-amps
i found the lm324, would that work? (http://www.electro-tech-online.com/custompdfs/2009/06/LM124.pdf)
it does not require a -Vcc which is a big plus for me as I will be powering my circuit via battery power
is that okay though? I do not get how an op-amp can not have a -Vcc.. pretty cool though

i need the op-amps to just be used a voltage gain
thanks!
 
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Speakerguy

Active Member
What is your location? Where you are on the globe affects what parts you can get, and what I will recommend.

The LM324 is very old. However it can be gotten anywhere and due to no biasing in the output stage is low power and good for battery systems. That also means it has high distortion so it is bad in that regard. There are better choices out there depending on where you live and your access to parts.

Also, if you could post the circuit it is going in and what it does it would help me make a recommendation.
 
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mneary

New Member
First, study the differences between comparators and operational amplifiers. Their symbols are the same, but they operate quite differently. lm124 (more popularly lm324) is an op amp, and lm 139 (popular lm339) is a comparator.

As speakerguy mentioned, your location (put into your UserCP) and a diagram of your application would help us to help you.
 

Hero999

Banned
If it's just low speed, the LM324 will be fine.

Some op-amps can't be used as comparators because they are unstable when the output is saturated or either input gets too near either power supply rail.

You can use a comparator as an op-amp but you need to add a pull-up resistor and a capacitor to stop it from oscillating and don' expect good performance.
 

AXmichigan

New Member
hi sorry for the delay in my response
first off, thanks for the replies!

i know the difference of between a comparator and an op-amp, i just didnt realize that the initial chip i was looking at was just a comparator and not an op-amp
(please forgive my comparator chip with 4 op-amp part, I have no idea what was in my head when I wrote that)


I am located in DC
I just need a reliable multiple op-amp chip that I can have to be used for both a voltage gain and a comparator circuit for two different parts
I know the LM324 is old (I graduated college and we basically only used older parts, including this) and I was just wondering what all your expertise would say on it.

The Vcc would only be 6V, and the comparator part would be set at 3V which is not a very high voltage. It will be from a battery.

One thing that highly intrigued me, is that it only requires a +Vcc and Ground (LM324 - Low Power Quad Operational Amplifier), am I reading that right?
Since I am using a battery it would be great to have only a +Vcc and a Ground, and no -Vcc. Thanks!
 

mneary

New Member
You're in the US; if we wanted to suggest a special part it's nice to know what your options are.

As a comparator, the LM324 is pretty good, you should put hysteresis (positive feedback) around it to make sure it switches cleanly. Make sure you're respecting its common mode range. (0V to Vcc-1.5V). When using your "6v" battery, remember that many battery chemistries (NiCd, NiMH, Alkaline) spend most of their discharge life at 1.2V per cell, so 4 cells is 4.8V. (Or less when under load.)

You are ccorrect that a single supply is OK for this part.
 

Hero999

Banned
What frequency does it need to operate at?

The LM324 is no good as a comparator over about 1kHz.
 

mvs sarma

Well-Known Member
You may very well use TL074 and / or TL084 from TI. ST Micro also makes them. perhaps Analog Devices have many good ones.
 
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Hero999

Banned
Sorry but the TL074/84 isn't any good as a comparator because it suffers from phase inversion when the common mode input range is exceeded.

Here's a newb friendly presentation which deals with the potential problems with using op-amps as comparators.
 

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Speakerguy

Active Member
If you want a straight-up comparator, the LM339 is cheap and available anywhere. If you need to use one or two out of the four as a true op amp you are better off with the LM324.

TL084/TL074 are better for true op amp applications where both + and - rails are available, and where you know the signal won't get near the - rail so you can avoid the phase inversion problem. It's best used as a cheap audio op amp where you can control the system gain to keep input voltages well away from the rails and where it doesn't see too much of a load since it can't drive high currents like say an NE5532 or OPA2134 (which are much better audio op amps).
 
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Hero999

Banned
If you need to use one or two out of the four as a true op amp you are better off with the LM324.
Depends, if I needed fast comparators but slow op-amps, I'd be more tempted to use the LM339 with one or two biased as op-amps, especially if the op-amps were to be set at quite high gains.
 

mneary

New Member
Using 2/4 LM339 and 2/4 LM324 could be considered. This "wastes" about 15 cents and less than half a square inch.
 

Hero999

Banned
In that case why not use the LM393 and LM358?

They are dual versions of the LM339 and LM324 respectively.
 
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