I have been using 324s for a number of things and I had a use where I really only needed one op amp so I swapped in a 741. No joy. It is a whetstone bridge feeding an op amp as a comparator. It is always on. I am guessing that is because of the single ended supply. Can I use a null offset to make this switch?
Why not use a comparator ? LM311 ?
Graham
I don't have one and I am a week away from any? I see the pinout is close so I may be able to try it but I was hoping I wasn't going to have to trash the board I have made.
I don't understand " I am a week away from any ".
Will fit in your 741 socket.
Why are you so wedded to obsolescent parts btw ?
Graham
I am in the swamp in Florida. If Radio Shack doesn't have one I am ordering it.
That one is what I need but I am still probably waiting by the mailbox for it. I was hoping I could use those offsets to push the inputs up into a usable range. I guess I don't really know much about op amps
The 741 has a limited common mode input range, as well as a minimum supply requirement. It's likely your problem lies herein, and 'tis up to you to make it happy.
HTH, James Arthur
I expect your input voltage is outsude the allowable common-mode input voltage range.
In which case I'm not sure the TLC271 would do the job either. Would need to check.
What is the output voltage from your bridge ?
Graham
Oh, and the supply voltage too.
Graham
A 741 makes a lousy comparator because the output will not swing down to the lower supply rail (ground right?). If you have split (+) and (-)
5-volt supplies you can make this work, but is it worth the headache? Put your 324 back in the circuit and think of the 3 remaining units as redundant backups. Now you're a rocket scientist.-- Joe Legris
I'm sure it can be made to work. Wheatstone bridge implies that both inputs are roughly mid supply with respect to potential? Output of the op amp should change state with the bridge - try it without connecting it to anything else. If that works its working as well as it can . . .
The output may never get low/high enough to turn off/on to satisfy you
- for that you have to add a zener or diode string to get around the common mode problems, and drive an open collector.
It ain't difficult. We used 741, 301's etc. on single supply long before the 324 was around. Basically you reference them to 1/2 the supply (the wheatstone should already be doing that) and massage the output with a zener if it is going into a switch, or isolate the DC with a cap if it is going to be amplified further.
They are not good with low voltage supplies and I don't remember trying to use one lower than 12V.
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In message , dated Fri, 8 Sep 2006, default writes
I have used a 741 as an audio-frequency amplifier (but not handling audio) on +/-4.5 V. It's OK IF you realise that it has limited performance. There is no point in denigrating it because you can't successfully use it outside its performance envelope.
-- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk There are benefits from being irrational - just ask the square root of 2. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
If the input signal is AC you could do it. If it's DC, the 741 on single supply has a tough time below about 2 v in, AIRC.
Ed
In the 70's & 80's the hobby magazines were full of 741 circuits using a single PP3.
That is what I am thinking. I will "blast off" tonight. Thanks.
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