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What’s an example of where you picked the wrong Op-Amp … and why?

baldengineer

I’m working on an episode about Op Amps and measuring some basic parameters. (For those like me who would rather measure something than go cross-eyed looking at a datasheet.)

Since there are more than a handful of op amps, I can imagine there are situations where people select one or re-use one without fully evaluating all of its characteristics. So, that got me thinking, what are some cases where you picked an op-amp for an application, but it was (clearly?) the wrong one… and why?

Bonus question: does anyone still use the ua741 … for anything?

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  • There is no substitute for risking the cross eyes by reading data sheets.

    There are loads of op amps and they are all different.

    There are a great mass of applications where the choice of op amp is quite flexible, but others are less so.

    In the present times of all sorts of parts being on long delivery it's even worse because availablity trumps everything else !

    To give an example, I have a current job where the key parameters are:

    low voltage noise (< 3nV rtHz @ 5kHz)

    work from 2.7V

    input common mode must include 0V

    rail to rail out

    > 50MHz GBW (200 would be nice)

    low input voltage offset

    less than 3mA supply current

    There are not many options !

    I can't think of any application where a 741 would be a good choice unless you have a tube of them gathering dust.

    The worst things about it, compared with modern op amps, are the limited input common mode range and limited output swing which means that the minimum supply voltage is 6V or +/- 3V (more realistically 10V or +/-5V).

    It is cheap.

    TI recommend the TLV9301, it's quite nice but not as cheap !

    MK

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  • There is no substitute for risking the cross eyes by reading data sheets.

    There are loads of op amps and they are all different.

    There are a great mass of applications where the choice of op amp is quite flexible, but others are less so.

    In the present times of all sorts of parts being on long delivery it's even worse because availablity trumps everything else !

    To give an example, I have a current job where the key parameters are:

    low voltage noise (< 3nV rtHz @ 5kHz)

    work from 2.7V

    input common mode must include 0V

    rail to rail out

    > 50MHz GBW (200 would be nice)

    low input voltage offset

    less than 3mA supply current

    There are not many options !

    I can't think of any application where a 741 would be a good choice unless you have a tube of them gathering dust.

    The worst things about it, compared with modern op amps, are the limited input common mode range and limited output swing which means that the minimum supply voltage is 6V or +/- 3V (more realistically 10V or +/-5V).

    It is cheap.

    TI recommend the TLV9301, it's quite nice but not as cheap !

    MK

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