I just received my TL974IN op amp. I have a prototype circuit for driving a MOSFET in a constant current dummy load, made with DIP socket for easy testing. I originally made it with LM324N, then changed it to MCP6001 to have a rail to rail op amp. Both worked, the MCP6001 was much better. I am trying to extend the the load capability of the setup, but for that I need to drive the MOSFET above 6V. I thought the TL974IN should be a direct drop in op amp just with higher supply voltage limit. To my surprise that is not the case. I ordered 2, neither one works. If I try them on a breadboard is not working like any other op amp i have. Could I have 2 bad IC-s shipped? I ordered the 14SOIC versions of them for the final circuit, but now I have doubts to use them.
Any help or ideas greatly appreciated.
A schematic of your circuit might be helpful, pictures being worth a thousand words and all that…
The probability of receiving faulty production parts is about a million times less than the probability of there being some sort of problem with a circuit under development; it is a theory of absolute last resort.
The most likely issue here is that the TL974 is not a single-supply op amp; its common-mode input range does not include the lower supply rail. Put differently it’s not going to function properly in circuits where the voltage presented to the two inputs approaches within a volt and change of either supply rail.
Please see this thread for more detailed information on op amp selection. In the case of the TL974, it would appear that the supply voltage range is incorrectly listed in our parametric search, suggesting that this part is single-supply capable. The error has been reported, and will be corrected as soon as possible.
I think you are right regarding the single supply issue. I got mislead by the datasheet on page 11, typical application. I’m new to this forum, don’t know how to attach a screenshot of the page.
Thanks for the reply.
I see what you mean… Section 9.1/p.11 of that datasheet is definitely not correct in context of the part; it’d be OK in terms of an ideal op amp, but TI doesn’t make those…
Unfortunately, the only part of a datasheet that’s considered to be guaranteed are the parametric minimums and maximums. Everything else needs to be taken with a grain of salt… I got bit by that a number of times early on and felt a bit chafed, but the experience brought a perspective that’s been profoundly valuable elsewhere in life.
Sorry for the confusion, and best of luck with your project.
I never use dual power supply, so these chips are useless to me. Do you think I can return them?
Do you have a suggestion similar to MCP6004, only higher supply voltage? That works really well for my project. (Make sure is not a fancy expensive one).
It looks like the LMC6484AIN/NOPB is a DIP-packaged op-amp that meets your requirements for higher input voltage (up to 15V), rail-to-rail input and output, and is in the same ballpark regarding specs as the MCP6004.
Here’s the surface-mount equivalent: LMC6484AIM/NOPB
A NCS20074DR2G might be an option worth looking at.
Considering that the cost of the parts involved is less than the value of the time it would take you to return them, it probably does not make sense to do so. I’d suggest putting them in your parts box and saving them for the next time you want to do something with audio or a similar AC-coupled, single-supply application.