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What kind of slew rate should I expect from LM 741 op amp

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arturbdg

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Hi,
I did an lab exercise and had a result of Slew Rate around 0.75V/us. Wanted to recreate the exercise at home and build the same circuit - an astable multivibrator with feedback resistor of 20kOhm, 100nF cap connected to negative input. 10kOhm resistor at the output going to the positive input and from that another 10kOhm resistor going to the ground.

At home I achieved a result of 0.93V/us - which seemed a bit high for me. For a while I thought that my oscilloscope at home is out of calibration, but I checked the time period - from calculations I had a 4.4ms and I read from oscilloscope a 4.6ms, so I'd guess that its not the issue with the calibration.

Could someone explain me why 741CN that I used at home have a slew rate of 0.93V/us, the one at the college had 0.75V/us and datasheet specifies typical slew rate of 0.5V/us for the LM741CN.

How can this be explained?? Any ideas, suggestions??

Any help is much appreciated.

Artur
 

Hi,
I assume that both ICs are not from same vendor...
You can have some other driving & load situation/other power supply (i.e. higher) voltages...
K.

Added after 7 minutes:

Atur;
I did checked one National datasheet yet: SR=0.5 V/us is TYPICAL data!
Nothing is to find over minimal/maximal values, in that case you can clear have -by some exemplars- really better values_ but worser data too... Your oscilloscope decalibration makes only ca. 5%, but your SR-deviation is higher:)
K.
 

Re: What kind of slew rate should I expect from LM 741 op am

karesz said:
Hi,
I assume that both ICs are not from same vendor...
You can have some other driving & load situation/other power supply (i.e. higher) voltages...
K.

Added after 7 minutes:

Atur;
I did checked one National datasheet yet: SR=0.5 V/us is TYPICAL data!
Nothing is to find over minimal/maximal values, in that case you can clear have -by some exemplars- really better values_ but worser data too... Your oscilloscope decalibration makes only ca. 5%, but your SR-deviation is higher:)
K.
Click to expand...

I think that they are from the same vendor, yet definitely from different batches, mine was bought 2 days ago, the one at college could be years old or more. I got +-16.3V college one had a +-15V, but shouldn't slew rate be kind of independent from external parameters, I mean obviously it can be different if you go at two extremely different cases like minimum supply vs max voltage supply, but apart from that the Slew Rate should be pretty much constant right?

And if there is no maximal value stated on the datasheet does it actually mean that it can be higher than stated. I thought that there might be some deviation allowed from typical value, but all within limits, and my SR deviation is way higher than the stated in datasheet.
 

OK, You can try lot of philosophy, :), but a typical data will be for ever a possible typical value & has a +/- range of (in that case)unknown wide_thats life...
ICs has usual a fabrication code, but its not every time simple to encode...
Typically are days or week of calendar + 2 characters of production year stamped, also i.e. 4 Nrs, but often are production places coded too...
You have it to check in accordance the special vendors coding system. I think, these isnot so relevant :)
K.
 

Re: What kind of slew rate should I expect from LM 741 op am

karesz said:
OK, You can try lot of philosophy, :), but a typical data will be for ever a possible typical value & has a +/- range of (in that case)unknown wide_thats life...
ICs has usual a fabrication code, but its not every time simple to encode...
Typically are days or week of calendar + 2 characters oy production year stamped, also i.e. 4 Nrs, but often are production places coded too...
You have it to check in accordance the special vendors coding system. I think, these isnot so relevant :)
K.
Click to expand...

I am not bothered about the vendor or the time when the IC was produced, but obviously when I will write the report the question that will need to be answered is why the slew rate is so different from the datasheet typical value, and "that's life" is not much for an answer.
A.
 

Re: What kind of slew rate should I expect from LM 741 op am

arturbdg said:
...when I will write the report the question that will need to be answered is why the slew rate is so different from the datasheet typical value, and "that's life" is not much for an answer.
A.
Click to expand...
Sorry my friend, I believ it enough detailed to have answered befor these small remarks over "realities in life"... You need it only attentive to read, pls.
Good progress!
K.,
 

Re: What kind of slew rate should I expect from LM 741 op am

karesz said:
arturbdg said:
...when I will write the report the question that will need to be answered is why the slew rate is so different from the datasheet typical value, and "that's life" is not much for an answer.
A.
Click to expand...
Sorry my friend, I believ it enough detailed to have answered befor these small remarks over "realities in life"... You need it only attentive to read, pls.
Good progress!
K.,
Click to expand...

well problem is that I am trying to find somewhere over the internet an 741 op amp with slew rate more than 0.5 V/us and cant find any reference, thus it makes me hard to understand my results.
 

I think, thes is a original Fairchild type, but after ca. 30-35 years is possible the chip design no more the same :)... You can try he datasheet from Fairchild_yet by TI; her:https://focus.ti.com/lit/ds/symlink/ua741.pdf
Well, its not much others as from NI and so on.
Can be that you have others capacitive load & Input signal Offsetts?
But remember pls, as I wrote it to my begin too: its a typical spec, with +/_ (maybe 20-50%??, nobody knows it better)values... Your professor must know it exactly so too.
K.
 

Re: What kind of slew rate should I expect from LM 741 op am

karesz said:
I think, thes is a original Fairchild type, but after ca. 30-35 years is possible the chip design no more the same :)... You can try he datasheet from Fairchild_yet by TI; her:https://focus.ti.com/lit/ds/symlink/ua741.pdf
Well, its not much others as from NI and so on.
Can be that you have others capacitive load & Input signal Offsetts?
But remember pls, as I wrote it to my begin too: its a typical spec, with +/_ (maybe 20-50%??, nobody knows it better)values... Your professor must know it exactly so too.
K.
Click to expand...

unfortunately I don't have more of 741 op amps,but I had several of TL072 op amps, their min slew rate is 5V/us , with typical of 13V/us. I checked 3 of them and I had this results: 14.11V/us 15.48V/us and 13.71V/us , so they swing quite a lot, thus it must be true what you are saying....

Question is then does anyone knows where to find information whether typical value have any limits in terms of deviation. I mean it is a technical document so it does need to have some standard right?

Thanks for your help

Artur.
 

I think in case uA741 it dos not exist_its one of the first Op Amp designs, the technology/design possibilities (& circuit techniques) are much others (& process stability too) as nowadays...
You can contact TI`s Apll Lab_eventuelly they gives you some/another answer? I can not believe it, but is not inpossible.
If you can moderner ICs select, you will see, their specifications are more better/exacter, but not from all vendors & all products, designers life is not every time simple, much parameters are for exampl. from most vendors not garanted, eventuelly not tested too...
Even technical documents are & can not be every times absolute exact!
K.
 

Re: What kind of slew rate should I expect from LM 741 op am

About 32 yeas ago, Motorola made an improved 741S. It had a high slew rate but was still with a poor frequency response and was noisy.
 

Re: What kind of slew rate should I expect from LM 741 op am

arturbdg said:
karesz said:
I think, thes is a original Fairchild type, but after ca. 30-35 years is possible the chip design no more the same :)... You can try he datasheet from Fairchild_yet by TI; her:https://focus.ti.com/lit/ds/symlink/ua741.pdf
Well, its not much others as from NI and so on.
Can be that you have others capacitive load & Input signal Offsetts?
But remember pls, as I wrote it to my begin too: its a typical spec, with +/_ (maybe 20-50%??, nobody knows it better)values... Your professor must know it exactly so too.
K.
Click to expand...

unfortunately I don't have more of 741 op amps,but I had several of TL072 op amps, their min slew rate is 5V/us , with typical of 13V/us. I checked 3 of them and I had this results: 14.11V/us 15.48V/us and 13.71V/us , so they swing quite a lot, thus it must be true what you are saying....

Question is then does anyone knows where to find information whether typical value have any limits in terms of deviation. I mean it is a technical document so it does need to have some standard right?

Thanks for your help

Artur.
Click to expand...

obtained 5 more 741 op amps and tested agains the other one I had, well they were pretty close together in terms of the Slew Rate the value oscillated around 0.79-0.85. They were all from the same batch so I would say it was expected to see results like that. The other one I got - which I tested previously have a slew rate of 0.95, now that is bigger than the others.
The one with 0.95 is 741CN National Semiconductor, the other 5 were 741CN Fairchild.

Now I was hoping to get my hands to at least one that have a Slew Rate around 0.5 as stated in the Datasheet no luck so far. Maybe one of you guys ever had a 741CN - standard one with a Slew Rate closer to 0.5 V/us.

Regards
Artur
 

Re: What kind of slew rate should I expect from LM 741 op am

The datasheet SR is based on certain conditions: unity gain configuration, and a load of 2K || 100pF. You are measuring a no-load (oscope probe capacitance only) positive feedback circuit. You should see a higher slew rate than the typical value. See Figure 1 in the TI datasheet and test that configuration. I bet you see something closer to .5V/us

stefannm
 

Yes,
as I wrote it at 14. Mar to first too...
K.
 

Re: What kind of slew rate should I expect from LM 741 op am

stefannm said:
The datasheet SR is based on certain conditions: unity gain configuration, and a load of 2K || 100pF. You are measuring a no-load (oscope probe capacitance only) positive feedback circuit. You should see a higher slew rate than the typical value. See Figure 1 in the TI datasheet and test that configuration. I bet you see something closer to .5V/us

stefannm
Click to expand...

well tried this configuration, but noticed one strange thing on the rising slope got bout 1V/us slew rate on falling edge got 0.575V/us...so which I should use for measuring a slew rate?
Artur
 

Hi,
of course both, if their are so others...
Then semic. devices are often different on speed( asymmetric) as rising or falling edges are checked.
K.
 

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