simple opamp circuit but square-wave messed up?! - Page 1
Forum section: electronics / beginners

author: daemonix
author_rank: Contributor
timestamp: June 25, 2014, 03:58:39 pm
content: Hi,I;ve got this very basic opamp test. Low frequency and Gain!!My knowledge fails me when it comes to understand this behaviour!Any insights will be helpful!Yellow is the output and blue is the f-gens input.EDIT: powered of a 9V and the opamp is a LM741

author: jlmoon
author_rank: Unknown
timestamp: June 25, 2014, 04:02:11 pm
content: perhaps a schematic would be better?

author: daemonix
author_rank: Contributor
timestamp: June 25, 2014, 04:56:41 pm
content: Quote from: jlmoon on June 25, 2014, 04:02:11 pmindeed!!

author: Andy Watson
author_rank: Super Contributor
timestamp: June 25, 2014, 04:59:12 pm
content: Looks like it is slew rate limited. Scope says approximately 0.4V/µS, datasheet says 0.5V/µS (typically).

author: theatrus
author_rank: Frequent Contributor
timestamp: June 25, 2014, 05:18:54 pm
content: Also, the LM741 is not a rail to rail output.

author: daemonix
author_rank: Contributor
timestamp: June 25, 2014, 05:25:01 pm
content: Quote from: Andy Watson on June 25, 2014, 04:59:12 pmat 1k SQ wave? Can the slew rate affect that low?

author: daemonix
author_rank: Contributor
timestamp: June 25, 2014, 05:25:52 pm
content: Quote from: theatrus on June 25, 2014, 05:18:54 pmoutput is 5VppEDIT: corrected, mistype

author: theatrus
author_rank: Frequent Contributor
timestamp: June 25, 2014, 05:34:10 pm
content: Quote from: daemonix on June 25, 2014, 05:25:01 pmA square wave, in ideal terms, has infinite bandwidth at the transition. This of course is impossible, so the slew rate limit applies.

author: jlmoon
author_rank: Unknown
timestamp: June 25, 2014, 05:35:56 pm
content: Quote from: daemonix on June 25, 2014, 05:25:52 pmHow come your scope Ch1 is indicating 5.04Vp-p? I see almost 5 volt p-p as wellyou're stating output is 4Vp-p.. .. a bit confused.. ,when making measurements in question, it is also good to use point of reference such as the center graticule line or major division as a measurement starting point.

author: daemonix
author_rank: Contributor
timestamp: June 25, 2014, 06:34:27 pm
content: Quote from: jlmoon on June 25, 2014, 05:35:56 pmSorry mistype! scope is definitely better than my eyes

author: jlmoon
author_rank: Unknown
timestamp: June 25, 2014, 06:42:00 pm
content: well I got a brand new pair of glasses.. guess they're working pretty good..

author: katzohki
author_rank: Frequent Contributor
timestamp: June 25, 2014, 08:06:14 pm
content: I can see it being slew rate. Why are you using a LM741? A lot of tutorials (and even classes) use this opamp, but I think you need to understand the opamp datasheet and buy for your application.

author: daemonix
author_rank: Contributor
timestamp: June 25, 2014, 08:55:04 pm
content: This is correct, I saw it online and I did this quick test.... then I added a TL071 and I realize the difference in specs!Very sharp Sq-wave with just a bit of ringing.I had the 741 from a tutorial.Thanks a lot!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 26, 2014, 01:01:04 am
content: Commuting in about 100us? Sounds about right. 741 is shite.Tim