741 op amp - anyone using it anymore ?  - Page 1
Forum section: electronics / projects

author: Greg J
author_rank: Regular Contributor
timestamp: January 01, 2012, 04:26:16 pm
content: I wonder, because I recently was caught with pants down on it - because I forgot about something calledsaturation voltage.Basically, I was trying to use it as a buffer. But output voltage would never go to 0.This is on circuit that works on 3.3V, so going to zero instead of 3.3->1.9 is quite important. 1.9 is technically still in 'high' level for most 3.3 circuitry.Interestingly enough, if I use it as negator - it goes down to 0 just fine. Since I had two outputs to buffer, one is a boolean not of the other - using negators it was. But still..Does an old rusty 741 have use these days ?I'm guessing folks now use mosfet output op amps instead. Would anyone recommend one that would be your default choice for stuff with under MHz bandwidth ?

author: Zad
author_rank: Super Contributor
timestamp: January 01, 2012, 05:30:50 pm
content: Not for years. I seem to use mostly LM324 and TL064/74/84.

author: slateraptor
author_rank: Frequent Contributor
timestamp: January 01, 2012, 07:31:31 pm
content: I'm don't understand what your question is.It almost sounds like you're trying to use the op amp in single supply configuration, which it wasn't designed for.741s are still very popular as a general purpose op amp in academia, probably because they're a classic jellybean that can be purchased in bulk for dirt cheap.

author: IanB
author_rank: Super Contributor
timestamp: January 01, 2012, 08:13:02 pm
content: I'm pretty sure the 741 will go down to 0 V if you power it from, say, a +/- 12 V supply and don't try to make the output go too close to the rails.

author: Afrotechmods
author_rank: Unknown
timestamp: January 04, 2012, 10:50:04 am
content: For 1Mhz & <5V I am a fan of Microchip's MCP600x series. They are cheap as dirt.http://ww1.microchip.com/downloads/en/DeviceDoc/21733h.pdf

author: Zero999
author_rank: Super Contributor
timestamp: January 04, 2012, 05:59:25 pm
content: In short, it's a crap op-amp. No one uses it except for students and hobbyists who either don't know any better or just have loads of them in stock.

author: slateraptor
author_rank: Frequent Contributor
timestamp: January 04, 2012, 06:16:35 pm
content: Quote from: Hero999 on January 04, 2012, 05:59:25 pmWhat do you feel is so crap about the 741?

author: im_a_human
author_rank: Regular Contributor
timestamp: January 04, 2012, 09:28:56 pm
content: Ive used the 741 for many years when i was a newbie to electronics and i still keep a few around. These days i choose op amps depending on how i need them to perform in a circuit be that low noise, input bias current, offset error, CMRR, THD, power consumption, low voltage operation, bandwith, gain, tempreture stability, input/output impedance, single rail or dual rail power supply requirements etc etc.

author: Zero999
author_rank: Super Contributor
timestamp: January 04, 2012, 11:35:35 pm
content: Quote from: slateraptor on January 04, 2012, 06:16:35 pmLook up op-amp tutorial, learn about the desired op-amp characteristics and what one would expect from a perfect op-amp (there isn't one). Now read the 741 datasheet and compare it with any op-amp IC made in the last 30 odd years and you'll see what I mean.

author: slateraptor
author_rank: Frequent Contributor
timestamp: January 05, 2012, 12:35:51 am
content: Quote from: Hero999 on January 04, 2012, 11:35:35 pmI'm intimately familiar with the characteristics of an ideal op-amp and real world non-idealities.That the uA741's specifications have been superseded by better performing devices doesn't necessarily render it crap. If the application doesn't call for it, why pay for performance that you don't need?

author: Short Circuit
author_rank: Frequent Contributor
timestamp: January 05, 2012, 12:43:05 am
content: I'm with Afrotechmods, MCP6001 is best gain for bucks these days.A quick check of a 741 datasheet shows a operating voltage range of +/-5 to +-22V.So for the average present day design with single 3.3V power, completely useless.Actually, it's even useless at 5V. Looking at the output swing vs supply voltage, andextrapolating to +/-2.5 V (or single 5V) the effective output swing is reduced toabout 2.5V. Not particulary useful for a general purpose opamp... (Not to mentionthat there's no guarantee that the device will work at all.)http://newton.ex.ac.uk/teaching/cdhw/Electronics2/DataSheets/LM741.pdf

author: slateraptor
author_rank: Frequent Contributor
timestamp: January 05, 2012, 01:29:46 am
content: Quote from: Short Circuit on January 05, 2012, 12:43:05 amOh come on now. Depending on your single supply application, the MCP6001 is fair and is comparable to the 741.Comparably, the 741 still has almost an order of magnitude better CMRR, better offset voltage spec, and built-in offset nulling. But they're usefulness is all dependent on application.

author: Zero999
author_rank: Super Contributor
timestamp: January 05, 2012, 06:30:30 pm
content: Quote from: slateraptor on January 05, 2012, 12:35:51 amWhy pay more for a rubbish op-amp when better alternatives can be found at lower prices? The 741 is expensive compared to many newer op-amps with better characteristics.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 05, 2012, 06:59:22 pm
content: its a legacy. but i wonder why some people still recommend using 741 esp in circuit example. newbie will be forced to be using it and hail 741 will never die.

author: amspire
author_rank: Super Contributor
timestamp: January 05, 2012, 09:28:17 pm
content: I haven't used a 741 in years, but if I was teaching analog design, I might easily choose it.It is one of the best documented designs in the IC world. I seem to remember a brilliant breakdown of the internal design from Fairchild (that I couldn't find), but there is great information the IEEE article "The Monolithic Operational Amplifier: A Tutorial Study" by James Solomon of National Semiconductors that is reprinted in this app note:http://www.ti.com/lit/an/snoa737/snoa737.pdf.I am sure I have seen complete Spice models of the actual 741 design, as apposed to idealized parameter-based spice models.It is the kind of circuit that you could try and build using discrete parts - no multi-emitter transistors, super beta transistors, unobtainable matched mosfets or other IC-only technologies.The limitations of a 741 make it excellent for teaching as you really appreciate the improved specs of the newer opamps. It is much easier to learn about input currents, input offset currents, and offset voltage and current temperature drifts in a 741, then in a newer mosfet-based opamp.In general though, if I see a design using a 741, I will replace it with a newer IC if I decide to build the design.Richard.

author: slateraptor
author_rank: Frequent Contributor
timestamp: January 05, 2012, 09:33:34 pm
content: Quote from: Hero999 on January 05, 2012, 06:30:30 pmSurely for some applications, better performance at cheaper price isn't necessarily desirable. Case in point: in academia (or at your personal workbench) as a learning tool. Imagine yourself having studied all these op amp non-idealities in lecture, but when you get to the lab to empirically verify these claims, the op amps you have perform so well that non-idealities were swamped out by other dominating external factors like probe loading and breadboard parasitics, viz. how do you learn to manually compensate for offset voltages and bias currents when the act of detecting the discrepancy actually becomes difficult? Use a single supply op amp like the MCP6001 and you might not discover just how bad bias currents can affect amplification, or that other op amps don't perform as well on the negative swing, of you might be misled into thinking that any op amp can be configured for single supply operation, or that rail-to-rail operation is universal.From a production standpoint, point taken. But I see the world as being a lot more than maximizing profits. Besides, unless you're in mass production, the price difference is on the order of pennies on the dollar; most people allow a larger price buffer zone when purchasing commodity products of much greater volatility--like toilet paper. I recall reading somewhere (wiki perhaps?) that the during its heyday, the 741 was used in medical instruments. If it was good enough for that back then, surely it's good for something today?Quote from: Mechatrommer on January 05, 2012, 06:59:22 pmThe 555 timer is also a legacy device, but variants are not as commonplace, whereas op amps are generally considered a basic building block these days so it's much easier to criticize the performance of a 741. I believe Fairchild was the seed of the original and they no longer manufacture the device. Others manufacturers do, maintaining the basic topology while capitalizing on more modern day materials, processes and packaging, as evidenced by a quick DigiKey search. To be frank, I hope it never dies because the 741 enabled many a engineer to aspire to their current status, and I hope that one day I too can earn the right to be included amongst them whilst acknowledging that the classic 741 was a stepping stone that contributed to my success. The vacuum tubes of yesteryear are all but gone, having been replaced by the transistor, and I feel like the engineers who lived through that transition were the ones who had the most to gain. Now, we live in a 21st century dominated by digital methods--the discrete analog to integrated digital transition, if you will. Analog engineers are dropping off like flies and the pedagogical zeitgeist has shifted to the point where large analog-based corporations like TI are awarding ridiculous scholarships to select pure analog design projects with the hopes of attracting young blood. I know that analog won't be disappearing any time soon, viz. digital engineering at sufficiently high frequencies is asymptotic to analog engineering, but I'm not going to let this once a generation opportunity to refine my knowledge base pass by simply because a more convenient sol'n can be had for pennies less, let alone unqualified assertions of the uselessness of legacy silicon devices.But I digress. I feel like I've just written a 741 manifesto.

author: slateraptor
author_rank: Frequent Contributor
timestamp: January 05, 2012, 09:37:17 pm
content: Quote from: amspire on January 05, 2012, 09:28:17 pm*high five*And thanks for that app note link.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: January 06, 2012, 12:31:43 am
content: Quote from: slateraptor on January 05, 2012, 01:29:46 amOf course, of course, nothing very special about the MCP6001 either. And indeed its all about therequirements of the application. In case of Greg J the topic owner:Quote from: Greg J on January 01, 2012, 04:26:16 pmAnd in real life, any other average application is single supply 3.3V also.

author: saturation
author_rank: Super Contributor
timestamp: January 06, 2012, 01:29:36 pm
content: I think it best to be flexible and use whatever you have in hand when prototyping, so one needn't wait for parts from a distributor, or when making one-off or very low volume designs. While always best to design for most efficient parts and lowest cost when going into production, my need is mostly time constrained: a designer may have only the time to get something designed and done now, and can't wait for parts to arrive and simply need a solution or a product that does the job.That said, I still use the 741 or its analogs whenever it seems applicable and I have some handy. Its often not cost effective to buy as you can get more capable op amps for the same money, but on occasion, you may run into a lot of them for under 10c each versus the 70c its typically sold for at Digikey, or you can salvage an old device with it in there.Perusing Digikey, there are ~30k op amps in their catalog, ~10K in stock, of these there are > 100 that have gain-bandwidth products of 1 MHz, with various other features superior to the 741. There are a myriad of choices, but unless I need to optimize parts count and cost, most of the time I need it now and will design with whatever is available ASAP either in my toolbox or what the distributor has in stock at lowest price!

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2012, 11:16:22 pm
content: Quote from: saturation on January 06, 2012, 01:29:36 pmAgreed. I also occasionally use the 741 one-off's but I consider using it for new designs to be bad practise.

author: SeanB
author_rank: Super Contributor
timestamp: January 10, 2012, 08:11:07 pm
content: I have a box of the TO100 can versions around. Nice thing about the 741 is the amount of abuse it can suffer. I used them to replace OP27's in a 16 bit controller ( on hand, and I had heatsinks to handle the half watt or so of heat they generated) which had amongst other things a bad tendency to kill the drivers of the motors, as they were run from +-26v rails to get a +-20v swing. They were good enough to use over the full aerospace temperature range to give reliable 12 bit plus accuracy, and did so for many years. There are some on the Voyager probes, and they are pretty much a staple of most older industrial controllers.Not the fastest, not the lowest offset, not the lowest noise device, but all radio stations have then in the audio links somewhere, and they were the mainstay for older mixing decks. You can get them selected for low noise, low offset from most suppliers, and they are available in all package formats. If you ever used an analogue hybrid module it likely had a 741 chip in it somewhere.