Re: The Venerable 741

john larkin <JL@gct.com> wrote:

On Sun, 3 Nov 2024 19:14:54 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

john larkin <JL@gct.com> wrote:

On Sun, 03 Nov 2024 18:07:35 +0000, Cursitor Doom <cd@notformail.com>
wrote:
 

It's been around an awfully long time and there are far better
alternatives out there. But is there still a case for using them in
certain niche applications in 2024?

 
I can't think of one. The design is 56 years old. It has its own
Wikipedia page.
 
There are faster, cheaper, lower noise, lower bias current/offset RRIO
amps around these days.
 
I remember the day when, still a kid in college, I decided to replace
LM709s with LM741s in a control system. The 741s were more expensive
(the cost of a pretty good lunch) but didn't need external
compensation parts or front-end-zener protection, and current limited.
 
The early 741s had bad popcorn noise, but I'd expect that to be better
now.
 
My default gumdrop amp is OPA197 now, in SOT23. It makes a good
comparator too. There are cheaper parts if you can tolerate low supply
voltages.
 
 

 
LM358s are still useful, though.  I use them in things like bias loops,
where their limited speed and fairly poor input accuracy don’t matter.
 
In our licensing conversations, pointing out that we’re saving more on the
BOM than the royalty costs is a pretty persuasive argument, entirely aside
from the improved performance.
 
Cheers
 
Phil Hobbs

 
358 is not bad, a dual opamp for 10 cents, but most have some shared
current sources that can make sections interact. And weird behavior if
any input goes slightly below ground.
 
 

AFAICT it was just the original 324 that had the shared current source
problem. I’ve never run into it in any 358 or 324A version.

The problem is pretty unsubtle, though. Pulling both (PNP) inputs of any
section high enough causes its tail source to saturate, so its beta tanks
and it sucks all the available drive, turning off the input stages of the
other 3 sections.

There are all sorts of Chinese parts on LCSC that are even cheaper and
apparently better, but the 358 is a known quantity, which matters a lot.

Cheers

Phil Hobbs
--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics