Working with LM741 in simulation - advice for more recent parts?

Thread Starter

CineDroid

Joined Jan 25, 2020
20
Hi all, this is a follow up to this thread I posted on the Power Electronics Forum:
https://forum.allaboutcircuits.com/threads/power-good-and-source-disconnect-mosfet-question.167699/

The goal is to have a visual representation of the state of a circuit: tripped fuse or not tripped.

I took @AlbertHall's suggestions into account and simplified the design by referencing the non inverting input to ground and the inverting input to the voltage after the fuse. So that Vout is low in regular operation and higher when V2 and V1 are closer to each other to power the red LED on.

I've also put in an Op-Amp with V+ and V- terminals (LM741) to try and think about power supply (I've only used ideal OpAmps in my simulations so far).

In the environment I want to use this in, I have a readily available voltage source regulated at 26.5V. I'm trying to use that to provide a steady voltage to V+ through a resistive voltage divider. In the current simulation V+(fault) is over 10V and V+(good) is under the 22V which are the limit values of the LM741 per TI's spec sheet.

I've read on this forum and elsewhere that the LM741 is super obsolete and I was wondering if anyone had any recommendations for an OpAmp I could order or a kit/series that could play nice in this configuration so I order the right parts since I don't have any OpAmps in my kit yet (first time designing something with OpAmps here :)

Thanks for reading,

CD.
 

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dl324

Joined Mar 30, 2015
10,758
I've read on this forum and elsewhere that the LM741 is super obsolete and I was wondering if anyone had any recommendations for an OpAmp
It's not obsolete. It's just inappropriate for your circuit. You can't operate an LM741 with a single supply because the input voltage range is 3V away from either rail so you can't ground the non-inverting input.

Since you're operating the opamp open loop, you should use a comparator instead. Since most comparators have open collector outputs, you need to modify the output circuit.
 

wayneh

Joined Sep 9, 2010
16,390
An LM358 would be my choice of op amp. Only a little newer than the 741 but cheap, ubiquitous and fine for this job.

I’d prefer a comparator for this job, though, such as LM339. Not a big deal, and I’d use the op-amp if I didn’t have the comparator on hand.
 

Thread Starter

CineDroid

Joined Jan 25, 2020
20
You can't operate an LM741 with a single supply because the input voltage range is 3V away from either rail so you can't ground the non-inverting input.
Good to learn, thanks!

An LM358 would be my choice of op amp. Only a little newer than the 741 but cheap, ubiquitous and fine for this job.

I’d prefer a comparator for this job, though, such as LM339. Not a big deal, and I’d use the op-amp if I didn’t have the comparator on hand.
I was browsing LT's catalog and I had a sense I should actually be looking for a comparator but then I got lost in spec sheets and trying to understand the difference and how to get the right part so thanks for suggesting the LM339.

My personal favorite is the MCP6024, it's a 5V rail-to-rail job that emulates an ideal opamp admirably.
I take a look :)
 

dl324

Joined Mar 30, 2015
10,758
thanks for suggesting the LM339.
That's a quad part. LM393 is the dual version.

While you can use opamps as comparators, the frequency compensation most include for stability cause them to be slow comparators. For noncritical applications, you can use comparators as opamps and vice versa. But it'll still make people who know better to scratch their heads.
I take a look [at MCP6024]
My philosophy is to never use a $2 part when a $0.25 part will do the job.
 
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Sensacell

Joined Jun 19, 2012
2,567
My philosophy is to never use a $2 part when a $0.25 part will do the job.
Agreed, but when it's not a production design, that $2.00 parts saves way more than it's cost not having to work around the annoying shortcomings of inferior opamps.
 
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