LM358 not working as expected

NuttyMonk · Joined: Jun 30, 2020 Posts: 63 Location: UK

Hi all,

i am trying to use the LM358 as a comparator using a 5V single-sided supply and i expected to get 5V out on the upper part of the comparison but i'm only get about 3.8V. The reason i got them was due to a suggestion here on EM. I expected them to be able to go up to the supply rail voltage but that isn't happening.

Can anyone advise on an opamp which will do what i want?

When u search on a local electronics supplier
https://uk.rs-online.com/
one of the stats that you can search with in their opamps section is "Rail-To-Rail", yes or no. Is this the stat i should be paying attention to when looking for an opamp to go to the full rail voltage for comparators?

Cheers

NM

dk · Joined: Feb 12, 2019 Posts: 115 Location: Europe

If you won't be using the chip for anything else, why not use a comparator chip? Something in the LM339 family perhaps?

NuttyMonk · Joined: Jun 30, 2020 Posts: 63 Location: UK

Yeah, i've been looking at comparators since i posted this. They seem simple enough to use. I've ordered some LM311's to try out since i see them a lot on schematics.

Thanks

NM

PHOBoS · Posted: Fri May 07, 2021 9:13 am Post subject: Re: LM358 not working as expected

In this case a comparator would indeed be useful, or you could place a logic gate after the opamp if you happen to have an unused one in the circuit.