Good rail to rail input opamp for at least 12 volt ? - Page 1
Forum section: electronics / projects

author: JanJansen
author_rank: Frequent Contributor
timestamp: January 29, 2018, 05:25:13 pm
content: Hi, i need a ( cheap ) rail to rail input opamp in DIP package,normally i use Microchip ones, they can not go higher then 5.5 volt.I am searching at Mouser, there is no catagory for rail to rail opamps.Do you know what opamp is good ?thanks

author: Benta
author_rank: Super Contributor
timestamp: January 29, 2018, 05:33:08 pm
content: I often use LMC6482, it's not very fast though (and dual).

author: capt bullshot
author_rank: Super Contributor
timestamp: January 29, 2018, 05:34:35 pm
content: TLV2374 (quad)/ TLV2371 (single)max. 16V supply, RR IO, 3MHz, and DIP package available

author: Zero999
author_rank: Super Contributor
timestamp: January 29, 2018, 05:46:02 pm
content: LM6132 (dual) LM6134 (quad)http://www.ti.com/lit/ds/symlink/lm6132.pdfLT1490 (dual) LT1491 (quad)http://cds.linear.com/docs/en/datasheet/14901fb.pdf

author: james_s
author_rank: Super Contributor
timestamp: January 29, 2018, 07:50:31 pm
content: What other characteristics do you need? That can have a large impact on component choice.Even many op-amps that claim to be rail to rail have considerably lower performance as the output nears the rails.

author: David Hess
author_rank: Super Contributor
timestamp: January 29, 2018, 08:48:33 pm
content: The LMC6482 is what I have used in the past but like most rail-to-rail input operational amplifiers, it has poor precision.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 29, 2018, 09:10:31 pm
content: Are you going to whine about cost?OPA4192IDR is especially good (full 30V range, precision), but not cheap.TLV2372 is good up to 16V, and isn't dripping with precision. Maybe good enough here?Tim

author: Zero999
author_rank: Super Contributor
timestamp: January 29, 2018, 11:22:31 pm
content: Quote from: james_s on January 29, 2018, 07:50:31 pmIf the output only needs to go to one rail, that can be bodged using a current source/sink, as in the LM358/324 IC.See the thread linked below for how this is done and the issues some SPICE models have with simulating it.https://www.eevblog.com/forum/projects/better-ltspice-tl072-model/msg999066/#msg999066

author: JanJansen
author_rank: Frequent Contributor
timestamp: January 30, 2018, 01:37:12 pm
content: Thanks for the replys, the TLV2372IP looks intresting, still expensive more then 2 euro.Quote from: james_s on January 29, 2018, 07:50:31 pmThe rail towards 0 volt is most important to me, the high rail does not matters, i wont get to 12 volt.Presicion is important to me, since i use it for a control voltage in a voltage controlled oscillator.Now i am using a NE5532, only the low notes are below the rail,any rail improvement is welcome, i better like a cheap opamp with a bit wider rail then a 2 euro opamp with almost no rail.Anyways the NE5532 is a small improvement over the TL072, maybe there is another "normal" opamp with less rail ?Low noise is better i think, speed dont matters for me.How presice is it compared to a TL072 or NE5532 ?, they work fine, you call that presicion or no presicion ?

author: capt bullshot
author_rank: Super Contributor
timestamp: January 30, 2018, 01:59:02 pm
content: Quote from: JanJansen on January 30, 2018, 01:37:12 pmIn that case, check the TLV274 / TLV272 / TLV271It is RR Out, and negative Rail (0V) in, Otherwise similar to the TLV2374These all have the typical "few" millivolts offset that are usual for a "non precision" (standard) OP-AMP (like a TL072). If you need better (less) offset voltage it quickly gets way more expensive. Usually this little offset should be trimable in your circuit (if required). Low drift is more interesting here (if the oscillator isn't part of a control loop).

author: JanJansen
author_rank: Frequent Contributor
timestamp: January 30, 2018, 03:28:54 pm
content: Hey thanks, i added the TLV272 to my cart,very good, now i dont have to pay for the unused 12v rail, nice.I have trimmers in my circuit no problem,temprature drift is indeed important, i want as stable as possible.

author: David Hess
author_rank: Super Contributor
timestamp: January 30, 2018, 05:48:24 pm
content: Quote from: capt bullshot on January 30, 2018, 01:59:02 pmI associate precision more with low offset drift, high common mode rejection, and high open loop gain. Offset can be calibrated or nulled out. Low common mode rejection is a precision killer unless the operational amplifier is used in inverting mode and then you do not need a rail-to-rail input because the input should not be moving.Bipolar rail-to-rail input parts reverse their input bias current at some point of their input common mode range, usually near the positive rail. Most parts have a large shift in offset voltage at that point as well. The mentioned LMC6482 avoids both of those problems but just has terrible common mode rejection.Texas Instruments has some parts where an extra input is used to select where in the common mode input range the input offset voltage and bias current shift. They also have some parts where the parallel input differential pairs are trimmed individually to minimize the offset voltage shift. I have no idea how to find these in their selection tables though.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 30, 2018, 10:04:10 pm
content: Ah, single supply, middling speed? Probably you want low noise more than low offset then?? OPA170 and 171 are nice.Tim

author: RobK_NL
author_rank: Frequent Contributor
timestamp: January 31, 2018, 10:43:10 am
content: Quote from: JanJansen on January 29, 2018, 05:25:13 pmTry searching atDigikey, they have a much more comprehensive search engine.