Rail to Rail op-amp for a beginner  - Page 1
Forum section: electronics / beginners

author: matteo83
author_rank: Newbie
timestamp: January 18, 2014, 09:43:09 pm
content: Hello everybody,this is my first post on the forum of this fantastic blog!I'm into informatics and just started learning the basics of analog electronics.I'm in the process of buying the essential ingredients to start making a few experiments with analog circuits.(I already have an arduino, a bunch of resistors, capacitors, diodes, etc.)I also have a few TL082 op-amp. I've read around that these are pretty good op-amps.However they require a somewhat high power supply (greater than 5v) and this is often problematic (for me).Furthermore, the are not rail to rail.QUESTION: I'd like to receive some suggestions about an op-amp easy to use for a beginners in a lot of situations (general purpose).This requirement means that it should work as close as possible to an ideal op-amp and this translates to me, and to my very limited point of view, as:1) Rail-to-Rail op-amp (so I don't have to worry about biasing it, etc). While I'm sure that this requirement is often not of greatimportance for experts, I'd really like to have rail-to-rail just for the conceptual simplicity.2) A wide voltage supply: min-voltage <= 3 and max-voltage >=12 are requirements.3) In a DIP package, so that I can use it easily with a breadboard.4) The higher the output current it can handle, the better.5) Furthermore, since I plan to do something with sound, it should behave well at frequencies at least up to 20khz6) Since I would buy about 10/20 of these (ideally to play with in my projects for at least 1 year), the price per unitshould be less or equal than 1$.7) Easy to find: mouser/digikeyThank you very much for any suggestion!

author: wiss
author_rank: Frequent Contributor
timestamp: January 18, 2014, 10:24:27 pm
content: tl07? For general junk, ca3140 and related for limited railtorail (noisy), ad820 for low bias, Icl7650 or ltc1052 for low offset, uA741 for the quaint feel...Ne5532 for low cost audio, not railtorail, not even close

author: fcb
author_rank: Super Contributor
timestamp: January 18, 2014, 10:28:30 pm
content: LM358 - general purpose, works on 5v and good o/p swing.

author: kg4arn
author_rank: Unknown
timestamp: January 18, 2014, 10:30:32 pm
content: In my opinion rail to rail op amps are not necessarily easier to use.Just starting out: get a +/- 15V supply and use some older PDIP available op amps.These will be less expensive as well.The audio classic is the NE5532 and they are less than $1 in quantities of 10 or more. TL072 often used at audio for an FET input op amp.Also there is less biasing considerations when using a split supply than when using a single supply.I agree with the others as well. LM358 is a pretty good general purpose dual opamp and I use them a lot.

author: matteo83
author_rank: Newbie
timestamp: January 18, 2014, 11:41:27 pm
content: Dear all,thank you very much for the very quick answers!I'd be grateful if you could also help me understand the datasheets of the LM358 (http://www.ti.com/lit/ds/symlink/lm358.pdf)and of the OP07 (http://www.ti.com/lit/ds/symlink/op-07-n.pdf).Starting from the LM358, I understand that:1) I can make the chip work with just 3V.2) Assuming a 3V supply (GND=0V, Vcc = 3V), both IN+ and IB- must be in the range 0V --> 3V-1.5 = 1.5V.This is how I interpret the value Vicr in the datasheet.3) The output will be in the range OL=20mV to OH= Vcc -1.5 = 1.5.Any intended output above these numbers will be cut.[Actually, the values in the datasheet have been tested with Vcc=5V so maybe they are not valid for Vcc=3V]Is this correct? Please correct me if I'm misinterpreting the data.Since I plan to build some (very simple) circuit powered with batteries (for example a 3.7V Lipo), I'm not sure if these numbers would be very good.About the LM07:1) The minimum supply voltage is 6v (+/- 3V).However, I'm not sure how to interpret the data to find the input voltage range (like IVR before) nor the output voltage range.There is a value for the output swing, but I would like to know the distance from the rails, both from the -Vcc and from the +Vcc.NEW QUESTION: Perhaps, narrowing a bit my previous question, I'm interested in an op-amp that can be used easily at low voltages (that's why I was asking rail-to-rail.) since I plan to work with a microcontroller like the atmega328.At the same time I'd be happy if the same op-amp could be used at higher voltage-supplies just in case I come up with something cool to do at, say, 12v. But I guess an op-amp can not have all the good properties at the same time :-PThank you very much once again for your answers.

author: Chris_PL
author_rank: Contributor
timestamp: January 18, 2014, 11:48:06 pm
content: Quote from: kg4arn on January 18, 2014, 10:30:32 pmTotally agree.To the OP:If you're just experimenting, without need of precision stuff, add a ICL7660 charge pump to your breadboard to get -5V rail (or thereabouts, it's far from perfect on noise, load basis and so on). With +5/-5V you'll be able to easily experiment with TL0xx's and even these "not jelly-bean" op-amps.And after you've done with your analog stuff you can easily add a level shifter to feed your output to uC's ADC.

author: poorchava
author_rank: Super Contributor
timestamp: January 18, 2014, 11:55:11 pm
content: First of all you need to know, that there are different types of rail-to-rail Opamps. Some have rail to rail input, some have outputs. Sometimes this includes lower rail, sometimes higher rail. In the end I do not know of any opamp that can go to actual 0V on the output when powered from single supply. Most of them will only go as low as couple militants or so at best.I'm typically using LM358, LM2904, TL08x and OP07 as my general purpose Opamps.

author: Rerouter
author_rank: Super Contributor
timestamp: January 19, 2014, 01:22:28 am
content: equally for rail to rail output that includes lower rail, that spec is only valid while driving a specific load, say 1K to ground, as it needs something to sink the leakage current on its output,