OPA 2237 as improvement to replace LM358 ?? - Page 1
Forum section: electronics / projects

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 20, 2025, 07:59:07 pm
content: HelloDoes that possile to swicht LM358 to OPA2237Pin out is the sameavailable in SOIC8offset is far lowernoise is lowerfrequency is similarlook to be possible .... I plan to rework some AD620 cheap boards to improve performances and supply in +/- 15VRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: June 20, 2025, 08:19:35 pm
content: Looks reasonable, if one needs single supply operation (common mode all the way to the negative supply). If one does not need single supply, there would be more and better choices (e.g. OPA2202).The classic improbed LM358 is the LT1013, but this one comes with an odd pinout in SOIC8.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 20, 2025, 10:28:06 pm
content: AD620 costs about 20x more then an LM358. If both are used in the same circuit, then LM358 almost certainly used in some very generic and non critical part of the circuit, and replacing it with a "better" opamp may be pointless.If you show the schematic, then some people here may have a better advice. Also state more clearly what the current problem is with that board, and which parameters you seek to improve.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 21, 2025, 06:31:13 am
content: Quote from: Kleinstein on June 20, 2025, 08:19:35 pmHelloPurpose to use +/- 15V on all IC , LT1013 have not the same pinout so that impossible to replace as it I use LT1013 usually but in this case that do not match the existing PCBThanks for the OPA2202 advice , price is inder 2 Euro but this purpose I need +/- 15VRegardsOS

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 21, 2025, 06:33:45 am
content: Quote from: Doctorandus_P on June 20, 2025, 10:28:06 pmHelloI link the circuit one side of the LM358 is used a ref for the AD620 the other is on the ouput , circuit is just a base circuit I will recheck and complete itSo Ref shall be stable as possibleOutput shall be without noise or at least reduced as possiblefor Ref supply I will use a dedicated IC as REF5050 to feed to the Op Amp rather to use V+ V- noisy and not stableRegardsOS

author: iMo
author_rank: Super Contributor
timestamp: June 21, 2025, 07:13:34 am
content: .. congratulation to your 50th thread you started..

author: peter-h
author_rank: Super Contributor
timestamp: June 21, 2025, 07:24:56 am
content: THE LESSON learnt by smart people during covid was that the LM358 was available while everything more specialised was hoarded.Use the LM358 everywhere you canYoung designers like to pick latest parts and that is largely what drove much of LT's business over the years...If you want really high DC spec, not great AC spec, check out the TLV2333. BTW, the TI version is much better than the cheaper Philips (ON SEMI) version...

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 21, 2025, 08:02:43 am
content: Quote from: peter-h on June 21, 2025, 07:24:56 amHelloI agree LM358 is a effective solution for a lot of project and new LM358B performance is far better than original LM358 from the past .In my case I need the lowest noise and offset possible , before to redesign a complete PCBRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: June 21, 2025, 08:16:40 am
content: The TLV2333 is not helping here, as it is 5.5 V max for the supply. In the circuit the OPA2202 should work as the voltages are not all the way to the rails.For the given circuit the LM358 may not even be that bad (for use with rel. high gain). The ref. divider and the ICL7660 charge pump (can cause quite some supply spikes and needs care with the layout and capacitors) are worse. A 100 K trimmer for the gain is also a fail: That would be for low gain like 1.3 to 3 and the trimmer adds drift.Using the supply as reference is not good, especially not using the simple divider from positive to negative supply. If one only needs the trim for a small offset, one could get away with the supply, but use and additional attenuator towards ground before the buffer. So somehing like 100 ohms to ground and 100 K to the pot wiper to get some +-12 mV trim range.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 21, 2025, 09:01:21 am
content: Quote from: Kleinstein on June 21, 2025, 08:16:40 amHelloThanksI plan to remove the 7660 and feed directly the PCB in -15V on the 7660 pin with a wirethe potentiometer gain ( entry quality pot ) is from my experience = junk as that noisy and not mecanical stable , I will set a good fixed value resistor .the ref will be provided by an Ref5050 + divider made with quality resistor , I have batches of Dales thin filmI have LM358B available I wil use one for test and swicht after to OPA2237 as I group shipping on Mouser order .RegardsOS

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 21, 2025, 09:57:15 am
content: I don't understand your circuit. AD620 has a worst case offset of 1mV or so, and you're doing something with that with a potentiometer that has an adjustment range of 8V (Assuming +/- 5V supply). What are you trying to compensate for here and what is the adjustment rate you really need?Your adjustment range is also not referenced to GND at all, so it will wobble with any change with any of the supply voltages (i.e. lack of proper reference as Kleinstein already mentioned. A simple way to reduce the adjustment range is to add a resistor (100 Ohm to 1k) between the wiper of the P2 and GND.I am also having doubt whether buffering the output of the AD620 has an advantage.And how did you manage to make such an foggy screenshot? May I suggest you to put some effort into learning about different image formats and their applications and limits. JPG is quite reasonable for photographs, but not well suited for line art. .PNG is much better for line art, as it does not apply lossy compression. It looks like the red/green schematic has multiple stages of jpg compression over it, and the black text box in the upper left only has one stage of jpg compression.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 21, 2025, 10:27:03 am
content: Quote from: Doctorandus_P on June 21, 2025, 09:57:15 amHelloI am not the designer of this circuit , I have a batch of then with the linked schematic on a paper sheet , I make some experimentsRegarding the LM358 at the AD620 ouput I agree that strange I can remove itRegarding the LM358 at the ref pin from my undertand I can connect to the groundI will remove it and make some measurements with Ref to the ground ,and output straight to to ADCRegardsOS

author: David Hess
author_rank: Super Contributor
timestamp: June 21, 2025, 12:48:34 pm
content: The OPA2237 has a very limited differential input voltage range compared to the LM358, but this probably does not matter in your circuit. Except for this, it looks like it was designed as an improved replacement.Quote from: Kleinstein on June 20, 2025, 08:19:35 pmThe odd pinout is because the LT1013 die is too large to fit inside of a SOIC8 without rotating it 90 degrees.

author: andrewtaylor
author_rank: Contributor
timestamp: June 21, 2025, 12:50:02 pm
content: Not mentioned yet, but might bei worth to take notice:When Budget ist very tight, Check the LM358B ..ti.com did some nice rework of the Chip.Of course, for high precision you have to choose some of the other OP mentioned above.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 21, 2025, 12:56:44 pm
content: Variants of the '358 have some of the lowest input capacitance values of any opamp, for those applications where that is important. That's a spec often omitted by spec sheets and difficult to tease out of the manufacturers, but even TI's Engineers confirmed it when we bugged them about it.Not all "old parts" are without value.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 21, 2025, 01:54:31 pm
content: Quote from: David Hess on June 21, 2025, 12:48:34 pmHelloThanks for this important detail , I will checkRegardsOS

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 21, 2025, 02:28:49 pm
content: Quote from: andrewtaylor on June 21, 2025, 12:50:02 pmHelloI will start with LM358B as the cost is very low , and that allow to make measurements and learn , on my usual strain gage amplifier boards than I use since years I have INA110 which are very good and frequency at gain 100 is far enought for the 30KHz mechanical impulseAD620 purpose is to compare accuracy between my usual INA110 and a basic amplifierRegardsOS