please suggest me on  opamp.. - Page 1
Forum section: electronics / beginners

author: rao
author_rank: Contributor
timestamp: November 29, 2020, 03:35:48 am
content: HiI want to buy integrated circuit between 36 and 44V for my project. please suggest me basic operational amplifier, voltage regulators in this range and affordable. Thank you all. Have a happening Sunday.

author: Dabbot
author_rank: Regular Contributor
timestamp: November 29, 2020, 04:17:15 am
content: What does your project do?

author: rao
author_rank: Contributor
timestamp: November 29, 2020, 04:42:33 am
content: want to construct regulated power supply which should supply 40V with OPAMP andNOT VOLTAGE REG.so i need some general purpose opamp (DIP, T0 package,etc) which could be used for through hole technology.

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 29, 2020, 05:00:53 am
content: LM741A

author: rao
author_rank: Contributor
timestamp: November 29, 2020, 05:03:45 am
content: sir,LM 741A is safer up to 36V.But my application will have maximum of 40V. Suggest me Some other opAMP where it has greater voltage than LM741..

author: Dabbot
author_rank: Regular Contributor
timestamp: November 29, 2020, 05:28:14 am
content: Some variants of the 741 will allow an absolute maximum of 44V:UA741I -https://www.st.com/content/ccc/resource/technical/document/datasheet/group1/d6/9e/4e/8a/fa/65/4c/d0/CD00001252/files/CD00001252.pdf/jcr:content/translations/en.CD00001252.pdf

author: BravoV
author_rank: Super Contributor
timestamp: November 29, 2020, 05:40:55 am
content: You are in India, are you willing to import say like Digikey and alike ?Will you pay about US$50for just one op-amp ? As India has crazy import tax regime, incl. the international shipping charge.Bottom line is, what is the budget ? Other wise, what ever people suggest here will be useless.

author: rao
author_rank: Contributor
timestamp: November 29, 2020, 05:53:13 am
content: Sir,I could be able to spend 30 Indian rupees for an OPAMP( less than half a dollar) .

author: BravoV
author_rank: Super Contributor
timestamp: November 29, 2020, 05:59:46 am
content: Then just live with what ever available in your place, as you do NOT have the luxury of choosing the right op-amp as you want.I doubt even India has 44V variant of 741, at least cheaply or easy to find.

author: exe
author_rank: Unknown
timestamp: November 29, 2020, 10:32:34 am
content: Why do you need 44V?

author: rao
author_rank: Contributor
timestamp: November 29, 2020, 10:43:33 am
content: SIR,A 30V transformer when rectified gives nearly 41V. so it is required 44V for Safety margin.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 29, 2020, 10:45:37 am
content: Use the parametric search of the distributor you are able to use. For example, sorting Digikey for parts rated at least maximum 44V, results in 433 items in stock and normally stocking:https://www.digikey.fi/products/en/integrated-circuits-ics/linear-amplifiers-instrumentation-op-amps-buffer-amps/687?FV=-8%7C687%2C659%7C100675%2C659%7C103590%2C659%7C143820%2C659%7C143822%2C659%7C143823%2C659%7C143825%2C659%7C143832%2C659%7C143845%2C659%7C143846%2C659%7C143849%2C659%7C143851%2C659%7C143854%2C659%7C143856%2C659%7C155208%2C659%7C155210%2C659%7C184608%2C659%7C184609%2C659%7C184610%2C659%7C184611%2C659%7C184614%2C659%7C208691%2C659%7C208719%2C659%7C215315%2C659%7C228770%2C659%7C228791%2C659%7C228792%2C659%7C233132%2C659%7C238748%2C659%7C249287%2C659%7C249359%2C659%7C257654%2C659%7C261832%2C659%7C267487%2C659%7C267512%2C659%7C267543%2C659%7C287651%2C659%7C287652%2C659%7C295254%2C659%7C295265%2C659%7C297472%2C659%7C305540%2C659%7C305544%2C659%7C66608%2C659%7C69642%2C659%7C69643%2C659%7C69645%2C659%7C69647%2C659%7C74541%2C659%7C74604%2C659%7C74612%2C659%7C74619%2C659%7C94761&quantity=0&ColumnSort=1000011&page=1&stock=1&nstock=1&pageSize=25The 741 obviously being the cheapest and most universally available. But 44V is the absolute maximum rating, the recommended is just 40V. So this is the caveat with parametric searches, you need to apply some more manual work because you don't know how the sales engineers actually classified the parts exactly.If the only available "distributor" is a local brick&mortar store or a component dealer on an alley, then why not chat with them, they likely know what they have available and might know at least the basics like voltage ratings of the parts they sell.Especially when availability is a problem, it's much easier to work with the component dealers to choose the part, than to ask generic advice here.

author: xavier60
author_rank: Super Contributor
timestamp: November 29, 2020, 01:46:55 pm
content: Or use a design that will work with common opamps.

author: exe
author_rank: Unknown
timestamp: November 29, 2020, 03:22:08 pm
content: Quote from: rao on November 29, 2020, 10:43:33 amDoes this account that under no load transformers output higher voltage?What if power grid voltage is above nominal transformer voltage? Say, transfomer expects 230V, but input is 240V.I'd suggest use an LDO on opamp rails to lower total supply voltage*. This way the range of available opamps becomes much larger.*If this is feasible. Without heaving schematics I can't tell if this is going to work.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 29, 2020, 03:49:44 pm
content: Quote from: exe on November 29, 2020, 03:22:08 pmI totally fail to see why you specify anLDO, specifically, when you have significant voltage headroom and want to bring it down. A normal linear regulator works.LDOs, especially older generation (looking at you, 1117) tend to be compromised compared to traditional normal-drop out linear regulators, for example having peculiar output capacitance requirements that need to be carefully followed to avoid oscillation.Availability of high-voltage LDOs is on a poor side as well because it's quite a niche use case to require LDO when you have a lot of voltage available. In any case, finally whether a manufacturer thinks the dropout is low enough to be called an LDO is quite arbitrary so setting yourself such meaningless limitation is not fruitful.

author: jmelson
author_rank: Super Contributor
timestamp: November 29, 2020, 04:47:42 pm
content: I've used the Linear Technology LTC2057HV in a project requiring about 60 V supply. It worked quite well. There is also the LTC2057 without the HV extension that would likely work in your project. It is a general purpose op-amp but can run off much higher voltages than typical parts.Jon

author: BravoV
author_rank: Super Contributor
timestamp: November 29, 2020, 04:57:01 pm
content: Quote from: jmelson on November 29, 2020, 04:47:42 pmDid you read the whole thread ? Or at least where the OP located, his limitation and also budget ($ 0.5) ?

author: exe
author_rank: Unknown
timestamp: November 29, 2020, 05:37:19 pm
content: Quote from: Siwastaja on November 29, 2020, 03:49:44 pmSorry, for me LDO == a regulator. Probably incorrect use of the term, but I'm yet to see a modern regulator that would have more than a volt of drop (except modern versions of, say, lm317). Of course old venerable regulators will work too.

author: fcb
author_rank: Super Contributor
timestamp: November 29, 2020, 07:16:14 pm
content: LTC2057HV is a good part (others have suggested).TL072 (from Texas) has a 40V rating, at least one other manufacturer of the TL072 (ST) rates it at 36V.If cost/availability is a big driver I'd probably roll my own amplifier from discretes, perhaps using MPSA42/92's.

author: girishv
author_rank: Regular Contributor
timestamp: November 30, 2020, 03:37:19 am
content: Quote from: rao on November 29, 2020, 04:42:33 amThe members of this forum are kind and helpful. Probably you are better off by sharing more details on your project. I am sure many of them would have done something similar to whatever you are trying to do and have suggestions for you.

author: Jwillis
author_rank: Super Contributor
timestamp: November 30, 2020, 07:53:11 am
content: LT1637https://www.analog.com/media/en/technical-documentation/data-sheets/1637fd.pdfSingle Supply Input Range: – 0.4V to 44VOPA445https://www.ti.com/lit/ds/symlink/opa445.pdf?ts=1606675922303WIDE-POWER SUPPLY RANGE ±10 to ±45 currently running these at 50V in power supply .

author: jmelson
author_rank: Super Contributor
timestamp: November 30, 2020, 04:35:09 pm
content: Quote from: BravoV on November 29, 2020, 04:57:01 pmYes. Sometimes, the OP asks for the impossible, and I give a solution that is "possible" but doesn't meet his list of requirements.There might be ways to do what he needs with ordinary op-amps and a transistor or two, but he really didn't give enough information to know if that could work.Jon

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 30, 2020, 05:40:57 pm
content: I believe we have lost the TS.He may already be lurking in another forum, to see if they can provide a satisfactory answer to his impossible requirements.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 30, 2020, 06:01:17 pm
content: The MC33171/2/4 are relatively simple OPs specified for 44 V.The MCP6V51 can be a lower cost alternative to the LTC2057HV - both are AZ OP and thus a little special.Some audio OPs are also specified for relatively high voltage. Especially the OPA604, that is even OK up to 48 V. However it is not that cheap and relatively fast.

author: Zero999
author_rank: Super Contributor
timestamp: November 30, 2020, 09:02:20 pm
content: The MC33171 is a good idea and cheap, but the through hole packages have been discontinued and the original poster wants through hole.How about the OP07? The trouble is the through hole packages are more expensive than the surface mount one.https://www.ti.com/lit/ds/symlink/op07c.pdfQuote from: rao on November 29, 2020, 10:43:33 amAs mentioned above, you need a higher voltage rating than 44V. Transformers output a slightly higher voltage, when operating under light loads and the mains voltage could be on the upper end of the tolerance band.Please post a schematic.There are ways to boost the input/output voltage of an op-amp, using cheap transistors.

author: BravoV
author_rank: Super Contributor
timestamp: December 01, 2020, 06:43:37 am
content: Quote from: schmitt trigger on November 30, 2020, 05:40:57 pmYep, thats typical.Kinda strange, probably its the cultural thingy, most of the times, asked question and expecting an answer that they want to hear. I've been observing this for so many years at many-many forums.

author: exe
author_rank: Unknown
timestamp: December 01, 2020, 11:18:07 am
content: Quote from: Zero999 on November 30, 2020, 09:02:20 pmI believe soic-to-dip adapters are cheap to buy and easy to use.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 02, 2020, 07:15:14 pm
content: SO8 to DIP and also sot23-6 to DIP adapters are an option if desperate and there is really no good alternative (e.g. AZ OPs). There are still a few older types that may be available in DIP (e.g. 741 variants, maybe LF411A, OP07, LM201A, RM4558 ). In a country with a difficult supply, one just has to check the options available locally - hard to find help for this from the outside. With a limited choice the list may not be that long.Also not that one can build a 40 V supply also with only OPs good for 5 V if needed. It depends on the type of circuit - so need an OP that can drive the full output range, but others only need enough to control a current source. To get some 40 V of active range for the output can be more demanding than a 44 V supply. For a relatively high voltage range it may be wort rethinking the topology of the regulator.

author: David Hess
author_rank: Super Contributor
timestamp: December 02, 2020, 07:30:48 pm
content: Tektronix often specified 44 volt parts for power supply designs up to 20 volts. You may be able to get away with grading 36 and 40 volts parts for operation up to 44 volts if they have a 44 volt version.The low cost options are the 741C which depending on the manufacturer is 44 volts, and the LF356 JFET operational amplifier which is also 44 volts and useful because its input common mode range includes the positive supply. Both are available in DIP packages making them easy to use. Also consider the LM201A bipolar part which also has an input common mode range extended to the positive supply although it is only available in surface mount now.The slightly more expensive TLE2141 has an input common mode range that includes the negative supply. It is a semi-precision device so has other uses.Beyond those are premium precision parts like the LT1637 which is rail-to-rail input and output, LT1006 which is a precision single 324/358, LT1001 which is similar to the old OP07, and LT1013 which is a precision 358. My favored low input bias current LT1008/LT1012/LT1097 and their rail-to-rail output descendants are only 40 volts. Beware that precision bipolar parts which are not single supply have a limited differential input voltage range, with exceptions of oddballs like the LT1637 making this part very universal.

author: Zero999
author_rank: Super Contributor
timestamp: December 02, 2020, 08:47:38 pm
content: Quote from: exe on December 01, 2020, 11:18:07 amIt'll probably push the budget over 30 Indian rupees though. If he's using strip board, he could cut the tracks in half, which is what I've done in the past, when I didn't have a an adaptor board handy, or there wasn't room for one. Another alternative is to stick the IC to the board with superglue and connect it to the tack, with fine copper wire. Both methods aren't optimal: cutting the strips in half is a pain and if it's glued to the board, it's almost impossible to replace, if it's faulty.

author: rao
author_rank: Contributor
timestamp: December 06, 2020, 06:03:42 am
content: THANKS TO ALL,I HAVE TO WORK FOR MY LIVELIHOOD, SO I DIDNT FIND TIME GO TO MARKET AND SEARCH FOR ICS.I REPAIRED MY WATER RO SYSTEM IN WHICH SMPS OF 30V @ 2.5 AMPS GOT BURNT.SO STARTED TO CONSTRUCT MY LINEAR POWER SUPPLY WHICH COULD BE ATTACHED OUT THE RO SYSTEM. I BOUGHT A TRANSFORMER OF RATING 30-0-30 @ 5 AMPS, SO THAT AFTER REGULATION I COULD GET OUTPUT OF 30V DC @ 3 AMPS DC.I DONT HAVE ANY SCHEMATICS TO BUILT. IT SHOULD HAVE BOTH VOLTAGE AND CURRENT CONTROL SO THAT I COULD USE IT FOR OTHER PURPOSE.SORRY TO ALL FOR RESPONDING AND HAPPY SUNDAY....

author: rao
author_rank: Contributor
timestamp: December 06, 2020, 08:01:19 am
content: you all can give suggestion for circuit schematic. went through design of regulated power supplies by national instrument documents. but those opamps lm 308 and lm101 were obsolete.you all can suggest me the schematic to build. thank you all.

author: David Hess
author_rank: Super Contributor
timestamp: December 06, 2020, 09:12:21 am
content: Quote from: rao on December 06, 2020, 08:01:19 amThat is still a design I would recommend. The LM101 is replaced with an LM201A or LM301A. The 308 is replaced with practically anything.

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2020, 10:46:49 am
content: Quote from: rao on December 06, 2020, 06:03:42 amDo you know why the switched mode power supply failed? Could it be because it was overloaded? have you tried powering it from a bench supply? There might be a fault elsewhere, which caused it to fail.Assuming it is the PSU, why didn't you just buy a replacement 30V switched mode power supply? It will probably work out much cheaper, than building your own linear power supply using a transformer.If you want to build a 30V 2.5A linear power supply for fun, there's no need for an op-amp IC. Use the LM317 and a transistor to boost the output current.

author: rao
author_rank: Contributor
timestamp: December 06, 2020, 12:06:16 pm
content: Sir,We could control the voltage with LM 317. How to limit the current sir using LM317? because i could use the RPS for charging the battery.

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2020, 01:46:51 pm
content: Quote from: rao on December 06, 2020, 12:06:16 pmYes, it's possible to add a current limit.What sort of battery do you want to charge?

author: rao
author_rank: Contributor
timestamp: December 06, 2020, 05:36:33 pm
content: 12V 6 ampere lead acid battery

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2020, 10:43:16 pm
content: Quote from: rao on December 06, 2020, 05:36:33 pmYes, but you need a much lower voltage transformer to make a 12V lead acid battery charger.

author: rao
author_rank: Contributor
timestamp: December 20, 2020, 03:58:51 pm
content: Dear all,I came through this circuit which would do voltage regulation and current regulation. But I could not understand the need of operational amplifier in the circuit.

author: Zero999
author_rank: Super Contributor
timestamp: December 20, 2020, 06:13:45 pm
content: Quote from: rao on December 20, 2020, 03:58:51 pmDid you read the data sheet, which is where the circuit is from?https://www.st.com/resource/en/datasheet/l200.pdfThe op-amp is only required for an adjustable current limit. It works by amplifying the voltage across the current sense resistor and feeding it into the L200's current error amplifier loop. Adjusting P1 alters the gain of the op-amp circuit, thus the current limit.

author: rao
author_rank: Contributor
timestamp: January 01, 2021, 05:59:42 am
content: New year Greetings to all,Can i use LM741 with Single supply operation in DC circuits? What are the conditions to be followed?

author: Zero999
author_rank: Super Contributor
timestamp: January 01, 2021, 10:03:22 am
content: Yes, the LM741 and LM741A will work at DC and up to 44V. Just don't use the LM741C, which is only rated up to 36V.

author: rao
author_rank: Contributor
timestamp: January 01, 2021, 10:51:43 am
content: whether it will work for 36V or plus or minus 18V?because specification says plus or minus 18V and i am constructing DC regulated power supply.You all suggest can me circuit based on opamp with constant current and constant voltage circuits.Similarly you all can suggest switching regulators because linear supplies cannot be used for high power supplies. hence you can Circuits using Buck Regulators(SG 3525)..

author: Zero999
author_rank: Super Contributor
timestamp: January 01, 2021, 07:05:54 pm
content: Quote from: rao on January 01, 2021, 10:51:43 amOp-amp's don't have a 0V pin, just + and - power supply pins, so ±18V is the same as 36V.QuoteThere are lots of circuits, but you really need a proper specification, before building anything.https://www.eevblog.com/forum/projects/how-to-design-fast-bench-supply-with-cc-and-cv/https://www.eevblog.com/forum/projects/good-quality-lm723-lab-power-supply/msg2097736/#msg2097736https://www.eevblog.com/forum/projects/general-purpose-power-supply-design-7488/

author: rao
author_rank: Contributor
timestamp: January 02, 2021, 01:26:03 am
content: Thanks a lot.The secondary rating of new transformer is 26V@ 5 amps. It is better to get 4 amps DC output after regulation. Suggest me some opamp based power supply design. But linear mode has to dissipate nearly 120 watt(30 volts*4 amps) . Hence smps will be suitable for this much power. I searched net and i got L296 for my construction. Suggest me the correct path.

author: Zero999
author_rank: Super Contributor
timestamp: January 03, 2021, 09:48:29 pm
content: Quote from: rao on January 02, 2021, 01:26:03 amI thought you wanted a linear regulator. The L296 is a switched mode controller. It isn't easy to use it to provide variable voltage and current limiting, as you desire.You could use a linear topology and a transformer with a centre tap, with a relay, to reduce the input voltage, when the output voltage falls below a certain threshold.

author: rao
author_rank: Contributor
timestamp: January 04, 2021, 01:06:51 am
content: Thank you sir. Can i get some literature to understand transformer with relay, so that i could reduce power dissipation in regulator. I could understand this but i have not seen any circuit.

author: xavier60
author_rank: Super Contributor
timestamp: January 04, 2021, 02:02:50 am
content: If the 2 secondary windings are separate and the same voltage as each other, a DPDT relay can be used to connect them in series or parallel.This gives higher current for the low voltage range.

author: rao
author_rank: Contributor
timestamp: January 04, 2021, 05:07:05 am
content: Schematics please???

author: xavier60
author_rank: Super Contributor
timestamp: January 04, 2021, 05:25:57 am
content: In my application, D2 feeds a 12V regulator to power the fan and relay coil circuits. It gets half wave while the secondary windings are paralleled.Edit: corrected capacitor polarities.

author: rao
author_rank: Contributor
timestamp: January 05, 2021, 04:14:31 pm
content: Thank you sir

author: rao
author_rank: Contributor
timestamp: January 09, 2021, 02:12:59 am
content: Recently I came through ic 723 where it can do voltage control and current control. Please suggest some circuit where it could be variableVoltage: minimum to 36VCurrent:minimum to 1 amps.I want current control to be up to 1ampere. I think this will be better option instead of searching for opamp above 40V...

author: exe
author_rank: Unknown
timestamp: January 09, 2021, 08:40:19 am
content: There is no "perfect" circuit. I suggest read through a few discussions about lm723, then make your judgement what's better for you.Getting a good performance power supply is challenging and requires research and understanding. So, if you want to get a good knowledge about power supplies be prepared to spend months on reading and experimenting. I suggest do not blindly copy someones design as there are plenty of bad designs on the net. It's also easy to make a mistake while assembling it. Fixing mistakes is very hard without understanding how things should work. I'd also challenge your specification. You want 36V, what for? May be building two floating 18V regulators is easier, so you can chain them into 36V when needed, or put them in parallel and get 18V at double current. Or may be you need a bipolar supply... So, even making a useful and realistic specs requires a lot of thinking.I can suggest reading this thread because there are many reputable people there:https://www.eevblog.com/forum/projects/good-quality-lm723-lab-power-supply/25/. If you are not bound to lm723, then I'd do this power supply:https://www.eevblog.com/forum/beginners/how-does-blackdog_s-psu-work/. I've been using this PSU for years, it works well for me:https://www.eevblog.com/forum/beginners/please-critique-this-linear-psu/(it needs a diode accross one cap in capacitor multiplier, and has high temperature drift due voltage ref circuit, but still usable).In any case, working with mains is dangerous, a mistake in a circuit can set your house on fire, or even kill. Please be careful.It might be better start with learning about safety.

author: exe
author_rank: Unknown
timestamp: January 09, 2021, 08:55:49 am
content: After some thinking, I highly recommend buy a two-channel lab power supply, and use it to supply your circuits. You also need at least two dmms, a two-channel oscilloscope. Start with building a power supply from two lm317. In the datasheet there is a circuit like this one:https://www.eevblog.com/forum/projects/lm317-_labratory_-power-supply/. It should be enough to start. Put lm317 on do some math), be sure they are isolated from each other. Oh, and read the datasheet of course!

author: BravoV
author_rank: Super Contributor
timestamp: January 09, 2021, 09:28:48 am
content: Save your breath guy, this kind of thread with this particular people from the region always change their requirement, based on what are available in hand but has no clue about electronics nor initiative to learn, and worst keeps nagging.Its like ... "I own a pipe from scrapyard and a screwdriver .... can somebody help me to make a big cannon gun like the one used in tank ? Please Sir !"We have countless of this similar request alone in this forum, and ended up abandoned.

author: rao
author_rank: Contributor
timestamp: January 09, 2021, 11:53:47 am
content: Thank you bravo... For your guidance through out this thread...

author: MK14
author_rank: Super Contributor
timestamp: January 09, 2021, 01:14:01 pm
content: Quote from: rao on January 09, 2021, 11:53:47 amTalking about GUIDANCE.Threads could do with GUIDANCE, as to exactly what they are about (Descriptive Title, and useful/detailed opening post(s) ).You still don't seem to have specified, what you are trying to do, what help you need (if any), and what resources are available to you.You have to some extent, done the above, but the details keep on changing, all the time. Making it rather difficult for anyone to help you.

author: BravoV
author_rank: Super Contributor
timestamp: January 09, 2021, 01:36:08 pm
content: Quote from: rao on December 06, 2020, 06:03:42 amQuote from: rao on January 09, 2021, 11:53:47 amGood, finally I've contributed significantly to your life and made you realized, go, go keep working for your life 1st, delay the tinkering with electronics until one days in the future, this hobby will become more affordable to you.And NO, you just can not keep nagging and whining people to supply you with a working schematic, with just 741 op-amp or 723 chip ... or what ever cheap components you could find in your drawer or junk yards with that high requirement of yours, again, read my analogy above on making military tank's cannon.Its like you ONLY have flour powder (atta) and water, and only can make "roti" (Indian very basic common peasant's bread/dough), and somehow you want us to help you to make a full fledged and rich Italian pizza with various luxury toppings, that is impossible, no matter how hard you nag.vs

author: rao
author_rank: Contributor
timestamp: January 09, 2021, 01:58:27 pm
content: Sorry all,With in two month, my specification has changed 3 times. I bought two transformer.Now I decided to construct rps from second transformer 26V@5Amps...learned the difference between smps and linear power supply. Smps will be suitable for high power because series element will be present in on conditions depending up on duty cycle.. I bought L296. I dropped that because I could not control voltage and current .Finally I came through lm723 which do voltage and current regulations.Myself has learned all this from this forum and no were else...I thank all of them...for their help.... Thank you all...