op amp test jig - Page 1
Forum section: electronics / projects

author: quadzillatech
author_rank: Contributor
timestamp: January 07, 2019, 10:46:22 am
content: Hi all,does anyone know of any plans,ie pcb layouts etc for a diy op amp test jig,a sort of go no go type of thing?,cheers Paul m3vuv.

author: ogden
author_rank: Super Contributor
timestamp: January 07, 2019, 11:48:26 am
content: Quote from: quadzillatech on January 07, 2019, 10:46:22 amYou mean something like diode checker? Like this?http://vakits.com/single-op-amp-tester-kit(just found using search)Opamps diffeer, by function and pinout, so there can't be universal "fits it all" test jig. Also test circuits to measure various characteristics of opamp, differ.Manufacturers like TI and AD provides provides unpopulated opamp evaluation boards, such as:http://www.ti.com/tool/OPAMPEVM-SOICHi-speed and RF amplifiers have purpose-built test jigs, such as:http://www.ti.com/tool/LMH6629SDEVALYou shall tell why you are asking and what kind of problem you are trying to solve.

author: quadzillatech
author_rank: Contributor
timestamp: January 07, 2019, 12:21:42 pm
content: Ive just built a 0-30 volt chineese psu kit from ebay,it doesent output,ive built it spot on,there is an opamp gets hot,i want a quick way of testing them and other op amps i have in my junk box,regards m3vuv.

author: coppercone2
author_rank: Super Contributor
timestamp: January 07, 2019, 12:30:35 pm
content: you could go through app notes that try to look at app notes that give test procedures on the specifications and try to make a one size fits all board for things like measuring bias currents etc, switch or relay controlled, but you would have problems when you have like dual op amps in the same form factor or op-amps with weird pins etc. it could end up quite complicated.

author: Zero999
author_rank: Super Contributor
timestamp: January 07, 2019, 01:10:48 pm
content: It depends on what you mean by checker?It's fairly easy to simply check the basic functionality of an op-amp, by making an LED flasher and it shouldn't be too difficult to make the circuit work with 99% of op-amps, but verifying it meets its specifications is more complex. A simple 1Hz Schmitt trigger oscillator will work with the '741, TL071, OP07 etc. but getting it to distinguish between the three is not simple. It's not possible to make a simple circuit which can spot the difference between a genuine op-amp and a fake.

author: exe
author_rank: Unknown
timestamp: January 07, 2019, 03:02:31 pm
content: Quote from: quadzillatech on January 07, 2019, 12:21:42 pmI just breadboard a unity buffer. A set point can be middle of supply. This way I can:1) check power consumption2) check input offset3) check input bias current with a DMM (on positive input).For smd components I use smd to dip converter. I also bought soic-8 socket to be able to change opamps quikly, but haven't tried it yet.PS don't forget bypass cap.

author: s8548a
author_rank: Regular Contributor
timestamp: January 07, 2019, 05:32:33 pm
content: another one from TI:http://www.ti.com/tool/diyamp-evm#1

author: David Hess
author_rank: Super Contributor
timestamp: January 07, 2019, 05:57:03 pm
content: Somethinglike thiswould be overkill but the test circuits give some idea of what is required.A simple tester might just measure:1. Input offset voltage.2. Input bias current.3. Input offset current.4. Supply quiescent current.5. Maximum output source current.6. Maximum output sink current.That covers the most common subtle failure modes and can be done with one test assembly. The next step up would be making those measurements over the common mode input voltage range which is easy enough to do. The next step above that would be also measuring the source and sink current versus output voltage.For what it is worth, the most common subtle failure I encounter is high input bias and/or offset current because the input stage was damaged.

author: quadzillatech
author_rank: Contributor
timestamp: January 09, 2019, 01:51:31 pm
content: i found one on another forum should fit my needs!,see attached,cheers m3vuv.

author: Zero999
author_rank: Super Contributor
timestamp: January 09, 2019, 02:06:50 pm
content: Quote from: quadzillatech on January 09, 2019, 01:51:31 pmYes, that should do a basic check. I'm not sure how well the '741 on the output will work, as it might have its input taken outside its common mode range though. No doubt it could be simplified somewhat.

author: rstofer
author_rank: Super Contributor
timestamp: January 09, 2019, 04:06:32 pm
content: Quote from: Zero999 on January 09, 2019, 02:06:50 pmI think the 741 may be hard to find. I need a bunch, in the metal can, if anybody runs across a source.I'm not sure what to substitute and there are hundreds and hundreds of op amps.

author: Zero999
author_rank: Super Contributor
timestamp: January 09, 2019, 04:26:50 pm
content: Quote from: rstofer on January 09, 2019, 04:06:32 pmThe 741 is widely available in SMT and DIP packages. The metal can is rare. I think I have some lying around but don't know if they work, so wouldn't sell them.https://www.digikey.co.uk/products/en?keywords=ua741https://uk.rs-online.com/web/c/semiconductors/amplifiers-comparators/op-amps/?searchTerm=ua741&redirect-relevancy-data=636F3D3126696E3D4931384E53656172636847656E65726963266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E5B5C707B4C7D5C707B4E647D2D2C2F255C2E5D2B2426706F3D31333326736E3D592673723D2673743D4B4559574F52445F53494E474C455F414C5048415F4E554D455249432673633D592677633D4E4F4E45267573743D7561373431267374613D756137343126&r=f&searchHistory=%7B%22enabled%22:true%7D

author: exe
author_rank: Unknown
timestamp: January 09, 2019, 04:46:27 pm
content: Quote from: rstofer on January 09, 2019, 04:06:32 pmWhy do you need exactly 741 and in metal can?

author: Zero999
author_rank: Super Contributor
timestamp: January 09, 2019, 05:15:20 pm
content: Quote from: exe on January 09, 2019, 04:46:27 pmMy first instinct was to say temperature, but after Googling the data sheets, I couldn't see any difference in the temperature rating, to the ceramic DIP. The only advantage for the metal can is heatsinking. The junction to case thermal resistance is specified for the can, but not for the DIP and TO-5 heatsinks are available.http://www.ti.com/lit/ds/symlink/lm741-mil.pdf?HQS=TI-null-null-mousermode-df-pf-null-wwe&DCM=yes&ref_url=https%3A%2F%2Fwww.mouser.co.uk%2FThe only other reason is authenticity. If one is repairing an old piece of equipment, using original parts can help to preserve its value.Mouser sell the TO-5 packaged 741 but it isn't cheap:https://www.mouser.co.uk/ProductDetail/Texas-Instruments/LM741H?qs=QbsRYf82W3H3APg1dDoXnw==