LM7171 from china seems legit ?! - Page 1
Forum section: electronics / rf-microwave

author: Atom
author_rank: Regular Contributor
timestamp: August 24, 2018, 01:51:55 pm
content: hi so today arrived my 10pcslm7171for 2 dollars i think, from aliexpress, i mean i took them for having a little bit of fun and i did know thatalmostevery specialized part is fakethere.so i mounted it on the breadboard adn tried it out ....it killed my ad9833 by feeding 10volts into it .........i don't know what happend so i smashed it and thought that it was kikley a fake part, so i wanted to see if there was a die or only a copper piece ...and there it was...let's see what it look like, picked up my phone mounted a dvd collimating lens on the camera and there it was the die, really pretty, but then i saw some printingsLM7171 NCS 1994is this a real part? goin on the upper part you can see a national logo and the chips were advertised as national instrumentsagain.so there is someone that could try to explain this , do we have any silicon expert ?i think this is really intresting and i would love to hear your thoughs on itthanks in advance for everyone that will answer . i will link a drive folder because the photos are to big to be attached in the forum ....see ya!https://drive.google.com/drive/folders/1IxKpqGK49XweEwLs_SNwks45SoQ7SblH?usp=sharing

author: wraper
author_rank: Unknown
timestamp: August 24, 2018, 02:07:11 pm
content: Specialized parts often are genuine as they won't work at all if you try sell something else in disguise. There is no guarantee that part was wasn't salvaged from old electronics and relabeled, likely with different grade.QuoteOpamp can output full voltage swing of power rails. If your circuit does not have protection against it, this is an issue with your circuit. You cannot simply set gain and expect that voltage won't go outside of the window you think. It could easily do this say during power up.

author: Atom
author_rank: Regular Contributor
timestamp: August 24, 2018, 02:11:07 pm
content: mmm the problem is that the 10 volts were being fed into the ad9833 from theinputof the opamp, i would not connect anything that is feeding voltage into those chips since they are quite fragile.the chips are in smd format end they seem not to be pulled from boards because the legs are clean; also on the die there is the name and the manufacturer of the chip, i think that if you want to make a fake part, you are not going that far.

author: wraper
author_rank: Unknown
timestamp: August 24, 2018, 03:22:25 pm
content: Quote from: Atom on August 24, 2018, 02:11:07 pmThey process parts quite extensively to make them look new. Terminals covered with shiny solder always is a suspect. The come as far as cutting old terminals off and welding new terminals on top. It could be just used faulty chip.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: August 24, 2018, 03:58:12 pm
content: Aside from being legit or not, I would be interested, how you wired up the AD9833 with the opamp. I'm often using LM7171 from China, also with various DDS chips and I never had an issue

author: Atom
author_rank: Regular Contributor
timestamp: August 25, 2018, 08:56:07 am
content: Well the opamp had only to amplifiy the signal from the dds it was in a inverting configuration , with a gain of 4 . I'm pretty sure that the opamp fed into the sd9833 chip some voltage .....thing that an opamp shouldnt doi tested another of the chip an it died on me after 30 seconds of beign powered from +-12 volts , so i guess they are factory rejects?(they should handle +-15)

author: wraper
author_rank: Unknown
timestamp: August 25, 2018, 08:59:24 am
content: Quote from: Atom on August 25, 2018, 08:56:07 amThat's a myth. Factory rejects are only a very tiny part sold among that crap. Post a photo of how IC looks like.