AMS1117 output higher than should - Page 1
Forum section: electronics / beginners

author: Nexxen
author_rank: Regular Contributor
timestamp: May 13, 2023, 03:22:31 pm
content: Hello!Beginner's question,I have issues with a motherboard and the AMA1117 has a +5V input and a 3.3 output, but output measured is 3.5V.I was wondering if this could be a faulty chip's output or if it is fine.Another 1117 on another board has a drop in outputV from 3.3V to 1.8, but the southbridge is shorting and I'm wondering if this short could actually casue this drop (probably yes, but how?).The 11117 gets scalding hot but deosn't fry. I also checked by soldering a known good 1117 and does the same.The 1117 are Vin with +5VSB.https://pdf1.alldatasheet.com/datasheet-pdf/view/49118/ADMOS/AMS1117.htmlCuriosity.Thanks fro any explanation

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 13, 2023, 03:38:30 pm
content: Quote from: Nexxen on May 13, 2023, 03:22:31 pmIs it marked "AMS1117-3.3"? Because if it doesn't have the 3.3 on the end, then it's an adjustable one and the voltage is set by 2 resistors. It could also be due to a fault elsewhere in the circuit where something that is connected to both the 3.3V and 5V rails has failed. It is also possible that the AMS1117-3.3 is bad. (spec says 3.333V is the max it should put out)QuoteThe AMS1117 has built in current limiting and thermal protection. So if the load draws too much current, or the regulator gets too hot, the AMS1117 will lower it's output voltage to protect itself.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 13, 2023, 04:52:27 pm
content: Correct type and value of output capacitor? Additionally to oscillation, wrong DC value is typically seen with wrong output capacitor with these ancient LDO regulators. Also for 1117, a lot of poor quality fakes exist.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 13, 2023, 05:23:31 pm
content: AMS1117 is very sensitive to the ESR of the capacitor at its output. If too small, it will oscillate.I've found Aliexpress modules with AMS1117-3.3 where I had to replace the ceramic capacitor on 3.3V with a 10uF electrolytic. That will stop the auto oscillations, and the output voltage becomes correct, 3.3V. Still heats (without any load) but way less than when it was oscillating.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 13, 2023, 06:11:39 pm
content: Also remember that 1117 from each manufacturer have different output capacitor requirements, preventing you from second-sourcing (or making it difficult at least); and second-sourcing is probably the only reason to use an 1117 in 2000's!

author: Nexxen
author_rank: Regular Contributor
timestamp: May 13, 2023, 10:58:28 pm
content: Quote from: Kim Christensen on May 13, 2023, 03:38:30 pmNo markings except AMS1117.361 (underlined) and 30A resistors.You guys know stuff

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 13, 2023, 11:27:23 pm
content: If those resistors are wired to the AMS1117 as depicted below, then 3.5V is the correct voltage:

author: Zero999
author_rank: Super Contributor
timestamp: May 14, 2023, 09:41:09 am
content: R1 should be 220R and R2 360R, for 3.3V out.

author: Nexxen
author_rank: Regular Contributor
timestamp: May 14, 2023, 12:43:16 pm
content: Quote from: Kim Christensen on May 13, 2023, 11:27:23 pmGuess it is its design and it is indeed correct. No issues on this. ThanksQuote from: Zero999 on May 14, 2023, 09:41:09 amYou know what, this was actually useful to check another baord. Thanks to you too.Thanks a lot for your asnwers (everybody), it did help me getting a little further.

author: palindrome
author_rank: Contributor
timestamp: May 15, 2023, 01:07:50 pm
content: Quote from: Siwastaja on May 13, 2023, 06:11:39 pmI am guilty of using AMS1117. I keep reading that it shouldn't be used, that is outdated etc. but when I try to find modern alternative, there doesn't seem to be any that provide similar parameters and simplicity of use.So I am always confused. Is there a secret 5V to 3.3V regulator with 0.5-1A current that I am missing out on?

author: Siwastaja
author_rank: Super Contributor
timestamp: May 16, 2023, 12:13:49 pm
content: Quote from: palindrome on May 15, 2023, 01:07:50 pmWat?? Almost every modern regulator has better parameters (lower drop-out voltage) and much better ease of use as they are stable with MLCC output capacitors and do not become oscillators just because you did not read the datasheet carefully enough or substituted with another manufacturer.Just use the parametric search of your distributor to find other parts, it's not rocket science.It's fine to use 1117, you should not stop using it because it's old or because someone says on the internez. If it's good enough for you and if it works, use it. It's just that opposite to what you say, it's inferior and more difficult to use.