Absolute max TL081 op-amp supply voltage  - Page 1
Forum section: electronics / beginners

author: TechJunkie97
author_rank: Contributor
timestamp: March 31, 2019, 05:48:50 pm
content: Hi,The datasheet of TL081 says that the max positive input rail can be +18V and negative rail can -18V. I was wondering if it is okay to apply a higher voltage to the positive rail while applying smaller amplitude to the negative rail (e.g. VCC+= +31V and VCC-= -5V) such that the difference between 2 rails is 36V (i.e. +18-(-18)).I actually bought the common 0-30V 0-3A adjustable power supply kit from ebay (https://www.ebay.com/itm/Red-0-30V-2mA-3A-Continuously-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-PCB/201751652278?hash=item2ef955e7b6:g:OxkAAOSwA3dYVCUd&frcectupt=true). When I tried using it after soldering everything, it didn't work. I was using 24V AC transformer to power it but the no-load output voltage of the transformer was around 26 Vrms.The op-amps (3 TL081) on the power supply are directly powered by the main rectifier cap (which is around 34V). There is a charge pump creating -5V (I think) for the negative rail for om-amps.The op-amps are clearly powered by more than 36V and they failed. I changed the op-amps and used a smaller transformer and the power supply is working now.I am just trying to figure out what is the maximum limit of the positive supply rail given that the negative rail is -5V. Maybe someone can recommend a different op-amp with higher voltage ratings.Thanks!

author: jlmoon
author_rank: Unknown
timestamp: March 31, 2019, 05:53:28 pm
content: According to the data sheets, probably not!"2) All voltage values, except differential voltages, are with respect to the midpoint between VCC+ and VCC−.""(3) Differential voltages are at IN+, with respect to IN−"Quoted per:http://www.ti.com/lit/ds/symlink/tl082.pdf

author: iMo
author_rank: Super Contributor
timestamp: March 31, 2019, 05:59:35 pm
content: A typical OPAMP does not see how its power voltages are organized (it has not got a "GND" pin).So for example with 30V opamp you can do Vcc-..Vcc+0..30V-3..27V-10..20V-20..10V-28..2Vetc.The "midpoint" between Vcc and Vcc- could be anywhere in between.Mind the 081 is not R2R.Also mind the input/output potentials of an opamp must always be within its Vcc-..Vcc+.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 31, 2019, 07:08:57 pm
content: It is not that easy to find a good replacement OP in a DIP package.At least for some of the OPs one could use µA741/LM741. OP07 could also work work though relatively slow and thus not so good for the current regulation, but definitely OK for the reference part.TLE2021 could also work, though hard to get in DIP.LF411A could also work. The A version is also rare through.In the kit it is actually only the OP for the voltage regulation that really needs the high voltage. So one could bodge in some voltage reduction for the other 2 OPs.There are quite a few tasks about that supply. There is a little more than just replacing the OPs.

author: Zero999
author_rank: Super Contributor
timestamp: March 31, 2019, 07:42:20 pm
content: That circuit has some issues. Audioguru proposed some modifications to it. There's an indepth thread here about it, but I can't find it.

author: jlmoon
author_rank: Unknown
timestamp: March 31, 2019, 07:52:36 pm
content: Beginners: Topic: 0-30V, 0-3A PSU - Audioguru's version

author: Cliff Matthews
author_rank: Unknown
timestamp: March 31, 2019, 11:20:09 pm
content: Yep, that's the one to focus on (maybe by years end it'll be like Madires' transistor tester..)https://www.eevblog.com/forum/beginners/0-30v-0-3a-psu-audiogurus-version/

author: TechJunkie97
author_rank: Contributor
timestamp: April 01, 2019, 12:02:48 am
content: Thanks everybody for the information and pointing me to the right thread!