how a noob blew up his opamp - Page 1
Forum section: electronics / beginners

author: amateur_25
author_rank: Regular Contributor
timestamp: January 04, 2019, 09:45:38 am
content: I understand in a voltage follower configuration the opamp basically tries to keep both of it's inputs the same.I have check my soldering and used a multimeter to buzz out the connnections to ensure it's right according to the schematic. So the tlc082 was powered from 5v but I did wire up 12v to it's minus input. Is there a limit as to how much voltage I can put on the inputs?

author: Fungus
author_rank: Super Contributor
timestamp: January 04, 2019, 10:01:02 am
content: Quote from: amateur_25 on January 04, 2019, 09:45:38 amYes.

author: amateur_25
author_rank: Regular Contributor
timestamp: January 04, 2019, 10:20:36 am
content: The spec am looking at is the common mode input voltage?God damn it am shit at electronics. I am not good at small detailsTime to get my hammer out

author: mvs
author_rank: Frequent Contributor
timestamp: January 04, 2019, 11:10:43 am
content: Quote from: amateur_25 on January 04, 2019, 10:20:36 amYes, but you have also violated input voltage in absolute maximum ratings section:Vi Input voltage (2)(4) max. +/- 15V(2) All voltage values, except differential voltages, are with respect to the midpoint between VCC+ and VCC−(4) The magnitude of the input voltage must never exceed the magnitude of the supply voltage or 15 V, whichever is less.

author: Fungus
author_rank: Super Contributor
timestamp: January 04, 2019, 11:19:01 am
content: Quote from: amateur_25 on January 04, 2019, 10:20:36 amIn your case, Vdd is 5.0V so you can only apply between 0 and 5V to the inputs.Quote from: amateur_25 on January 04, 2019, 10:20:36 amRecognizing that is a good start.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 04, 2019, 11:55:47 am
content: even if you passed voltage supply absolute maximum and common mode range, there's one thing you need to watch out...differential input limit. i check TLC082 its forgiving at ±VDD differential input limit, meaning you can put 0V on -ve input and Vdd at +ve input and the opamp will be still ok, there are few (usually higher bandwidth, cfb or more expensive opamp) that cannot tolerate this even if its within Vsupply or common mode range, their differenctial limit is close to zero or 1-2V at most. so some opamp if you put (or mistakenly wires or unintentionally enforce or clipped to such condition doesnt matter they are all semantically meaning the same to the spec and result will be the same) 1V at one input and 5V at another input (thats 4V differential), even if your supply is 12V to -12V, the opamp will burn, done that.

author: Zero999
author_rank: Super Contributor
timestamp: January 04, 2019, 02:18:50 pm
content: Yes it's possible to destroy most op-amps by taking their input voltages outside the power supply rails.Another thing to note is the common mode range, which is the voltage range on the inputs that ensures proper operation. The TLC082 has a common mode range of 0V to 3.5V, when operated from a 5V supply, so exceeding 3.5V in won't damage it, but it might not work properly. The output voltage rage will also limit the performance of the amplifier and will be depend on the load impedance: with a light load, the typical maximum output voltage will be 4.3V, with a 5V supply.

author: amateur_25
author_rank: Regular Contributor
timestamp: January 04, 2019, 03:10:44 pm
content: Guys thanks for the replies.Am currently on a mission of completing projects I been wanting to do in hope to redeem myself somewhat.Right now am building a DC current source. Since I can't trust myself to remember the limitations of equipment I build/ engage brain before plugging it in, I tend to try build them so I can make stupid mistakes like wiring a psu backwards.So I was following daves design but I thought I would make it tolerent to 30v whilest having the opamp at 5v with a seperate plug pack. So I read lm358 opamp allows 32v bteween it's outputs and 32v on it's inputs.So I should be ok with this right?

author: piguy101
author_rank: Regular Contributor
timestamp: January 05, 2019, 02:33:37 am
content: That should work fine with the LM358, as long as the voltage at the input terminals does not go outside the range of the supply voltages. Ex: no input voltage greater than (Vcc) and no input voltage lower than negative supply pin (which may be 0 V or a negative voltage depending on how you are using the op amp).