Help opamp getting too hot - Urgent!

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The heating is only one problem.
The second problem is that the output is at -13.5V instead of near 0V. Therefore the IC is fried or it is a fake.
 

Audioguru said:
I think your opamps are defective or they are fakes.
With no input the output should be close to 0V.
Click to expand...

I bought them through digikey, so chances are its not fake. I do think that it is defected too. But, as I said before I'm trying to understand and learn the reason before I swap the new one. I was running the circuit with a lab supply, so the power applied is pretty clean.

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pplus said:
why you did not do
Click to expand...

I apologize, I was pulled into other things yesterday and was out of town most of the time. I'll be looking into it in a while and update you.
Thanks.

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keith1200rs said:
A typical IC is what you typically get! The worst case is the worst IC over the full operating temperature range. I assume he isn't working at maximum or minimum ambient temperature.

Keith
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No, I'm not. Its room temperature.

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I do agree part of the reason was LTspice. Also, the initial requirement was to have a low noise and high precision, as the output is used to control a motor.

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Thanks keith1200rs , for your detailed direction. I'll consider these, and update the results as soon as possible. I'am also looking into alternate op amps that would fit the same layout.
 

pplus said:
Disconnect R5 and short C2. Tell my voltage on OUT1 and OUT2
Click to expand...

Test1
OK
Opamp - New
R5 Removed
C2 Shorted
inputs grounded

Outputs are measuring 0. However opamp is hotter than before; shows 0.05A on the supply. Actually when the board is powered, it shows 0.005A for two seconds, and then all of a sudden increases to 0.05A, and makes it hotter.

Test 2
Opamp - New
R5 Removed
C2 NOT Shorted
inputs grounded

Still warm (not hot as before)
Output 1 ~0
Both inputs for opamp A is 0
Input B+ oscillates around 7v
output B is also oscillating around ~12v.
Oscilation is actually building up over the time from an initial 12v constant.
Supply shows 0.02A supply.
 
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So it should be in normal operation of the opamp.


Seems to be true, the scheme is a positive feedback C1 R6, which can lead to the generation.

Connect R5 (return to the original scheme), it should work. On both outputs - 0. If it is not - measure all voltages and write. If so - you can try to apply the input signals and to look at the operation of the scheme.
 

gvardan said:
...shows 0.05A on the supply. Actually when the board is powered, it shows 0.005A for two seconds, and then all of a sudden increases to 0.05A, and makes it hotter.
Click to expand...
That sounds like high frequency oscillation that only starts after a couple of seconds. I'm not sure why you'd have a problem with HF stability though - maybe something to do with the layout?

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gvardan said:
Test 2
Opamp - New
R5 Removed
C2 NOT Shorted
inputs grounded
Click to expand...
That leaves the 2'nd opamp's input open circuit for DC, so results will be random/meaningless.
 

Sorry I did not update the thread.
We tried the same circuit on a bread board with LM324 opamp and everything seems to be working fine. May be godfreyl is right; It might be something to do with the layout. At this point we are just using the breadboard setup. Let's see.

Thanks for the assistance everyone.

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Sorry I did not update the thread.
We tried the same circuit on a bread board with LM324 opamp and everything seems to be working fine. May be godfreyl is right; It might be something to do with the layout. At this point we are just using the breadboard setup. Let's see.

Thanks for the assistance everyone.
 

Notice to everybody: This is ANOTHER case where a high frequency opamp oscillates and gets hot when its circuit is built on a solderless breadboard.
 

No, it was the version built on a PCB that was giving problems (see post 1).
 

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