Electronics > Beginners
OPA445 Op amp question.
rstofer:
--- Quote from: Jwillis on March 27, 2019, 11:02:15 pm ---
--- Quote from: rstofer on March 27, 2019, 10:50:39 pm ---If you used that 9-12V supply, you have nowhere near enough voltage. The minimum is +-10V so you need 20V across the rails. MINIMUM!
--- End quote ---
I put 25volts across the rails to as high as 30volts with no response .Isn't 25v that the same as +12.5 and -12.5 and 30v the same as -15 and +15 ..This is whats confusing me, there should be enough supplied voltage.
--- End quote ---
You still need a valid circuit and the starting point is a simple voltage follower. If that doesn't work, nothing will. That you have two independent sources tied together make things easy. You actually have a 'ground' to measure from.
Since you can adjust the + pin input voltage, you should be able to see the output change. Relative to ground, it doesn't need to change very much. You could even use a 1.5V battery. If you put +1.5V at the + input pin, you should get 1.5V on the output. Both measured relative to 'ground'. Turn the battery around and you should get -1.5V at the output. Whatever the voltage is on the + input pin, you should get the same on the output.
rstofer:
Have you watched Daves Op Amp videos?
How about w2aew
These are excellent introductions to op amps. Maybe you'll see something that helps.
Jwillis:
Yes I did watch some but still leaves me scratching my head. But if I use a similar circuit like this but with a 25 supply and inject a maximum of 7 volts into the input I should see a voltage at the output?
rstofer:
Assuming I am reading the schematic properly, the input voltage will be 2.5V above ground and the output should be as well. Again, assuming +-12.5V rails and 'ground' is the point where they are tied together.
Jwillis:
Ok so I can assume that these are no good and not worth further investigation. That's fine they were used and free so no great loss.
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