Electronics > Beginners

OPA445 Op amp question.

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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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