Op Amps

F

Fitzy_89

New Member

• Dec 6, 2009

• #1

Hi i have an electronics exam tommorrw and i was just wondering how would i calculate the output voltage of a circuit

E.G

Vin=0.8V
Rf=330kohms
Rin=82kohms

Any help would be greatly appreciated

 

audioguru

Well-Known Member

Most Helpful Member

• Dec 6, 2009

• #2

I guess your opamp circuit is inverting.
Then 50 million tutorials on the web say that the voltage gain at DC and low frequencies is 330k/82k= 4.024490243. Then the output voltage is 3.33V.

But the input offset voltage of the opamp will vary the output voltage a little.

Didn't your teacher teach you this??

 

F

Fitzy_89

New Member

• Dec 6, 2009

• #3

How did you get it as 3.33V..??

 

audioguru

Well-Known Member

Most Helpful Member

• Dec 6, 2009

• #4

Fitzy_89 said:

How did you get it as 3.33V..??

Click to expand...

Sorry, my calculator goofed.
The input is 0.8V. The gain is 4.xxxxxx.
Then the output voltage was calculated wrong, it should be 3.22V.

 

B

BrownOut

Banned

• Dec 7, 2009

• #5

This is incorrect. If the amplifier is inverting, then the output is -Rf/Rin. Thus the output is -3.22V. The sign is crucial, either on an exam or in real circuits.

 

Last edited: Dec 7, 2009