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### Network # Operational amplifiers

#### Mbetts

Feb 22, 2013
4
Hi guys I recently started a degree in electronic and electrical engineering I come from an advanced apprenticeship background and I'm not the best mathes student.

My lecturer gave me the worksheet pictured.

I used the formula as follows for calculating inverted and non inverted amplifiers.

Inv: Vo R2
--- = - ---
Vi R1

Non-inv: Vo R2
--- = 1 + ---
Vi R1

I transposed the inverted op amp formula and got all the answers right. Got onto the non-inverting op amp and got most of the answers right except the R2 ohmage. Do you think this is his typo or am I wrong (I'll put my thought process down.)

(Vo )
(--- - 1) X R1 = R2
(Vi )

With this in mind.

(11.75 )
(------- -1) x 1000 = 46k
(0.250 )

Any help or guidance is greatly appreciated also any sites and books I could read?

Thanks

#### Laplace

Apr 4, 2010
1,252
R2=46K is the correct answer. But how can you be sure?

Look at the schematic for the non-inverting amplifier. Realize that whenever an (ideal) op amp is in its linear operating range the voltage at the '+' and '-' inputs has exactly the same value. Here the voltage at the '-' input is the result of a voltage divider from Vo so the equation V'+'=V'-' gives 0.25=11.75(1/(1+46)). You know your answer is correct if 11.75/47=0.25

#### Mbetts

Feb 22, 2013
4
Thanks for the reply.

You are the second person to have confirmed this for me I used stand the op amps input works with the output the create a ratio that gives the output when working Vo anyways I understand a bit better now,

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