Op Amps

Question 1

What are the three main assumptions for operational amplifiers?

Answer 1

• No current flows into or out of the two inputs.
• The potential difference between the two inputs = 0.
• The output operates as an ideal potential source.
  
  • This means 0 resistance (no potential drop across output resistance).
  • can source or sink any currnet.

Question 2

Is the amplifier in the image an inverting amplifier or non-inverting? Why?

Answer 2

Non-inverting.

Vin is connected to the non-inverting input terminal (+).

Question 3

Is the amplifier in the image an inverting amplifier or non-inverting? Why?

Answer 3

Inverting.

Vin is connected to the inverting terminal (-)

Question 4

What is Rf and what is the role of Rf in the following circuit?

How does it work?

Answer 4

Rf is the feedback resistor. Rf reduces and controls the overall gain of the amplifier.

It uses a process called negative feedback, where a fraction of the output signal is fed back to the inverting (negative) input terminal. This results in the output voltage increasing/decreasing in order to balance the 2 input voltages.

Question 5

In the following circuit, is R2 an example of positive or negative feedback?

Answer 5

Negative feedback,

It connects the output back to the inverting (-) input terminal.

Question 6

What is the equation for voltage gain in a NON-inverting amp? (in terms of R).

Answer 6

Gain = 1+(R2/R1)

Gain = 1 + (Feedback resistor / Input resistor)

Question 7

How would the output voltage behave in an op amp with no negative feedback?

Answer 7

Without negative feedback, the output voltage would rise and fall directly with the input voltage, and inversely with the load current.

Question 8

In the following circuit, what would be the maximum output voltage? Why?

Answer 8

The maximum output voltage is limited by the power supply voltage limits.

In this case 15v is being supplied to the amp and so the maximum voltage will be 15v.

Minimum will be -15v.