Help needed Analyzing a real op amp with both positive and negative feedback

In summary: When the input voltage is higher than the reference voltage (the voltage at the input that is not connected to the output), the output will go high. When the input voltage is lower than the reference voltage, the output will go low. When the input voltages are equal, the output will stay at the reference voltage. The output will be at −5V when the inputs are balanced. When the input voltages are unbalanced, the output will be anywhere from 0V to 5V depending on how far out of balance the inputs are.
  • #1
Rio20
3
0
Hi
this is my first subject in this forum and i hope you can help
1.we have been given an assignment to analyze this non-ideal op amp with both positive and negative feedback and to be honest i don't even know where to start


i know i should post an attempt of trying to solve but honestly i don't know how to ,, so please give me hints or ideas and i will go through them

thanks forum
 

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  • #2
Rio20 said:
Hi
this is my first subject in this forum and i hope you can help
1.we have been given an assignment to analyze this non-ideal op amp with both positive and negative feedback and to be honest i don't even know where to start


i know i should post an attempt of trying to solve but honestly i don't know how to ,, so please give me hints or ideas and i will go through them

thanks forum

Welcome to the PF.

Is there more to the question? What are the initial conditions of the circuit? Is there some Vi(t) somewhere, or just the circuit?

And what is the 1uF cap doing on the output of the "equivalent circuit" on the right?
 
  • #3
It's going to oscillate with a frequency determined by the pot.

Ignore the positive feedback and consider the negative. Draw the circuit as an ideal OpAmp with a capacitor on the output. You'll see that the OpAmp charges the cap to a point where the output flips and then reverses so that the cap is discharging.

The positive feedback determines the trip points and therefore the frequency.
 
  • #4
berkeman said:
Welcome to the PF.

Is there more to the question? What are the initial conditions of the circuit? Is there some Vi(t) somewhere, or just the circuit?

And what is the 1uF cap doing on the output of the "equivalent circuit" on the right?

thnx for welcoming me berkema :D .

there is no Vi(t) and the equivalent circuit is drawn next to it ,, we asked asked to analyze the following op amp in a non ideal way and get the voltage that will be on the capacitor and draw it ,,, it's more like an really very very complex RC circuit
 
  • #5
Antiphon said:
It's going to oscillate with a frequency determined by the pot.

Ignore the positive feedback and consider the negative. Draw the circuit as an ideal OpAmp with a capacitor on the output. You'll see that the OpAmp charges the cap to a point where the output flips and then reverses so that the cap is discharging.

The positive feedback determines the trip points and therefore the frequency.

thnx antiphon and i think i got ur point ,, but can u show me some equations so i can fully understand ur point and thnx
 
  • #6
Rio20 said:
thnx antiphon and i think i got ur point ,, but can u show me some equations so i can fully understand ur point and thnx

Sorry I can't take the time to work it out.

Assume that the output is clamped to the power supply levels when the inputs are not balanced. This simplifies your analysis to an RC circuit and the voltage dividers on the inputs.

The OpAmp will act like a comparator.
 

Related to Help needed Analyzing a real op amp with both positive and negative feedback

1. What is an op amp and how does it work?

An operational amplifier (op amp) is an electronic component that amplifies the difference between two input voltages and outputs the result. It typically has two inputs, a non-inverting (+) and an inverting (-) input, and one output. The output voltage is proportional to the difference between the two input voltages, making it a very versatile and useful component in electronic circuits.

2. What is positive feedback and how does it affect an op amp's operation?

Positive feedback occurs when the output of the op amp is connected back to its non-inverting input. This causes the output to be amplified even further, resulting in an unstable circuit that can potentially oscillate. In some cases, positive feedback can be used to create a comparator circuit where the output switches between two stable states.

3. What is negative feedback and why is it important in op amp circuits?

Negative feedback is when the output of the op amp is connected back to its inverting input. This results in a stable circuit with reduced gain and improved linearity. Negative feedback is important because it helps to reduce distortion and stabilize the output of the op amp.

4. How do I analyze an op amp circuit with both positive and negative feedback?

To analyze an op amp circuit with both positive and negative feedback, you can use the basic principles of op amp analysis. First, assume that the op amp is in a closed loop configuration and that the inputs draw no current. Then, use the rules for op amp circuits (e.g. virtual short between the inputs) to simplify the circuit and determine the overall gain and output voltage.

5. What are some common applications for op amps with both positive and negative feedback?

Op amps with both positive and negative feedback are commonly used in applications such as amplifiers, filters, oscillators, and comparators. They are also used in active circuits for signal conditioning and feedback control systems. In general, the use of both positive and negative feedback allows for greater control and precision in electronic circuits.

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