Op Amp : Design the circuit such that

In summary, the conversation discusses designing a circuit with an ideal op amp to achieve a specific output voltage. The initial attempt at a solution is incorrect, and the correct KVL equations are provided. The correct solution is then determined, and the conversation ends with a recommendation for a helpful resource on op amps.
  • #1
ElijahRockers
Gold Member
270
10

Homework Statement



JrxFC.jpg

Assume the op amp is ideal.
Design the circuit such that Vo = Va + 2Vb + 3Vc

The Attempt at a Solution



Not sure how to go about this one.

I started with

[itex]\frac{V_a}{R_a}+\frac{V_b}{15k}+\frac{V_c}{R_c} = 0[/itex] since the op amp is ideal, the sum of the currents going into the non-inverting input must be 0.

From here I haven't got any ideas how to proceed. But what is the voltage at the inputs? I'm assuming it's zero because Vn/20k = 0 : Vn = 0

EDIT: Alright I found Ra to be 30k, Rc to be 10k. Now I have to find the currents ia, ib, and ic, when Va=.5, Vb=.7, and Vc=1.2. Shouldn't that just be Va/Ra =ia? I know one of them must be negative since the total current flowing in must be 0, but how do I know which one?

I found Vo =5.5 at those values for Ra,Rb,Va,Vb,Vc.

Ok... I figured it out. I guess sometimes it just helps to type it out on a forum haha. For anyone wondering, Vo=6Vn (by KCL at the negative terminal). Since Vo = 5.5, then Vn = .9166...
 
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  • #2
ElijahRockers said:

Homework Statement



JrxFC.jpg

Assume the op amp is ideal.
Design the circuit such that Vo = Va + 2Vb + 3Vc

The Attempt at a Solution



Not sure how to go about this one.

I started with

[itex]\frac{V_a}{R_a}+\frac{V_b}{15k}+\frac{V_c}{R_c} = 0[/itex] since the op amp is ideal, the sum of the currents going into the non-inverting input must be 0.

This equation is incorrect. Write down the correct KVL equations.
 
  • #3
ElijahRockers said:
Ok... I figured it out. I guess sometimes it just helps to type it out on a forum haha. For anyone wondering, Vo=6Vn (by KCL at the negative terminal). Since Vo = 5.5, then Vn = .9166...
You really can't get "Vo = 5.5" when the op-amp has supply voltages of ±5 volts. ☹
 
  • #4
How can you get numerical answers of any kind when your inputs are symbols?
Are you pulling somebody's leg? :rolleyes:
 
  • #5
I founded an ebook that very helpful for you: Op amp for every one

www.ti.com/lit/an/slod006b/slod006b.pdf
 
Last edited by a moderator:
  • #6
rude man said:
How can you get numerical answers of any kind when your inputs are symbols?
Are you pulling somebody's leg? :rolleyes:
See post #1
 

Related to Op Amp : Design the circuit such that

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

An op amp, or operational amplifier, is an electronic component that amplifies the difference between two input signals. It typically has a high gain and is used in a variety of circuits to perform mathematical operations such as addition, subtraction, and integration.

2. What factors should be considered when designing an op amp circuit?

Some key factors to consider when designing an op amp circuit include the desired gain and bandwidth, the input and output impedance, and the power supply voltage. It is also important to consider the op amp's specifications, such as its input offset voltage and slew rate.

3. What is the difference between an inverting and non-inverting op amp circuit?

In an inverting op amp circuit, the input signal is connected to the inverting input terminal of the op amp. The output signal is then inverted and amplified. In a non-inverting op amp circuit, the input signal is connected to the non-inverting input terminal, and the output signal is amplified but not inverted.

4. How do I choose the appropriate op amp for my circuit design?

When choosing an op amp, it is important to consider the specifications and requirements of your circuit, such as the desired gain, bandwidth, and input/output impedance. You should also take into account the op amp's power supply requirements and any other features that may be necessary for your specific application.

5. Can an op amp circuit be used for both analog and digital signals?

Yes, op amp circuits can be used for both analog and digital signals. However, it is important to choose an op amp with appropriate specifications for your specific signal type and application.

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