Inverting operational amplifier circuit won't work

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Discussion Overview

The discussion revolves around troubleshooting an inverting operational amplifier circuit using a 741 op amp. Participants are examining issues related to the output voltage not matching expected values, the configuration of the circuit, and the power supply connections.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant describes their circuit setup, noting a feedback resistor of 150 kohms and an input resistor of 100 kohms, which they calculate gives a gain of 1.5, with an input voltage of 5.33 V.
  • Another participant questions the power supply setup, pointing out that only three batteries are visible and asking how the participant is achieving +/- 18 volts.
  • Concerns are raised about the input voltage source, with suggestions to use a lower voltage for testing purposes.
  • Several participants highlight the lack of a proper ground connection in the circuit, indicating that the midpoint of the power supply needs to be connected to the input's ground reference.
  • There is a disagreement regarding the circuit configuration, with one participant asserting that the setup is a non-inverting amplifier rather than an inverting one, which contradicts the original claim.
  • Another participant notes that the output voltage is significantly lower than expected and mentions that a different op amp (LF356N) shows no output voltage at all.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the circuit configuration and the power supply connections. The discussion remains unresolved, with no consensus on the correct setup or the cause of the output voltage issue.

Contextual Notes

Limitations include unclear connections in the provided circuit image, potential misunderstandings about the circuit type (inverting vs. non-inverting), and the need for proper grounding which has not been established in the discussion.

gothloli
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I'm making a simple circuit on the breadboard with a 741 op amp. The feedback resistor is 150 kohms, and the input resistor is 100 kilo ohms, means the gain is 1.5. The input voltage is about 5.33. The power supply is ±18 V. For some reason the output voltage is 0.98 V instead of the amplified voltage. Also when I try the LF356N it doesn't show any output voltage at all.

Below is a picture of my circuit
 

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I can only see three batteries. How are you getting +/- 18 volts?

How are you getting 5.33 volts input? I can't see any divider resistors. I would make this 1 volt for test purposes anyway.

The red wire on the top battery doesn't seem to go anywhere.

Are you using this circuit?

images?q=tbn:ANd9GcQD70c1nUYza0Ed6zb6IPRKS1YZSqSrOaxcPkzstrbafsl0wpMe.png
 
yah I'm using that circuit.
But the battery I used for the input signal is 5.33 because I burnt it out, because I don't have 1.5 volt batteries around
 
Do you have a meter?
 
I don't see any connection between the midpoint of the two supply batteries, pin 3 and your input's "zero" side. Those three things need to be connected together.
As has been pointed out, your supply only seems to be +/-9V. That should be just about enough though.
 
gothloli said:
yah I'm using that circuit.
But the battery I used for the input signal is 5.33 because I burnt it out, because I don't have 1.5 volt batteries around

No, you're not using that circuit (inverting amp). You're using this circuit. Its a non-inverting amplifier. Gain = 1 + R2/R1 ( = 2.5 in your case)

op-amp_basic_non_inv.gif


Also give the circuit a common ground by connecting the middle of +-18V battery to the negative terminal of your input. (i.e. at the other end of the resistor you took out from pin 2)
 
gothloli said:
I'm making a simple circuit on the breadboard with a 741 op amp. The feedback resistor is 150 kohms, and the input resistor is 100 kilo ohms, means the gain is 1.5. The input voltage is about 5.33. The power supply is ±18 V. For some reason the output voltage is 0.98 V instead of the amplified voltage. Also when I try the LF356N it doesn't show any output voltage at all.

Below is a picture of my circuit

I look at you breadboard. The top battery is supposed to be the input voltage. The black wire is connected to the 100K which connect to pin 2 as input. Problem like Vk6kro said, the red wire of the battery is not connected to the breadboard! If I see you picture correctly, you are not going to get anything meaningful out of this. I can't see where the clip on the black wire goes to as your picture don't show. You need to have connection to the ground reference to establish the potential. The ground reference is the junction of the red wire of the lower battery on the left side and the black wire of the lower battery on the right side. You have no connection of the ground reference to any other points.
 
Last edited:
vk6kro said:
I can only see three batteries. How are you getting +/- 18 volts?

How are you getting 5.33 volts input? I can't see any divider resistors. I would make this 1 volt for test purposes anyway.

The red wire on the top battery doesn't seem to go anywhere.

Are you using this circuit?

images?q=tbn:ANd9GcQD70c1nUYza0Ed6zb6IPRKS1YZSqSrOaxcPkzstrbafsl0wpMe.png

He has only +/-9V. He used an empty clip to hold the red of the left battery to the black of the right battery.
 

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