What's wrong with my circuit simulation?

In summary, the oscilloscope showed a lack of gain at the amplifier output, which was caused by incorrect wiring and a power supply that wasn't correctly related to ground. By fixing these issues, a gain of 10 was observed at the output.
  • #1
red123
22
0
What's wrong with my circuit simulation? No gain is observed at the amplifier output. The intent is for the output gain of the 741 operational amplifier to be equal to R2/R1.

2kok1x.jpg
 
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  • #2
You can't just leave pin 3 hanging. You have a wire wrong there, and when you look at what pin3 should do in your test circuit, you should see which one it is.
 
  • #3
As well as the wrong inputs, the output (pin 6) is corrected direct to ground, so what would you expect its voltage to be except 0V?

The oscilloscope is connected straight across the AC voltage generator, so that is what it will display.

A more subtle problem is that your 15V power supply isn't related to your "ground" voltage. The simplest way to fix that is use two 7.5V batteries between ground and pin 4, and ground and pin 7. if you don't do that, the op amp will probably "lock up" with the output stuck at one of the supply voltages, even when you fix the other problems.
 
  • #4
What am i doing wrong? Still no observed gain.

1t4tp2.jpg

1jtbg9.jpg
 
  • #5
You still have your output connected directly to ground... not sure what you expect that to do except act as an expensive but inefficient heater.
 
  • #6
5vnpra.jpg

Ok, a gain is observed now. Output amplitude is 8.032V but a gain equal to R2/R1 is intent, what am I doing wrong?
 
  • #7
That looks better, you still have the scope lead hooked up wrong. You want to measure output voltage vs. ground (I imagine), not output voltage vs. oscillating input voltage.
 
  • #8
Your output and input are both connected to Channel A input. Break the output connection and reconnect it to the Channel B input. Then you can compare Channels A & B to see the gain...
 
  • #9
juy793.jpg

Like this? Output is square wave and amplitude is 6.618V, gain is still not equal to R2/R1.
 
  • #10
You are just overdriving the circuit.

1 volt RMS sinewave is 2.8 volts peak to peak.

So to have an undistorted gain of 10, the output would be 28 volts peak to peak.

But the supply is only 15 volts total, so the opamp can't possibly produce 28 volts out.

Try reducing the input to 0.1 volts RMS. This is 0.28 volts peak to peak, so a gain of 10 would mean 2.8 volts peak to peak.
 
  • #11
Thanks everyone, the circuit finally works.
 

1. Why is my circuit simulation giving incorrect results?

There could be several reasons for incorrect results in a circuit simulation. It could be due to incorrect component values, improper connections, or errors in the simulation software. Double check your circuit design and make sure all components are properly connected. Also, check if the simulation settings are accurate.

2. Why is my circuit simulation not running at all?

If your circuit simulation is not running at all, it could be due to missing or incorrect component models, wrong simulation settings, or a software bug. Make sure you have all the necessary component models loaded and check the simulation settings to ensure they are correct. If the problem persists, try using a different simulation software.

3. Why am I getting unrealistic or impossible results in my circuit simulation?

This could be due to several reasons such as incorrect component models, wrong simulation settings, or a faulty circuit design. Check all the component models and make sure they are accurate. Adjust the simulation settings to ensure they are appropriate for your circuit. If the problem persists, review your circuit design for any errors.

4. Why is my circuit simulation taking too long to run?

A circuit simulation can take a long time to run if it has a large number of components or if the simulation settings are set to a high level of detail. Try simplifying your circuit design or adjusting the simulation settings to reduce the simulation time. Also, make sure your computer meets the minimum requirements for running the simulation software.

5. Why is my circuit simulation crashing or giving errors?

Circuit simulations can crash or give errors due to several reasons such as incorrect component models, insufficient memory, or a software bug. Check all the component models and make sure they are accurate. If you are using a large circuit design, try simplifying it to reduce the memory usage. If the problem persists, try updating your simulation software or using a different software.

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