Filter Circuits: Removing Capacitor Causes High Voltage

In summary, the conversation discusses a lab experiment using an active low pass filter with an op amp. The result of removing the capacitor in the circuit was an extremely high voltage. The participants are trying to understand the behavior of the circuit without the capacitor and figure out its classification. They also discuss using transfer functions to analyze the circuit and the possibility of it becoming an amplifier without the capacitor.
  • #1
JSBeckton
228
0
I did a lab using an active low pass filter with an op amp and at the end we were instructed to remove the capacitor that was in parallel with the resistor. The result was an extremely high voltage compared to the voltage with the capacitor in the circuit. We are asked to explain what kind of circuit this is w/o the capacitor, and why it behaves this way. I have re-read the entire chapter and am at a loss.

With the capacitor in the circuit, the capacitor acts as a short when the frequency is high--> so the voltage goes to zero. So i can understand why the voltage would not go to zero quickly with the capacitor removd, but I have no idea what you call thei circuit and why it goes so high.

Can anyone better explain this or point me in the right direction?

Thanks
 
Physics news on Phys.org
  • #2
I realize that you may be talking about a 'bog standard' filter with an op amp but could we have a circuit diagram. I don't want to go off on one about a circuit different to yours and confuse matters.
 
  • #3
You say the result was an extremely high voltage. At all frequencies? I'll take a guess, that your initial active low pass filter looked like figure 1 in http://engr.astate.edu/jdg/Electronics/Lab1/04LowPassFilter.html [Broken] reference. When you take the cap out of that type of circuit, write out the transfer function and see what you get. If you do that properly, I suspect you will recognize the type of circuit you have.

JSBeckton said:
I did a lab using an active low pass filter with an op amp and at the end we were instructed to remove the capacitor that was in parallel with the resistor. The result was an extremely high voltage compared to the voltage with the capacitor in the circuit. We are asked to explain what kind of circuit this is w/o the capacitor, and why it behaves this way. I have re-read the entire chapter and am at a loss.
 
Last edited by a moderator:
  • #4
Ouabache said:
You say the result was an extremely high voltage. At all frequencies? I'll take a guess, that your initial active low pass filter looked like figure 1 in http://engr.astate.edu/jdg/Electronics/Lab1/04LowPassFilter.html [Broken] reference. When you take the cap out of that type of circuit, write out the transfer function and see what you get. If you do that properly, I suspect you will recognize the type of circuit you have.

Yes, that's is. It started out at about 28 volts and began to decay at about 4000Hz reaching near zero at around 1MHz.
We have not dealt with transfer functions, can you be more specific?

Thanks
 
Last edited by a moderator:
  • #5
Mike Cookson said:
I realize that you may be talking about a 'bog standard' filter with an op amp but could we have a circuit diagram. I don't want to go off on one about a circuit different to yours and confuse matters.

It is the circuit in fogure 1 that the other poster linked to.

Thanks
 
  • #6
Does the removal of the capacitor make it an amplifier? This would explain the amplified voltage.
 
  • #7
Yes, using that circuit without the capacitor changed it into being an amplifier, with the resistor between inverting input and output as the feedback, as you should know that in theory a Opamp has infinite input impedance and infinite gain, so you need a feedback resistor to control the actual gain of the overall system.
 

1. What is a filter circuit?

A filter circuit is an electronic circuit that is used to remove unwanted noise or signals from a desired output. It is typically composed of resistors, capacitors, and inductors.

2. How does a filter circuit work?

A filter circuit works by selectively allowing certain frequencies to pass through while blocking others. This is achieved by using different combinations of resistors, capacitors, and inductors to create a specific frequency response.

3. What is the purpose of a capacitor in a filter circuit?

The purpose of a capacitor in a filter circuit is to store and release electrical energy. In a filter circuit, it is used to block low frequency signals and allow high frequency signals to pass through.

4. Why does removing a capacitor in a filter circuit cause high voltage?

Removing a capacitor in a filter circuit can cause high voltage because the capacitor serves as a buffer for the voltage. Without the capacitor, the voltage can build up and cause a surge in the circuit.

5. How can high voltage be prevented when removing a capacitor in a filter circuit?

To prevent high voltage when removing a capacitor in a filter circuit, it is important to discharge the capacitor first before removing it. This can be done by shorting the leads of the capacitor with a resistor or using a discharge tool.

Similar threads

  • Engineering and Comp Sci Homework Help
Replies
4
Views
1K
  • Engineering and Comp Sci Homework Help
Replies
16
Views
908
  • Engineering and Comp Sci Homework Help
Replies
15
Views
5K
  • Engineering and Comp Sci Homework Help
Replies
7
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
5
Views
800
  • Introductory Physics Homework Help
Replies
20
Views
256
  • Engineering and Comp Sci Homework Help
Replies
8
Views
4K
  • Engineering and Comp Sci Homework Help
Replies
8
Views
989
  • Engineering and Comp Sci Homework Help
Replies
34
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
Back
Top