My op amp doesn't work well under AC input

[athrun200]

The type of op amp I am using is Voltage-to-Current Amp.

Under DC voltage input, it works perfectly well, boosting the current of a signal generator (DC mode) up to 250mA with the help of single supply working at 25V.

However, when I turn the signal generator in AC mode, hoping to achieve AC current oscillating between the value of +125mA and -125mA by adjusting the offset, I found that the negative current won't decrease.

By decreasing the offset, the positive value keep decrease (from 250 to 200mA), but the negative one get stuck at -4mA.

When the offset is lowered to a certain value, the positive value suddenly drop to negative.

I have no idea what's going on. It is my first time to play with a op amp, I didn't expect it to be so complicated.

 

[davenn]

hi there

well let's start by you giving us the actual type of Op-Amp ( model #)
then let's get a circuit from you that you are working from
Then a photo or 2 of your actual made up circuit

Then some of us may be able to see if you have made an error either in your circuit or construction etc

cheers
Dave

 

[analogdesign]

Indeed, we don't even know what frequency you are operating at, or if you are slewing.

Analog circuits are a bottomless pit of complexity.

 

[Averagesupernova]

Analog circuits are a bottomless pit of complexity.

Well said!

 

[alphy]

Based on the information provided, it seems that your op amp is not functioning properly under AC input. This could be due to a number of reasons, such as incorrect circuit design, inadequate power supply, or a faulty op amp.

Firstly, it is important to make sure that the circuit design is appropriate for the type of op amp being used. In this case, a voltage-to-current amp may not be the best choice for AC input. It is possible that the op amp is not able to handle the AC signal and is therefore malfunctioning.

Additionally, it is important to ensure that the power supply is adequate for the op amp to function properly. A single supply working at 25V may not be enough to handle the AC input and could be causing issues with the op amp.

It is also possible that the op amp itself is faulty and needs to be replaced. This can happen with any electronic component and it is important to test and troubleshoot all components in a circuit to determine the source of the issue.

In conclusion, it is important to carefully consider the circuit design and power supply when using an op amp, and to test and troubleshoot all components to determine the source of any issues. It may also be helpful to consult with a more experienced colleague or seek further resources to better understand the complexities of using an op amp.

 

[alphy]

It sounds like there may be a problem with the op amp's ability to handle AC inputs. This could be due to a number of factors, such as the op amp's frequency response or its ability to handle negative voltages. It is important to carefully select the right op amp for your specific application and to ensure that it is capable of handling both DC and AC inputs.

There are a few steps you can take to troubleshoot this issue. First, check the datasheet for your op amp and make sure it is rated for the frequency and voltage range of your AC input. If it is not, you may need to consider using a different op amp.

Another potential issue could be the feedback circuitry in your circuit. Make sure it is properly designed and connected, as this can greatly affect the performance of the op amp.

You may also want to consider using a dual supply instead of a single supply, as this can sometimes improve the performance of the op amp under AC inputs.

If you are still experiencing issues after checking these factors, it may be helpful to consult with an experienced engineer or reach out to the manufacturer for further assistance. Troubleshooting and understanding the behavior of op amps can be complex, but with careful consideration and proper selection, you can achieve the desired results.