Current sensing_Time

Luis Meza

Hi, good evening. I'm measuring an AC current of 50mA @ 5A and must be less than 50 ms its response. This, I've got a TC and an array of opamp peak detector and a filter at the output to try to make it as similar to a DC signal, but I have some questions. If I want to measure the amplitude, this configuration is valid for OPAMP (peak detector)? I say this because I am not measuring the negative part of the AC signal and do not know if losing accuracy and speed of detecting a change in current.

Cheers
LAMC

over 8 years ago

0 Pete%20Semig over 8 years ago

TI__Mastermind 25775 points

Hello Luis,

I think you ultimately want to select the right amplifier (e.g. op amp, instrumentation amplifier, current shunt monitor, or difference amplifier) for your solution. Please refer to the following series for help in selecting the appropriate device:

www.eetimes.com/.../A-Current-Sensing-Tutorial-Part-1--Fundamentals

www.eetimes.com/.../A-Current-Sensing-Tutorial-Part-II--Devices

www.eetimes.com/.../A-Current-Sensing-Tutorial-Part-III--Accuracy

www.eetimes.com/.../A-Current-Sensing-Tutorial-Part-IV--Layout-and-Troubleshooting-Guidelines

I assume you're talking about slew rate when you state "..must be less than 50ms its response". Assuming a 5V output transition, 50ms equates to a slew rate of just 0.0001V/us, which is not a problem for any of the aforementioned amplifiers. If you're stating the the period of the input signal is 50ms, that equates to a frequency of just 20Hz. Though you will need to know the gain of the amplifier to ultimately determine the required amplifier bandwidth, this shouldn't be an issue either. For more information about slew rate and bandwidth, please take a look at our TI Precision Labs series of videos at www.ti.com/precision-labs .

0 Luis Meza over 8 years ago in reply to Pete%20Semig

Prodigy 30 points

Pete,
Thank you very much for answering. Indeed, one of my questions was to choose the right device, now with links, it became clear. Another question is whether it is correct to use the peak detector or full-wave rectifier using OPAMP's.
My signal is 60 Hz, input ranges is 10 mV rms @ 500

Regards,
LAMC

0 Pete%20Semig over 8 years ago in reply to Luis Meza

TI__Mastermind 25775 points

Hello Luis,

Though it's hard for me to definitively state which is best for your situation, a full-wave rectifier will give you a representation of the entire waveform. You can then digitize it using an ADC and can then run algorithms in software to extract whatever information is required for your system. We have a couple full-wave rectifier TI Precision Designs. Here are the links:

http://www.ti.com/tool/TIPD124
http://www.ti.com/tool/TIPD139

0 Luis Meza over 8 years ago in reply to Pete%20Semig

Prodigy 30 points

Thank you! In short I reviewed and commented my results.
Regards

Amplifiers

Amplifiers forum

Current sensing_Time