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OPA2211A: Precision Rectifier for input signal from 10 mV to 500mV

TI-CSC
Genius 14480 points
Part Number: OPA2211A
Other Parts Discussed in Thread: OPA211, OPA1662

Tool/software:

Hello E2E Experts,

Good day.

 I am trying to build an leakage current meter and for this application i want to convert my rogowski sensor output to the DC signal so that i can feed this signal to microcontroller for further processing.

Basically i want to rectifiy signal range from 10mV to 500mV @ 50Hz.

I have checked the shcematic of precision rectifier of of OPA2211 but i think the starting range is 20mV whereas i want from 10mV to 500mV.

I am not working in any company so i am not having any company mail id and thats is the reason i am raising my query through this channel.

If you can share some IC datasheet and application note for above mentioned application then it will be your great help.

I kindly request you to provide your kind support and guidance. 

Regards,

TI-CSC

  • 0
    TI__Mastermind 26238 points

    TI-CSC,

    Precision Full-Wave Rectifier, Dual-Supply is a good document covering the precision rectifier using the OPA211.  Is this the document you are looking at?  I reviewed the document but did not see the 20mV range limit you mentioned.  Figures 14, 15, and 16 show measured results for this circuit.  The limitation of this circuit is more related to the bandwidth and slew rate of the op amp.  Basically, the amplifier will need to slew its output to overcome the forward drop of the diodes used.  So, for fast signals you can get some artifacts for low voltages as the amplifier slews to overcome the diode drop.  Figure 16 shows a 50mVpp 1kHz sinusoidal rectification.  You can see in this example that there are some errors for low voltages (for signals < 10mV).  This error would be worse for higher frequency inputs.  You could minimize this error further by adding pre amplifier in gain (i.e. a gain of 10V/V could be used to amplify your 10mV to 500mV to 100mV to 5.0V).  This would minimize the error from the diode turn on behavior.  In your case your applied frequency is quite low so the pre-amp may not be needed.

    Best regards, Art

  • 0 in reply to Art Kay
    TI__Genius 14480 points

    Hello Art,

    Good day.

    Before we close this case, can you please give your suggestion and inputs on the below questions.

    Yesterday, I have referred the application note which you have shared with me and as per your suggestion i have also added pre-amplifier with a gain of 10 and then precession rectifier followed by 1uF capacitor C1 at the final output to convert pulsating DC to ripple free DC output.

    1. I have checked the simulation output but even after connecting filter capacitor on output i am still getting pulsating DC instead of ripple free DC. i think if i will practically assemble this circuit then i hope i will get ripple free DC output. For your reference purpose i have attached the image of the same

    what's your suggestion on this?

    2. I found OPA1662 IC which is 2 channel op-amp. so can you please confirm whether i can proceed with this IC or i should continue with OPA2211?

    Regards,

    TI-CSC

  • 0 in reply to TI-CSC
    TI__Mastermind 26238 points

    TI-CSC,

    To answer your questions:

    1. We started this post looking for a full-wave rectifier.  A full-wave rectifier will basically invert all negative signals and make them positive.  This kind of circuit will naturally have a lot of ripple as it will just follow the input signal when it is positive and follow the inverted the negative signals.  I understand you a filtering this and want a DC signal.  I think perhaps you are looking for a "peak-detector" circuit.  This post provides a lot of detail on peak detector:  Peak-detector E2E .  Alternatively, perhaps you just want heavy filtering of the rectified circuit.  This could be done with a passive filter as shown here: PWM filter .  You could use an active low pass filter using this tool:  https://www.ti.com/tool/WEBENCH-CIRCUIT-DESIGNER .  The lower you set the cutoff frequency the more the ripple will be reduced.
    2. When doing an op amp full-wave rectifier, the slew rate and bandwidth are generally the key concern.  Both these amplifiers are relatively fast, but the OPA2211 is faster.  I am not sure why you are considering the OPA1662.  You mention that it is a dual, but so is the OPA2211.  Note that the nomenclature is OPAx221 where "x" is the channel count.  If there is another reason for choosing the opa1662 let me know.

    I hope this helps!  Best regards, Art

  • 0 in reply to Art Kay
    TI__Genius 14480 points

    Hello Art,

    Good day.

    Basically I have Rogowski sensor whose output is 10mV to 500mV and my microcontroller is unable to read this AC signal but it is giving proper output when DC signal is applied. and for this application i want a circuit which can convert Rogowski sensor AC signal to DC signal.

    So based on your reply and suggestions, can i just connect Non-inverting amplifier (for higher gain 10V/V) followed by Peak detector (instead of Precision rectifier) and PWM filter?

    I agree with your suggestion regarding my second question on OPA2211 IC.

    Regards,

    TI-CSC

  • 0 in reply to TI-CSC
    TI__Mastermind 26238 points

    TI-CSC, 

    I made the suggestion based on the fact that you did a full-wave rectification followed by an integrator.  This is basically a peak detector.  I have not spent a lot of time working with Rogowski sensors, so I am not really sure what the requirements are.  So, I did a search on Rogowski amplifier circuits to see what people are doing (i.e. are they doing a peak detect).  Based on my search I did not see anyone rectifying the Rogowski signal.  From your comment I think you did the rectification because your ADC cannot accept bipolar signals.  Although rectification converts your bipolar signal into a unipolar signal, I am not sure that this will yield the desired Rogowski measurements.  Active Integrator for Rogowski Coil Reference Design With Improved Accuracy for Relays and Breakers provides a reference design for Rogowski coils.  This design achieves the bipolar to unipolar conversion with a level shifter op amp circuit.  The output of this circuit would retain the same wave shape as is generated from the integrated Rogowski coil, but would shift it so that it is always positive.  I think that rectifying the Rogowski signal would lead to a rectification of your current sense.  In other words, when the Rogowski coil detects negative current flow that would be inverted so that you could not differentiate between the negative and positive current flow in your current sense.  Maybe this isn't a problem.  I can help you to achieve the amplifier function that you want, but I am not really knowledgeable on what is required for a Rogowski coil.  Sorry if I introduced any confusion.

    Best regards, Art