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OPA330: AC Current Measurement

Prafulla Salunke
Intellectual 660 points
Part Number: OPA330
Other Parts Discussed in Thread: TLV333, OPA325, TLV9002, OPA191

Hello ,

Using TINA TI, i have designed AC current measurement circuit using OPA330. Simulation file is attached. Below are the requirements:

1. AC Current Range: 5mA to 6A rms (with 12 Bit SAR ADC)

2. V+ =3.3V, Vref=1.65V

1. Review the circuit and let me know if any improvement needs to be done.

2. Considering 31st Harmonics on Current input, how i can tune the design.

* In Simulation , CS1 is equivalent model for Current Transformer of Ratio 1000:1.

Thank you in advance

OPA330.TSC

Regards,

Praful

  • 0
    Intellectual 660 points

    Also let me know, low cost equivalent opamp for OPA330.

  • 0 in reply to Prafulla Salunke
    TI__Guru 63790 points

    Praful,

    The circuit works properly in simulation (see below) and the lower price version would be TLV333.

    Having said that, since OPA330 (and TLV333) are chopper amplifiers, you may run into an error issue related to a mismatch of the gain resistors.  Not only will this show as a gain error but also may result in a commutation of the input bias, IB, current spikes (caused by closing/opening front-end switches), across the mismatched resistors. If this causes a problem, an alternative would be to use a non-chopper amplifier like OPA325. 

  • 0 in reply to Marek Lis
    Intellectual 660 points

    Hi Marek,

    Thank you for your view and sharing additional information.. I went through datasheet of OPA325. Its current consumption is of 0.750mA which is higher for my low power application. I am looking for cost optimized part with low offset, drift and current consumption upto 100uA suitable for my application.

    I tried simulation of same circuit with TLV9002 as well. I need your further help on retuning circuit (if necessary) for measuring upto 31st harmonics.How filters has to be designed for it.

    Adding to above, how i can tune values of C1, C2, C3, C4 to get better gain & phase margin considering harmonics?

    Regards,

    Praful

  • 0 in reply to Prafulla Salunke
    TI__Guru 63790 points

    Praful,

    If you could increase the minimum supply voltage to 4.5V, OPA191 (max Vos<25uV, IQ~140uA) would be another option. TLV9002 belongs to GPAMPS.

  • 0 in reply to Marek Lis
    Intellectual 660 points

    Hi Marek,

    I wish i could use it. But my cost sensitive application not allows me to use it. Hence i went for TLV9002. Also, i can not increase my supply voltage more than 3.3V. Can you suggest equivalent low cost part?

    Regards,

    Praful