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OPA237: High-Current Coil Driver with Push-Pull Configuration and OPA237 Configured as a Differential Amplifier

TRILOK SAWANT
Prodigy 20 points
Part Number: OPA237
Other Parts Discussed in Thread: OPA454, DRV421,

Tool/software:

High current Measurment doc.pdf

Hello everyone,

I have a question regarding the OPA237 with PushPull, specifically about its configuration. I'm referring to the content by Javier Contreras on high current measurement evaluation with the DRV421, particularly the schematic in Option 1 that shows the OPA454 in a push-pull configuration.

I’m having difficulty understanding how this configuration works and how the error signal is generated. I believe it might be related to the ICOMP1 and ICOMP2, but I would appreciate some clarification on this. Additionally, I'm unclear about the function of the R1 resistor in the push-pull configuration, as I’m concerned about potential cross-talk and the biasing of the BJTs.

Furthermore, I’m also having trouble understanding the control method, particularly because the base resistor is not present in the BJT configuration and how collector current is controlled.

Any insights would be greatly appreciated!

  • 0
    TI__Mastermind 32340 points

    Hello Trilok,

    The way the circuit works basically a feedback loop that brings the magnetic field at the sensor location to zero.  How you can think of it is the sensor measures the field from the core due to the primary field then it adjust the output (Icomp1, Icomp2) pins bring the field back to zero by driving a compensation coil on your magnetic core.  

    Normally this is driving a compensation coil directly with the DRV421.  The limitation on these pins is 250mA and about 4.2V at 5V supply.  To fight this limitation with the voltage and current we used the BJT to amplify the voltage and current capabilities.  The limitations comes from either larger resistance on the compensation coil or the current requirement in general depending on the number of windings on the compensation coil.

    TRILOK SAWANT said:
    Additionally, I'm unclear about the function of the R1 resistor in the push-pull configuration, as I’m concerned about potential cross-talk and the biasing of the BJTs.

    I took the resistor from this design along with the output stage from here: https://www.ti.com/lit/ug/tidu820/tidu820.pdf

    I asked the designer of the original design and was told this was for the cross over help from going from positive to negative or as the transition from one to the other.  I do not remember why I placed a higher resistance than the design above.  The voltage output of the DRV421 is controlled through the feedback.  So the voltage on the BJT will be controlled through the full loop which involves the magnetic coupling.  This will clearly be seen if the feedback is correct incorrectly it will rail just like an amplifier feedback loop.

    Hopefully this helps.

    Regards,

    Javier Contreras