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Bridge amplifier using OPA549

Thomas Witzel
Prodigy 60 points
Other Parts Discussed in Thread: OPA549, INA146

Hello,

I'd like to design a voltage-to-current amplifier to drive current in a near purely inductive load (say L approx 5 uH, R 0.5 - 2 Ohm). I have design an amp using the master-slave configuration in Fig. 14 from the datasheet and that seems to work out well. Now I'd like to switch to a single-supply design (but output needs to swing positive and negative), so I was playing with bridge configurations. I have not been very succesful with that. While I was able to get voltage amps to work okay, driving a current and controlling feedback via a current sense resistor has miserably failed. Has anybody used the OPA549 in this kind of application before ? A reference design would be awesome.

Thank you so much in advance,

Thomas

  • 0
    TI__Guru* 93105 points

    Hi Thomas,

    I apologize for it taking a long time for us to respond. We have been trying to squeeze in some vacation before the end of summer and some inquiries have regrettably slipped through the cracks.

    I have not seen an application where a OPA549 bridge amplifier has been used to drive a purely inductive load. I expect this can be done, but achieving and maintaining a stable system may prove a difficulty. When you sampled the current with the sense resistor, how was that accomplished? Did you use a difference amplifier, or current shunt amplifier?

    Circuit simulation may be the best tool to help you arrive at a solution.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 60 points

    Hello,

    I have meanwhile backed off from the bridge amplifier and just worked with TINA to get a stable non-bridged amplifier to work. I'm using a INA146 differential amplifier to sense current over a 0.1 Ohm current sense resistor. I'm still having some difficulties making the output current follow the input voltage with decent accuracy. I'm now also facing glitching around the zero-crossing, that I'm looking at right now........

    Can I send you the TINA model somewhere ?

    Thanks, Thomas

  • 0 in reply to Thomas Witzel
    Prodigy 60 points

    At the risk of talking to myself, I'll just close this thread with saying that the bridge configuration does work, where the "master" amplifier is a current source and the "slave" is a simple G=-1 voltage amplifier. This provides a clean +/- 10A current source with nice slewing abilities into the inductive load due to the double voltage range in the bridge configuration. Inductive load turned out not to be the problem once I figured out the correct loop compensation circuit.

    Thomas

  • 0 in reply to Thomas Witzel
    TI__Guru* 93105 points

    Hello Thomas,

    Thank you for the feedback regarding your success using the OPA549 in the master/slave bridge amplifier configuration. Your application information is useful to us as well.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Witzel
    TI__Guru 64125 points

    Hi Thomas W.

    Out of curiosity, would you mind sharing the compensation circuit you employed to stabilize the inductive load in your circuit? 

    Thanks and Happy Holidays,
    Collin Wells
    Precision Linear Applications