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LM3886 Parallel operation while in current mode.

Jeff Starkell
Intellectual 505 points
Other Parts Discussed in Thread: LM3886

I developed a small test board using a LM3886 operating in current mode. The circuit drives a CT that then drives a non-linear load. The circuit works well as shown.

I have three of these, one for each phase.  I would like to increase the output current by connecting the three devices in parallel (with a 0.1 Ohm resistor in series with pin 3). Based on AN-1192 connecting multiple LM3886's in parallel appears viable. However AN-1192 demonstrates parallel operation while operating as a voltage amplifier, while I'm using it as a current source. Does anyone foresee any problems if I run in parallel current mode?

Thanks,

Jeff

  • 0
    TI__Guru**** 189401 points

    Hi, Jeff,

    Unfortunately, we don't have any experience running this in current mode.

    -d2

  • 0 in reply to Don Dapkus
    Intellectual 505 points

    I tried this today, and it does not work.I tried the following:

    1. Same drive signal, separate loads, works fine.
    2. Connect the returns together, but drive independent loads, works fine.
    3. Connect source 2 pin 3 to load 1 via a low value resistor, current from source 2 flows into source 1 instead of the load. As I decrease the resistor value from source 2, the current from source 2 increases but it flows into source 1 not the load.
  • 0 in reply to Jeff Starkell
    Intellectual 505 points

    Update,

    It's working, but I took another approach.

    Each current source drives a 500:500 CT that then drives the input of the device I'm testing. I tried connecting the secondaries of the CT's in parallel and it works. I just tried two in parallel and was able to push a bit over 7A rms through the load, so with three it should be be more than 10A and that will suffice.

    I did have to run the power supplies at +/-40V

    Cheers,

    Jeff