• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 50 subscribers
  • Views 431 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA547: Feed an inductive load

Sylvain
Intellectual 455 points
Part Number: OPA547
Other Parts Discussed in Thread: OPA564

Hello,

I would like to amplify a sinus signal (100 kHz) from a DDS to feed a coil that is 2 ohms and 47 µH. I was thinking about a high-current opamp because I need a current of 100~300 mA max.

I would like to know if the OPA547 is able to feed a low impedance load (2 ohms).

Thank you

  • +1
    TI__Guru* 93105 points

    Hi Sylvain,

    You don't mention the input voltage and the gain you would require the OPA547 to deliver. The OPA547 has a Gain-Bandwidth product of 1 MHz, and at 100 kHz it only has about 20 dB of open-loop gain remaining. If you try and operate it with almost any amount of closed-loop gain the loop gain, the difference between the open-loop and closed-lop gains, is terribly low. I don't think you will receive satisfactory performance from the OPA547 in this application.

    Take a look at the OPA564 datasheet. It has much higher Gain-Bandwidth (17 MHz) and a 40 V/us slew rate. I think it will provide much improved performance at 100 kHz due these higher specifications.

    https://www.ti.com/lit/ds/symlink/opa564.pdf

    The complex (R+jXl) load is likely okay for the OPA564 providing the op amp is operated within its specifications. The 47 uH inductor exhibits about 30 Ohm of inductive reactance at 100 kHz so the load is predominantly inductive. Power op amps usually are able to drive an inductive loads, but one has to be careful to consider and include back-EMF protection. See Figures 54 and 55 in the OPA564 datasheet for examples of back-EMF protection. 

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 455 points

    Thank you very much for your answer!