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How to build a current mirror with discrete components?

Lee Young
Prodigy 250 points

Other Parts Discussed in Thread: OPA548, OPA549

Hi all,

    I am trying to build a current mirror circuit for my application, however, I can only do this with discrete components on a PCB, which I suspect it is possible since I have no control over the W and L of the MOS to have desired gain. So my questions are:

(1) Is it possible to build current mirror with discrete components ? How can I tune the gain ?

(2) Are there any current mirror ICs off-the-shelf that I can have a small current input and an amplified current output?

    Thank you for help!

  • 0
    Guru 140200 points
    Hi Lee,

    have a look at the REF200.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 250 points
    Hi Kai,
    Thanks for your reply! Actually, the current mirror will be used as a driver, ideally, it requires Amps of current output. Do you have any suggestions in this case?
  • 0 in reply to Lee Young
    Guru 140200 points
    Hi Lee,

    can you show a schematic? Can you explain the purpose of the current mirror? Why is the current mirror necessary?

    Kai
  • 0 in reply to kai klaas69
    Prodigy 250 points

    Hi Kai,

      I am trying to duplicate the gate driver circuit as discussed in the attached paper, basically this is a current mirror with controllable current reference. The circuit in the paper can have output current of 200mA max., I am trying to follow the design, but scale up the output to 2-5A max.

    gate driver with 10ns in transition variable drive current and 60% reduced current dip.pdf

  • 0
    TI__Guru* 93105 points

    Hi Lee,

    I do not know of any off-the-shelf ICs that can provide the high-power, current mirror function you propose. If the function doesn't require the very fast speeds that are discussed in the paper you mentioned, where it states "The driver presented in this paper can operate at voltages up to 60V, and it is able to change the gate current in 10 / 15ns (rise / fall delay)" then there may be a reasonably straightforward analog solution.

    An op amp transimpedance amplifier (current-to-voltage converter) can be used to convert a low input current range, to an specific output voltage range. A second stage, a voltage-to-current converter such as an Improved Howland Current Pump, could then be used to convert that output voltage range from the previous stage, to a high current output range.

    You can find a quick study on transimpedance amplifiers in the e2e blogs:

    Designing high-performance, cost-sensitive transimpedance op-amp circuits
    This post is co-authored by Raphael Puzio . Photodiode-based light sensing is a common application of operational amplifiers (op amps) used in medical equipment, industrial automation, robotics, point…
    By in Archives > Precision Hub

    And for information regarding the Improved Howland Current Pump (V-to-I) see this Application Note:

    Also, search the e2e forum for the transimpedance amplifier, Howland Current Pump, and OPA548 and OPA549 power op amp subjects. They should provide you with useful information useful for setting up the I-to-V and V-to-I circuits. TI produces the OPA548 and OPA549 power op amps which can handle the voltage and current levels you mention.

    Sorry I can't spend a lot of time on this interesting university project, but have limited engineering resources that we can provide for such endeavors.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 250 points

    Hi Thomas,

        Thank you for you reply! These should be some good reference to learn, I will take a look at them first. Thank you!

    Regards,

    Lee