current source,4-5A

Want to use the op amp to set up a constant current source with output current of 4-5A, the power supply of the op amp can be ± 12V or 5V. Is there any recommended circuit

  • Hi Jack,

    To reccomend you a suiting circuit, you should specifying the following:

    - Do you only want sourcing positive current (or sinking current to ground)?
    - Is this current fixed (or adjustable)?
    - What accuracy / Stability you need?
    - How dynamic is your Load?
    - What is maximum voltage you need on the output?

    The standard method is, that you have a small shunt resistor and a transistor in the current path.
    And with the OP you regulate the transistor, hence the voltage drop on that shunt:
    With the OP you sense this shunt voltage and compare that to a reference voltage, that set your output current.

    In the internet you will probably find a lot of circuits.
    But if you specify the above and reply to this post in recenable time, I can reccomend a circuit for you.

  • Hi Jack_167,

    It seems to me that your requirements has error

    shunt resistor 5 Ω

    15 A current will create 75 V drop voltage at this shunt, this is unacceptable large value.

    load: Resistive load 1-2.5 ohms

    That you mean? If I understand it correctly, this is resistor between battery and power transistor? What function do you want to assign to this resistor?



  • Hi,

    In your case, this circuit will have a very significant power dissipation. We can neglect the internal resistance of the battery and the shunt resistance in the first approximation and find the worst value of power dissipated at the transistor 15 A * 29 V = 435 W. In reality this value will be smaller because some of the power will be dissipated inside the battery and on the shunt but still remain very large. A single transistor can't handle it. Several transistors in parallel can work but this will require very efficient cooling, since the total power dissipation of this entire design will remain as large.

    I recommend you look at PWM current sources, it is perfectly suited for your purposes and much more effective.