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programmable AC current source 0A-10A

shivakumar L V
Prodigy 90 points
Other Parts Discussed in Thread: OPA549

I intend to make a circuit that has a constant current output with programmable ranges {e.g 1A, 1.5A,2A ...etc}, can I use master slave combination of OPA549  as voltage controlled current source.so please help me if you have any good idea rather than my own one.

  • 0
    TI__Guru* 93105 points

    Hello  Shivakumar,

    I expect that the load connected to the output of your cuurent source will be required to have one connection to ground. If so, the Improved Howland Current Pump may be your best option for the current source. Here is a resource on the subject:

    http://www.ti.com/lit/an/snoa474a/snoa474a.pdf

    The OPA549 is a good power op amp candidiate for high-current pumps. Its maximum output current is 10 Amps, however, that can only be sustained within the limits in the safe operating area (SOA) graph. It can be found on page 6 of the data sheet. Paralleling the outputs of two OPA549 devices is an effective way to split the power dissipation between two devices. The parallel output connection is shown in page 14 of the data sheet.

    I took the parallel output concept and applied it to the Improved Howland Current pump Circuit and then set it up in TINA Spice. The single output sense resistor had to be doubled in value because the two amplifier outputs are essentially in parallel. You can see the circuit in the image shown below. Also, I have attached the TINA Spice circuit should you want to test it.

    I selected the pump circuit resistors so that the transconductance gain (I/V) is 1 A/V. Thus, if you set the input voltage to 10 V, the output current is 10 Amps.

    The circuit shown is the basic dc circuit. If the output load is anything other than resistive, i.e. resistive, plus reactive, the circuit may require compensation to keep it stable. Also, the resistors must be highly accurate for good precision. Resistors having a 0.1 % tolerance can yield a current source accuracy as high as 1 %.

    Regards, Thomas

    PA - Linear Applications Engineering

    OPA549_Howland_Parallel_01.TSC
  • 0 in reply to Thomas Kuehl
    Prodigy 90 points

    Dear Thomas Kuehl

     i will use this for power protection development protection. but will it work for sine wave input? 

  • 0 in reply to shivakumar L V
    TI__Guru* 93105 points

    Hello Shivakumar,

    Yes, the Improved Howland Current Pump can be used as an ac current source. This has been discussed here on the Precision Amplifiers E2E forum a number of times. You can find one of the discussions here:

    http://e2e.ti.com/support/amplifiers/etc_amplifiers__other_linear/f/18/p/53816/192847.aspx#192847

    If you use the "Search Community" box near the top of the page (uncheck "Just this area") other threads about the subject should be listed.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 90 points

    Dear Thomas Kuehl

    can I add another opa549 to this How land Current Pump circuit in order to  increase current output range?

  • 0 in reply to shivakumar L V
    TI__Guru* 93105 points

    Hi Shivakumar,

    You sould be able to follow the master with more than one slave. However, you may find that compensation - if required - may be different as amplifiers are added.

    If you use the one master, plus two slaves, the sense resistors at the outputs would have to be increased to 300 milliohms, from the current 200 milliohms, as shown in the OPA549 TINA schematic.

    Regards, Thomas

    PA - Linear Applicaitons Engineering