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Floating VCR

ettore ruscino81
Prodigy 20 points

Hello, I'm searching for a power variable resistor. It must vary in range  0 - 0,6 Ohm  and must be capable to bring a current up to 8 Amp. OK for passive resistance but I'm asking if exist an active component like power mosfet with which you can do this. It is important that Mosfet  source is not connected to the ground but is floating. The Mosfet gate could be driven with a logic  ciruit. I'm not able to find in TI website an IC with  this skills. Please, could you help me to find this component?

Thanks!

Ettore.

  • 0
    TI__Mastermind 46290 points
    Ettore,

    This topic was assigned to the DAC product line which is also responsible for our Digital Potentiometers. From our portfolio we do not have such a device. You may check this landing page if you haven't already: www.ti.com/.../overview.html

    I am also reassigning this thread ownership such that someone better suited with these offerings can try to provide you with an answer.
  • 0
    TI__Expert 7905 points
    Ettore,

    Thanks for posting.
    You will need to run the MOSFET in the linear region to generate up to 600mOhm, the power dissipation will be in the region of 4.8W (0.6Ohms x 8A). With this power dissipation you will need a large die MOSFET with a low thermal resistance to dissipate the power and keep junction temperatures low.
    In addition you will need to be very careful that you do not get thermal runaway while operating in the linear region. As shown in Fig3 of TI MOSFET datasheet and all competitor datasheets, there is a transfer characteristics curve, this shows that in the linear region ( below where resistance is guaranteed and above threshold) there is an area where all power MOSFETs allow more current to conduct with an increase in temperature. If the MOSFET temperature keeps rising due to increase current then you can get thermal runaway if operating permanently in this mode.