oscilloscope current probe

Discussion in 'General Electronics Chat' started by strantor, Oct 11, 2011.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
    I am going to need to take current readings on my oscilloscope soon. I googled Tektronix Current Probe and the results are (monetarily) scary. Do I need to use a tektronix probe with my tektronix scope? Even the other brands are expensive. I could use a hall sensor I guess, but it might be too big. So, how do you guys (on a budget) measure the current through a MOSFET leg?
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    You solder in a small resistor. Then you clip your scope probe on to this resistor. The gnd alligator clip on one end, and the scope probe on the other end. Your scope channels share the same ground. So you will only be able to measure with one scope channel using this method
  3. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
    the problem is that this mosfet is going to (hopefully) be switching 50 to 70A. I may eventually be including super low value current sense resistors, but they aren't the type thats easy to just solder in.

    EDIT: And I need to measure current on 2 channels at the same time
    Last edited: Oct 11, 2011
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    Adding a resistor may upset operation, particularly in the source leg, where inductance may be as much a problem as resistance if di/dt is at all high. Physically large resistors with long connections are likely to be troublesome in this respect. Small all-metal resistors might be the way to go, but of course they do need to be big enough to handle your 70A.
    strantor likes this.
  5. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
    Valuable tip; I had selected some long large resistors. good thing you pointed that out!
  6. crutschow


    Mar 14, 2008
    Measuring current without a resistor in the circuit is not easy or cheap. A current probe is the easiest way. You can use any current probe with any oscilloscope.
    strantor likes this.
  7. MrChips


    Oct 2, 2009
    The current probe I use is a Tektronix P6022 AC Current Probe.
    Note that you cannot measure DC with this. It must be AC or a current pulse.
  8. someonesdad

    Senior Member

    Jul 7, 2009