How to measure high impedance current source

Technical Discussion
4

Hi @mathankumar,

I confirm that the waveform you sent shows -1.6 µA, not the 20 mA you anticipate.

Just to double-check:

  • IN+ is connected to the output of your supply
  • OUT+ is connected to the load
  • The load is not connected to the output of the supply or IN+

As with all systems, I recommend simplifying the problem to build confidence in your system and your instruments. For example, here is one approach:

  1. Disconnect your load and your Joulescope from the supply.
  2. Select a resistor with approximately the same impedance as your target load.
  3. Connect a simple resistor between your supply out and ground.
  4. Turn on the supply and use a multimeter to measure the voltage across the resistor.
    Using Ohm’s law, you expect I = V / R.
  5. Insert your Joulescope between the supply and the resistor. Check that your Joulescope current measurement matches the multimeter current measurement.
  6. Replace the resistor with your target load.

Let me know what you find!