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Our objective is to sink a current pulse of 20A at 20V for a duration less than 1.5 ms, which should be possible according to the data sheet spec (region 3 in the pulse region spec).
However, when I try to sink a smaller current of 1A @ 20V for 1 ms, the current goes haywire, momentarily shooting to over 7A, and our system bus trips ( , yellow: current ; green: system bus). Even when I disconnected my DUT and directly loaded the 20V supply, I saw similar a waveform. I am a little apprehensive about testing this at 20A due to the fear of the instrument's erratic behavior damaging my other components.
Next, I loaded my supply with 1A @ 1 V (lesser voltage) for a longer duration of 10 ms. What I observed was there was there was a lot of jittering before and after the 10 ms pulse arrived ( ). I changed my supply and still observed similar results.
When I shorted the SMU terminals and tried the same, I got a perfect 20A current pulse for 1 ms ( )
1) Could you please clarify if the tests we want to perform are possible with this instrument?
2) If so, why are we not able to observe the pulse we expect when I load my supply or system with the Keithley sourcemeter?
We would really appreciate a quick response, as we have been stuck with this for a while now.
- Keithley Applications
- Posts: 1263
- Joined: October 15th, 2010, 10:35 am
- Country: United States
What output off mode are you using?
The normal/default output off state (blue light off) is to force 0 volts with current limit of 1mA.
If using this, then the SMU is in compliance limiting and applying a short circuit to your voltage source when the blue light is off.
When you subsequently program it to turn the output on and sink current, it has to come out of compliance limiting.....which can cause some interesting waveforms.
Rather than the High Z output off mode (which uses a finite life relay), consider the zero output off mode where it forces 0 Amps and with a voltage compliance higher than the voltage of the supply that you are connected to. Using a higher V limit than the voltage source is very important.
Thank you for your response.
1) Yes, we are connecting the 2651A to an active voltage source (B & K precision 9117) that can supply over 100A of current.
2) Initially I was using the default output off mode. As you advised, I tried all the three output off modes, but I did not observe any significant change in my waveforms (only minor improvements).
I have attached the tsp file that I am using: Could you please take a look at it and see if there is something I am missing? Or provide any other suggestions?
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