Generate current pulse using PXI 6251 counter output

[Smyky]

Hi there,

I am Michael Panganiban from Philippines. I am simulating a pulse current generation using DAQ PXI 6251, Source measure unit (Keithley 2420) and an N-ch Enhancement Mode High Speed MOSFET. My requirement is to produce a 1.5A pulse current at tp=100microseconds.
I will initialize Keithley 2420 to output a 1.5A current at the drain terminal of MOSFET. I will use the counter output of DAQ to pulse a TTL signal as Gate-Source voltage and set set high time and low time to 100us (CO Pulse Time). Since my source measure unit is not yet available, I tried to simulate it using 5V DC signal but I can't produce the expected output. With this set up, specs of MOSFET and resources used (counter output), is it possible to produce the above requirements? Thanks
Hoping for your response. Any ideas, comments and critique is highly appreciated.

thank you very much and best regards,
Michael Panganiban

[Neal M]

Hello Michael Panganiban,

It seems like your setup should work.  I am not horribly familiar with your specific SMU and MOSFET, but I am with the PXI 6251, so I can help you program that. What program are you using to create your pulse? I would reccomend using the Gen Dig Pulse example (In the LabVIEW Example Finder under Hardware Input and Output»DAQmx»Generating Digital Pulses).  This example will output a pulse with a high and low time you specify and an intial delay. If you want more than one pulse, than the other examples in that folder will allow you to accomplish that as well.

If this doesn't work, is there any way you can scope the output of the PXI 6251?  This would allow us to make sure that the MOSFET is getting a signal.  If that is working, then we can start troubleshooting the rest of the system.

Hopefully this gets to the root of your problem, post back if you have any questions.

[Smyky]

Hello there Neal,

Thank you very much for your reply. I did checked the output of my digital pulse coming from PXI 6251 and I can simulate it perfectly in my scope. And when I did simulation with the MOSFET in 10Hz to 100Hz, I can still get a good signal. But when it comes to 1000Hz and above, the signal is already distorted. I am new in using power MOSFET and can you please recommend me some stuff regarding this? I attached the specs of the available MOSFET we have here. If you have suggestions and comments, I really appreciate it. Again, my goal is to simulate a tp=100us pulse signal. Thank you for dropping by Neal. Hope to have response from you again.

with best regards,

Michae P

[Neal M]

Hello Michael P,

I am glad to hear that you can simulate your signal perfectly from our card, however I am a bit confused as to exactly what is going on.  When you say that when you input a 1000Hz signal, "the signal is already distorted."  Do you mean the signal from your PXI 6251? Or the signal coming out of your MOSFET?  I ask this because there are several things that could be going on, and the better I understand exactly what is going on, the easier the troublshooting becomes.  Is there any way that you could post a screenshot of the distorted signal as well?  That way I could see how the distortion looks which may lead to the cause. An actual schematic (do you have anything else but the MOSFET?) could help as well.

Just as a note, if the behaivior is being caused by your power MOSFET, you may have better luck posting to a general EE forum or contacting the maker of the MOSFET.  This forum is full of people (like myself) who know NI hardware/software inside and out, but may not be the best at actual circuit troubleshooting.