Control PXI-4130 SMU output with sense line?

[GS]

I'm wondering if the output voltage of the PXI-4130 SMU can be controlled with sense line. I know that's not what the sense line is for, but I'm curious if it can work. We have an application where we'd like to be able to control the power supply's output via an analog control line (which could be faster than doing it in software). I figured if the sense line is used to bring the supply voltage to the right value then why can't the sense line be tugged a bit to control the power supply? Am I nuts or could this work?

George

[Nathan_R]

Hi GS,

            The remote sense line on the PXI-4130 SMU is designed to compensate for lead resistance affecting the voltage that you are delivering to your device under test. It was not designed to directly control the output voltage of the SMU. This should be done through software. A detailed explanation of remote sense can be found in the NI_DC_Power_Supplies_Help file. Let me know if you have any more questions. Take care.

Thanks

[JeremyDC]

George:

Let me provide a little more information for you. 

The PXI-4130 is a programmable Source-Measure-Unit, meaning that you program it to output a current/voltage and expect to see that value at the output.  The remote sense feature just accounts for losses in the output leads of the module to ensure voltage at the load terminals is as accurate as possible.  It sounds like a better solution to your application is an amplifier (Voltage controlled voltage source) instead of a Programmable Power Supply or SMU.  Connecting the sense leads to anything other than the load the output leads are connected to will result in the PXI-4130 output getting stuck at one of the module's voltage rails.

For example, lets say you programmed the PXI-4130 to output 10V.  If you then connected a 6V source across the sense leads, the PXI-4130 would try to raise its output voltage until it saw 10V at the sense leads.  Since the 6V supply is the only thing connected to the sense leads, the sense lead voltage will never get to 10V, and the PXI-4130 will end up with its output at 25V or so (it can't go any higher than this, or it would..).  If the voltage you apply to the sense leads is larger than the programmed output voltage, the PXI-4130 will end up at the other supply rail, -25V.

Message Edited by JeremyDC on 02-21-2008 02:42 PM

[GS]

Thanks much. That helps a lot.

George

[GustavoC]

George,

what Jeremy says is correct, however, that is assuming you're using the sense line in an open-loop setting.  If you close the loop (just like with any op-amp circuit) you may be able to come up with some creative app.

Now, let me say though, sounds more like what you need is a plain power amplifier (even audio amplifier may work if you're after AC signals). This is not intended use and therefore can not guarantee that will work to your satisfaction, but here it goes...

For example, if you connect your sense_low to low terminals you may use the sense_hi terminal for negative feedback.  So, like Jeremy said, if you program the output to be 0V but drive the sense terminal positive, the output will pull negative and viceversa... voila, that's your negative feedback.  Now we can extend this by adding a summing node and once you've satisfied the loop, you can introduce a signal that modulates the output.

Can I have a little more insight about what you're trying to do? Is it an AC signal? how fast do you need to go?

Gustavo
National Instruments
Power Supplies & SMUs