Sink current with PXI-4130

[GS]

I'm trying to program my PXI-4130 SMU to sink current. According to the manual channel 1 should be able to operate in all 4 quadrants. I tried the soft panel from MAX and it won't let me program a negative current. What am I missing? Should I be able to do this?

George

[Nick_F1]

Hi George,

When you have Channel 1 set as DC Voltage, the Current value that you type in is the current limit that you want to set.  It does not actually set the current level.



For instance, if you have the voltage set at 5V, the current will be flowing from the HI channel to the LO channel.  When you voltage set at -5V, the current will then be flowing from the LO channel to the HI channel.  Both of these cases are still sourcing and not sinking.  Quadrant I & Quadrant III.

In order to be Sinking, you will have to have an active element.  Please refer to the image below. 



If you have your PXI-4130 supplying 3V to a 3.7V battery, what is going to happen is current will be flowing in the opposite direction.  Since the 3.7V battery is at a higher potential the current flows into the PXI-4130.  At that point you are in Quadrant IV since the PXI-4130 is providing a positive voltage and is drawing current which means you are sinking.

If you have any other questions, please let me know.


Message Edited by Nick F on 05-06-2008 03:50 PM

[cpshang]

Hi Nick, 

Instead of  using active element, are there any other ways to sink negative current?

Thank,

Grace

[enderWiggin10]

In order  for the device to sink current, it requires an external source to provide the current in order to sink it.  This is what the active element is in this case.  Therefore, it is required.

Best,

[cpshang]

Hi Adam,

let say i now have PXI-4310,  i want to test LED, now i need the SMU to provide me negative current source(reverse current), so that i can measure the "Reverse forward voltage".

So, the PXI-4310 cant directly output me a negative current source? 

Please Advise,

thank you

[enderWiggin10]

Hi cpshang,

If we take a look at the four quadrants, listed in the earlier post, we can source a negative current, but it will end up being a negative voltage as well.  If you need positive voltage with negative current, you will need an active element to accomplish this.

Best,

[enderWiggin10]

Please let me correct myself.  We can only specify the current limit, and the SMU can source current to that limit, and can also sink current to that opposite limit.  For example, if the threshold is 1 Amp, it could source up to 1A, and allow a negative current to be sinked to -1A.

Best,

[RT_RF]

Hello,

I intend to check the maximum current delivered by a 3V voltage supply (this supply comes from a rectified RF signal). In other words, this 3V voltage generator, delivering a ~1ma current, will drop when the i_load current (sunked) will reach a specific value: i want to measure this i_load current. Should i be able to do this, and how?

 

let's imagine my 3V generator, how to configure the PXI-4130 so that it sinks my 3V generator current with a very specific and controled i_load current?

For example, if i want to load the 3V generator with a 200ua current, i guess i need to set i_limit= -200ua. What about for the voltage to be applied by the SMU Channel (V_SMU_hi & lo): i guess this must be a voltage lower than 3V, like 2V? In that case, the i_load will be the 200ua sunked current (the current limit will immediately be enforced). Will the V_SMU (2V) tend to 3V as well, therefore the sunked current will no longer be -200ua?

Then, considering that i am able to control the sunked current (i_load), should i be able to monitor (measure) my 3V level to track when it drops down?

Best regards.

Considering here below

image:

[enderWiggin10]

Hi RTRF,

The current limit setting that you can configure is only a postive value.  You can then set your votlage to be postive or negative.  This current limit allows you to source current up to that limit, and also sink current up to that limit.  The amount you sink/source will depend upon the load and the source.

How are your achieving the 200mA of current? I am confused as to why you need to source a voltage to the 3V source.  Can you elaborate on this?  Would it be possible to use a DMM to accomplish this?

Best,

[RT_RF]

Hi cyclone and thank you for considering my request,

The object of my request is to know if the PXi-4130 can fit my needs, i ll try to explain the situation better:

i have an RF device that provides on one pin a "voltage" supply: rectifiers will turn an external RF signal into a 3V DC regulated voltage.

and i want to characterize this 3V DC voltage, because this kind of "DC supply" is limited in sourcing current. In other words, the 3V DC regulated voltage will be garanted for a maximum load that i want to find out.

2 options, i intended:

- option1: to measure the 3V voltage by applying an decreasing load (ohmic resistance) until the 3V drops down because the sunk current will be to high,

- option2: to use a device able to sink current from my device 3V pin. In that case, i would search for the maximum current my 3V supply can be garantied. For this option, my idea was to use the PXi-4130 to sink current from my 3V pin. Is this achievable? and how?

hope this can help you have a better understanding,

regards.