Keithley SMU as electronic load?

[dzseki]

A question just for sainty. At work we don’t have any electronic load, but we have a few SMUs (mainly Keithley 2612) laying around. If I want to use the SMU as an electronic load the best is to set the desired source current -1x, ie. if I want to dump 1A from a circuit under test (a power supply, obviously) then I set the SMU to „Source I: -1A” is it that simple? Providing that I stay within the power specifications the Keithley.

[Mr. Scram]

I've wondered about the electronic load portion of SMUs too and how that'd work exactly. Like whether you could source and sink power with the same SMU or you'd need two units for that.

[Yansi]

As the smu (2600) is i think a 4quadrant psu, you can pf course sink and source current. However i woud be very cautious about the dissipated power inside the smu. So please consult the manual thoroughly. It is an expensive piece of kit to get damaged.

[JxR]

if I want to dump 1A from a circuit under test (a power supply, obviously) then I set the SMU to „Source I: -1A” is it that simple? Providing that I stay within the power specifications the Keithley.

Yes, it is that simple.

[dzseki]

Thank you for the answers.
Basically what I want to look at the moment is to characterize some low voltage lines up to 15V, and up to 1A. The Keithley is specified for 1.5A up to 20V, so I guess I should be OK dissipationwise.

[JxR]

Thank you for the answers.
Basically what I want to look at the moment is to characterize some low voltage lines up to 15V, and up to 1A. The Keithley is specified for 1.5A up to 20V, so I guess I should be OK dissipationwise.

You should be fine with those ranges.  My 2450 will complain about internal temps if I keep it sinking 1A of current over a long period of time, but it will auto-shutoff if it becomes a problem. 

I'm not really familiar with the 2612 personally, but for the 2450 you can set the output to "high-z" mode which will put a relay between the inputs when the output is switched off. Maybe not a big deal if your just dealing with power supplies, but if you want to use it as a load for batteries in the future that is the mode you want to have the output on.  Either way, it is an additional safety feature you may be interested in when operating as a current sink.

[Mr. Scram]

You should be fine with those ranges.  My 2450 will complain about internal temps if I keep it sinking 1A of current over a long period of time, but it will auto-shutoff if it becomes a problem. 

I'm not really familiar with the 2612 personally, but for the 2450 you can set the output to "high-z" mode which will put a relay between the inputs when the output is switched off. Maybe not a big deal if your just dealing with power supplies, but if you want to use it as a load for batteries in the future that is the mode you want to have the output on.  Either way, it is an additional safety feature you may be interested in when operating as a current sink.

I assume you can't sink and source with the same SMU at the same time?

[JxR]

I assume you can't sink and source with the same SMU at the same time?

No, it can only source/sink either current or voltage (but not both) at a time per output.  There is a model or two that have more than one output though.

Also, whatever your sourcing you set a maximum limit for the "measure" function.  IE, when sourcing Voltage, you set a current limit.  When sourcing Current, you set a voltage limit.

Edit: Technically, you can do strange things like connecting two SMUs, and have SMU#1 sink current, and measure voltage.  Then have a SMU#2 sink voltage and measure current.  Then SMU#1 would show both negative current and negative voltage on its display.  Although still, there is only a single source for each unit, regardless if it is positive or negative.

[aronake]

I want to use a SMU to test some LT3045 based voltage regulators to see how they behave the more current they draw.

The problem i have is as i increase current sink, the LT3045 shuts off at certain current. If I then continue to increase the current draw, the SMU will start applying a negative voltage on the output of the LT3045 to achieve the set current sink. I dont want this to happen, but the SMU behave like an electronic load i.e. lower resistance with higher current until when the LT3045 stop delivering current and the SMU turns into a short. Can this be done?

[aronake]

I want to use a SMU to test some LT3045 based voltage regulators to see how they behave the more current they draw.

The problem i have is as i increase current sink, the LT3045 shuts off at certain current. If I then continue to increase the current draw, the SMU will start applying a negative voltage on the output of the LT3045 to achieve the set current sink. I dont want this to happen, but the SMU behave like an electronic load i.e. lower resistance with higher current until when the LT3045 stop delivering current and the SMU turns into a short. Can this be done?

I figured this out myself.  I though current source mode was supposed to be used, but ofcourse not! Set the SMU to source 0 volt, and then use current limits/compliance to allow it to drain like an electronic load.

[aronake]

I want to use a SMU to test some LT3045 based voltage regulators to see how they behave the more current they draw.

The problem i have is as i increase current sink, the LT3045 shuts off at certain current. If I then continue to increase the current draw, the SMU will start applying a negative voltage on the output of the LT3045 to achieve the set current sink. I dont want this to happen, but the SMU behave like an electronic load i.e. lower resistance with higher current until when the LT3045 stop delivering current and the SMU turns into a short. Can this be done?

I figured this out myself.  I though current source mode was supposed to be used, but ofcourse not! Set the SMU to source 0 volt, and then use current limits/compliance to allow it to drain like an electronic load.

And reading this again now when I have tried things, this is what is being confirmed in 4th post in this thread.