Circuit to prevent high power through digital potentiometer


I am trying to build a V-I tester for a solar panel. So far I have succesfully used a setup to test a single cell, using the process in the attached image. As voltage and current sensor I am using an INA219.

Having a light source directed onto the cell I turn up the potentiometer, thereby sweep the voltage and plot the V-I characteristic.

For the cell that works fine with a manual potentiometer, because the power is low. For a better controlled and quicker sweep, I would like to move to a digital potentiometer.
For a whole panel I expect to operate at around 30-40V and 0.2-0.3A which will blow the digital potentiometer.

Do you know what circuit I might need, to get around that problem?

Thanks a lot,

Depending on the detail of your setup, the easiest way to limit current is a resistor rated for the circuit you’re designing…
For the voltage, the simplest would be two resistors - a voltage divider. Same rules.

of course, you can combine these, or step up to a more complex power monitoring solution.

Sorry, but IMO this is another XY problem. Why do you need the potentiometer in the first place?

Right, it were sufficient to control a programmable current source and measure the voltage related to the selected current. Search for current source circuit diagrams.

A transistor with variable base/gate drive?

Better a BJT with a fixed emitter resistor as current sensor/stabilizer. The collector current then is controlled by the base voltage.

Sorry, but IMO this is another XY problem. Why do you need the potentiometer in the first place?

The pot is acting as the load for the PV cell.
By changing the load under constant light conditions you can draw up a characteristic graph of the PV performance and importantly its Maximum Power Point.

I gather the OP wants to automate the process by having the load automatically sweep from low to high load while recording the current and volts across the PV.
It would make a nice jig for PV comparisons and MPPT controller development.

Tom... :slight_smile:

Thank you all for the replies. I will have a look into it and see how this can be applied to my problem.

@TomGeorge: You phrased my problem much better than I did :slight_smile: