I bet you face lots of problems in design process where you simply need to test power supply, or LED by providing/drawing constant current regardless to voltage change. Such device is called a dummy load. You can find lots of DIY dummy load projects and we won’t be talking about commercial ones right now. Nick found out that most DIY dummy loads tend to be complicated or unavailable. So without struggling he decided to start his own simple and reliable load.
He wanted it to be simple, self powered and indestructible. Indestructible means that it won’t burn in voltage range up to 30V. With BTS141 FET this became possible as it has built in over-current and over-voltage protection built in. Controlling is done with simple potentiometer attached to operational amplifier positive input. Negative input is connected from current sense resistor. The project is OSHW which can be found on github as re:load. [source]