Constant Current load video from eevblog

Using Arduino General Electronics
1

Got a quick question after watching the video

At 2:10, Dave mentioned a LM317 could be used a constant current load when you ground the output. So WHY MOSFET solution (On the same white board) you need a power resistor going to ground but LM317 does not need one?

Any idea?

Thanks, BTFDev.

2

Not sure I understand your question. Both circuits have a power resistor to ground and both for the same reason, to measure the current flowing.
In the simple circuit this is used to back off the voltage across the regulator, in the better circuit an op amp uses the current information to feed the FET with the right voltage to keep the right ammount of current flowing.