# Power supply over-current protection mode: constant current

I am researching power supply over-current protection modes, and I have a question about constant current.

Wikipedia claims (https://en.wikipedia.org/wiki/Foldback_(power_supply_design)) that the current remains constant while the voltage goes to zero. Doesn't this violate Ohm's Law? R is not changing, I is not changing, but somehow the voltage can change willy nilly?

What gives?

• If R and I don't change, V doesn't change too. – PlasmaHH Mar 20 '17 at 15:52
• Even if it's a switching or linear regulator, there are two main regulation modes: constant voltage or constant current. And they are ORed in feedback circuit. So, if one (constant voltage) fails (by a short or overload) the other (constant current) will take control. Thus, in constant current mode, you shouldn't expect constant voltage. – Rohat Kılıç Mar 20 '17 at 15:57
• R is changing, and Ohm's law tells you that for a constant current and decreasing R the voltage decreases with R. When R approaches 0, so does V. – JimmyB Mar 20 '17 at 16:16
• I see, I guess I misunderstood the part where the graph defines the behavior as the load changes. That should have been obvious. Sorry! – user2913869 Mar 20 '17 at 18:31