So that a short circuit or a wiring mistake draws only a small, controlled current instead of whatever the supply can deliver. With the limit set just above what the circuit should need, a fault shows as the supply switching into current-limiting mode rather than as a burnt part.
A bench supply has two knobs or two settings, and the second one — current — is the one that protects the work.
How the two settings interact
The supply holds the voltage that was set as long as the circuit draws less than the current limit. If the circuit tries to draw more, the supply lowers the voltage until the current stays at the limit. The display usually shows which mode it is in: constant voltage or constant current.
Why it matters on a new circuit
A reversed component, a solder bridge or a wrong wire can create a short. Without a limit, the supply pushes as much current as it can, and something heats quickly. With a limit, the current stays small, the voltage collapses, and the fault is visible on the display before anything is damaged.
A simple routine
Set the voltage with the outputs off. Short the output leads together and set the current limit, or use the supply’s own limit setting if it has one. Remove the short, connect the circuit, switch on and watch the display. If the supply goes straight into constant-current mode, switch off and check the wiring.
What the supply’s published figures say
The maximum voltage and current, the number of channels and the protections a supply lists are published figures reported here as the maker states them. A supply’s limit protects the circuit on the bench; it does not replace the ratings of the components or the maker’s instructions for anything connected to mains power.
Questions makers ask before buying
How do I know what limit to set?
Start from what the circuit should draw — from the parts’ datasheets or the project’s documentation — and set the limit a little above it. A first power-up can use a lower limit and raise it once the circuit behaves.
How do I see that the limit has been reached?
Most supplies show a constant-current indicator and the voltage drops below the value that was set. That is the sign to switch off and look for the fault.
Last reviewed 15 September 2026