# Am I interpreting power supply current limit function correctly?

A bench power supply has one variable and two fixed voltage outputs. Below are the related specs:

I highlighted the 5V output specs to focus on it for simplicity of the question.

Regarding 5V fixed output the nominal output current is given as 1A. The limited current is given lets say 1.5A. It says it can be between 1.2 and 1.6 but lets say ours is 1.5A.

Now what I understand from these is: if I connect a 5 Ohm load across 5V output the current will be 1A.

If I vary the load to 3.333 ohm the load will see 5V and pass 1.5A.

But if I vary the load to 1 ohm the load will pass 1.5A but the voltage across the load will be 1.5V.

Are my above conclusions based on the specs correct?

(I’m trying to verify whether this supply has such functionality and whether I understand constant current compliance concept.)

It is hard to determine from the datasheet alone and may need testing to be sure.

I have seen supplies similar to this one do one of two things when reaching the limit:

2. Pulse the load. i.e. when the current limit is crossed, voltage goes to zero then tries again a moment later, only to reset again immediately.

I see nothing in the linked datasheet that clues me into which of these two situations would apply.

• What else could the current limiting used for? Do you mean if the limited current set by the knob is reached the voltage will cut off to zero?
– cm64
May 3, 2019 at 19:18
• Yes, well, not the knob value, the fixed value (1.2 - 1.6)...I mean it acts as a re-settable circuit breaker. Most I have used behave like #1, but I have used more than one unit that behaves like #2 on the fixed output. May 3, 2019 at 19:19
• The variable output should always behave like #1. May 3, 2019 at 19:20
• I also cannot see a value for short circuit overload current in the datasheet . Not clear at what current it will cut off the output.
– cm64
May 3, 2019 at 19:30
• It is probably that same value. May 3, 2019 at 19:38

All of the bench power supplies that I have used that have a constant-current mode will supply exactly that -- a constant current, up to the voltage setting. If you plotted the voltage vs. current that the thing would supply as a load resistor was increased, it'd be level at constant voltage until the current limit was hit, then vertical down to zero voltage at the current limit.

I would not trust this to be the case for a fixed output, such as the 12V or 5V outputs -- in that case, you may see pulsing or folding. I would be pleased to see a nice constant current, but not surprised if I did not. I would be extra-pleased, and extra-unsurprised, if it was a cheap bench supply and not a name brand like Tek, Agilent, or even B&K Precision.