LED Over Current Indication: Circuit

Hello Community,

For my project’s power supply circuit, I have as 12V source going through a fuse before going into the regulator.

The fuse is set to trigger at 3A. When this occurs, I want have an LED to indicate over current draw.

I was wondering what would be the best solution to do this?


See the diagram below.

Hello LarryD,

Thanks for getting back to me, I was looking at comparators and high-side current sensing, but this seems like an easier implementation.

Rather, I would prefer once the fuse is blown there is no more current feeding through the load.

I cannot think of how to modify your circuit to get what I want. Are there types of fuses that will act like a switch when triggered?


Have an NPN after the fuse, and LED powered from before the fuse. When powered, the NPN will be on and is used to pull the LED anode low. When the fuse blows, the NPN turns off and current is allowed to flow into the LED to light it up. Put the LED current limit resistor between the supply and the anode, and the NPN collecter to the anode, with emitter to Gnd. Fused power goes thru resistor to NPN base. True, power will still be active when the fuse blows; mount the current limit resistor close to (right at) the supply, so only a few mA can flow no matter what (thru the NPN, or thru the LED).

Are there types of fuses that will act like a switch when triggered?

Grasshopper fuse.
When the fuse goes the spring leg releases and hits a contact in the fuses socket (not shown here).

12-5-2013 3-14-10 PM.jpg

Here is another circuit that might be to your liking. Kind of like CrossRoads suggestion, but using a small MOSFET.