Using Bi-Colour Led to show state of fuse.

[kkeeley]

Hi,

I am wishing to place a small circuit on each of my power rails between my power supply and test circuits so that I can tell when a voltage rail goes over current. I have found a circuit that I think will work nicely for the positive voltage rails, but I'm not 100% sure how to make it work for the negative voltages. Below is an example of the positive voltage circuit, the switch would be replaced by a re-settable fuse and the load would be placed between S1/R1 and ground.




Can I reverse/change the transistors for the negative voltages or will I also need to reconfigure the bias resistors as well. If so what would be the best way to reconfigure the circuit?

Thanks in advance,
Kenneth

 

[BradtheRad]

For the fun of it, I made a simulation of your circuit.

Switch off... one led glows.

Switch on... other led glows.

Screenshot with two identical circuits side by side (switch positions are different):



Changing the supply voltage only makes the led's change in brightness.

 

[kkeeley]

Thanks for the reply, I was fairly certain that the circuit would work for a positive voltage rail, my question is how to make the idea work for a negative voltage.

ps. what program did you simulate the circuit in? I like the way the current paths appear to be highlighted when active, and the leads changed colour.

 

[E-design]

You may consider a simpler solution without transistors.

 

[kkeeley]

Thank you E-design for your circuit, this circuit should be perfect, it handles both the positive and negative voltages and will allow me to use either two leg or three leg bi-colour leds. All I need to do is adjust the resistor values to suit the different voltages.

Kenneth

 

[BradtheRad]

ps. what program did you simulate the circuit in? I like the way the current paths appear to be highlighted when active, and the leads changed colour.

The simulator is Falstad's interactive animated simulator. Free to download and use at www.falstad.com/circuit.

I had it create a weblink containing my entire schematic. It will open the falstad website, load my schematic into his simulator, and run it on your computer.

https://tinyurl.com/khtnuwd

The wires turn green to show positive, red to show negative.

Yellow dots travel down the wires, at a speed proportional to amperage.

 

[kkeeley]

Thanks for the link, I'll have a play with it.