|
Hi all, I need to limit the current going to a DC circuit to max 5A. The problem is there is a variable DC input of 12V, 24V, 36V and 48V. I'm trying to find a 25W surface mount power resistor (with aluminium heat sink shell). My maths is failing me!! I think something around 25W/6ohm may do it? It doesn't matter if the current is limited to less than 5A but could really do with some advice please. Thank you! |
February 01, 2023 |
|
A possible solution is to use an automatic resettable fuse, such as the RHEF450 (4.50 A, there is none for 5 A, but there is another one for 5.50 A) from Littelfuse. There also have other models (check the max voltage and other features). |
February 01, 2023 |
|
Thank you for taking the time to respond - much appreciated. The fuses are limited to 36V so I don't think they're going to do the job. I guess a 25W 6ohm resistor might do it but am in the dark a bit!! |
February 03, 2023 |
|
A more complex possible solution with two BJT. You have to worry about the power dissipation in the various elements. I suggest using a multiturn potentiometer (0 to 1 Ohm) for fine tuning. |
February 03, 2023 |
|
Note: we can add a diode at the emitter of Q2 which will allow to increase the maximum current without having to reduce the resistor too much at Q1 (here, R5 || R6). On the other hand, that makes the circuit more influenced by temperature variations. |
February 05, 2023 |
No answers yet. Contribute your answer below!
You must log in or create an account (free!) to answer a question.
Anyone can ask a question.
Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.
CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.
We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.
Acceptable Questions:
Unacceptable Questions:
Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!
CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.