I am putting together a design for an RGB LED controller using PWM to control color and intensity on RGB LED's. I want the controller to work with various LED's, so I am using a 4 position screw terminal. The controller just supplies 12 volts and switches ground on the 3 other terminals to effect the PWM. Then, on the LED module, I will use the appropriate resistors to work with the 12V power supplied from the controller.
I use an NPN transistor with a current rating of 800mA to switch the grounds, and the transistor is controlled by a microcontroller. I am trying to add some sort of circuit protection such that the transistor will not be destroyed, even if the user of the device does something they shouldn't - like shorts the PWM-switched grounds right to power (which would happen if the LED wires are not inserted well into the controller).
In my prototype design I tried resettable fuses from Littelfuse, but the transistor was still destroyed when I tried shorting it to ground. I think the fuses are not fast enough, despite being marketed as super fast.
Can anyone offer suggestions? I am sure there are feedback circuit designs out there that would turn off the output if the current rose above a given value, or perhaps there is an easier solution out there? Board space is at a premium so I am trying to keep the circuit as physically small as possible.
Any input is appreciated!
Thanks CJ