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
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