hello , I connected the IRl640 ( gate to 5v , drain to LEDs to 12V , source to ground ) and control the gate current with a switch as shown in the video , please check the video you see that the operation of the IRL640 is incorrect , what is happening ?

http://www.youtube.com/watch?v=1sAsyH0PUk0&feature=youtu.be

 

"This video is private."

Post a schematic.

 

sorry , watch it now

 

It looks to me like you left out the current limiting resistors on the LEDs and burned them all out.

Post a schematic, and get better answers.

 

In addition to my concern about the lack of current limiting resistors on the LEDs, I don't see any pull down resistor on the the gate of the MOSFET. Without one, the MOSFET can remain in the on position even when the gate voltage is removed, and the gate is left floating.