Powering a fan with external input using arduino

Hello,

For a project I want to power a fan using Arduino. The power for the fan comes from a external adapter with the following specifications:

AC/DC switching adaptor
output: 9v , 4.45A , 40W max

I think this problem is solvable with a DigitalOut pin and a transistor. The problem is that I do not know what type of transistor and what it's capacity (?) should be. Can someone help me out with this?

Greetings,

Niek

Use a logic MOSFET that handles some more current than 5 Amps. 9 volt is no problem. Such transistors can be connected directly to most Arduinos.