darlington transistor help required

[Zammi]

my arduino output is 0.04 amp which i want to covert to 0.15 amp for my 12v dc fan. how to design darlington transistor for that. The gain of transistor involved in darlington pair is very small and i could not get the model number of such transistor. So please help me.

[pebe]

You don't need a Darlington for that application. Use a transistor like a 2N3704. It has a nominal gain of 50 and will switch up to 800mA.