I am completely lost here! :(
I am HOPING someone will be able to help me in here?
I am trying to power 4 x 1W LED's on four different pins using an external 3.5v supply, through a 2N5551 Transistor. I have trawled the net for information on what current limiting resistor I should use. Some say you don't need a resistor between the output pin and the Transistor Base ass there is no more than 400mA. But if the Arduino is powered via an external PSU, there is potentially 900mA.
If I understand correctly, this resistor is needed to limit current to the transistor to prevent damage. I see 470 ohm and 1K resistors recommended.
If I power the Arduino with a 3.5v PSU, the the LED's from the same source, then what value resistor would I need to protect the base?
Apologies if this is a STUPID question, but I'm learning as fast as I can.
Thank you in advance for your help guys!