Dummy question for you guys.
I'm switching a parallel array of 10 leds (3.2v, 20mA with each led ballasted with a 82R resistor) with a 2N2222 transistor. The led supply is 5V as is the base voltage (from an Arduino digital pin).
How do I calculate the value of base resistor will I need for the transistor? I've tried many methods suggested to me but always end up with a different value each time! The latest formula I used was RB
= 0.2 x RL
with values of 8.2R for RL
and 300 for hFE
. That gave me a value of 492R. Does that sound right? I have seen values of as high as 100K being used with this transistor, so have I used the right formula and values?
Any help gratefully received