I am using atmega328p and PNP transistor FMMT720.
Goal is simple to switch on and off transistor with GPIO.
For specification part:
Datasheet says continuous collector current is 1.5 A and my requirement is 500 mA.
base current according to my calculation is 27 mA and it may change as my voltage changes but still within range of 20 to 40 mA, which is tolerable by atmega328p on individual pin.(Schematic shown below) Gain is pretty high, more than 100 so output current should not be problem.
Problem: For PNP transistor base needs to be pulled down to turn it on. What I noticed is base is not getting proper low voltage from the pin hence transistor stays off. Although I can see a change of 0.4 V during the 2 second time (transistor ON time for my application) but not enough to turn it on. In addition it does turn on sometimes and thing works perfectly but not always.
Is there any problem in calculation part? Is this really a problem with transistor? I am also using PCINT with other hardware can it affect anyhow?
Circuit I am using is quite large so giving necessary part. Ask if need more clear idea. Thank you.