I'm working on a proximity detection project to drive up to 25 IR led on 38Khz with 3.6v mcu.I'm planing to make them parallel with 100 ohm resistor (limit their current to 20ma for each led).MCU pwm pin can not handle 500 ma (may be less because of PWM but for safety reason I assume max), so as you guess I need to use BJT or FET to drive them. Because of some project restriction, I want to use only one mcu pin to drive IR Leds on 38Khz, and other pins for each photo diode sensor.
My questions are,
I can connect different number of led (up to 25) depends on application or if any led in this parallel line burn or not work properly some reason, will it be a problem ? The reason I'm asking that; load of FET's or BJT's will change regarding to count of led in the parallel line.If so, how can I solve this problem ? Shortly , what kind of circuit should I use to drive safely 1 to 25 parallel led without damage any mcu pin, drive electronic or any other leds in the parallel string.
Which BJT or FET should I use ? I have BD135 and IRFZ44N now.I want to use them because to make running prototype.If one of them fit my project, I can change more suitable (current,price etc) BJT or FET later.