I am driving columns of eight PIN diodes, each in an array for a project. All of the columns are tied to a common ground. I expect the current of the parallel diodes to be approximately 90 mA (11 mA per diode x 8). See schematic below. I am using the Arduino Uno R3 as my digital controller. To my understanding, Arduino Uno R3's digital output pins can only handle 20 mA per pin. I need a solution to drive my digital signals with 90 mA current. I purchased ULN2003A High-Current Darlington Transistor Arrays (https://www.ti.com/lit/ds/symlink/uln2003a.pdf). I can light up LEDs using the ULN2003A, but I am confused about using it for my application. Since all 256 diodes (16 columns x 8) in my array are tied to a common ground, I'm not sure the ULN2003A is a workable solution. How do you recommend that I drive each 90 mA column without damaging my Arduino? Is there a workable solution using the ULN2003A?
My column schematic with 8 PIN diodes in parallel:
I don't think that I have a way to ensure all PIN diodes will conduct identical currents. How much of an issue is this?
My confusion is that I expected the current driver to be between V1 and R1, but FET switches seem to want to be between the diode and ground. I have seen papers that do what I am attempting to do, but I am unsure how to drive 90 mA.
Thank you for the recommendation. I understand why it is better to place a resistor with each PIN diode. Still, I don't think it is possible for the electromagnetic surface I am building (similar to the graphic posted above). Each PIN diode is embedded in a reflecting metallic patch.
