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:
Example of UNL2003 with diodes: ULN2003 IC Pinout, Features, Equivalents & Datasheet
Are ALL the PIN diodes from the same wafer? How do insure they will all conduct identical currents and at the SAME time?
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.
The columns of diodes in my project are similar to what is shown below:
But it gets worse - 16 groups!
I consider the ULN2x03 obsolete, you use the TPIC6B595 instead, but as you note, this can only source current.
You probably want a couple of UDN2983. Not very elegant, but should work.
Can you not have a resistor for each PIN diode?
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.
It's an active reflector antenna. The PIN diodes function as phase-shifting switches.
If you are building the surface, can you not incorporate resistors into the surface?
In fact, is the surface grounded - could you not make the reference, the 5 V positive and connect the anodes of the diodes to that?
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