Reading the ULN2803A datasheet, especially the part "Figure 13. ULN2803A as Inductive Load Driver" and after various fails to properly drive 12v RGB led strips, as i can't find the proper mosfets. i was thinking to get more of those ULN2803 and use them like a "mosfet".
500-mA-Rated Collector Current
Total substrate-terminal current –2.5 A
This means if i connect one pin of my 3.3v or 5v microcontroller to all 8 intputs , and all 8 outputs (gnd) to the leds , basically solder them all together, i get a max of firstname.lastname@example.orgA=30W on one ULN2803A.
Using PWM on 3x ULN2803A, doing the same as above, would allow me to get email@example.comA=90W Led strip to run properly.
Would i be able to properly power the 2x 5m led strip or less, assuming i have 7.5A@12v=90W and the strip consumes 7.2W/m*10m=72W, without problems (except the obious voltage drop on a 10m strip)?
Said that, if it's correct, the ULN2803A is for 3.3v & 5v and so has already all the protection and logic stuff inside, so i don't need any resistors, diodes, transistors or whatever to protect my Microcontroller?
Basically i just need to connect the Arduino(5v) OR Raspberry (3.3v) signal pins to the ULN2803A inputs, the GND of the led strip to the outputs and the ground to the microcontroller and 12v powersupply.
note.: i use a industrial 12v 10A/5A(with a shorter led strip) power supply if everything is clear
btw if i connect the Raspberry that has very low output (20-40mA) on one single 3.3v PIN how much current sucks each ULN2803 input?
II(on) Input current VI = 3.85 V, See Figure 6 0.93 1.35 mA
So if max is 1.35mA, let's say 1.5mA*8inputs=12mA there are no problems to power them all with just one pin???
And regarding the length of the strip this would also allow me to easely gie power at every 1-2 or 3m to have a nice stable 12v....And so i would have no voltage drop.
What about PWM on 8in and 8out... it could create some errors on the linearity of the PWM signal???
"No, your totally wrong, the reaspberry has not enough mA to power all 8 inputs with one PIN" or "Yes, you can handle 7.5A at 12v and the Raspberry is safe" would be enough as answer.
I'm not a electronical enginer. So sorry for my low knowledge about electronics.
Are my assumptions correct?