The goal of my project is to individually control 10 LEDs in order to display patterns. The LEDs I got for this project require about 300-350 mA in order to be bright enough for my application (they are rated to withstand a maximum current of 1 Amp).
Because these LEDs require far more current than my Arduino Uno can provide, I decided I'd try to use N-channel MOSFETs to control the LEDs and an external power supply to power them. I'm using the FQP30N06L: N-Channel MOSFET 60V 30A - COM-10213 - SparkFun Electronics
I pulled the schematic seen below off the internet because my circuit is set up very similarly. For the sake of testing, I have five MOSFETs set up the same way, each with their own digital pin. All five LEDs are wired in parallel and powered by an external supply.
The problem I'm encountering is that I can only light up three LEDs at a single time. When I try to light up a fourth simultaneously, three of them light up very dimly and one either doesn't light up at all or does so extremely dimly. When I try to light up all five, only three light up dimly, one is either off or barely showing any light, and one is completely off.
The only limitation I can possibly run into on the Arduino is the maximum output current, correct? I measured the gate current to peak at 6-7 mA, therefore the Arduino isn't even close to hitting its 200 mA maximum. However, looking at the FQP30N06L datasheet, I calculated the theoretical gate current to be 66.67 mA. The turn-on delay time is typically 15 ns with a rise-time of 210 ns, and its total gate charge is 15 nc. So the gate current should be (delay time + rise time)/(total gate charge) = 15 nc/225 ns = 66.67 mA. It's just odd that I'm measuring 6 or 7 mA for the gate current using a multi-meter.
Either 1) my multi-meter is wrong and the current actually is ~67 mA, which would perfectly explain why I can only light up 3 LEDs before hitting the 200 mA maximum output current. I would try to power the Uno through the barrel jack to increase the maximum output current and see if it can now power more MOSFETs and light up more LEDs BUT I somehow managed to fry a bunch of the LEDs and will have to wait a few days until more arrive.
Or 2) my math is wrong and I could use some help to figure out the real cause of this problem.
Any help is appreciated!