Firstly, I have no formal training in electrical engineering and only know what I’ve been able to understand from google searches.
Anyway, my issue. I recently ordered several Microchip 2N7000 (n-channel, enhancement-mode MOSFET) transistors for a project I’m working on, and after my initial test for a portion of the project failed, I began testing individual components, and ran into issues with the transistors.
So, the test setup: All assembled on a breadboard, receiving power from an Arduino Uno rated at 5V (though my multimeter read 4V). The source of the transistor was connected to +5V, the drain connected to an LED, which was connected to ground through a 560 Ohm resistor. The gate was connected to a momentary switch which was, in turn, connected to +5V. Upon providing power to the Arduino, the LED immediately lit, and would not go out regardless of the position of the switch.
I tried this on a second, unused transistor with the same results.
Then I tried flipping the source and drain connections on the transistor. In this configuration the LED was initially lit only very dimly, but upon closing the momentary switch the LED lit to full brightness and would not dim again regardless of the position of the switch.
At this point I consulted with a friend who is in Uni for Electrical Engineering, and at his advice adjusted my circuit to have the source connected directly to ground, the drain connected to +5V through the LED and resistor, and the gate still connected to +5V through the momentary switch, but I still got the same result.
I then tried adding a 4.7 KOhm resistor in series with the 560 Ohm resistor to give me a total of roughly 5.1 KOhms (to bring my current draw below the 1mA ‘Zero Gate voltage drain current’ rating in the datasheet, though I will admit I do not know what that rating actually means), but still had the same results.
At each step in this process I also tried using a new and unused transistor, in case I had inadvertently damaged the others in testing. I double checked my circuit on the breadboard multiple times to be sure I had wired it correctly.
Is this just a batch of faulty transistors? or am I doing something seriously wrong?