I am having trouble getting some MOSFETs I have to behave like I expect, but I am just testing them with an oscilloscope, battery, and appropriately high voltage digital output on a microcontroller.
Do I need to attach a load such as a motor, solenoid, or light bulb to bench test a MOSFET?
I don't know how a MOSFET works physically, so if there is some sort of capacitance that needs to be charged inside the MOSFET for it to work (i.e. current received and charge stored from the source), then the oscilloscope might not be supplying this.
The MOSFET I am using is this.
This is the setup I have: The battery is 6V, and the Gate is a wire. If I hook up the wire to ground (drain pin) or 6V, the meter reads 0V and 6V respectively, so it does seem to be switching now that I removed the microcontroller. This 6V is stable, and does not revert to 0V until the Gate is discharged to ground. Interestingly, if I hook up the Gate to the source pin, I get 5.5V output, not 6V. This 5.5V is stable (and needs to be "reset" by touching Gate jumper to ground).
simulate this circuit – Schematic created using CircuitLab I found out that the strange stuff occurs while using my microcontroller to switch the MOSFET. If I hook up the ground from my Teensy3.1 3V microcontroller to the MOSFET drain, the meter jumps up to 6V, as if it was switched on. This 6V is also noticeably more noisy than the 6V of the battery. This 6V is not stable, and the meter immediately drops to 0V when the microcontroller ground is disconnected.
If I instead connect the digital output (3V) of the microcontroller to the Gate of the MOSFET, the output of the meter jumps from 0 to 4.5V, with 1.5V square pulses I am sending from the microcontroller riding on top. 4.5V + 1.5V = 6V obviously, but confused. I expected the pulses read on the meter to be 6V in amplitude, from a baseline of 0V. I checked and the control voltage pulses I am sending from the microcontroller are 3V as expected.
If I now connect the microcontroller ground to the drain of the MOSFET, the voltage meter output jumps to 6V, and these 1.5V square waves riding on top of the 4.5V disappear. This effect is reversible.