I bought a handful of IRF5305PBF p-channel FETs to try out. There's a couple of things that have confused me on the
datasheet though.
1 - What's with the voltage values all being negative? Is this characteristic of p-channel FETs and just indicates the polarity of the flow through the device, or does it mean something else?
2 - I thought I'd chosen a good logic-level option (V
GS(th) is listed as -2 to -4V). However it won't turn off until a full 5.7V and has a fading ramp between about 5.2 and 5.7V. I tested three and they were identical. Am I completely misunderstanding the spec here?
I'm powering the circuit with a 6AA pack, a 1k resistor and a 3mm yellow LED, and using my power supply to trigger the gate. Both grounds are tied together. Is the threshold voltage an absolute or related to the other voltage?
It's just occurred to me as I'm typing this that the -2 to -4V could mean 2 to 4 volts below Source voltage, which would mean the 5.7V being 3.3-ish volts below the nominal 9V I could expect from 6AAs is about right. Am I on the right track?