Today, from ignorance I have fallen head-first into the world of MOSFET transistors. In my scramble to find some information on the MOSFET I will be using as a switch (HEXFET actually), I learned that MOSFETs in general come in two modes, enhancement mode, or depletion mode.
When I tried to find out which mode the IRF3710 was, from the datasheet, I found that it does not say (or maybe I need glasses). At this point I started searching to find how to tell the difference between the two modes. After some time I gathered that the schematic symbols differ:
Enhancement-mode MOSFET:
Depletion-mode MOSFET:
The difference being the highlighted part below.
Three separate lines means enhancement-mode (left) and one solid line means depletion mode (right).
So, my question: Is this the only way to tell which is which, or is there a quicker way to tell (by markings on the device maybe?). Also, are there symbols out there which use a different method to differentiate between them?
I am asking here for my own learning, but also for other people who might have the same experience as me. I did not find that much helpful info in my searching.
Best Answer
Two things I want to add to the answers already given:
Don't trust the schematic symbol. You'll see the depletion-mode symbol used pretty often for an enhancement-mode part because it's easier to draw. (The symbols suggested on the manufacturer datasheets won't make this error, but some random application circuit schematic from the web is not trustworthy at all)
How to tell from the datasheet whether the part is enhancement mode or depletion mode. For an n-channel FET, if the \$V_{gs({\rm th})}\$ is greater than 0, then it's an enhancement mode device. If \$V_{gs({\rm th})} < 0\$ it's a depletion mode device. For p-channel, it's the opposite: \$V_{gs({\rm th})} < 0\$ means enhancement mode, \$V_{gs({\rm th})} > 0\$ means depletion mode.