How can I tell the difference between a Mosfets strengths and weaknesses?

There are two ways to distinguish between Mosfet advantages and disadvantages.

The first: qualitatively distinguish junction Mosfet electrical level

Multimeter will be dialled to R × 100 gear, the red pen randomly connected to a foot tube, the black pen is connected to another foot tube, so that the third foot to maintain the suspended state. If you find the needle has a slight jitter, it proves that the third foot for the gate. If you get more obvious observation of the actual effect, you can also be close to the electronic vibration or finger touch hanging in the air feet, only to see the needle deflection, that is, indicating that hanging in the air feet is the gate, the other two feet are the source and drain, respectively.

Distinguish the reason: JFET's input resistance is more than 100MΩ, and the transconductance is very high, when the gate is led, the indoor space magnetic field is very easy to detect the working voltage data signal on the gate, so that the pipeline tends to be up to, or tends to be on-off. If the body induction voltage is immediately added to the gate, because the key electromagnetic interference is strong, the above situation will be more significant. If the meter needle deflects sharply to the left, it means that the pipeline tends to be up to, the drain-source resistor RDS expands, and the amount of drain-source current decreases IDS. Conversely, the meter needle deflects sharply to the right, indicating that the pipeline tends to be on-off, RDS goes down, and IDS goes up. However, the exact direction in which the meter needle is deflected should depend on the positive and negative poles of the induced voltage (positive direction working voltage or reverse direction working voltage) and the working midpoint of the pipeline.

The second: qualitatively distinguish the advantages and disadvantages of mosfet

First use the multimeter R × 10kΩ block (embedded 9V or 15V rechargeable battery), the negative pen (black) connected to the gate (G), the positive pen (red) connected to the source (S). To the gate, the source of the middle battery charge, then the multimeter needle has a mild deflection. Then change to the multimeter R × 1Ω block, the negative pen to the drain (D), the positive pen to the source (S), the multimeter marked value if a few ohm, it shows that the mosfet is good.