A field effect transistor (FET) converts changes in input voltage into changes in output current. The gain of a FET is equal to its transconductance, defined as the ratio of the change in output current to the change in input voltage. Commonly available on the market are generally N-channel and P-channel. The commonly used packages of SMD MOS tubes are SOT-23 SOT-523 SOT-323 TO-252 TO-263, etc. Commonly used mos tube models: 2N7002 SOT-23 2N7002K SOT-23 2N7002E SOT-23 2N7002T SOT-523 2N7002W SOT-323 A03401 SOT-23 AO3400 SOT23 AO3415A SOT-23 SI2300 SOT-23 SI2301 SOT-23 SI2302 SOT-23 SI2305 SOT-23 IRFR3518 TO-252 IRLR3110Z TO-252 IRLR2908 TO-252 2N60 TO-252 4N60 TO-252 5N20 TO-252 FQB6N60C TO-263 IRF830AS TO-263 and other models. MOS tube function: 1. Rectification 2. Detection 3. Voltage stabilization 4. Electronic switch 5. Voltage and current amplification 6. Oscillation 7. Impedance transformation 8. As variable resistor 9. Constant current