MOS transistor is also commonly known as FET, including junction FET and insulated gate FET (further divided into enhanced and depleted FET).
MOS tube application.
The use of MOS transistors is the same as that of transistors, and the usage of discrete MOS transistors is mostly used as switches, and only the usage of switches is discussed here.
The enhanced MOS has the following characteristics: If the gate G is not voltaged initially, then the source S and drain D are not conductive. Under certain conditions, it can be turned on: the conduction condition of the NMOS tube is that when the gate G voltage is greater than a certain value of the source S voltage, the MOS tube is turned onOn the other hand, the PMOS tube is turned on when the gate G voltage is less than the source S voltage by a certain value.
The "certain value" mentioned here is different according to different types of MOS, and it is necessary to consult their manuals to determine, there are low-voltage 1 2V can be turned on, and there are also high-power 10V or more to be conducted. If this value is not reached, it may not be fully conducted, or it may not be conducted.
In actual use, because there is a parasitic diode inside the MOS, it can only be used as one-way conduction and cut-off, and cannot be reversed, otherwise the current will flow directly from the diode and cannot be turned off.
Comparison of MOS tube with ** tube.
The MOS transistor is a voltage driving device, which is different from the transistor that is driven by current, so the driving circuit of the two is different.
When the MOS transistor is turned on, the equivalent resistance is very small, which can reach the milliohm level, and the voltage drop between D and S will be very small when used as a switchWhen the transistor is saturated, there will always be a voltage difference of a few tenths of a volt between C and E, which sometimes produces a large power lossTherefore, when it comes to switching with higher currents, MOS transistors are more suitable.
As long as the MOS transistor satisfies the voltage relationship between G and S, the current can be forwarded or reversed, but because there is a parasitic diode inside, it will not be turned off if it is reversed, so only one direction can be turned off in actual useThe current of the transistor can only flow in one direction, the NPN type can only flow from collector C to emitter E, and the PNP type can only flow from emitter E to collector C.