MOSFET is a field-effect transistor that can be widely used in analog and digital circuits. MOSFETs can be divided into two types, "N-type" and "P-type" according to the polarity of their "channels" (working carriers). They are usually called NMOSFET and PMOSFET. Other abbreviations include NMOS, PMOS, etc. .
In general electronic circuits, MOS tubes are usually used in amplifying circuits or switching circuits. In the power supply regulator circuit on the board, the MOSFET plays a major role in judging the potential.
MOSFET structures and circuit symbols
(a) Schematic structure of n-channel MOSFET (NMOS) and circuit symbols for (b) MOSFET, (c) n-channel MOSFET, and (d) n-channel MOSFET when the bulk (substrate) potential has to be specified in a circuit.
Complementary MOSFET pairs
Schematic structure of Complementary MOSFET (CMOS) and circuit symbols for p-channel MOSFET (PMOS). Minuses and pluses show the depletion regions.
There are many parameters of field effect tube, including DC parameters, AC parameters and limit parameters, but generally pay attention to the following main parameters:
1. IDSS—Saturated drain-source current. Refers to the drain-source current when the gate voltage UGS=0 in the junction or depletion-type insulated gate field effect transistor.
2. UP—Pinch off voltage. It refers to the gate voltage when the drain-source is just cut off in the junction or depletion-type insulated gate field effect transistor.
3. UT—Turn on the voltage. It refers to the gate voltage when the drain-source is just turned on in the enhanced insulated gate field effect transistor.
4. gM—transconductance. It represents the gate-source voltage UGS—the ability to control the drain current ID, that is, the ratio of the change in the drain current ID to the change in the gate-source voltage UGS. gM is an important parameter to measure the amplification ability of the field effect tube.
5. BUDS—Drain-source breakdown voltage. It refers to the maximum drain-source voltage that the FET can withstand when the gate-source voltage UGS is constant. This is a limit parameter, and the working voltage applied to the FET must be less than BUDS.
6. PDSM—Maximum power dissipation. It is also a limit parameter, which refers to the maximum allowable drain-source power dissipation when the performance of the field effect tube does not deteriorate. When in use, the actual power consumption of the field effect tube should be less than that of the PDSM and leave a certain margin.
7. IDSM—Maximum drain-source current. It is a limit parameter, which refers to the maximum current allowed to pass between the drain and the source when the FET is working normally. The working current of the FET should not exceed IDSM.
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