What is a Mipotson MOS tube?

In addition to the use of PFC technology in the switching power supply part of the current high-definition, LCD, and plasma TV sets, the switching tubes on the components are all replaced by MOS tubes with excellent performance. High-power transistors greatly reduce the efficiency, reliability and failure rate of the whole machine. Since MOS transistors and high-power transistors have essential differences in structure and characteristics, in application, the driving circuit is also more complicated than that of transistors, which makes it difficult for maintenance personnel to analyze circuits and faults. This article is aimed at this problem. , the MOS tube and its application circuit are briefly introduced to meet the needs of maintenance personnel.  

What is MOS tube The full English name of MOS tube is MOSFET (Metal Oxide Semiconductor Field Effect Transistor), that is, metal oxide semiconductor type field effect transistor, which belongs to the field effect transistor insulating gate type. Therefore, MOS transistors are sometimes referred to as insulated gate field effect transistors. In general electronic circuits, MOS tubes are usually used in amplifier circuits or switch circuits.  

1. The structure of MOS tube;  

On a P-type semiconductor silicon substrate with low doping concentration, two N+ regions with high doping concentration are fabricated by semiconductor photolithography and diffusion process, and metal aluminum Two electrodes are drawn out as drain D and source S, respectively. Then, the surface of the P-type semiconductor between the drain and the source is covered with a thin layer of silicon dioxide (SiO2) insulating film, and an aluminum electrode is installed on this insulating film as the gate G. This constitutes an N-channel (NPN type) enhancement mode MOS transistor. Obviously its gate and other electrodes are insulated.  

The same method as above is used to fabricate two highly doped N-type semiconductor silicon substrates with semiconductor lithography and diffusion process on a low-doped N-type semiconductor silicon substrate. The P+ region and the same gate fabrication process described above are made into a P-channel (PNP type) enhancement MOS transistor.

There are two back-to-back PN junctions between the drain D and the source S of the enhanced MOS transistor. When the gate-source voltage VGS=0, even if the drain-source voltage VDS is added, there is always a PN junction in the reverse bias state, and there is no conductive channel between the drain-source (no current flows), so at this time the drain Current ID=0.  

At this time, if a forward voltage is applied between the gate and the source, that is, VGS>0, a SiO2 insulating layer between the gate and the silicon substrate will generate a The gate points to the electric field of the P-type silicon substrate. Since the oxide layer is insulating, the voltage VGS applied to the gate cannot form a current, and a capacitor is formed on both sides of the oxide layer. VGS is equivalent to charging this capacitor, and An electric field is formed. As VGS gradually increases, attracted by the positive gate voltage, a large number of electrons gather on the other side of this capacitor and form an N-type conduction channel from drain to source. When VGS is greater than When the turn-on voltage of the tube is VT (generally about 2V), the N-channel tube starts to conduct, forming the drain current ID. We call the gate-source voltage when the channel starts to form the turn-on voltage, which is generally represented by VT. MPS MOS tube

Controlling the size of the gate voltage VGS changes the strength of the electric field, so as to achieve the purpose of controlling the size of the drain current ID, which is also one of the ways that the MOS tube uses the electric field to control the current. Important features, so it is also called a field effect transistor.