FETs are divided into JFETs and MOSFETs. According to the conductive method: depletion type and enhanced type, the junction field effect transistors are all depletion type, and the insulated gate type field effect transistors are both There are depletion type, there are also enhanced.

Field effect transistors can be divided into junction field effect transistors and MOS field effect transistors, and MOS field effect transistors are divided into N-channel depletion type and enhanced type; P-channel depletion type and enhanced type are four major types.

A Junction Field Effect Transistor (JFET)

1. Classification of Junction FETs: Junction FETs come in two forms. They are N-channel junction FETs and P-channel junction FETs.

Junction field effect transistors also have three electrodes, they are: gate; drain; source.

The direction of the arrow in the gate of the circuit symbol can be understood as the forward conductive direction of the two PN junctions.

2. The operation principle of the junction field effect transistor, the structure and symbol of the N-channel structure type field effect transistor, because the carrier in the PN junction is exhausted, the PN is basically non-conductive, forming a so-called exhaustion. Area, when the drain power supply voltage ED is constant, if the gate voltage is more negative, the depletion region formed by the PN junction interface is thicker, and the narrower the channel between the drain and source is, the drain current ID is smaller. The smaller, and vice versa, if the gate voltage is not so negative, the channel becomes wider and the ID becomes larger, so that the change of the drain current ID can be controlled by the gate voltage EG, that is, the field effect transistor is a voltage control element.

Second, the insulated gate field effect tube

1. Classification of Insulated Gate MOSFETs (Insulated Gate Field Effect Transistors): Insulated gate field effect transistors also have two types of structures. They are N-channel type and P-channel type. No matter what the channel is, they are divided into two types: enhanced and depleted.

2. It is composed of metal, oxide and semiconductor, so it is also called metal-oxide-semiconductor field effect transistor, or MOS FET for short.

3. Working principle of insulated gate field effect transistor (using N-channel enhancement MOS field effect transistor as an example) It is how to use UGS to control the “inductive charge” to change the conductive trench formed by these “inductive charges”. The condition of the track then reaches the goal of controlling the drain current. In the manufacture of the tube, a large amount of positive ions appear in the insulating layer through the process, so that more negative charges can be induced on the other side of the interface. These negative charges connect the N region of the hypertonic impurity to form a conductive channel. Even though VGS = 0, there is a large drain current ID. When the gate voltage is changed, the amount of electric charge induced in the channel also changes, and the width of the conductive channel also changes accordingly, so the drain current ID changes with the change of the gate voltage.

The FET works in two ways: when the gate voltage is zero, there is a large drain current called depletion; when the gate voltage is zero, the drain current is also zero, and after a certain gate voltage must be added Drain current is called enhanced.