Top ten most commonly used electronic components (III)

Field effect transistor:

Field Effect Transistor (FET) is abbreviated as FET. The majority of carriers participate in conduction, also known as unipolar transistors. It belongs to a voltage controlled semiconductor device. It has high input resistance (108～109Ω), low noise, low power consumption, large dynamic range, easy integration, no secondary breakdown, wide safe working area, etc. It has become a powerful bipolar transistor and power transistor. competitor.

Field effect transistors have the advantages of high input impedance and low noise, and are therefore widely used in various electronic devices. In particular, the field effect tube is used as an input stage of the entire electronic device, and it is possible to obtain a performance that is difficult to achieve with a general transistor.

The FET is divided into two types: junction type and insulated gate type, and the control principle is the same.

Comparison of FET and transistor

(1) The field effect transistor is a voltage control element, and the transistor is a current control element. In the case where only a small current is allowed from the signal source, the FET should be used; and when the signal voltage is low and the current is taken from the signal source, the transistor should be selected.

(2) FETs use majority carriers to conduct electricity, so they are called unipolar devices, and transistors have both majority carriers and minority carriers.

(3) The source and drain of some FETs can be used interchangeably. The gate voltage can also be positive or negative, and the flexibility is better than that of the transistor.

(4) The FET can work under very low current and very low voltage conditions, and its manufacturing process can easily integrate many FETs on one silicon chip, so the FET is in large scale integrated circuit. It has been widely used.

sensor:

A sensor is a physical device or biological organ that detects and senses external signals, physical conditions (such as light, heat, humidity) or chemical components (such as smoke) and transmits the detected information to other devices or organs.

The national standard GB7665-87 defines the sensor as: "A device or device that can sense a specified measured object and convert it into a usable signal according to a certain rule, usually composed of a sensitive component and a conversion component." The sensor is a detecting device that can sense the measured information and can transform the detected information into an electrical signal or other required form of information output according to a certain law to meet the information transmission, processing, storage, Requirements for display, recording and control. It is the first step in achieving automatic detection and automatic control.

"Sensor" is defined in the new Wei-style dictionary as "receiving power from one system, usually in another form, to power the device in the second system." According to this definition, the role of the sensor is to convert one energy into another, so many scholars also use the "Transducer" to refer to the "sensor-Sensor".

transformer:

Transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are the primary coil, the secondary coil and the core (core). In electrical equipment and wireless circuits, it is often used as lifting voltage, matching impedance, safety isolation and so on. In the generator, whether the coil motion passes through the fixed coil through the magnetic field or the magnetic field, the potential can be induced in the coil. In both cases, the value of the magnetic flux is constant, but the number of magnetic fluxes intersecting the coil is Change, this is the principle of mutual induction. A transformer is a device that uses electromagnetic mutual induction to transform voltage, current, and impedance. The functions of the transformer mainly include: voltage conversion; current conversion, impedance transformation; isolation; voltage regulation (magnetic saturation transformer).