Simply put, devices that require energy (power) power are called active devices, and devices that do not require energy (power) power are passive devices. Active devices are generally used for signal amplification, transformation, etc., and passive devices are used for signal transmission or signal amplification through directionality. Capacitance, resistance, and sense are all passive devices, while ICs and modules are all active devices. (In layman's terms, those that require a power supply to display their characteristics are active components, such as triodes. Those that can display their characteristics without a power supply are called passive components)

 

Simple Definition of Passive Components

  If an electronic component works without any form of power supply inside it, the device is called a passive device. From the perspective of circuit properties, passive devices have two basic characteristics:

 

(1) It either consumes electric energy by itself, or converts electric energy into other forms of energy.

(2) Only need to input signal, it can work normally without external power supply.

Basic Definition of Active Devices

  If an electronic component has a power source inside it when it is working, the device is called an active device.

From the perspective of circuit properties, active devices have two basic characteristics:

 

(1) It also consumes electric energy.

(2) In addition to the input signal, there must be an external power supply to work normally.

 

  It can be seen from this that the working conditions and working methods of active devices and passive devices are completely different, which must be paid attention to in the learning process of electronic technology.

 

  Common passive electronic devices Passive devices in electronic systems can be divided into circuit devices and connection devices according to their circuit functions.

1. Circuit devices

(1) diode (diode)

(2) resistor (resistor)

(3) Resistor network

(4) Capacitor (capacitor)

(5) Inductor

(6) transformer (transformer)

(7) relay (relay)

(8) Button (key)

(9) Buzzer, horn (speaker)

(10) switch (switch)

2. Connection devices

(1) connector (connector)

(2) Socket (shoket)

(3) Connecting cable (line)

(4) Printed circuit board (pcb)

Common Active Electronic Devices

  Active devices are the main devices of electronic circuits. From the perspective of physical structure, circuit function and engineering parameters, active devices can be divided into two categories: discrete devices and integrated circuits.

1. Discrete devices

(1) bipolar transistor (bipolar transistor), generally referred to as triode

（2）场效应晶体管（field effective transistor）

（3）晶闸管（thyristor），也叫可控硅

（4）半导体电阻与电容——用集成技术制造的电阻和电容，用于集成电路中

 

 2、模拟集成电路器件

  模拟集成电路器件是用来处理随时间连续变化的模拟电压或电流信号的集成电路器件。

 

基本模拟集成电路器件一般包括：

(1) 集成运算放大器(operation amplifier)，简称集成运放

 

(2) 比较器(comparator)

(3) 对数和指数放大器

(4) 模拟乘/除法器(multiplier/divider)

(5) 模拟开关电路(analog switch)

(6) pll电路(phase lock loop)，即锁相环电路

(7) 集成稳压器(voltage regulator)

(8) 参考电源(reference source)

(9) 波形发生器(wave-form generator)

(10) 功率放大器(power amplifier)

3、数字集成电路器件

(1) 基本逻辑门(logic gate circuit)

(2) 触发器(flip-flop)

(3) 寄存器(register)

(4) 译码器(decoder)

(5) 数据比较器(comparator)

(6) 驱动器(driver)

(7) 计数器(counter)

(8) 整形电路

(9) 可编程逻辑器件（pld）

(10) 微处理器(microprocessor，mpu)

(11) 单片机(microcontroller，mcu)

(12) dsp器件(digital signal processor，dsp)

  无源元件主要是电阻类、电感类和电容类元件，它的共同特点是在电路中无需加电源即可在有信号时工作。

1、电阻

 电流通过导体时，导体内阻阻碍电流的性质称为电阻。在电路中起阻流作用的元器件称为电阻器，简称电阻。电阻器的主要用途是降压、分压或分流，在一些特殊电路中用作负载、反馈、耦合、隔离等。

The symbol of resistance in the circuit diagram is the letter R. The standard unit of resistance is the ohm, denoted as R. Commonly used are kilohm KΩ and megohm MΩ.

  IKΩ=1000Ω 1MΩ=1000KΩ

2. Capacitance

Capacitor is also one of the most common components in electronic circuits, it is a component that stores electrical energy. A capacitor is composed of two conductors of the same size with a layer of insulating medium sandwiched between them. When a voltage is applied across the capacitor, charges will be stored on the capacitor, and once there is no voltage, as long as there is a closed loop, it will release electric energy again. Capacitors prevent direct current from passing through the circuit and allow alternating current to pass through. The higher the frequency of alternating current, the stronger the ability to pass through. Therefore, capacitors are commonly used in circuits for coupling, bypass filtering, feedback, timing and oscillation.

The letter code of the capacitor is C. The unit of capacitance is Farad (denoted as F), commonly used are μF (microfarad), PF (ie μμF, picofarad).

1F=1000000μF 1μF=1000000PF

The characteristics of capacitance in the circuit are nonlinear. The resistance to electric current is called capacitive reactance. Capacitive reactance is inversely proportional to capacitance and frequency of the signal.

3. Inductance

 Like capacitors, inductors are also energy storage components. Inductors are generally made of coils. When an AC voltage is applied to both ends of the coil, an induced electromotive force is generated in the coil, which hinders the change of the current passing through the coil. This hindrance is called inductive reactance. Inductive reactance is proportional to the inductance and the frequency of the signal. It does not hinder DC (regardless of the DC resistance of the coil). Therefore, the role of inductance in electronic circuits is: blocking current, voltage transformation, coupling and cooperating with capacitors for tuning, filtering, frequency selection, frequency division, etc.

The code name of the inductor in the circuit is L. The unit of inductance is Henry (denoted as H), commonly used millihenry (mH), microhenry (μH).

1H=1000mH 1mH= 1000μH

Inductors are typical components of electromagnetic induction and electromagnetic conversion, and the most common application is transformers.

active device

Active components are the core of electronic circuits, and all oscillation, amplification, modulation, demodulation, and current conversion are inseparable from active components.

electron tube 

Electron tubes are also known as vacuum tubes, so they are also called electric vacuum devices. Regardless of whether the electron tube is two-pole or multi-pole, it has an anode and a cathode. Under the action of an external power supply, the cathode emits electrons and flows to the anode. The external power supply can be directly added to the cathode, and can also be added to another heating filament. It is because of this that they are collectively referred to as active devices.

Electron tubes are the earliest active electronic components, divided into diodes, triodes and multipolar tubes. With the development of electronic technology, electronic tubes have successively given way to transistors and integrated circuits due to their shortcomings such as large size, heavy weight, and high power consumption. However, there are many occasions where the tube continues to function.

A device that can independently exhibit its external characteristics without relying on the existence of an external power supply (DC or AC) is a passive device.

Beyond that are active devices. The so-called "external characteristics" is to describe a certain relational quantity of the device, although voltage or current, electric field or magnetic field pressure or velocity are used to describe the relationship.

The external characteristics of passive components have nothing to do with whether they exist as driving sources. 

The concepts of passive and active not only exist in electrical components, but also in the fields of machinery, fluid, heat, and acoustics.