Simply put, devices that require a power source are called active devices, while those that do not are called passive devices. Active devices are generally used for signal amplification and conversion, while passive devices are used for signal transmission or "signal amplification" through directionality. Capacitors, resistors, and inductors are all passive devices, while ICs and modules are active devices. (In layman's terms, components that require a power source to exhibit their characteristics are active components, such as transistors. Components that do not require a power source to exhibit their characteristics are called passive components.)
Simple definition of passive devices
If an electronic component operates without any form of internal power source, it is called a passive component.
From the perspective of circuit characteristics, passive devices have two basic features:
(1) It either consumes electrical energy itself or converts electrical energy into other forms of energy. (2) It can work normally without an external power supply, only requiring an input signal.
Basic definition of active devices
If an electronic component has an internal power source when it is working, then such a component is called an active component.
From the perspective of circuit characteristics, active devices have two basic features:
(1) It also consumes electrical energy itself.
(2) In addition to the input signal, an external power supply is required for it to work properly.
Therefore, it can be seen that active and passive devices have completely different requirements for the operating conditions and operating modes of circuits, which must be paid close attention to during the learning process of electronics technology.
Common passive electronic devices
Passive components in electronic systems can be classified into circuit components and connection components according to their circuit functions.
1. Circuit devices:
(1) Diode
(2) Resistor
(3) Resistor network
(4) Capacitor
(5) Inductor
(6) Transformer
(7) Relay
(8) Key
(9) Buzzer, horn
(10) Switch
2. Connecting devices:
(1) Connector
(2) Socket
(3) Connecting cable (line)
(4) Printed circuit board (PCB)
Common active electronic devices
Active devices are the main components of electronic circuits. Based on their physical structure, circuit function, and engineering parameters, active devices can be divided into two main categories: discrete devices and integrated circuits.
1. Discrete components
(1) Bipolar junction transistor (BJT), commonly referred to as a transistor.
(2) Field-effect transistor
(3) Thyristor, also called silicon controlled rectifier
(4) Semiconductor resistors and capacitors – resistors and capacitors manufactured using integrated circuit technology for use in integrated circuits.
2. Analog integrated circuit devices
Analog integrated circuit devices are integrated circuit devices used to process analog voltage or current signals that change continuously over time.
Basic analog integrated circuit devices generally include:
(1) Integrated operational amplifier (op-amp)
(2) Comparator
(3) Logarithmic and Exponential Amplifiers
(4) Simulated multiplier/divider
(5) Analog switch circuit
(6) PLL circuit (phase lock loop)
(7) Integrated voltage regulator
(8) Reference source
(9) Waveform generator
(10) Power amplifier
3. Digital integrated circuit devices
(1) Basic logic gate (logicgate circuit)
(2) Flip-flop
(3) Register
(4) Decoder
(5) Data Comparator
(6) Driver
(7) Counter
(8) Shaping circuit
(9) Programmable Logic Device (PLD)
(10) Microprocessor (MPU)
(11) Microcontroller (MCU)
(12) DSP device (digital signal processor, DSP)
passive components
Passive components mainly consist of resistors, inductors, and capacitors. Their common characteristic is that they can operate in a circuit without a power supply when a signal is present.
1. Resistance
When current flows through a conductor, the property of the conductor's internal resistance to oppose the current is called resistance. A component in a circuit that acts as a current-blocking element is called a resistor, or simply a resistor. The main uses of resistors are voltage reduction, voltage division, or current division; in some special circuits, they are used as loads, feedback, coupling, and isolation.
The symbol for resistance in a circuit diagram is the letter R. The standard unit of resistance is the ohm, denoted by R. Other commonly used units include kiloohms (kΩ) and megaohms (mΩ).
1 kΩ = 1000 Ω 1 MΩ = 1000 kΩ
2. Capacitor
Capacitors are among the most common components in electronic circuits; they are devices that store electrical energy. A capacitor consists of two conductors of the same size and material sandwiching an insulating dielectric layer. When a voltage is applied across its terminals, the capacitor stores electrical charge. Once the voltage is removed, it releases electrical energy as long as there is a closed circuit. Capacitors block direct current (DC) while allowing alternating current (AC) to pass through; the higher the frequency of the AC, the stronger its ability to pass through. Therefore, capacitors are commonly used in circuits for coupling, bypass filtering, feedback, timing, and oscillation.
The letter symbol for a capacitor is C. The unit of capacitance is the farad (F), commonly found in μF (microfarad) and pF (μμF, picofarad).
1F = 1,000,000 μF 1 μF = 1,000,000 pF
The characteristics of a capacitor in a circuit are non-linear. The impedance to current is called capacitive reactance. Capacitive reactance is inversely proportional to capacitance and signal frequency.
3. Inductance
Like capacitors, inductors are energy storage devices. Inductors are generally made of coils. When an AC voltage is applied across the coil, an induced electromotive force is generated in the coil, hindering the change in current flowing through it. This resistance is called inductive reactance. Inductive reactance is directly proportional to the inductance and the frequency of the signal. It does not impede direct current (ignoring the DC resistance of the coil). Therefore, the functions of inductors in electronic circuits are: current blocking, voltage transformation, coupling, and, in conjunction with capacitors, tuning, filtering, frequency selection, and frequency division.
The symbol for inductance in a circuit is L. The unit of inductance is the henry (H), with common units being millihenry (mH) and microhenry (μH).
1H = 1000mH 1mH = 1000μH
Inductors are typical components for electromagnetic induction and electromagnetic conversion, and their most common application is in transformers.
Active devices
Active components are the core of electronic circuits; all oscillation, amplification, modulation, demodulation, and current conversion are inseparable from active components.
1. Vacuum tube
Electron tubes are also known as vacuum tubes, and are therefore also called electro-vacuum devices.
Whether diode or multi-electrode, a vacuum tube has an anode and a cathode. Under the influence of an external power source, the cathode emits electrons that flow towards the anode. This external power source can be applied directly to the cathode or to a separate heating filament. It is because of this external power source that they are collectively referred to as active devices.
Vacuum tubes were the earliest active electronic components, including diodes, transistors, and multi-electrode transistors. With the development of electronic technology, vacuum tubes, due to their large size, heavy weight, and high power consumption, were gradually superseded by transistors and integrated circuits. However, in many situations, vacuum tubes continue to function; devices that can independently exhibit their external characteristics without relying on an external power source (DC or AC) are called passive devices. Otherwise, they are active devices.
The so-called "external characteristics" are certain relational quantities that describe a device, even if they are described using quantities such as voltage or current, electric field or magnetic field, pressure or velocity.
The external characteristics of passive devices are unrelated to whether they exist as a power source.
The concepts of passive and active are not only found in electrical components, but also in fields such as mechanics, fluid dynamics, thermodynamics, and acoustics.
