Electronic products have become an indispensable part of our lives. From smartphones to electric cars, from wearables to smart home systems, there is a key component behind every electronic device - the passive component.

Passive components refer to electronic components that can work without power supply, mainly including resistors, capacitors, inductors, etc. Although they do not have functions such as amplification or switching, they play a crucial role in circuit stability, filtering effect and signal processing. Let's understand the common classification and characteristics of passive components. (Summary from INFINITECH)

1. Inductors

Classification by structure:

Hollow coil: no magnetic core, suitable for high frequency circuits.

Ferrite core inductors: The use of ferrite as a magnetic core material is common in RF and power applications.

Core inductors: The use of iron or other high permeability materials as magnetic cores for low-frequency circuits.

Air gap inductance: An air gap is left in the core to control the inductance value and Q value.

Adjustable inductance: The inductance value can be adjusted by changing the number of turns of the coil and the position of the magnetic core.

Classification by package type:

Plug-in inductors: suitable for conventional circuit board assembly techniques.

Chip inductors: Small size, suitable for high-density installation.

Shielding inductance: with metal shielding layer to reduce electromagnetic interference.

By application:

Power inductors: Used for filtering and energy storage in power conversion circuits.

Rf inductors: Used in RF circuits, such as oscillators, filters, etc.

Audio inductors: Used in audio amplifiers and speaker frequency division networks.

Coupling inductors: for signal transmission or transformer applications.

Classification by characteristics:

High frequency inductors: Designed for high frequency operating environments.

Low frequency inductors: Designed for low frequency operating environments.

High current inductor: can withstand large current.

Low current inductors: Suitable for applications requiring low current.

Classification by manufacturing process:

Winding inductance: The wire is wound by hand or machine.

Thin film inductor: using thin film technology.

Multilayer ceramic inductors: Manufacturing method similar to multilayer ceramic capacitors.

Special types:

Common mode choke: used to suppress common mode noise.

Choke: Used to block AC signals and allow DC signals to pass through.

Filter inductor: Used to filter out noise in power or signal lines.

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2. Resistor

Classification by structure

Wire-wound resistor

Universal wire-wound resistors: Low cost, suitable for general use.

Precision wire-wound resistors: With high precision and good temperature stability, suitable for precision circuits.

High-power wire-wound resistors: capable of withstanding large powers, suitable for applications requiring high power dissipation.

High frequency wire-wound resistors: Specially designed for high frequency circuits with low distributed capacitance and inductance.

Thin film resistor

Carbon film resistor: low cost, widely used in a variety of electronic equipment.

Synthetic carbon film resistors: Similar to carbon film resistors, but usually with better performance.

Metal film resistors: High accuracy and low temperature coefficient for demanding applications.

Metal oxide film resistor: has good temperature stability, suitable for high temperature environment.

Chemical deposition film resistor: deposited by chemical methods, with stable resistance values.

Glass glaze resistor: Excellent stability and heat resistance.

Metal nitride film resistors: Suitable for applications requiring high stability and low noise.

Solid resistor

Inorganic synthetic solid carbon resistors: suitable for applications requiring high stability and reliability.

Organic synthetic solid carbon resistor: low cost, suitable for general use.

Sensitive resistor

Varistor: Sensitive to voltage changes and commonly used in overvoltage protection.

Thermistor: Resistance values vary with temperature and can be used for temperature detection or compensation.

Photoresistor: resistance value changes with the light intensity, used in light induction circuit.

Dynamistor (FSRs) : Resistance values vary with pressure and are used for pressure detection.

Gas resistor (: resistance value changes with gas concentration, used for gas detection.

Humidity-sensitive resistor: The resistance value changes with the humidity, used for humidity detection.

Classification by function

Common resistors: Suitable for most conventional circuit applications.

Fuse resistor: built-in fuse mechanism, in the case of overcurrent can self-fuse protection circuit.

Variable resistor:

Potentiometer: Used to manually adjust the resistance value in the circuit.

Semi-variable resistor: usually used to fine-tune circuit parameters, simple structure.

Classification by material

Wire resistance: The use of high-resistance alloy wire wound on the insulation skeleton, and coated with heat-resistant glaze insulation layer or insulating paint.

Carbon synthesis resistor: pressed from carbon and synthetic plastics.

Carbon film resistor: made by plating a layer of carbon on a porcelain tube.

Metal film resistance: made by depositing a metal film on a ceramic substrate.

Metal oxide film resistance: made by depositing metal oxide film on ceramic substrate.

Classified by package type

Plug-in resistors: Suitable for traditional circuit board assembly technology, easy to service and replace.

Patch resistor: small size, suitable for high-density installation, high automatic production efficiency.

Bank resistors: Multiple resistors are packaged side by side to facilitate board layout and save space.

Classified by special purpose

Cement resistors: Coated with cement or other insulating materials to improve heat dissipation, suitable for high-power applications.

High frequency resistors: Specially designed for high frequency circuit applications, with low distributed capacitance and inductance.

High power resistor: can withstand high power dissipation, suitable for power amplifier and other applications requiring high power.

Classification by precision

Common precision resistor: The general accuracy is between ±5% and ±10%, suitable for most common applications.

Precision resistors: Accuracy of ±1% or better, suitable for applications requiring precise control of resistance values, such as precision measuring instruments.

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3. Capacitors

Classification by structure

Fixed capacitor: The capacitance cannot be changed.

Nonpolar capacitor

Polar capacitor

Variable capacitor: The capacitance can be adjusted continuously within a certain range.

Trimmer capacitor: The capacitance adjustable range is very small, usually used for fine adjustment.

Classification by use

High-frequency bypass capacitor

Low-frequency bypass capacitor

Filter capacitor

Tuning capacitor

High-frequency coupling capacitor

Low-frequency coupling capacitor

Classification by electrolyte

Organic dielectric capacitor

Inorganic dielectric capacitor

Electrolytic capacitor

Electric heating capacitor

Air dielectric capacitor

Classification by manufacturing material

Ceramic capacitor: widely used in high-frequency circuits, with low loss and high stability.

Polyester capacitor: Low cost, suitable for low frequency circuits.

Electrolytic capacitors: Divided into aluminum electrolytic capacitors and tantalum electrolytic capacitors, with large capacity and low equivalent series resistance (ESR).

Tantalum capacitors: Low ESR and high stability, suitable for high frequency circuits.

Polypropylene capacitors: Excellent frequency characteristics and stability.

Mica capacitor: has very low loss and high stability, suitable for high frequency circuits.

Film capacitors: including polyester (PET), polypropylene (PP), etc., with low loss and high stability.

Monolithic capacitors (multi-layer ceramic capacitors) : small size, wide capacity range, suitable for various frequencies.

Classified by package type

Chip capacitors: Small size, suitable for high-density installation.

Plug-in capacitors: Long pins for traditional plug-in installations.

Classification by polarity

Polar capacitors: including electrolytic capacitors and tantalum capacitors, etc., must be installed in accordance with the correct polarity.

Non-polar capacitors: including ceramic dielectric containers, polypropylene capacitors, etc., no polarity requirements.

Special type capacitor

Supercapacitors: have extremely high capacitance values and are commonly used for energy storage and rapid charge and discharge applications.

Self-healing shunt capacitors: with the ability to automatically restore damaged areas, used in high-voltage power systems.

Thin film capacitors: High stability and low loss, suitable for high frequency circuits.

Characteristics of various types of capacitors

Aluminum electrolytic capacitors: wide capacity range, low cost, suitable for power filter and decoupling.

Thin film capacitors: Low loss, high stability for high frequency and safety applications.

Tantalum capacitors: Low ESR, high stability for high frequency and low voltage applications.

Ceramic capacitors: small size, light weight, high temperature resistance, suitable for high frequency circuits.

Supercapacitors: With extremely high capacitance values, suitable for energy storage and power backup.

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4. Transformer

Classification by cooling mode

Dry transformers: do not use insulating oil, rely on air natural cooling or forced air cooling. No fuel tank, simple maintenance, high safety, suitable for indoor installation.

Oil-immersed transformer: Use insulating oil as cooling medium and insulating material. Good heat dissipation effect, relatively low cost, suitable for large power transmission.

Classified by moisture-proof method

Open transformer: no housing, directly exposed to the air. Low cost, but susceptible to environmental impacts.

Pot-sealed transformer: The interior is filled with insulating material, such as resin. Good moisture resistance, suitable for harsh environment.

Hermetically-sealed transformers: completely enclosed, filled with inert gas or vacuum treatment. Dustproof and waterproof, less maintenance, suitable for outdoor environment.

Classified by core or coil structure

Core transformer: iron core around the coil. Compact structure and high efficiency.

Shell transformer: coil around the iron core. Good heat dissipation for large capacity applications.

Ring type transformer: The iron core is annular and the coil is wound around it. Small magnetic leakage, small size, high efficiency.

Metal foil transformer: The use of metal foil as the core material.

Classification by operating frequency

Low frequency transformer: suitable for power frequency (50Hz/60Hz). Large structure, high efficiency.

Medium frequency transformer: suitable for frequency range from several hundred Hertz to several thousand Hertz. Moderate size for specific applications.

High frequency transformer: suitable for frequencies above several thousand Hertz. Small size, suitable for high frequency applications such as switching power supplies.

Classified by core material

Iron powder core: suitable for high frequency transformer. Low loss, high permeability.

Integral core: Suitable for specific applications, such as certain types of power transformers. : Robust construction for high-power applications.

Classification by voltage level

Low-voltage transformers: Used for power distribution in homes and commercial buildings. Simple structure, low cost.

Medium voltage transformers: Used in industrial and power distribution systems. High reliability and easy maintenance.

High voltage transformer: used for long-distance power transmission. The structure is complex and the safety requirement is high.

Classification by use

Power transformer: Used for voltage conversion in power systems. Large capacity, high reliability.

Distribution transformers: Used to supply power from the power system to the end user. Small size, suitable for residential areas.

Fully sealed transformers: for applications under specific environmental conditions. Dustproof and waterproof, suitable for harsh environments.

Modular transformers: Integrate multiple functions such as voltage conversion and filtering. Multi-function integration saves space.

Dry transformers: do not use insulating oil, rely on air cooling. No maintenance, good security.

Oil-immersed transformer: Use insulating oil as cooling medium. Good heat dissipation, suitable for large capacity applications.

Single-phase transformer: Used in single-phase AC system. Simple structure for home and small business applications.

Electric furnace transformer: Used for special occasions such as electric arc furnace. High current output, high temperature resistance.

Rectifier transformer: used to convert alternating current to direct current. Special winding design to suit the needs of the rectifier circuit.

Reactor: Used to limit alternating current. For current control and protection of power systems.

Anti-interference transformer: used to reduce electromagnetic interference. Special design to reduce signal distortion.

Lightning protection transformer: Used to protect the circuit from lightning strikes. With special protective measures.

Box type transformer: transformer integrated in a box. Easy to transport and install, suitable for outdoor environment.

Test transformer: Used for laboratory testing. Provides high voltage output for testing insulation performance of equipment.

Angle transformer: used to change the phase Angle. Used for phase matching of power systems.

High current transformer: For applications requiring high current. Special winding design to accommodate high current requirements.

Excitation transformer: An excitation system for a generator. : Provides stable excitation current.

Other categories

Classification by number of phases: single-phase transformers and three-phase transformers.

Classification by winding form: autotransformer, double-winding transformer, three-winding transformer.

Classification by core type: core type transformer and shell type transformer.

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5, crystal oscillator

Classification by material

Quartz crystal oscillator: Using the piezoelectric effect of quartz crystals, with high accuracy and stability. Good temperature stability, high frequency accuracy, suitable for applications requiring high stability.

Ceramic crystal oscillator: The use of ceramic materials, low cost. Low frequency accuracy and fast starting time make it suitable for applications that do not require extremely high accuracy.

Classified by internal circuit

Active crystal oscillator: contains an oscillating circuit that can directly generate a clock signal. No external circuit support, high stability and accuracy.

Passive crystal oscillator (crystal resonator) : contains only the crystal itself and requires an external circuit to produce oscillations. Simple structure, low cost, high flexibility.

Sort by output mode

Single-ended crystal oscillator: The output signal is a single-ended signal. Simple structure, low cost.

Differential crystal oscillator: The output signal is a differential signal. It has better anti-interference ability and lower radiation interference.

Classification according to temperature characteristics

Temperature compensated crystal oscillator (TCXO) : With built-in temperature compensation circuit to reduce the impact of temperature changes on the frequency. Suitable for applications that require high temperature stability, such as communication equipment.

Ordinary passive resonator: no special temperature compensation measures are taken. Low cost, suitable for occasions with low temperature stability requirements.

Classified by function and technology

Common clock crystal oscillator (SPXO) : simple structure, complete by the crystal free oscillation. It is suitable for occasions where the stability requirement is not high, and the frequency accuracy is generally of the order of 1E-4 ~ 1E-5.

Voltage controlled crystal oscillator (VCXO) : Its frequency output can be controlled by an external voltage. The frequency accuracy is in the order of 1E-5 to 1E-6, suitable for applications requiring frequency fine-tuning.

Constant temperature crystal oscillator (OCXO) : The temperature of the crystal is kept constant using a constant temperature tank to improve the stability of the frequency. It has extremely high frequency stability and is suitable for applications requiring extremely high stability, but it has high power consumption, large volume and long startup time.

Temperature compensated crystal oscillator (TCXO) : By sensing the ambient temperature, and using a certain functional circuit to generate a voltage signal opposite to the crystal temperature frequency characteristic, to offset the effect of temperature changes on the frequency. Compared with ordinary crystal oscillator, it has better temperature stability and is suitable for communication equipment.

Other categories

Classification by package type: metal shell, glass shell, ceramic or plastic package, etc.

Classification by cutting pin: Different cutting pins will affect the performance of the crystal oscillator.

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6. Filter

Classified by frequency response

Low-pass filter (LPF) : allows low frequency signals to pass through and suppresses high frequency signals. Subwoofer driver and anti-aliasing filter of analog signal used in audio system.

High-pass filter (HPF) : allows high frequency signals to pass through and suppresses low frequency signals. Tweeter drivers used in audio systems to remove the DC component of the signal.

Bandpass filter (BPF) : allows signals within a specific frequency range to pass through, suppressing signals below and above this range. It is applied to channel selection and biomedical signal processing in wireless communication.

Band-stop filter: allows signals below and above a specific frequency range to pass through, suppressing signals within that range. Acts to remove specific frequency interference, noise elimination in audio signals.

Classified by design method and performance

Bartworth filter: The frequency response curve in the pass band is flat to the maximum, and the stop band gradually decreases. It is used in audio signal processing and image processing.

Chebyshev filter: There are equal ripples in the pass band, and the stop band drops faster.

Bessel filter: has the best phase linear characteristics, that is, the phase delay is linear to the frequency.

Categorized by implementation

LC filter: Built using inductors and capacitors, suitable for lower frequencies. Applied to power filter, RF signal processing.

Cavity filter: Built using cavity resonators, suitable for higher frequencies.

Surface acoustic wave filter: Built using the properties of sound waves propagating on solid surfaces, suitable for high frequencies. It is used in mobile communication and satellite communication.

Bulk acoustic wave filter: Built using the properties of sound waves propagating inside solids, suitable for high frequencies.

Spiral filter: Built with spiral structure, suitable for high frequency.

Dielectric filter: built using the characteristics of dielectric materials, suitable for high frequencies.

Classified by application

Frequency converter filter: used to suppress the harmonics generated by the frequency converter.

Harmonic filter: Used to suppress harmonic interference in the power supply.

Sine wave filter: Used to generate or improve the quality of sine wave signals.

Classified by the components that make up the circuit

RC filter: Built using resistors and capacitors, suitable for lower frequencies.

RLC filters: Built using resistors, inductors and capacitors for a wide frequency range.

Crystal filter: Constructed with quartz crystals, it has extremely high frequency stability.

Ceramic filter: Built with ceramic materials, suitable for high frequencies.

Mechanical filter: Built using mechanical resonators, suitable for high frequencies.

Classified by whether it contains a source device

Active filter: Built using active devices such as operational amplifiers that amplify signals.

Passive filter: Built using only passive components and cannot amplify the signal.

Classified by response characteristics to signals

Linear filter: The relationship between the output and the input is linear.

Nonlinear filter: The relationship between output and input is nonlinear. For specific signal processing tasks, such as peak detection.

Classification by interference type

Common mode filter: Used to suppress common mode interference. For example, power line filtering and signal line filtering.

Differential mode filter: Used to suppress differential mode interference.

Classified by interference suppression mode

The use of capacitors through the characteristics of high-frequency isolation of low frequency: the high-frequency interference current into the ground wire (common mode) or the live line into the neutral line (differential mode).

Using the impedance characteristics of the inductor coil: the high-frequency interference current is reflected back to the interference source.

The use of interference to suppress ferrite: a certain frequency band of interference signals can be absorbed into heat.

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7. Connector

Classification by use:

Power connector: used to transmit power, common power plug, socket, etc.

Acoustic connectors: For the connection of audio devices, such as headphone jacks, speaker jacks, etc.

Printed board connector: Used for the connection on the circuit board, such as pin, bus, etc.

Cabinet connector: Used to connect server cabinets or other large devices.

Specialized connectors: Connectors customized for specific applications, such as medical equipment, military equipment, etc.

Classification by frequency:

Low-frequency connectors: Usually used for circuits below 100MHz.

High frequency connector: suitable for circuits above 100MHz, often using coaxial structure.

Sort by shape:

Circular connectors: widely used in military and aviation fields.

Rectangular connector: Printed circuit board for electronic devices.

Bar connectors: For simple wire-to-wire connections.

D-type connector: For example, DB-9, DB-25, and so on.

Classification by structure:

Threaded connector: fixed by thread.

In-line connector: Directly inserted connection.

Bolt connector: Use a bolt to secure.

Push-pull connector: Push-pull connection for quick connection and disconnection.

Bayonet connector: fixed using the bayonet mechanism.

Connectors of special structure:

Component plug-and-pull connectors: Allow quick replacement of components.

Rubber connector: waterproof and dust-proof.

Rotary connector: Allows rotary motion while keeping the circuit connected.

Split connector: A connector that can be split into two parts.

Optical fiber connector: used for optical signal transmission.

Other categories:

Onboard connector: Connector mounted on a printed circuit board.

High frequency connector: used for high-speed data transmission.

Power connector: for high current transmission.

Modular connector: Connector for replaceable modules.

Hot-swappable connector: Can be plugged in and out without turning off the power.

By application scenario:

Mobile phone connector: For mobile phones and other portable devices.

High voltage connector: For high voltage applications.

Automotive connectors: For automotive electronic systems.

Aviation connectors: For avionics.

High-speed signal connector: for high-speed data transmission.

Optical fiber connector: Used for optical fiber communication systems.

By installation type:

Cable connector: directly installed at the end of the cable.

Panel connector: Installed on the device panel.

Through-wall connector: Used for connecting through walls or partitions.

Common connector examples:

USB connector: includes Type-A, Type-B, Micro USB, Mini USB, and Type-C.

HDMI connector: For high-definition video and audio signal transmission.

VGA connector: Used for video signal transmission.

RJ45 connector: Used for Ethernet connection.

PCIe connector: Used for internal computer expansion cards.

SATA connector: Used for hard disks and other storage devices.

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8. Switch

Classified by function

One-on (single-link/one-bit) : a switch with only one key. Simple and easy to install.

Two-open (dual/two-position) : a switch with two buttons. Two separate circuits can be controlled.

Triple open (triple/triple position) : a switch with three keys. Three separate circuits can be controlled.

Quad-open (quad/quad) : a switch with four buttons. Four separate circuits can be controlled.

Classification by appearance

Flat insert: Used in China, the United States, Canada, Japan and other countries and regions. Flat pins.

Square insert: Used in Hong Kong, the United Kingdom, Singapore and other countries and regions. Square pins.

Round insert: Used in European countries. Round pins.

Classification by function

Two pole: Only two pins. Suitable for electrical appliances that are not grounded.

Two-two insert: This may be a description error, which usually does not appear.

Three-pole plug: There are three pins, including the ground pin. Suitable for electrical appliances that need to be grounded.

Two-three plug: May refer to a socket with both two and three poles. Suitable for different types of electrical appliances.

Two two three insert: This may be a description error, which does not usually occur.

Three-phase four-wire socket: Used in three-phase power supply system. Suitable for three-phase equipment in industrial and commercial applications.

Classification by control type

Knob switch: Change the resistance value by rotating. Can be used to adjust volume, frequency, etc.

Rocker switch: Change resistance by swinging up and down or left and right. Common in remote controls, game consoles, etc.

Push-button switch: a manually operated electrical switch. Usually used in control circuits, contacts allow less current to pass through.

Position detection switch: also known as travel switch or limit switch. A stroke or position used to limit mechanical movement.

Isolation switch: used to reliably isolate the part of the high-voltage distribution device that needs to be cut off from the live part. Suitable for safety isolation in high voltage distribution systems.

Classified by other functions

Proximity switch: A sensor that is triggered when approaching an object. Contactless, non-contact, suitable for position detection of automation equipment.

Load switch: Used to control the load in the circuit. Different types of switches can be selected according to the size of the load.

Open load switch: Manually operated switch used to control the on-off of the circuit. Suitable for low-power devices.

Isolation switch: Used to isolate the circuit. Suitable for high voltage circuit.

Special type switch

Timing switch: A switch with the timing function. The switch time can be set.

Photoelectric switch: A switch that uses a light beam for detection. Non-contact, suitable for occasions where the presence or absence of objects needs to be detected.

Thermal switch: A switch triggered when the temperature reaches a certain value. For temperature monitoring and protection.

Sound switch: A switch triggered by sound. Suitable for voice-activated systems.

Vibration switch: A switch triggered by vibration. Suitable for vibration detection.

In addition to the above common passive components, there are some special passive components worthy of attention, such as Bridges, chokes, memristors, and so on. By the way, if you have component information inquiry and procurement needs, please click to visit INFINITECH.