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Aug 10, 2019, 02:00 AM
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What is the difference between passive and active devices?

Simply speaking, a device that requires an (electrical) source is called an active device, and a device that does not require an (electrical) source is a passive device. Active devices are typically used for signal amplification, conversion, etc., passive devices are used for signal transmission, or "signal amplification" by directionality. Capacitors, resistors, and inductors are passive devices, and ICs, modules, etc. are all active devices. (Commonly speaking, it is the active components, such as triodes, that require a power supply to display their characteristics. A passive component is called without a power supply.)

1. Basic definition of passive components
If an electronic component operates without any form of power supply inside it, the device is called a passive device.

From the nature of the circuit, passive components have two basic characteristics:

(1) It either consumes electrical energy or converts electrical energy into other forms of other energy.

(2) Just input the signal and it will work without external power supply.

2. Basic definition of active devices
If an electronic component has a power supply inside it, the device is called an active device.

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

(1) It also consumes electricity itself.

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

It can be seen that the active device and the passive device have different working conditions and working modes for the circuit, which must be paid attention to in the learning process of electronic technology.

First, common passive electronic devices
Passive devices in an electronic system can be classified into circuit type devices and connection type devices according to the circuit functions they perform.

Circuit type device

(1) Diode

(2) Resistor

(3) Resistor network

(4) Capacitor

(5) Inductor

(6) Transformer

(7) Relay (relay)

(8) button (key)

(9) Buzzer, speaker (speaker)

(10) Switch

2. Connection device

(1) connector (connector)

(2) socket (shoket)

(3) Connecting cable (line)

(4) Printed circuit board (pcb)

Passive components are mainly resistors, inductors, and capacitors. Their common feature is that they can operate when there is no signal in the circuit.


When a current passes through a conductor, the property of the conductor internal resistance to block the current is called a resistor. A component that acts as a choke in a circuit is called a resistor, or a resistor. The main purpose of the resistor is to step down, divide or shunt, and use it as load, feedback, coupling, isolation, etc. in some special circuits.

The symbol of the resistor in the circuit diagram is the letter R. The standard unit of resistance is ohms, denoted as R. Commonly used are thousands of ohms KΩ, megaohms MΩ. 1KΩ=1000Ω 1MΩ=1000KΩ


Capacitors are also one of the most common components in electronic circuits, and they are components that store electrical energy. The capacitor is composed of two layers of insulating medium sandwiched between two identical conductors. When a voltage is applied across it, a charge is stored on the capacitor. Once there is no voltage, as long as there is a closed loop, it will release power. The capacitor blocks DC through in the circuit and allows AC to pass. The higher the frequency of the AC, the stronger the ability to pass. Therefore, the capacitors are commonly coupled in the circuit, bypass filtering, feedback, timing, and oscillation.

The letter code of the capacitor is C. The unit of capacitance is Farah (denoted as F), and μF (micro method) and PF (μμF, pico method) are commonly used. 1F=1000000μF 1μF=1000000PF

The characteristics of a capacitor in a circuit are non-linear. The impedance to the current is called the capacitive reactance. The capacitive reactance is inversely proportional to the capacitance and the frequency of the signal.


Inductors, like capacitors, are also energy storage components. The inductor is generally made of a coil. When an alternating voltage is applied across the coil, an induced electromotive force is generated in the coil, which hinders a change in current passing through the coil. This hindrance is called inductive resistance. The inductive reactance is proportional to the amount of inductance and the frequency of the signal. It does not hinder DC power (regardless of the DC resistance of the coil). Therefore, the role of the inductor in the electronic circuit is: blocking, voltage transformation, coupling and cooperation with the capacitor for tuning, filtering, frequency selection, frequency division, and the like.

The code of the inductor in the circuit is L. The unit of inductance is Henry (denoted as H), commonly used are millihenry (mH), microhenry (μH). 1H=1000mH 1mH=1000μH

Inductors are typical components of electromagnetic induction and electromagnetic conversion. The most common application is a transformer.

Second, Common active electronic devices
Active devices are the main components of electronic circuits. From physical structure, circuit functions and engineering parameters, active devices can be divided into discrete devices and integrated circuits.

Discrete device

(1) Bipolar transistor, generally referred to as triode, bjt

(2) Field effect transistor

(3) Thyristor (thyristor), also known as thyristor

(4) Semiconductor resistors and capacitors - resistors and capacitors fabricated using integrated technology for use in integrated circuits.

Analog integrated circuit devices

Analog integrated circuit devices are integrated circuit devices used to process analog voltage or current signals that vary continuously over time.

Basic analog integrated circuit devices generally include:

(1) Integrated operational amplifier, referred to as integrated operational amplifier

(2) Comparator

(3) Logarithmic and exponential amplifiers

(4) Analog multiplier/divider

(5) Analog switch circuit (analog switch)

(6) pll circuit (phase lock loop), that is, phase-locked loop circuit

(7) Integrated voltage regulator (voltage regulator)

(8) Reference source

(9) Waveform generator

(10) Power amplifier

Digital integrated circuit devices

(1) logic gate circuit

(2) Flip-flop

(3) Register (register)

(4) Decoder

(5) data comparator (comparator)

(6) driver

(7) counter (counter)

(8) shaping circuit

(9) Programmable logic device (pld)

(10) Microprocessor (mpu)

(11) Microcontroller (mCU)

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

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

A device that can independently exhibit its external characteristics without relying on the presence of an external power source (DC or AC) is a passive device. Beyond the active devices.

The so-called "external characteristic" is a measure of the relationship of a device, although the relationship between voltage or current, electric field or magnetic field pressure or velocity is used to describe the relationship.

The external characteristics of passive components have nothing to do with whether they exist as a source of motivation.

The concept of passive and active is not only found in electrical components, but also in the fields of mechanics, fluids, heat, and acoustics.
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