What is an active device

What is an active device? Active components are the core of electronic circuits. All oscillation, amplification, modulation, demodulation, and current conversion are inseparable from active components. From the nature of the circuit, active devices have two basic characteristics:

(1) It also consumes electricity.

(2) In addition to the input signal, an external power supply is required for normal operation. It can be known that active devices and passive devices have completely different working conditions and working methods of the circuit, which must be paid great attention during the study of electronic technology.

Common Active Electronic Devices

Discrete devices: field effective transistor, thyristor, also known as thyristor, bipolar transistor, generally referred to as triode, BJT, semiconductor resistor and capacitor-manufactured using integrated technology Resistors and capacitors used in integrated circuits.

Analog integrated circuit device: comparator, analog multiplier / divider, integrated operational amplifier (operation amplifier), referred to as integrated op amp, logarithmic and exponential amplifier, PLL circuit (phase lock loop), that is, Phase-locked loop circuit, analog switch circuit, reference source, power amplifier, wave-form generator.

Passive components

The definition of passive devices is as follows: passive devices are used for signal transmission, or "signal amplification" through directivity. Capacitors, resistors, and inductors are all passive devices, and ICs and modules are all active devices. Passive components are mainly resistive, inductive, and capacitive components, and their common feature is that they can work when there is a signal without adding power to the circuit.

 Passive components

Capacitance: The letter of the capacitor is C. The unit of capacitance is farad (denoted as F), and μF (micro method) and PF (ie, μF, pico method) are commonly used. A capacitor is also one of the most common components in electronic circuits. It is a component that stores electrical energy. Capacitors consist of a layer of insulating dielectric sandwiched between two conductors of the same size and homogeneity. When a voltage is applied across it, the capacitor

Charge will be stored on it. Once there is no voltage, as long as there is a closed loop, it will release electricity. Capacitors prevent direct current from passing in the circuit, but allow alternating current to pass. The higher the frequency of the alternating current, the stronger the ability to pass. The characteristics of a capacitor in a circuit are non-linear. The impedance to the current is called capacitive reactance. The capacitive reactance is inversely proportional to the capacitance and the frequency of the signal.

Resistance: The symbol for resistance in the circuit diagram is the letter R. The standard unit of resistance is ohms, denoted R. Commonly used are kiloohm KΩ and megohm MΩ. When a current passes through a conductor, the nature of the conductor's internal resistance to the current is called resistance. The components that play a role in blocking current in the circuit are called resistors, or resistors for short. The main purpose of the resistor is to step down, divide or shunt, and it is used as load, feedback, coupling, isolation, etc. in some special circuits.

Inductance: Inductance is a typical component of electromagnetic induction and electromagnetic conversion. The most common application is transformer. Like a capacitor, an inductor is also an energy storage component. An 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 prevents the current flowing through the coil from changing. This obstacle is called inductive reactance. The inductive reactance is proportional to the inductance and the frequency of the signal. It does not hinder the direct current (excluding the DC resistance of the coil). Therefore, the role of the inductor in the electronic circuit is: blocking, transforming, coupling and cooperating with the capacitor for tuning, filtering, frequency selection, frequency division, etc.

The difference between active and passive devices

After understanding the definition of active and passive devices, let's take a look at the difference between the two.

In electronics, a circuit containing a transistor element is usually called an "active circuit" (such as an active speaker, an active filter, etc.), and a circuit composed of only a resistor-capacitor element is called a "passive circuit". 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. Outside are active devices. The so-called "external characteristics" is to describe some kind of relationship between the devices, although the voltage or current, the electric or magnetic field pressure or speed and other quantities are used to describe the relationship. The external characteristics of passive devices have nothing to do with whether they exist as a driving source.

 The difference between active and passive devices

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. Outside are active devices. The so-called "external characteristics" is to describe some kind of relationship between the devices, although the voltage or current, the electric or magnetic field pressure or speed and other quantities are used to describe the relationship.