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Difference between Active and Passive Components

In this post difference between Active and Passive components are thoroughly explained. The active and passive components are categorized considering various functionality of the components. The various parameters are as follows

  • Component function
  • Flow of electron
  • Nature of operation
  • Nature of source
  • Power gain
  • Nature of energy

Active component and passive components are widely used in  electric circuit.Components like capacitor, inductor, resistor, diode , transsitor, MOSFET, SCR are the basic building block of a electrical network or electronic circuit.

Let us first understand what is active and passive component.

Active Component  

The active components are those components which requires external power source for its operation. If external power source is not applied to active device, the active devices can not function. The majority of the active devices are semiconductor devices. The active devices are able to control the flow of electrons through it if  the active devices are governed through  proper biasing by external power source. Thus, the active devices can be used for signal amplification.

Examples of Active Components

The examples of the active devices are almost all the semiconductor devices. The devices are;
  • Bipolar Junction Transistor (BJT)
  • Field Effect Transistor (FET)
  • Metal Oxide Field Effect Transistor ( MOSFET)
  • Silicon Control Rectifier (SCR)
  • TRIAC
  • Unijunction Transistor (UJT)
  • Diodes, Zener Diodes, Tunnel diode, Photo Diode, Schottkey Diode and LED
  • Integrated Circuits (ICs)
  • Application Specific Integrated Circuits(ASICs)
  • Battery
  • Voltage and Current Source
Let us understand why the above given devices fall under the category of active components.

Active Component- Bipolar Junction Transistor (BJT)

Transistor is used as a switch and as a amplifier. The small DC voltage control the base current and it leads to increase in the collector current according to the current gain of the transistor((IC =β IB). Where, β is the current gain of the transistor.  The below given circuit shows how  transistor is used as an amplifier.
VCC and VBB is the supply voltage given to collector and base of the transistor. The transistor is biased at the base terminal of the transistor in order to flow of base current. The small base current gets added in the signal current and thus the total base current gets amplified.

From above explanation it is lucid that without external DC voltage the transistor can not function. That is why the transistor is a active component.

Active Component- Silicon Controlled Rectifier (SCR)

Silicon controlled rectifier (SCR) is used as a switch and it is also used as a AC voltage controller. By Changing the firing angle the voltage is controlled. The SCR is widely used in DC drive, soft starter applications. The SCR functions only if trigger pulse at gate terminal is applied.
Silicon controlled rectifier (SCR) is used as a switch and it is also used as a AC voltage controller. By Changing the firing angle the voltage is controlled. The SCR is widely used in DC drive, soft starter applications. The SCR functions only if DC trigger pulse at gate terminal is applied. It is clear that SCR functions if the external voltage is applied at the gate terminal, therefore SCR is active component.

Silicon controlled rectifier (SCR) is also used as a voltage regulator. The external voltage applied to gate terminal of the SCR make it ideal for voltage regulator. The SCR can be fired at particular instant of the AC waveform and accordingly output voltage is governed. The circuit diagram is as shown below.

Active Component- Metal Oxide Field Effect Transistor(MOSFET) 

MOSFET is widely used as a switch and as an amplifier. MOSFET is a three terminal semiconductor device. It has gate, drain and source terminal. The voltage applied at the gate terminal make the MOSFET in conduction state. The external DC voltage at the gate terminal is responsible for conduction of MOSFET. Therefore, MOSFET is a active component. The circuit diagram of MOSFET as an amplifier is given below.

MOSFET is widely used as a switch and as an amplifier. MOSFET is a three terminal semiconductor device. It has gate, drain and source terminal. The voltage applied at the gate terminal make the MOSFET in conduction state. The external DC voltage at the gate terminal is responsible for conduction of MOSFET. Therefore, MOSFET is a active component. The circuit diagram of MOSFET as an amplifier is given below.

Active Component- Voltage Source

A voltage source is an example of active component. A voltage source supplies energy to the circuit.  The battery supplies energy to the electric circuit, therefore it is active component.

Active Component- Current Source

A current source also fall in the category of the active component. The current supplied by an ideal current source does not depend on the circuit voltage. A current source controls the flow of electric charge in a circuit. Therefore, current source is considered as a active component. A voltage source supplies energy to the circuit.  The battery supplies energy to the electric circuit, therefore it is active component.

Passive component

A passive components can not control the flow of electric charge through it.  A passive component either dissipate,absorb or store the electric or magnetic field. A passive component does not require any external power source to operate. The passive devices can not amplify, oscillate or provide power gain.

Examples of Passive Components

The followings are the examples of passive components used in an electric circuit.

  • Resistor
  • Capacitor
  • Inductor
  • Transformer

The passive components can be further divided into two categories.

  • Lossy or Dissipative:These devices can not absorb the electric power, rather these devices dissipate the power through it.Resistor is the example of lossy or dissipative passive component.
  • Lossless: These devices store the electrical energy. The examples of lossless passive devices are inductor, capacitor and transformer.

The most of the passive components are two terminal devices and referred as two port terminal.

Passive Component- Resistor

Resistor as its name implies resist the flow of electron. Resistor recives the energy from the source and it dissipates the energy as heat during flow of electric current through it. Resistor is a passive component because it does not amplify the power, rather it disspiates the power. The amount of opposition to flow of electric charge is called the resistance. It is denoted by the symbol “R”. The resistor follows the Ohm’s law. The power dissipated by the resistor is equal to I2R . Where I is the current and R is the resistance of the circuit. There are four types of resistors- carbon film, metal film,wire wound and adjustable resistors- are widely used in an electrical circuit.

Inductor

The inductor resist the change in the current of the circuit. The inductor does not dissipate the energy; it stores energy in its magnetic field and later it delivers the energy, but not on continuous basis. The energy stored by an inductor in its magnetic field is equal to 1/2 L* I2. Where, L is the inductance of the inductor and I is the current flowing through it. The energy absorption and its deliverance is transient in nature, and it depends on the time constant of the circuit. That is why inductor is a passive component.The inductor has very high impedance on AC and very low impedance on DC. The inductors are widely used in power supply,SMPS and AC/DC converter.

Passive Component- Capacitor

A capacitor stores the energy in its electric field. That is why capacitor is a passive component. The capacitor stores the energy and later on it deliver the same, but not continuously. The capacitor is used in electronic circuit. Capacitor is also used for power factor improvement. The energy stored by a capacitor in its electric field f is equal to 1/2 C* V2. Where, C is the capacitance of the capacitor and V is the voltage applied across it.

Transformer

The transformer is static electrical equipment which transfer the electric power from primary side to secondary side without changing the frequency. The transformer simply transfers the energy, and that is why it is a passive component.

Key difference between active and passive component

  • Active components require an extra power for its operation.Passive components do not require extra power for its operation.
  • Active component produce energy in the form of voltage or current. Passive component stores, transfer and utilize the energy. The inductor and capacitor store the energy in the magnetic and electric field respectively, and transformer transfers the energy from primary side to secondary side.
  • Active components are non linear devices. The current does not vary in the proportion of the increase in voltage. The active devices does not obey the Ohm’s law. Passive components are linear devices, and current through these devices increases with increase in the applied voltage, thus these devices follow the Ohm’s law.
  • Active components have capability to provide power gain, whereas the passive components can not provide power gain.
  • Active components can control the flow of electron or electric current.Passive components can not control the flow of electric current passing through it.
  • Active components are energy donor, whereas passive components are energy acceptor.