Basic Electronics Terms


Transistor is a three terminal device which transforms current flow from low resistance path to the high resistance path . The transfer of current through resistance path given the name to the device transfer resistor as transistor.

Transistor consists of three parts Emitter,Base,Collector.The base region thin region compared to emitter and collector.The most common transistor common emitter configuration.

Two Types of transistor

  • NPN
  • PNP
  • Basic Electronics Terms Transistor

    The arrow in a transistor symbol represent the direction of current flow.The base emitter junction is always forward biased and collector base junction reverse biased .

    Emitter Current(Ie) = Ib+Ic

    In NPN transistor base is more positive than emitter.While in the PNP emitter is more positive than the base
    Transistor can be used as an amplifier in three configuration

  • Common base
  • Common emitter
  • Common collector
  • Field Effect transistor

    Bipolar Junction Transistors (BJT)
    Junction Field Effect Transistor (JFET)
    Metal Oxide Semiconductor FET (MOSFET) Bipolar Junction Transistors (BJT)
    Bipolar Junction Transistors (BJT)

    BJT is a three terminal device consisting of two P-N junction connected back to back . It can be either NPN or PNP . Since current flow inside this transistor is caused by two opposite polarities of charge carriers (holes and electrons), this transistor is more approximately called BJT.

    Junction Field Effect Transistor (JFET)

    JFET Likes BJT are three lead semiconductor device. JFETs are used for electrically controlled switches, current amplifiers and voltage controlled resistors. JFET are controlled by voltage no need bias current like BJT. JEFT are on when Vg-Vs=0.Two types JEFT n-channel and P-channel.

    Metal Oxide Semiconductor FET. Its similar to JFET, A metal oxide insulator is placed at the gate obtain a high input impedance at the gate. Two types of MOSFET Enhancement and Depletion types.

    Switching devices

    Silicon controlled rectifier is four layer PN PN three terminal silicon device in which the end P layer from the anode, the end N layer from the cathode and the p –Layer near to cathode forms the gate .

    Basic Electronics Terms scr

  • SCR can conduct current in onr direction only there for it can control only dc power
  • Finger voltage :The minimum voltage which required between anode and cathode of an scr to trigger it to conduction.
  • Finger voltage 2 to 2.7 v.
  • Latching current The minimum current required to latch the device from off state to on state.
  • .

  • Typical value 8 MA to 10 MA.
  • Holding current 3 MA to 5 MA.
  • Turn on time :150 ns to 200ns.
  • Advantage :Compactness, Fastness in response, Highly efficient, less power consumption ,little maintenance, noise less operation large current capacity.
  • Application: Electronic switching, Controlled rectifier, relay controls, motor control,

    Triac its also three terminal silicon device . however like SCR is a bidirectional device ,It can block voltage of either polarity and conduct in either direction.

    Basic Electronics Terms TRIAC

  • Applications: Due to this by directional property of TRIAC is mostly used for a.c power.
  • Phase controller, static switch, light controller, motor speed controller.
  • DIAC

    Diac is two terminal three layer semiconductor device .

    Light dinner ,Motor speed control, fan regulator, heat control .


    The process of increasing amplitude of an input signal is called amplification.and the device is called amplifier. Main parts of an amplifiers are transistor, FET or op-amp. Which has two input terminal with the output signal being much grater than input signal as it been amplified.

    Basic Electronics Terms Amplifiers

  • Gain: The difference between the input signal and output signal is known as gain.
  • Inter stage coupling: In multi stage amplifier the output of the one stage is the input of the next stage .There fore it is necessary to use a coupling network between the output one amplifier and the input of the following this amplifier known
  • Resonant frequency: High impedance at particular frequency is called resonant frequency
  • Table comparison Class A, Class B, Class C power amplifier

    Class A Class B Class C
    Collector current flow For whole cycle of the input signal For one half cycle of the input signal For less than one half cycle of the input signal
    Base bias Forward bias Zero bias Reverse bias
    Q point In the middle of a. c load line At cut off (Ic =0) Beyond cut off
    Power output low high higher
    Efficiency Less than 50% 50 to 60% 80%
    Application Single ended power amplifier systems Power amplifiers in push pull arrangement RF tuned amplifiers
    Feedback amplifier

    Feedback is the process of injecting a fraction of out put energy of some device back to the input . Mainly two types of feedback amplifier positive feed back and negative feed back.

  • Positive feed back: The resultant input signal is equal to the sum of the original input and feed back input. Since the feedback voltage adds to the original input voltage this type of feed back is called positive feed back.
  • Negative feed back: Since the feed back voltage subtracts the original input voltage is known as negative feed back .
  • Tony

    Hi, Myself Tony George. An Electrical Engineer by Education, a Software Developer by Profession and an Education Blogger by Passion. In the past, I had been working as an Engineer in KSEB. The knowledge that I have acquired I would like to share here with you. I will be happy if these articles can give you a way to your career growth. Feel free to contact me.

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