Basic Electronics Notes

Electronics

The word “Electronics “stands for Electron mechanics .Hence electronics deals with the motion of electron under the influence of applied electric/magnetic field.

Application of Electronics

    Communication : Telegraphy, satellite communication
    Medical :x-ray, Electron microscope , C.T scan
    Defence : Radar, Guided missiles
    Instrumentation: CRO, VTVM
    Industrial: H.F heating ,Resistance welding
    Entertainment : Radio & TV broadcasting.
Classification of materials.

Based on the energy gap Eg ,the materials are classified as


Conductor
Conductors are large number of free electrons exist at room temperature so Eg does not exist. The valance and conduction band are overlapped.
Eg: copper, aluminium , silver
Insulator
The energy gap Eg is large of the order of 7eV.At very high temperature or under high voltage also these materials do not conduct.
Eg: Wood , mica , plastic
Semiconductor
The energy gap Eg is about 1 eV. At very high temperature increases, this materials can conduct heavily as more free electrons generated .
Eg: Silicon ,Germanium.
Two types of semiconductor

N- Type semiconductor

When small amount of pentavalent impurity is added to pure semiconductor it is called n-type semiconductor.

basic electronics notes-Tutorials n-type semicondutor

When small amount of pentavalent impurity is added to pure semiconductor it is called n-type semiconductor. The pentavalent impurity has five valance electrons These elements are such as arsenic,bismuth, phosphorous and antimony. Due to this predominance of negative charged electrons start conduction.

N-Type consists :Free electrons(Majority carriers), Holes( Minority carriers),Immobile Negative irons.

P-Type semiconductor

When a small amount of trivalent impurity is added to pure semiconductor it is called P-type semiconductor. The trivalent impurity has three valance electron These elements are such as gallium, silicon .

basic electronics notes-P-Type semiconductor

The silicon crystal each atoms of the impurity forms covalent bonds by sharing their three valance electrons. The fourth neighboring silicon atom is unable to form covalent bond with the impurity atom. Hence fourth covalent bond is incomplete having one electron short that become hole. This hole having tendency to snatch electrons .This holes movements start conduction .As the holes treated as positive charged, the material is known as P-type semiconductor.

P-type semiconductor consists: Holes (majority carriers), Electrons (Minority carriers),Immobile positive ions.

Notes
  • Intrinsic semiconductor: A semiconductor in its purest form is known as intrinsic semi-conductor. Impurity content in an intrinsic less than one part in 100milins parts of semiconductor.
  • At absolute zero temperature pure semi conductor be haves as perfect insulator.
  • Negative temperature coefficient of resistance: The resistance of the semiconductor decreases with rise in temperature.
  • Mean life time: The average time an electron or holes will exist before recombination is called mean life time of the holes and electrons.
  • Doping: The process of adding impurity to pure semiconductor is called doping.
  • Extrinsic semiconductor: The doped semiconductor called extrinsic semiconductor.
  • Donor: Small amount of impurity has a large number of atoms. it provides millions of free electrons and hence fifth valance electrons called donors.
  • Example: Antimoney, phosphorus, Aresenic etc.

  • Acceptor: Each atom of trivalent impurity gives one free hole to the crystal by accepting one electron in its outer most orbit and hence this type of impurity is called acceptor.
  • Example: Gallium, Indium, Boron .

  • Drift current: The flow of electric current due to the motion of the charge carriers under the influence of external electric field.
  • Diffusion current:
  • In semiconductor is the current which flows as result of gradient of carrier concentration.

  • Depletion region : The recombination of holes and electrons a narrow width of fixed negative charges on the N-side of the junction and fixed negative charges on the P-side of the junction forming barrier. it’s also called space region.
  • PN junction barrier potential :Silicon = 0.7V, Germanium = 0.3V.
  • Zener break down

    When in increasing reverse bias across a PN junction ,the electric filed at the junction also increases . This high electric field causes covalent bond with in the crystal to break.

    basic electronics notes-Zener-Diode-in-Biasing

    Thus a large number of charge carriers become available .This causes large current to flow through the junction .This phenomenon is called zener brek down.

    Avalanche breakdown

    The high electric field across the junction provide higher velocity to minority charge carriers. These minority charge carriers with their acquired energy break covalent bond ,these continues and large number of free charge carriers become available and causes reverse current .This mechanism is known as avalanche breakdown.

    Note
  • Effect of temperature on diode:
    The cut in voltage decreases as the temperature increases .The diode conducts smaller voltage and larger temperature.
  • The reverse saturation current increases as temperature increases.

  • Applications of diodes:Rectifiers, Switch in digital logic circuit, clamping network in TV receivers, Modulator/De modulator.
  • Diode

    A diode is a 2 lead semiconductor that acts as a one way gate to electron flow.

    basic electronics notes-diode

    Rectifier

    Rectifier is a device which convert a.c voltage to pulsating d.c voltage.
    Types of rectifier

  • Half wave rectifier
  • Full wave rectifier
  • Bridge rectifier
  • Half wave rectifier

    Rectifying element conducts only during the positive half cycle of input ac supply. The negative half cycles of a.c supply are eliminated from the output. The half wave rectifier gives output wave form of positive sinusoidal pulses. Hence the output is called pulsating.

    Full wave rectifier

    The full wave rectifier conducts during the both positive and negative half cycles of input ac supply. In order to rectify both the half cycles of a.c input , two diodes are used in this circuit.

    Bridge rectifier

    Bridge rectifier circuit essentially a full wave rectifier circuit ,using four diodes forming the four arms of an electric bridge . to one diagonal of the bridge the ac voltage is applied through the transformer if necessary ,and the rectified dc voltage is taken from the other diagonal of the bridge .the main advantage of this circuit is that does not require a center tap on the secondary winding of the transformer.

    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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