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.
Based on the energy gap Eg ,the materials are classified as
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
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
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
When small amount of pentavalent impurity is added to pure semiconductor it is called n-type semiconductor.
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.
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 .
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.
Example: Antimoney, phosphorus, Aresenic etc.
Example: Gallium, Indium, Boron .
In semiconductor is the current which flows as result of gradient of carrier concentration.
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.
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.
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.
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.
A diode is a 2 lead semiconductor that acts as a one way gate to electron flow.
Rectifier is a device which convert a.c voltage to pulsating d.c voltage.
Types of 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 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.