ZENER DIODE

A properly doped crystal diode which has a sharp breakdown voltage is known as zener diode.  A zener diode is like an ordinary diode except it is properly doped.   A zener diode is always reverse connected (reverse biased)  Zener diode has sharp breakdown voltage i.e zener voltage.

ZENER CURRENT, ZENER VOLTAGE

When the reverse bias on a crystal diode is increased, a critical voltage, called break down voltage is reached.  where the reverse current increases sharply to a high value.  The explanation for the breakdown region is given by C.Zener.  therefore breakdown voltage is called zener voltage and the sudden increase in current is known as zener current.
The breakdown or zener voltage depends upon the amount of doping.  If the diode is heavily doped, depletion layer will be thin and consequently the breakdown of the junction will occur at a lower reverse voltage.  A lightly doped diode has a higher break down voltage.

FILTER CIRCUITS

A Rectifier is required to produce pure D.C supply for using at various places in the electronic circuits.  However, the output of a rectifier has pulsating character.  It contains A.C and D.C components.  The A.C component is undesirable  and must kept away from the load.  To do so, a filter circuit is used which removes the A.C component and allows only the D.C component to reach the load.

A filter circuit is a device which removes the A.C component of rectification output but allows the D.C component to reach the load.

RIPPLE FACTOR

The output of a rectifier consists of a D.C component and an A.C component ( also known as Ripple)
The A.C component is undesirable and accounts for the pulsation in the rectifier output.  The effectiveness of a rectifier depends upon the magnitude of A.C component in the output.  The smaller this component, the more effective is the rectifier.

The ratio of r.m.s value of A.C component to the D.C component in the rectifier output is known as Ripple Factor.   Ripple factor is very important in deciding the effectiveness of a rectifier.

FULL WAVE RECTIFIER

In full wave rectification, current flows through the load in the same direction for both half-cycles of input A.C voltage.  This can be achieved with two diodes working alternatively.  For the positive half cycle of input voltage one diode supplies current to the load and for the negative half cycle the other diode does so, current being always in the same direction through load.  Therefore a full wave rectifier utilises both half cycles of input A.C voltage to produce the D.C output.

EFFICIENCY OF HALF WAVE RECTIFIER

The ratio of D.C power output to the applied input A.C power is known as Rectifier Efficiency.

HALF-WAVE RECTIFICATION

In Half-wave rectification, the Rectifier conducts current only during the positive half cycles of input A.C.Supply.  The negative half-cycles of A.C supply are suppressed.  i.e during negative half cycles no current is conducted and hence no voltage appears across the load.  Therefore current always flow in one direction (i.e D.C) through the load.

SEMI CONDUCTOR DIODE

A p-n junction is known as semi conductor diode or crystal diode.  The out standing property of a crystal diode to conduct current in one direction only permits it to be used as a rectifier.

P-N JUNCTION

p-n Junction conducts current easily when forward biased and practically no current flows when it is reverse biased.  This unilateral conduction characteristic of P-n junction is similar to that of a vacuum diode.

DISADVANTAGES OF HALF-WAVE RECTIFIER

Half-wave rectifier is seldom used in practice because
1) The rectification efficiency is low
2) The D.C output is small
3) Secondary transformer carries the rectified current, thus producing direct magnetisation of the transformer core.
4) Because of short heavy pulses of current, the heating of transformer winding is large compared to the current delivered.

RECTIFIER

Rectifier is an electronic device that converts alternating current into direct current is called rectifier.
A rectifier changes A.C into D.C by eliminating the negative half cycles of the alternating voltage.  It may work as a switch that closes a load circuit during the positive half cycle of A.C supply and opens the circuit during the negative half cycle.  Therefore a rectifier provides one-way path for electric current.

VACUUM TUBE

Vaccum Tube is an electronic device in which the flow of electrons is through a vacuum is known as vacuum tube.  A vacuum tube usually contains a cathode which is the electron emitter, an anode(plate) which is the electron collector and one or more electrodes (called grids) for controlling the flow of electrons between cathode and plate.  These electrodes are housed in a highly evacuated glass envelope.  The plate is held at positive terminal with respect to cathode so that emitted electrons are attracted to plate to provide current in vaccum.

THEVENIN'S THEOREM

Thevenin's Theorem is used to find a particular branch current in a circuit as the resistance of that branch is varied while all other resistances and voltage sources remain constant.

"Any two terminal network containing a number of e.m.f sources and resistances can be replaced by an equivalent series circuit having a voltage source Va in series with a resistnce Ra."

where Va=voltage between two terminals
          Ra=Resistance between two terminals

AMPLIFICATION

The process of raising the strength of a weak signal is known as amplification.  Electronic devices can accomplish the job of amplification are known as amplifier.

RECTIFICATION

The conversion of A.C into D.C is called Rectification.

ELECTRONICS

The branch of engineering which deals with current conduction through a vaccum or gas or semi conductor is known as Electronics. An Electronic device is that in which current flows through a vacuum or gas or semi conductor.

STEPPER MOTORS

The Stepper Motor is a form of synchronous motor which is designed to rotate a specific number of degrees for each electrical pulse received by its control unit.  The stepper motor is used in digital control systems where the motor receives open loop commands as a train of pulses to turn a shaft or move a plate by a specific distance.  A typical application for the motor is positioning a work table in two dimensions for automatic drilling according to programme.

SERIES MOTORS

A Series Motor has has ability to run on either alternating or direct current.

RECTIFIER

Rectifier circuit is used to convert A.C Current into D.C. Rectifier is a circuit assembled from diodes and thyristors.  Which supplies direct current to the armature and field to and field of the motor from the A.C supply line.

INVERTERS

Inverters are used to transfer energy from a dc source to an ac load of arbitrary frequency and phase.  Inverters are used to supply uninterrupted ac power to computers, house hold appliances and to convert energy between ac and dc from at the terminals of high voltage dc power transmission systems.