DC motor construction and working

Introduction:- A DC motor is a device / machine which converts DC power to mechanical energy. It consist of a stationary outer body known as yoke and a rotating armature inside the yoke. Yoke holds main field poles and inter-poles with the help of bolts.Two end covers are fixed on each side of yoke they supports armature with the help of bearings. Armature consist of a shaft armature core, armature winding commutator. Rocker arm holds the brush holders is fixed on free end side end shield. Carbon brushes are hold by brush holder and maintain proper brush position and pressure on commutator.

Magnetic Circuit of DC Motor:- It consist of Main Pole body, Pole Shoe  Armature core again Pole shoe Main pole body and returns through yoke body as shown in diagram.

Electrical circuit consist of field winding and armature winding. Main field winding produces main working flux in motor is wound on main poles. All four poles windings are connected in series. Final two leads of main field winding  are connected to rated supply voltage. This winding is known as shunt field winding as it is connected in parallel to supply voltage. Series field winding is also wound on main poles. All four pole coils are connected in series. Final two leads are connected in series with armature winding. Series winding helps the maintain flux lavel during load condition.Interpole winding is wound on interpoles and is connected in series with armature winding. Interpole winding helps to improve commutation. when supply is given to field winding it produces flux. The supply given to armature produces set of current carring conductors in magnetic field which causes production of tourqe on armature. So armature start rotating. The direction of motor can be changed by changing the polarity of either shunt field winding or armature winding. The speed of motor is proportional to applied voltage to armature and inversaly proportional to field winding current.

P N Junction diode baising

P N Junction diode

Introduction:- Silicon and germanium are the main semiconductors used for production of diode, transistors and Integrated Circuit(ICs.). Semiconductor materials contain 4 electron in their outer most orbit. A pentavalent impurity is added to make P type semiconductor. P type semiconductor has hole in surplus makes them positively charged. A trivalent impurity is added to make N type semiconductor. N type semiconductor has electrons in surplus makes them negatively charged.

PN Junction Diode:- When a P type semiconductor and N type semiconductor are bring together by doping they form a PN Junction diode. In this Junction there are more holes in P layer and more electrons in N layer.

Baising:-

Forward bais:-When Positive voltage is given to P layer and Negative voltage is given to N layer the junction is said to be forward baised. Due to emf of cell holes from P layer and electrons from N layer moves towards the junction and current starts flowing.This is forward bais condition where diode starts conducting.

Reversed bais:-When Negative voltage is given to P layer and Positive voltage is given to N layer the junction is said to be reversed baised. Due to emf of cell holes from P layer and electrons from N layer moves away from junction so that no current can flow through junction.This is reversed bais condition where diode can not conduct.

Transformer introduction and construction

Transformer introduction and construction

Introduction:- Transformer is an static electrical machine. It is used to increase or decrease  voltage, Basically a transformer has two winding and a magnetic core. Winding are Known as primary winding and secondary winding.Primary winding is connected to supply and secondary winding is connected to load.When alternating voltage is applied to primary winding an alternating magnetic flux setsup in core. Due to that flux in core alternating voltage is induced in secondary winding which causes current to flow through load circuit.

Basically transformer are of two type

1. Step up transformer:- It is used to increase the voltage in secondary side.

2. Step down transformer:- It is used to decrease the voltage in secondary side.

Transformation ratio- It is the ratio of number of turns in secondary winding to number of turns in primary winding.
K = N2/N1 also K=V2/V1 and K= I1/I2 with this formula we can find the number of turns in secondary winding if primary winding turns are known.

In Electronics generally step down transformer are used for power supplies. for example 230/12v 2A, 230/18v 3A etc. Example of step up transformer is ignition coil of bike, EHT transformer in TV, high voltage transformer in microwave oven etc.

Transformers are classified on the basis of their use

1. Power transformer used in power supplies.
2. Driver transformer used in driver circuit of audio amplifiers.
3. Output transformer used in output circuit of audio amplifiers.
4. Impedance matching transformer used inside moving coil microphones.
5. Multiple secondary winding:- these transformer have multiple secondary windings for different          voltages.
6. Auto transformer:- these transformers have single winding with tapping for primary and secondary      windings.

Transformers are also classified on the basis of core material used.

1. Iron core:-  Power transformer, battery charger transformer, input/output transformer etc.

2. Ferite core transformer-   Driver transformer, EHT transformer in TV. SMPS transformer etc. these transformer works at frequency of 15 KHz. there size is also small due to high frequency working.

3. Air core coils:- used in radio and tv circuit.

In addition to this very large transformers are used in power system.

Bridge rectifier circuit diagram with working explanation

Bridge rectifier circuit

Introduction :-  In full wave rectifier circuit we need a centre tapped transformer.Some times centre tapped transformers of require voltage is not available in market or price of transformer is more. To solve this problem bridge rectifier is used.

Description:- It consist of four diodes connected as shown in diagram.When supply is given to primary winding, 12 volt ac is induced in secondary winding.During Positive half cycle point 'a' of transformer become positive and point 'b' becomes negative.The current flows trough diode d1 to load and returns through diode d2. During Negative half cycle point 'a' of transformer become Negative and point 'b' becomes positive.The current flows trough diode d3 to load and returns through diode d4. In this way both the half cycles flow through the load making full wave rectification. Capacitor C1 and C2 are used as filter circuit. At many places bridge rectifier is used
without transformer at 230 volt.in such cases PIV of diodes must be more than 1000 volt.

HALF WAVE RECTIFIER CIRCUIT

Introduction:- Half wave rectifier is the simplest form of rectification. It requires only one diode in circuit. Only positive half wave of ac voltage is rectified to dc output. Output  voltage is not very smooth and contains more ripples. 

Parts required:- A step down transformer of required voltage and current rating(say 12 volt 2 ampere). One number diode. Two filter condenser and resistance for pie filter circuit. All components are connected as per circuit diagram.

When ac 230 volt is given to primary winding 12 volt is induced in secondary winding. During positive half  cycle diode gets forward bias and conduct current, which charges the capacitor. During negative half cycle diode gets reverse bias hence not conduct any current. During  this time capacitor supplies the load current. In this circuit only half wave of ac voltage come in output  that's why it is known as half wave rectifier. It is generally used in battery charging system where very smooth dc supply is not required. In cheap circuits only one capacitor is used which gives more ripples. To reduce ripples pie filter circuit with two capacitor as shown in circuit to be used. In many small current circuit series resistance is used in place of transformer to reduce voltage.

FULL WAVE RECTIFIER WORKING WITH CIRCUIT DIAGRAM

FULL WAVE RECTIFIER

Introduction - Full wave rectifier is used to make smooth ripple free power supply. It requires a centre tapped transformer of required voltage and current rating. for example 230 volt/12-0-12 volt 2 ampere for 12 volt 2 ampere dc power supply. Two diodes of 2 Amp. rating with 500/1000 volt PIV value. Peak inverse voltage must be more than twice the required output voltage. Two numbers filter condenser of 2000 mfd 25 volt rating. one 2 ohms 5 watt resistance and one 1000 ohms 1 watt resistance. The above value may be changed as per need.
All the components are joined as per circuit diagram

Description :- The function of transformer is to step down 230 volts to 12- 0- 12 volt. 12-0-12 volt means transformer output winding has three points. Centre point is commen and other two points are 12 volt points 180 degree out of phase. When 230 volt supply is given to primary winding 12 volt ac induced in the secondary winding. The  centre point of transformer becomes the negative point of dc supply.Two diodes d1 and d2 conduct positive half of each ac cycle alternatively. Condenser C1 and C2 act as filter capacitor for smoothening dc supply. resistance R1 act as series filter resistance and R2 act as bleeder resistance.

Diode - Diode is a component use in all electronics circuits. It has two leads named as cathode and anode.It conducts electric current only in one direction that is from anode to cathode.This property of diode make it suitable for use as a rectifier. A rectifier mean a circuit which converts ac current to dc current.All electronics devices and equipment work on dc supply.
   There are  three type of rectification circuit
1. Half wave rectifier
2. Full wave rectifier
3. Bridge rectifier