Transistor

Transistor is the crystal which three doped crystal like N P and N.

There are mainly three terminal they are

a)Emitter(E)

It is heavily doped part of the transistor.Its main task is to carry majority charge carrier. It denoted by symbol E.

b)Base(B)

Middle part of transistor called base.It is very thin part of its.As compare to other region it is 10^-6m thin. Its main task is to pass the majority charged carrier from emitter to collector.It is very lightly doped to minimized the reunion of free electron and holes. Its denoted by the symbol B.

c)Collector(C)

It is the last or third region of the transistor. It is moderately doped region. Its task is to collect the majority charge carrier endow by emitter and pass through base. Mainly this region is physically larger than other region because to evaporate the greater heat generated in the collector.

There are two type of transistor they are:-

1)N-P-N Transistor
It is the transistor formed by growing a thin layer of p type crystal between two layer of N type crystal. In the NPN Transistor free electron are the majority charge carrier in the emitter and collector in other hand holes are the majority charge carrier in the base.

Working process of N-P-N Transistor

The circuit diagram of NPN transistor is shown in figure. Here battery VBE acts as forward bias and reverse bias by battery VCB to the transistor. When collector base junction is forward bias then VBE>0.7V for silicon and 0.3V for germanium. Then hole act majority charge carrier in N type flow from emitter  toward the P type base resulting the flow of current through the emitter known as emitter current Ie. The base is thin and likely doped as compared to emitter and collector. Thud 5%of the hole recombined with the electron in the base region resulting the flow of current through the base known as base current Ib.The majority of hole 95% enter into the collector region. The flow of this electron in the collector region called collector current Ic. The electron in the collector region attract toward the positive terminal of the battery VCB and recombined at the same time and equal number of electron entre the emitter regions from the negative terminal of the battery VBE.

2)P-N-P Transistor

It is the exactly opposite to the NPN transistor. We have already learn the function or working process of  NPN transistor. It is the transistor formed by growing of thin layer of N type crystal between two P type of crystal.In the PNP Transistor free electron are the majority charge carrier in the base in other hand holes are the majority charge carrier in the collector and emitter.

Working process of P-N-P Transistor

We have already said that it is exactly opposite to the NPN transistor,The circuit diagram or figure also clearly show that. The circuit diagram of PNP transistor is shown in figure. Here battery VBE acts as reverse bias and forward  bias by battery VCB to the transistor. When collector base junction is reverse bias then VBE>0.7V for silicon and 0.3V for germanium. Then hole act majority charge carrier in P type flow from emitter  toward the N type base resulting the flow of current through the collector known as collector current Ic. The base is thin and likely doped as compared to emitter and collector. Thud 5%of the hole recombined with the electron in the base region resulting the flow of current through the base known as base current Ib.The majority of hole 95% enter into the emitter region. The flow of this electron in the emitter region called emitter current Ie. The electron in the emitter region attract toward the positive terminal of the battery VCB and recombined at the same time and equal number of electron entre the collector regions from the negative terminal of the battery VBE.

Rectifier

An electrical circuit which converts the AC current into DC current.Such process is known as rectification.There are two type of rectifier i.e

1)Half wave rectifier

2)Full wave rectifier

1)Half wave rectifier

Rectifier which rectified only half of its AC current to DC. Output is obtain only during alternating half cycle of input AC current.

Working process of half wave rectifier

Its working is based on the fact that the resistance of p-n junction become low when forward bias and become high when reverse bias.

The circuit diagram of half wave rectifier is shown in figure. Its consist of a Transformer a p-n junction diode 'D' and the load resistance 'RL'. The primary coil of the transformer is connected to the AC mains and the secondary coil is connected to the load resistance RL through the diode D. The DC output is drawn from the load resistance RL. During the positive half cycle of secondary voltage the diode D is forward bias therefore the current flow through the diode and the load resistance hence diode conduct easily.Similarly during half cycle of secondary voltage the diode act as reverse bias therefore there is no conduct of current through diode and load resistance. In this way half wave rectifier works.

2)Full wave rectifier

The rectifier which rectified full of its AC current to DC voltage.Output is obtained during both half cycle of its AC supply input. There is two type of full wave rectifier.

a)Center tapped full wave rectifier

Rectifier which rectified full of AC input to DC output by using two diode connected to the center tapped secondary coil of the transformer and load resistance 'RL'.

fig:a

fig:b

Working process of center tapped full wave rectifier

We have already discuss about full wave rectifier. It is based on the fact that the resistance of P-N junction becomes low when forward bias and become high resistance when reverse bias.

The circuit diagram of a full wave rectifier is shown in figure. The diode (D1 and D2) are connected to the center tapped secondary coil of the transformer and the load resistance (R) in such a way that the diode conduct during alternate cycle of the input AC supplied.

During positive half cycle of secondary voltage upper diode D1 is forward bias and lower diode D2 is reverse bias. Thus the current flows through diode D1 and load resistor R. During negative half cycle of secondary voltage upper diode D1 is reverse bias and lower diode D2 is forward bias. Thus the current flows through diode D2 and load resistor R.Here the half wave of input AC supplied Vin is rectified by one diode D1 and the next half wave is rectified by diode D2. Fig(b) show the rectified output voltage Vout obtain across the load resistor R for the supplied input AC voltage. The current flows through R are the same direction for both half cycle. Thus the output current through the load is said to be direct current.

b)Bridge rectifier

Rectifier which rectified full of AC input to DC output by using four diode connected to form a bridge.

Working process of bridge rectifier

Its working is based on the fact that the resistance of p-n junction become low when forward bias and become high when reverse bias.

The circuit  diagram of bridge rectifier  is shown in figure it consist of four diode D1,D2,D3 and D4 connected to form bridge. the input of acis applied across the primary coil  of the transformer the end of the secondary coil are connected to the two opposite end and the b and d are connected to the load resistance .The voltage drop across the load resistance give the output voltage.

When an AC input is applied to the primary coil of the transformer the voltage induced in the secondary coil .During positive half cycle of the secondary voltage suppose one end X of the secondary coil 'S', is positive and its other end Y is at negative. Then the diode D4 and D2 is forward bias and D1 and D3 are reverse bias. D2 and D4 conduct current through the load resistance and D1 and D doesn't conduct current.Again during the negative half cycle of secondary voltage suppose one end is Y at positive then the diode D2 and  D4 act as reverse bias so it doesn't conduct current but diode D1 and D3 act forward bias so they conduct current through the load resistance .In both cycle the current through cycle the AC input supplied is rectified full input dc. This way bridge rectifier work.

Diode

fig; symbol of diode

A diode is a  electronic component having two terminal and of low resistance that conducts current in single direction.But it have opposite nature to opposite direction i.e high  resistance in the another direction. A semiconductor diode, the most common type diode which are mostly used in our daily life equipment.It is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals.

Diode are mostly made up of silicon and germanium.

There are many type of diode some common diode which are used in our daily life are 

1)PN junction diode

2)Zener diode

3)Tunnel diode

4)Schottky diode

5)Varacfor diode

1)PN junction diode

When p type of semiconductor is join with a n type of semiconductor so as to form one piece ther assemble so obtain known as p-n junction diode or simply junction diode. Holes are the majority charge carrier and electron are the minority charge carrier in p type of crystal and simirally in n-type of crystal the electron are majority charge carrier and holees are minority charge carrier.

 2)Zener diode

It is a reverse bias strongly doped silicon or germanium p-n junction diode which is used in the breakdown rregion where current is limited by for external resistance and dispassion of diode. Its is mainly used in breakdown region in reverse bias condition so that its also known as breakdown diode.