PN junction
When a P-type semiconductor is joined to an N-type semiconductor, the junction is formed which is called the PN junction. The PN junction leads to the invention of diode transistors and Integrated circuits (I.C).
Depletion region and potential barrier
When the p-type semiconductor is joined with an N-type semiconductor charge carrier diffuses as spreads from the high concentration region to the low concentration region. so the free electrons from N-region diffuse into P-region and combine with the hole to get neutralized. Similarly, the holes from the P-region diffuse into the N-region and combine with electrons to get neutralized
The P-region near the junction is left with an immobile negative charge and the N-region near the junction with an immobile positive charge due to the electron-hole recombination. so, a thin layer around the junction becomes depleted of the free charge carrier. This region is called the depletion region.
Due to the presence of different charges near the junction, a potential difference is established with percent further diffusion of charge this potential is called barrier potential.
Semiconductor diode (P-N junction diode)
A device forward by connecting P-type semiconductor with N-type semiconductor called P-N junction diode. It has two terminals namely an anode and cathode. Anode refers to the p-type region and cathode refers to the N-type region the symbolic representation of the P-N junction diode is given below
Biasing of P-N junction diode
The process of applying a potential difference across the P-N junction diode for its operation is called biasing of the P-N junction. Depending upon the connection of the P-N junction diode with an external battery, there are two types of biasing.
1. Forward biasing
2. Reverse biasing
1. Forward biasing
A diode is said to be forward biasing if its p-side is connected to the positive terminal and N-side is connected with the negative terminal of the battery.
Fig: Forward biasing
In forward biasing the positive and negative terminal of the battery repels the hole towards the free electron towards the Junction these free electrons and holes at the junction combine with each other which reduces the width of the depletion region hence the potential barrier, also decreases so in forwarding biasing current will flow.
Its Characteristics
Characteristics of a junction diode are:
The graph shows the relation between bias voltage and circuit current of a Junction diode called Characteristics of a Junction diode. Its type is;1. Forward bias characteristics
2. Reverse bias characteristics
1. Forward bias characteristics
It is a graph showing the variation of circuit current with forwarding biasing voltage. The forward voltage is gradually increased. In steps and corresponding millimeter reading is noted. A graph is plotted then between voltage and current. Practically current doesn’t flow until the forward voltage across the barrier potential. When a forward voltage is greater than barrier potential the current increases rapidly known as knee voltage.
2. Reverse bias characteristics
It is a graph showing the variation of circuit current with negative biasing voltage is gradually increased in steps and corresponding microammeter readings are noted. If the graph is plotted between voltage and current then at one point current is rapidly increased. This voltage when the current rapidly increases called the breakdown voltage.
Rectifier
A device that is used to convert ac into dc is called a rectifier and the process of conversion of ac into dc is called rectification.
When the P-N junction is forward biased it offers low resistance hence current will flow through it. But reverse biasing have high resistance and no current will flow. This property of the P-N junction is used for the rectifier.
There are two types of rectifiers1) Half wave rectifier
2) Full wave rectifier
Full-wave rectifier
It is a device that is used to convert that full cycle of AC into DC. There are two types of full-wave rectifiers. They are
a) Central tapped full wave rectifier
b) Bridge Rectifier
a) Central tapped full wave rectifier
It is a rectifier that converts the full cycle of AC into DC. The circuit diagram of the full-wave rectifier is shown in the figure below in which the AC is applied across the primary coil of the transformer and the secondary coil is connected to the diodes D1 and D2. The load resistance R2 is centrally tapped from the middle of the secondary coil.
.png "Central tapped full wave rectifier")
Fig: Center tapped full wave rectifier
During the positive half cycle, A is positive & B is negative so is the diode.
D1 ---> Reverse ( Does not conduct current)
D2 ---> Forward (Conduct current)
The current flow is D2
the waveform of input and output voltage is
Fig: Output and Input voltage in a central tapped full-wave rectifier
b) Bridge Rectifier
A Bridge rectifier is a rectifier that converts the full cycle of ac into DC. It consists of 4 diodes D1, D2, D3, and D4 in form of a Wheatstone bridge. The AC input is applied across the primary coil of the transformer and the ends of the secondary coil are connected to the two opposite ends A and C of the Wheat stone bridge network and load resistance R is connected across the two remaining ends B and D is shown in the figure below:
Fig: Circuit diagram of the bridge rectifier
During the positive half cycle: A becomes positive & B becomes negative so diodes
D1 and D ---> forward (conductor current)
D2 and D4 ----> Reverse (not conductor current)
The current flow through AD1BRLDD3CA
During the negative half-cycle: A becomes negative B becomes positive then diodesD1 D3---> Reverse (conductor current)D2 D4---> forward (not conductor current)
The current flow through CD2BRLDD4AC
In this way in both cycle unidirectional current flow through load resistance so the bridge rectifier acts as a full-wave rectifier.
The waveform of input and output voltage in the case of the bridge rectifier is shown in the figure below,
Logic gate
An electronic circuit that gives a logical decision as an output signal due to the result of one or more inputs is called a logic gate. A logic gate has one or more inputs but only one output. The input and output states are on and off i.e. on for 1 and off for 0.
1) OR gate
A logic gate is said to be an OR gate if the high (1) output obtained for one or more of its inputs is high (1). If A and B are two inputs for the OR gate then a logic symbol of the OR gate is given by,
| input | output | |
|---|---|---|
| A | B | Y = A+B |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
2) AND gate
| input | output | |
|---|---|---|
| A | B | |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
3) NOT gate
It is a single input and single output gate whose output is high if its input is low and vice-versa. Its symbol is
| input (A) | output (y = A) |
|---|---|
| 0 | 1 |
| 1 | 0 |
4) NAND gate
| input | output | |
|---|---|---|
| A | B | Y = A.B |
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
5) NOR gate
| input | output | |
|---|---|---|
| A | B | Y = A+B |
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
NAND gates as universal gates
The NAND gate is a universal gate because from if all other gates are formed.
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i think pdf ko print mode on garnu vako vaye hunthyo tapailey ,sajilo hunthyo print garera padna ,hajur ko water mark ni xa so i don't think copyright issue hunxa...anyways thank you for the notes daiii...been following most of your notes to complete my notes
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