PN junction diode biasing of diode VI characteristics zener diode
P-N junction: -
If P-type and N-type semiconductor are mixed together then the P-N junction is formed. In fact, the P-N junction is not formed from two separate pieces, P-N junction is also called the P-N junction diode.
Symbol of the diode:
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| PN junction diode |
Depletion layer: -
When P and N are mixed together, the large no. of holes moving from p-side to n-side and large no of electron move from n-side to p-side. Due to the recombination of holes and electron, a layer is formed. This layer is called the depletion layer. After the Depletion region is formed, the p and N side holes and electrons cannot cross the depletion layer to be recombined among them. Only negative ions remain in the depletion area of the P side, whereas + ve ion remains in the area with n sides.
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| depletion layer of PN junction layer |
Potential Barrier: -
In the PN junction, there is a negative charge due to -ve ions in the depletion area of P side, whereas in the area of N side + ve ions cause a positive charge, hence due to the opposite charge on either side, in the junction The electrical field gets reduced. This sector is called the potential barrier. Potential barrier, only due to stable ions. There are no moving charges (electron or hole). Therefore, the Potential barrier is also called space charge. The value of the potential barrier in Silicon is 0.7volt, whereas for Germanium it has a value of 0.41volt. (Depletion area should be between a P and N between a very low voltage small battery, whose plate is negative and the second is positive, But the stream does not flow between the two.)
Knee Voltage: -
In the forward bias, the voltage at which the current of the diode starts to move rapidly, the voltage is called the knee voltage.
Type of current: -
Semiconductors have two types of current flows.
1) - Drift current: -
Leaving electrons or holes in their place and moving to the place of another electron or hole is said to be drift, and the flow of this type is called Drift current. Normally the stream is flowing in the same way. The direction of the flow of electrons in the drift current is in contrast to the direction of the flow of the holes.
2) - Diffusion current: -
At the time of doping in semiconductors, holes become more in some places and some places have a low density of holes. Because of which the holes tend to flow towards the region with less density than the area with higher density. This stream due to the holes is not caused by any charge or aided area. Hence this type of current is called Diffusion current.
Biasing of P-N junction Diode: -
The method of connecting the P-N junction with a static circuit is called biasing. Biasing happens in two types.
1 Forward Biasing: -
in the forward biasing, the P-N diode is connected to a battery. The P side of the diode is connected to the positive terminal of the battery, whereas the N side is connected to the negative terminal of the battery. The potential barrier value is very low in PN junction, so the barrier ends with a slight voltage. (When the voltage given by the battery is equal to the voltage of the potential barrier, then the potential barrier is finished.) After that, free electrons of the N side easily move into the P side. N side continuously supplies electrons from the negative terminal of Battery. Similarly, Hole of P side also easily crosses the N side and goes towards the negative terminal of the battery. P side continuously supplies the supply of Holes from the positive terminal of Battery. After the expiry of the potential barrier, the volume of the stream increases very rapidly even though the slight voltage increase. |
| PN junction diode in forward bias |
Reverse Biasing: -
In the reverse biasing, the P side is connected to the negative terminal of the battery and the N side is connected to the positive terminal of the battery. When applying the voltage, all the holes of the P side are attracted towards the negative terminal of the battery, whereas all the electrons of the N side are attracted to the positive terminal of the battery. In this way, due to the power of the power in the opposite direction, the width of the potential barrier becomes even more. Due to this, the majority carrier cannot cross the P-N junction, so there is no stream flowing due to the majority of carriers. But the P side's minority carrier (due to some bond breakdown, some electrons are produced) easily cross the junction and move to N side. Similarly, the N side's minority carrier (due to breakage of some bonds, the hole made in N side) crosses the junction and moves into P side. Thus, due to the minority carriers of both sides, the flow of very small amounts continues to flow. This section is called Reverse Leakage current. If the voltage is continually increased in the reverse bias on the P-N treaty, then the value of the stream increases very rapidly, on a voltage. This value of the voltage in the reverse bias is called break down voltage and this is called Avalanche Breakdown. Due to having too much reverse voltage on the breakdown, the bonds of the junction atoms of the joints begin to break very fast, and a large amount of minority carrier starts growing. |
| PN junction diode in reverse bias |
Zener Breakdown: -
If PN diodes are made by a lot of doping, then when the reverse bias is applied on the diode, the reverse breakdown becomes very low voltage. This type of breakdown is called Zener Breakdown, and this type of diode is called Zener Diode. Generally, in the Zener diode, there is a breakdown in less than 6 volts. A zener diode is used in the reverse bias. |
| zener diode |
Applications of Zener diode: -
Zener diode plays an important role in voltage regulation. It is used in parallel in circuits, where fixed DC voltage is desired.V-I Characteristic of P-N junction diode : -
For forward bias, connect the P side of the P-N diode to the +ve end of the battery and connect the N side to the –ve end of the battery. To control the voltage applied to the diode by the diode, there are variables in the circuit. (Variable resistance is to reduce the voltage applied to the PN junction diode.) For measuring the voltage and current, a voltage meter and an ampere meter are also installed in the circuit. Now the voltage is gradually increased on the diode. As long as the voltage applied on the diode is not equal to the potential barrier of the diode, no stream flows in the circuit, and the amplitude Meter shows the reading. But as soon as the voltage is more than the voltage of the potential barrier, the value of current starts increasing rapidly. After this, the volume of the stream increases very rapidly even after slightly increased voltage.
In the circuit of the reverse bias, the diode's position is the opposite. Now the P side of the diode is connected to the end of the battery - and the N side + ends. As soon as the voltage is applied on the diode, the very small volume stream starts flowing in the circuit. This stream flows due to the minority carrier, and it is called reverse leakage current. Increasing the volume of voltage increases the flow of excessive streams in the circuit. This section says Avalanche break down. In this situation, ordinary diodes are destroyed by burning.
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| VI characteristics of PN junction diode |
The capacitance of diode (P-N diode capacitance): -
P-N junction consists of + holes on the P side, while on the N side there are -electrons. Depletion layer acts as a dielectric between the two. Therefore, in the diode the opposite charge is stored at both ends, causing the P-N diode to act as a capacitor. P and N sides of the diode behave like two plates of capacitors. The higher the cross-sectional area (A) of P and N, the higher the capacitance (C) and the greater the width (d) of the depletion layer, the lower the value of C.So C = Ô‘A / d where Ô‘ = semiconductor's superficiality.
Parameters of PN diode: -
A diode has three main parameters.
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