Pn junction diode electronics club basic electronics. Such pn junctions are called zener diodes and are used as voltage references or overvoltage protectors in electrical cir. Oct 10, 2017 mar 15, 2020 forward and reverse biasing class 12 notes edurev is made by best teachers of class 12. The process of applying the external voltage to a p n junction semiconductor diode is called biasing. The p n junction is a versatile element, which can be used as a rectifier, as an isolation structure and as a voltagedependent capacitor. There are three biasing conditions for p n junction diode and this is based on the voltage applied. The p n junction is the fundamental building block of the electronic age. A zener diode when forward biased behaves like an ordinary p n junction diode. It is a twoterminal device which conducts current only in one direction. If you have done upto this, the forward bias circuit of pn.
Forward biasing is when voltage is applied across a p n junction in the forward direction, according to. A large current drives the diode to behave in a way that beyond the ideal pn junction diode theory. Zero bias is the condition of the diode without any external supply. The forwardbias and the reversebias properties of the pn junction imply that it can be used as a diode. Such junctions show a pronounced rectifying behavior. This type of forward characteristic shows that resistance is not constant during the operation of the pn junction. Forward biased pn junction when we connect ptype region of a junction. A p n junction is the metallurgical boundary between the n and p regions of a semiconductor crystal. The diode conducts current in only one direction, and it is made by joining a ptype semiconducting layer to an ntype semiconducting. External voltage to the p n junction diode is applied in any of the two methods. Not all of the applied voltage is dropped across the depletion region when series resistance is taken into consideration.
Jul 31, 2017 in this physics digital electronics video lecture in hindi for class 12 we explained forward and reverse bias in p n junction diode in terms of depletion layer and potential barrier. A diode pn junction in an electrical circuit allows current to flow more easily in one direction than another. Forward biasing a pn junction diode is very simple. In forward biasing of p n junction a very small amount of current will pass from the junction until the forward voltage crosses the value of junction barrier potential i. If the average forward current exceeds its value the diode gets over heated and may be damaged. The forward bias means the positive region is connected to the pterminal of the supply and the negative region is connected to the ntype of the device.
In forward biased pn junction diode, the positive terminal of the battery is connected to the ptype semiconductor material and the negative terminal of the battery is connected to the ntype semiconductor material. To find cutin voltage for silicon pn junction diode. Likewise, different voltage v 2 across this same diode a diode of course results in a different current i 2. Aug 14, 2019 here the biasing voltage, width of the depletion region based on biasing and the current generated in the circuit are related to the general characteristics of the pn junction diode.
Animation p n junction semiconductor works forward. P n junction diode is a device which conducts when it is forward biased and does not conduct when it is reverse biased. In forward biasing the external voltage is applied across the pnjunction diode. Over this reverse voltage diode will go for breakdown due to its. Biasing of p n junction semiconductor diode the process of applying the external voltage to a p n junction semiconductor diode is called biasing. Forward bias is the condition that allows current through the pn junction. Working of pn junction diode with biasing, characteristics. There is no external voltage applied to the p n junction diode. It is acting as normal diode while forward biasing. If the p n junction diode is forward biased, it allows the electric current flow. Hence, very small electric current flows in the p n junction diode. Forward biased pn junction diode free online tutorials. An external voltage which decreases the potential barrier is said to act in the forward bias direction. A pn junction diode allows electric charges to flow in one direction, but not in the opposite direction.
The biasing conditions of pn junction s diode clearly state that during forward bias the diode is in conducting mode acting like a closed circuit. Feb 21, 2019 in this physics video in hindi we explained forward biasing and reverse biasing of a p n junction diode with vi characteristics for class 12. Pn junction diode explained forward bias and reverse bias. Pn junction diode baising and its vi characteristics. Apr 07, 20 thus the p n junction diode allows the electrons flow only when p is positive. Forward diode capacitance zwe have already seen that a reverse biased diode acts like a capacitor since the depletion region grows and shrinks in response to the applied field. Pn junction diode, characteristics and applications 2020. Consider a forward biased pn junction showing the change in concentration. P n junction forward bias condition is used in all led lighting applications.
This leads to our discussion of diodes, in the next section. They are also called pn diodes in analogy with vacuum diodes. Or reversed bias meaning the diode voltage polarity are revered or cut off, depends on the diode but it will leak some current. A pn diode is a type of semiconductor diode based upon the pn junction. In case of a p n junction there are two bias conditions. But this is possible only in case of an ideal diode. The basic diode structure and symbol of pn junction diode is shown in the figure below. Whereas during reverse bias the diode is in nonconducting or acting as an open circuit. A a diode has two state either on forward conduction. If a current is flowing in the same direction as the pn junction diode called forward bias, then things will work smoothly with the positive holes. Pn junctions consist of two semiconductor regions of opposite type.
This note explains the concept and working of p n junction diode. The p n junction is a versatile element, which can be used as a. Forward biased pn junction diode physics and radioelectronics. When forward biased, the barrier resistance is decreased, and a larger electron current flows. P n junctions consist of two semiconductor regions of opposite type. By applying an external voltage v we can vary the potential barrier. Under no voltage or unbiased condition, the p n junction diode does not allow the electric current. Oct 10, 2019 when the p type semiconductor material is joined with the n type semiconductor material, a p n junction is formed, hence resulting p n junction is also called as a p n junction diode. Biasing a diode means applying voltage to it so that charges inside it can be made to move towards a particular direction. The same number of minority carriers are being swept. It is the forward biased current due to the drift electron flow or the majority carriers. And the working of this pn junction diode under forward and reverse bias has been. The direction of external voltage applied in reverse bias is opposite to that of external voltage applied in forward bias. A pn junction diode is one of the simplest semiconductor devices around, and which has the characteristic of passing current in only one direction only.
Dec 04, 2019 the bias a diode, you apply a dc voltage across it. It has a particular voltage known as break down voltage, at which the diode break downs while reverse biased. Under no voltage or unbiased condition, the pn junction diode does not allow the electric current. A significant deviation of current behavior occurs when the applied forward bias is close to v bi. Forward biasing means putting a voltage across a diode that allows current to flow easily, while reverse biasing means putting a voltage across a diode in the opposite direction. In this video, the pn junction diode has been explained. Diodes 2 in simple terms, a diode is a device that restricts the direction of flow of charge carriers electrons in this class 1.
A zener diode conducts excellently even in reverse biased condition. Forward and reverse bias of pn junction explained electrical4u. A reverse bias does just as the name suggests, reversing the flow of the current through the diode. Zener diode is a p n junction diode specially designed to operate in the reverse biased mode. When the p n junction is reverse biased, the barrier resistance is increased, so little or no electron current flows. The value of forward current is directly proportional to the external power supply and inversely proportional to the internal resistance of the junction diode.
Image source forward biasing a pn junction diode is very simple. Working of pn junction this simple pn junction animation video clearly explains the topics pn junction semi conductor or diode, what is forward bias and reverse bias, what is diffusion current. This article provides a more detailed explanation of pn diode behavior than that found in the articles pn junction or diode. Silicon a single silicon atom consists of fourteen negatively. The figure above represents the symbol for p n junction diode, which symbolizes the direction of the current. The forward voltage, at which the current pass the p n junction starts very quickly, is called knee voltage or the cut in voltage.
If the external forward voltage applied on the p n junction diode is increased from zero to 0. Zero bias no external voltage potential is applied to the pn junction diode. It is the reverse biased havily doped silicon or germanium p n junction diode which is operated in the breakdown region where current is limited by both external resistance and power dissipation of the diode. The behaviour of the pn junction with regards to the potential barriers width produces an asymmetrical conducting two terminal device, better known as the pn junction diode. Oct 03, 2017 forward biased means connecting positive terminal of supply to diodes positive and negative terminal of battery to negative terminal of diode,in this case depletion region between p and n region becomes smaller and diode act as switch reverse bia. You just need to take a battery whose values can be varied from o to v volts, connect its positive terminal to the p side of pn junction diode and then connect the negative terminal of battery to the n side of the pn junction diode.
This voltage cancels the potential barrier and provides the low resistance path to the flow of current. Applying forward bias to the pn junction diode causes a low impedance path for the junction diode, allows for conducting a large amount of current known as infinite current. Silicon is preferred to diode because of its higher temperature and current capability. The basic difference between a forward bias and reverse bias is in the direction of applying external voltage. Apr 05, 2019 the forward characteristic of a pn junction diode is non linear, i.
The pn junction is a versatile element, which can be used as a. An ideal p n junction diode does not conduct in reverse biased condition. A dc voltage source connected by a conductive material contacts and wire across a diode in the direction to produce forward bias. They are also called p n diodes in analogy with vacuum diodes. The slope of the forward characteristic of a pn junction diode will become very steep quickly. Automatic switch when the diode is forward bias,the switch is closed. This shows that resistance is very low in forward bias of the junction diode. This document is highly rated by class 12 students and has been viewed 1436 times. Pn junction diode vi characteristics in forward and reverse bias. There are two operating regions and three possible biasing. In the case of normal diodes the diode damages at the break down voltage. This property is used for the conversion of ac into dc,which is called rectification 23. In the image above, you can see that an external voltage is applied across the semiconductor diode where the p side of the diode is connected to the positive terminal and the n side is connected to the negative terminal of the battery.
The positive terminal of the voltage potential is connected to the p type while the negative terminal is connected to the n type. When an external voltage source is applied to p n junction diode, it is called diode biasing. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the p n junction. Forward and reverse biasing describe the ways in which current flows through p n junctions. Semiconductor diode forward bias and reverse bias byjus. These diodes operate at a precise value of voltage called break down voltage.