EST 130 BASICS OF ELECTRONICS ENGINEERING || BIASING OF PN JUNCTION DIODES || KTU

Hi All, Welcome to the 8th lecture of Basic Electronics. Today we are going to discuss about Biasing of a Diode. What is Biasing? Biasing is the process of connecting an external DC voltage or battery to a diode. If we do not apply any external voltage to the diode, there will be no current flow in it. Biasing of a diode is applying a DC voltage across the diode to establish a working condition for the diode. Biasing is the process of applying a DC voltage across the diode to establish a working condition for the diode. Mainly there are two ways of biasing. First one is forward biasing and second one is reverse biasing. We can do forward biasing of a diode or reverse biasing of a diode. First, let us see what is forward biasing of a diode. When we study p-n junction, we have studied about p-region, n-type semiconductor, p-type semiconductor and n-type semiconductor. When they are fused, they form p-n junction or a diode. The carriers in p-region move to n-region. Electrons in n-region move to p-region. As a result, recombination occurs. Immobile ions are deposited in this junction. This is called depletion region. This depletion region is called barrier. A potential is developed through the electric field. This is called barrier potential. If this barrier potential is overcome or if this potential barrier is cancelled, what will happen? Current conduction will occur through this p-n junction. What will happen when current conduction occurs? This barrier will be lost. For that, we connect a DC voltage externally. When external DC voltage is applied to the junction, it is in such a way that it cancels the potential barrier. This permitting current flow is called forward biasing. This process is called forward biasing. What is forward biasing? An external DC source is connected to it. This is the DC source. How to connect this? Positive region of the battery. This big line is positive of the battery. This small line is negative of the battery. Positive region is connected to P region and negative region of the battery is connected to N region. This is called forward biasing. How to connect an external DC source? How to connect this junction? P section is connected to the positive pole of the battery. N section is connected to the negative pole of the battery. This diode is called forward biasing. What will happen when this barrier is reduced? This barrier will be lost. Current conduction will occur through this. When forward bias, the positive poles in the P section are repelled by positive poles of the battery towards the PN junction. What will happen when forward bias? What will be more in P region? It will be holes. Forward biasing means that the holes in P region are connected to the positive charge of the battery. P region is connected to the positive charge of the battery. The charge of the holes is positive. Since it is the same charge, it will be repelled. Since the positive charge is connected here, it will push the holes here. It will push the holes in P region towards the junction. Similarly, the N section of the battery is connected to the negative pole of the battery. The electrons in the N section will be repelled by the negative pole of the battery. The electrons will come to the junction. When the positive poles and electrons in the N region come to the junction, the width of the junction or depletion region will be reduced. Once the forward voltage exceeds the barrier potential, the depletion region will vanish. The depletion region will vanish. The width of the depletion region will be reduced as the voltage increases. Once the forward voltage exceeds the barrier potential, the depletion region will vanish. The junction resistance becomes almost zero. The junction resistance becomes zero. The low resistance path is created at the junction. The current flows through the circuit. The forward current is the current that flows through the circuit. The width of the depletion region will be reduced as the external voltage increases. At the end, the barrier potential will become zero. the current will flow through the p-n junction through a low resistance path. This is called forward current. This is the current shown here. The current from here flows through here. This is an explanation of this. Initially, there is a depletion region here. This is the depletion region. This is the battery junction. This is the depletion region here. This is the depletion region. Positive current of the battery is connected to the p region and negative current of the battery is connected to the n region. This switch is not being used to apply any external voltage. What will happen when the external voltage is applied? The depletion region will be gone. It is possible that the current will flow through that region. This is the process of forwarding the p-n junction diode. Now in reverse biasing, the P region is connected to the negative side of the battery and the N region is connected as positive of battery. We already connected P region as positive of battery and N region as negative of battery. But in reverse bias, P region is connected as negative of battery and N region as positive of battery. What will happen in that case? What will attract the holes in P region? Negative terminal of negative battery will attract. Positive terminal of positive battery will attract the electrons in N region. All the holes in P region will move to N region. All the electrons in P region will move to N region. As a part of that, the width of the depletion region will increase. Potential barrier will increase. This process is called reverse biasing. As we said, when PN junction is reverse biased, the holes in P side get attracted towards the negative terminal of the battery. And therefore, holes move away from the junction. At the same time, electrons or majority carriers in the N section gets attracted towards the positive terminal. Move away from the junction. Thus, the width of the depletion region increases. Majority carriers in P side move away from the junction. Electrons or majority carriers in N side move away from the junction. As a result, current conduction through P side does not occur. Current conduction occurs due to minority carriers. As a result, current conduction occurs due to minority carriers. Minority carriers in P side are electrons. Minority carriers in N side are holes. As a result, holes in N side move away from the junction. As a result, electrons in P side move away from the junction. Minority carrier concentration is very low. The order of this is in micro ampere range. The order of the reverse current produced by minority carrier is in micro ampere range. Generally, micro ampere range is obtained in micro ampere range if it is a diode used in Germany. If it is a diode used in silicon, the value is still less. Reverse saturation current is only in nano ampere range. So, only a very small amount of current is used to produce reverse saturation current. Next, let us look at diode current equation. A diode current equation is an equation that correlates the voltage and current of a diode. You can learn the derivation of I is equal to in higher semester. You can learn the derivation of diode current equation in higher semester of electronics. You can learn this equation now. I is equal to I0 into e raised to V divided by eta VT minus 1. This is the diode current equation. I is diode current. I0 is diode reverse saturation current. V is external voltage. V is external voltage connected to the battery. Eta is a constant. Eta value is 1 in case of Germany. Eta value is 2 in case of silicon. Eta is a constant value. VT is volt equivalent temperature. The equation of VT is KT divided by Q. K is Boltzmann constant. T is temperature. Q is charge. KT by Q is the value of VT. In room temperature, the value of VT is 26 mV. K is the value of Boltzmann constant. Q is the value of electric charge. T is the junction temperature of the diode. This equation relates the voltage and current of a diode. I hope everyone understood this class. In the next class, we will see the characteristics of a diode. Thank you.