Diode and Transistor Concepts PDF

2. Diodes – Basic Diode Concepts Biasing the PN-Junction * Reverse Breakdown: As reverse voltage reach certain value, avalanche occurs and generates large current. Diode Characteristic I-V Curve 1 Diode Testing...

2. Diodes – Basic Diode Concepts Biasing the PN-Junction * Reverse Breakdown: As reverse voltage reach certain value, avalanche occurs and generates large current. Diode Characteristic I-V Curve 1 Diode Testing 2  Application Rectifier Circuits * Rectifiers convert ac power to dc power. * Rectifiers form the basis for electronic power suppliers and battery charging circuits. Half-Wave Rectifier Ideal diodes act as perfect conductor and perfect insulator. Practical diodes ideal cannot act as perfect conductor and perfect insulator. Ideal diode draws no current when reverse biased. Practical diode draws very low current when reverse An ideal diode is a diode with a forward voltage of practical biased. 3 zero that only passes current in one direction. MCQ The forward voltage drop across a silicon diode is about ………………… (a) 0.3 V (b) 3 V (C) 7 V (d) 0.7 V The forward voltage drop across a germanium diode is about-0.3 V 4  Shockley Equation * The Shockley equation to solve for diode current as a function of diode voltage.   vD   i D = I s exp  − 1   n VT   where I s  10 -14 A at 300K is the (reverse)saturation current, n  1 to 2 is the emission coefficient, Ge=1,Si=2 kT VT =  0.026V at 300K is the thermal voltage q k is the Boltzman' s constant, q = 1.60  10 -19 C  vD  when v D  0.1V, i D  I s exp   n VT  This equation is not applicable when v D  0 5 Bipolar Junction Transistor(BJT) Bipolar Junction Transistor(BJT) The transistor is made of two PN junction diode. Types: NPN and PNP The transistor in which one p-type material is placed between two n-type materials is known as NPN transistor. In NPN transistor, the direction of movement of an electron is from the emitter to collector region due to which the current constitutes in the transistor. Such type of transistor is mostly used in the circuit because their majority charge carriers are electrons which have high mobility as compared to holes.  Construction of NPN Transistor The NPN transistor has two diodes connected back to back. The diode on the left side is called an emitter-base diode, and the diodes on the right side are called collector-base diode. Name Size Doping Emitter Between Base and collector- High Base less less Collector Huge Between Base and emitter Working of NPN Transistor The forward biased is applied across the emitter-base junction, and the reversed biased is applied across the collector-base junction. When the forward bias is applied across the emitter, the majority charge carriers move towards the base. This causes the emitter current IE. The electrons enter into the P-type material and combine with the holes. The base of the NPN transistor is lightly doped. Due to which only a few electrons are combined and remaining constitutes the base current IB. The reversed bias potential of the collector region applies the high attractive force on the electrons reaching collector junction. Thus attract or collect the electrons at the collector. Thus, we can say that the emitter current is the sum of the collector or the base current. PNP Transistor PNP Transistor The transistor in which one n-type material is doped with two p- type materials such type of transistor is known as PNP transistor. The PNP transistor has two crystal diodes connected back to back. The left side of the diode in known as the emitter-base diode and the right side of the diode is known as the collector-base diode. The hole is the majority carriers of the PNP transistors which constitute the current in it.  Construction of PNP Transistor The construction of PNP transistor is shown in the figure below. The emitter-base junction is connected in forward biased, and the collector-base junction is connected in reverse biased. r  Working of PNP Transistor The emitter-base junction is connected in forward biased due to which the emitter pushes the holes in the base region. These holes constitute the emitter current. When these holes move into the N-type semiconductor material or base, they combined with the electrons. The base of the transistor is thin and very lightly doped. Hence only a few holes combined with the electrons and follow base path while remaining are moved towards the collector. Hence develops the base current. The collector base region is connected in reverse biased. The holes which collect around the depletion region when coming under the impact of negative polarity collected or attracted by the collector. This develops the collector current. Thus, we can say that the emitter current is the sum of the collector or the base current. Region of Operation of Transistor Region of Operation of Transistor Region of Operation of Transistor  Region of Operation of Transistor Reverse Active Region- Description: In the reverse active region, the emitter-base junction is reverse biased, and the collector-base junction is forward biased. This is the opposite of the standard (forward) active region. Conditions: Emitter-Base Junction: Reverse biased. Collector-Base Junction: Forward biased. *The efficiency of the transistor as an amplifier decreases significantly. Forward Active Region: High current gain, normal operation mode for amplification. Reverse Active Region: Low current gain, less efficient amplification. It is generally not utilized due to the significant decrease in performance compared to the forward active region. Region of Operation of Transistor White board  I1=2 A I2=2 A https://circuitspedia.com/thevenin-theorem-with-solved- examples/ Common base Input Characteristics Discussions Discussions Operational Amplifier (OPAMP)  Operational Amplifier (OPAMP) ❖We can perform addition, subtraction using amplifier. ❖Just by connecting few resistors- It is possible to perform the mathematical operations. Operational Amplifier (OPAMP) Operational Amplifier (OPAMP) Operational Amplifier (OPAMP) Operational Amplifier (OPAMP)