Electronics The Eleventh and Twelfth Lectures Seventh week 30/ 1/ 1438 هـ - 3 / 2/ 1438 هـ أ / سمر السلمي

Outline for today Solving the Second homework Chapter 3: Bipolar junction transistor Calculation gain coefficient β and α Calculation Emitter Efficiency coefficient γ The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits I – V Characteristic of BJT in emitter common configuration and load line I – V Characteristic of BJT and his job as Switch

Time of Periodic Exams The third homework The first periodic exam in / 2 / 1438 هـ 7 - 8 , Please everyone attend In her group The third homework I put the third homework in my website in the university homework Due Tuesday 22 / 2/ 1438 H in my mailbox in Faculty of Physics Department , I will not accept any homework after that , but if you could not come to university you should sent it to me by email in the same day

Solving the Second homework

How amplification occurs in the transistor Here also, we deal with npn type and active mode but we now use emitter common configuration . When hole current enters from base, potential reduce between emitter and base (forward bias). If WB the thickness of base is small, we will assume that % 1 of electronic current recombine with hole current in base and 99% of electronic current go toward collector Therefore, output current from collector IC almost 99% higher from base current IB Thus, we can say when a small amount of current enters of IB , it will create high current of IE also of IC because most electronic current go from emitter to collector. We can say IE ≈ IC =

Calculation gain coefficient β and α Gain coefficient α when base common configuration & gain coefficient β when common emitter configuration . We start with gain coefficient β when common emitter configuration , so when we discussed about amplification in this configuration, we mentioned how base current effect on emitter current. thus, gain coefficient β is ratio between collector current &base current When we assume that few recombination in base duo to its small thickness so IE ≈ IC Here emitter current proportional with emitter doping and base current proportional with base doping. therefore, gain coefficient β equal to is ratio between collector doping & base doping Here also efficiency transistor depend on gain coefficient , so when gain coefficient is big , the efficiency transistor is increases

Calculation gain coefficient β and α Gain coefficient α when base common configuration & gain coefficient β when common emitter configuration. However, the Gain coefficient α when base common configuration equal to is ratio between collector current & emitter current We can find relation between gain coefficient β & gain coefficient α Or

Calculation gain coefficient β In the diode, we derive diffusion current density for excess of minority - carriers of electrons and holes Since transistor is as two diodes, diode’s calculation will be the same for transistor’s calculation . current density equal to current per area (the area is the same for 3 part) therefore, for npn And when assume base thickness is small (WB ≈ Ln ) also from previously relation By substitute in gain coefficient this relation is approximately =

Calculation gain coefficient β Final approximately relation for gain coefficient β in npn is Where is time of minority – carriers life in base And is time of transit electrons to base =

Calculation Emitter Efficiency coefficient γ It know as ratio between electronic current (npn) which injection from emitter and total current Since total current is , therefore: In transistor of n+p n type , so IEp < IEn . therefore =

The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits Previously, we discussed about gain coefficient α and β to two of common base configuration & common emitter configuration , respectively. In two cases the equation was Here, we will calculate voltage, current and power gains Av , Ai & Ap respectively for the three common configurations in addition to the characteristics of their circuits. In the three circuits, we will focus at active mode . Aslo, we must remember the equation IE = IB + IC =

emitter common configuration The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits emitter common configuration This circuit is the most important and used in amplifiers for transistor input current is base current & output current is collector current input voltage is Vin & output voltage is Vout . the output signal opposite to input signal ,mean Out of phase with 180o , so it is Inverting Amplifier circuit input resistance Rin is lower duo to forward bias & output resistance RL is higher duo to reverse bias Current gain is Voltage gain is The gain in this circuit less than base common configuration power gain is

base common configuration The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits base common configuration input current is emitter current & output current is collector current input voltage is Vin & output voltage is Vout . the output signal the same to input signal ,mean In of phase , so it is non inverting Amplifier circuit the ratio between output resistance RL &input resistance Rin is higher Current gain is In most case approximate value is one and IB is small, thus IE ≈ IC Voltage gain is power gain is

collector common configuration The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits collector common configuration input current is base current & output current is emitter current input voltage is Vin & output voltage is Vout . the output signal the same to input signal ,mean In of phase , so it is non inverting Amplifier circuit input resistance Rin is higher & output resistance RL is lower in the circuit input voltage contact direct to base while output voltage is taken from load resistance Current gain is Voltage gain is Always is less than one duo to power gain is

The calculation of gains of voltage, current & capability to three contact methods for BJT’s circuits Characteristic Common Base Emitter Collector Input Impedance Low Medium High Output Impedance Very High Phase Angle 0o 180o Voltage Gain Current Gain Power Gain

I – V Characteristic of BJT In chapter two, we study I – V Characteristic of diode in lecture and Lab, so we know about proportional relation in addition to load line. Also, in this chapter we will study I – V Characteristic of BJT and its calculation and duo to different contact methods, there will be different curves , however, the relation always proportional I – V Characteristic emitter common I – V Characteristic base common

I – V Characteristic of BJT in emitter common configuration and load line we will deal with emitter common configuration to see relation between IC & VCE 1- we notice that IC increases rapidly by change VCE at beginning in region called Saturation Region. Than, The increase becomes very slow unnoticed which consider as constant in region called Amplification Region or Active Region. 2- when we change IB , IC will also change duo to input voltage (means that IC control by IB) 3- the third region called Cut Off Region which is region under current value IB =0

I – V Characteristic of BJT in emitter common configuration and load line 4 - load line will cut y- axis Saturation point (S –point) and x- axis cut off point (C –point) 5- at operation point (Q- point) cut of load line with I – V Characteristic load line equation 6- from equation and figure, we notice cut off point when IB =0 & IC =0 thus VCE = VCC Saturation point when VCE =0 thus The mean operation point is )

I – V Characteristic of BJT and his job as Switch we can describe job’s BJT as switch 1- Saturation Region: which represent an close switch (Fully-ON) input voltage and base contact with VCC VBE > 0.7V the maxim value of collector current The two junction at forward bias ideal Saturation at VCE =0

I – V Characteristic of BJT and his job as Switch we can describe job’s BJT as switch 2- Cut Off Region : which represent an close switch (Fully-OFF) input voltage and base contact with grounded 0V VBE < 0.7V The two junction at reverse bias There no current flow to collector IC = 0