Bipolar Transistor: Structure, Working Principle, and Configuration, Cheat Sheet of Electronics

Download Bipolar Transistor: Structure, Working Principle, and Configuration and more Cheat Sheet Electronics in PDF only on Docsity! DC and AC analysis Be Prepared by: Engr. Jesus Rangcasajo ECE 321 Instructor Terminals Junction >» E— Emitter Two pn Junctions: » B— Base » C - Collector > Emitter-Base Junction > Collector-Base Junction >a 1. Bipolar Junction Transistor > It is a three layer semiconductor device consisting of either two N- type and one P-type layers of materials or two P-type and one N- type layers of semiconductor materials. >a Three Regions of BJT vBase vEmitter B ! : vyCollector Cc >a BJT Structure and Construction Base Collector ce Planar Structure BJT Modes Of Operation > There are two junctions in bipolar junction transistor. » Each junction can be forward or reverse biased independently. > Thus there are different modes of operations: Forward Active. Cut off. Saturation. Mode EBJ CBJ Cutoff Reverse Reverse Active Forward Reverse Saturation Forward Forward Base Base Emitter 4 Collector Emitter } Collector P IN] P N P|} N ATX ATX Forward Reverse Farward Reverse Bias Bias Bias Bias Approximations Values: Emitter and collector currents: Base-emitter voltage: VpE = 0-7V (for Silicon) >a Transistor Currents and Configuration © Common Emitter Configuration <_— I, =I, +l te > The emitter is common to both input (base- emitter) and output (collector—emitter). > The input is on the base and the output is on the collector. I-= a1-+ Icgo where I,p9 = minority collector current lcgo is usually so small that it can be ignored, except in high power transistors and in high temperature environments. Relationship between amplification factors a and B . I I using B=—— , a= l; E and Ip =Ie tT, I I 1 © =J,+£ + -—=1 a a B=aPr+a=(P+)a p a. pet Pa Relationship Between Currents Ic =Plp) In=@+DIp Biasing Determining the proper biasing arrangement for a common- emitter npn transistor configuration. Biasing Transistor Testing Checking the forward- biased _ base-to-emitter junction of an npn transistor Checking the reverse- biased base-to- collector junction of an npn transistor. Open a Q j i fa ‘ ak ™ Higher Lower E Resistance Resistance What will happen to our resistance? Transistor Currents and Configuration Gamma (0) ° the ratio of collector current to the base current . Recall the following basic relationships for a transistor: V op =0.7 V I =(B+)I, Ie =I, >a The DC input establishes an operating or quiescent point Ie (mA) called the Q-point. Saturation \} 10 Ver (V) The Three States of Operation Active or Linear Region Operation > Base-Emitter junction is forward biased > Base-Collector junction is reverse biased Cutoff Region Operation > Base-Emitter junction is reverse biased Saturation Region Operation > Base-Emitter junction is forward biased > Base-Collector junction is forward biased ac input o——_] signal C Fixed bias circuit DC equivalent The Base-Emitter Loop KVL @1 To find: TI, +Vec —IpRg —- Ver = 0 Collector-Emitter Loop + KVL @ 2 : 2 et py \CTr Vee = Veo -IcRe Vee oe Collector current: os = >a I. =BlI, What is the purpose of adding Re — Resistor @ Emitter? Adding a resistor (Re) to the emitter circuit > stabilizes the bias circuit Improved Biased Stability Stability refers to a circuit condition in which the currents and voltages will remain fairly constant over a wide range of temperatures and transistor Beta values. >a Base-Emitter Loop From Kirchhoff’s voltage law: + Vcc -IpRpe - Ver -I-; Rp = 0 Since I, = (6 + II,: Vcc -IpRg -(B+ DIpReE = 0 Solving for I,: Vocc - VBE Ip = — “CE B Rp +(B+DRE Voltage Divider Bias Analysis Re Thevenin Circuit DC Circuit >a Thevenin Circuit Analysis Inserting the Thévenin equivalent circuit E,W I= E TI th" BE v Vee —1e (Ro +Rz) > 5 Rm +(B+DR, Collector-Emitter Loop Applying Kirchoff’s voltage law: Ip Re+ Veg + I'CRe - Voc = 0 + Since I’. =I, and I, =I: Voc I(Re + Rg) + Veg -— Vee =0 Solving for V.;: Vee = Veco — Ic (Re + Re) Emitter Follower (Common Collector) Configuration = t aot tomas | — Ver >The output is taken >a off the emitter terminal. Regions of Transistor Action lo: LOADLINE Vee | : Ri |: ACTIVE ~ a ~ oO ae Ee ~ <_Q-POINT co > ws Z ~ ~ CUT- OFF Vec BREAKDOWN < 0 m Regions of Transistor Action Active region =Base-emitter junction is forward biased and the collector—base junction is reversed biased. "Transistors active operation as an amplifier. Saturation region = Both junctions are forward biased. = Switch on operation for the transistor. Cut off region = Both junctions are reverse biased. itch off operation for the transistor. Loadline and Q-Point Loadline -Is a straight line drawn on the collector curves between’ the cut-off and Saturation points of the transistor. Q-point (Quiescent point ) -Is the operating point of the transistor with the time varying sources out of the circuit. >a Model > an equivalent circuit that represents the AC characteristics of the transistor > uses circuit elements that approximate the behaviour of the transistor. >a Capacitors chosen with very small reactance at the frequency of application — replaced by low-resistance or short circuit. Removal of the de supply and insertion of the short-circuit equivalent for the capacitors. Transistor small-signal ac equivalent circuit Summary: AC equivalent of a network i. Setting all DC sources to zero and replacing them by a= short circuit equivalent 2. Replacing all capacitors by a short circuit equivalent 3. Removing all elements by passed by the short circuit introduced by step 1 and 2 4. Redrawing the network in a more convenient and logical form >a Investigate the re model for CE, CB and CC BJT Common Emitter Configuration | Circuit Design | Pe Equivalent resistance was simply your DIODE RESISTANCE Diode Resistance _ 26mV Tq = Ih 26mV Te = Loop 1: To solve V,, | Bl, I —_ V 50 =1,r, FAN oan V; Vpe I, =(AI, +1, )r, =(B+))i,¥, Ws = (B+1)r, = pr, Zi-Zo Circuit Diagram € o | 0: é Notes: - The more the change in Vce for the same change in Ic, the larger will be the output resistance. Common Base r, equivalent circuit The output resistance ry 1s quite high. typically extend into the megaohm range. (a) Determine ICQ and VCEQ. (b) Find VB, VC, VE, and VBC. r. >47e0 Common Emitter Fixed Bias Configuration Voc Rc Rp 3 I, L; Cc ——|{—e Vo ae B C2 a 7 Zz I Network after the removal of the effects of Ve. G and CG. Common-emitter fixed-bias configuration Phase Relationship Demonstrating the 180°phase shift between input and output waveforms. Pe Determine r,, Z, (with r,=0o), Z, (with r,=0o), A, (with r,=00). Repeat with r,=50 kQ. Let us find first the Common-Emitter Voltage-Divider Bias Vee