NAME: NIDHI PARMAR ENR.NO.: GUIDED BY: RICHA TRIPATHI

 A bipolar transistor is a semi-conductor device that acts as a variable resistor  Applications  Amplifiers  Voltage and Current Regulators  Electronic Switches Made up of three alternating layers, which form two P-N junctions. Emitter: heavily doped region that supplies majority current carriers. Base: Thin and lightly doped region that controls current flow through the transistor. Collector: Large, lightly doped region used to collect current carriers from emitter.

BJTs – Basic Configurations Fluid Flow Analogy Difference between FET (field effect transistor) and BJT Technology of BJTs pnp BJT npn BJT

 Construction drawing can be simplified as a “sandwich” of semiconductor materials.  Can be either NPN or PNP transistor  Schematic Symbol: Arrow always points between base and emitter  Direction designates type ▪ NPN = Not Pointing iN ▪ PNP = Pointing iN Properly  Also points in direction of conventional current flow Collector Base Emitter Collector Base Emitter

 Base to Emitter Junction (V BE )  Forward biased for majority current carriers to flow from emitter to base, where they become minority carriers  Base to Collector Junction (V BC )  Reverse biased to allow minority current carriers from the emitter flow from base to collector Q1Q1 Base Emitter Collector V BE V BC

How does I C vary with V CE for various I B ? Note that both dc sources are variable Set V BB to establish a certain I B

 With the Base to Emitter Junction forward biased, majority current carriers flow from emitter to base, where they become minority carriers  This is emitter current (I E )  Since the base is thin and lightly doped, very few current carriers recombine in the base  This is base current (I B )  The rest of the current carriers are swept across the base to collector junction  This is collector current (I C ) NN P E B C IEIE Conventional Current Flow Electron Current Flow IBIB ICIC

 Base to emitter junction is forward biased  Low resistance, so small  in V BE causes a large  in I E  The base is thin and lightly doped  Few current carriers recombine to form more base current  I B  only slightly  The rest of the current carriers are swept across the base to collector junction  I C  greatly NN P E B C

 Current Relationships  Emitter current equals base current plus collector current  Alpha (α): Ratio of Collector Current to Emitter Current ▪ Typically 0.95 – 0.98  Beta (β): Ratio of Collector Current to Base Current ▪ Ranges from 40 to >100 depending on application  Gamma (γ): Ratio of Emitter Current to Base Current ▪ Slightly greater than β

 Typical Characteristic Curve  Shows relationship between I B, I C and V CE  I C relatively constant for a given V CE  I C dependant on I B  Saturation  I C no longer increases for an increase in I B ▪ I C is maximum ▪ V CE is minimum (V CE ≈ 0.2VDC)  “ON” state when used as a switch  Cutoff  Transistor not biased to conduct ▪ I B, I C, I E = 0A ▪ V CE is maximum for circuit  “OFF” state when used as a switch Saturation Cutoff

 Load Line  Straight line drawn between saturation and cutoff, representing range of operating points  Quiescent Point (Q-Point)  The steady-state values of I B, I C, and V CE with no AC input applied  Determined by circuit design Saturation Cutoff Q-Point Load Line

 Emitter is “common” to both input and output  Input applied to base to change V BE  Output taken from collector  Gain  Medium voltage gain and current gain  High power gain  Impedance  Medium input and output impedance +V CC RBRB RCRC V out V in Q1Q1 C1C1 IBIB ICIC IEIE

 Positive Half Cycle  V in  (+)  V b  (+)  V be   I b, I c, I e   V RC   V c  (+)  V out  (+)  Negative Half Cycle  V in  (-)  V b  (+)  V be   I b, I c, I e   V RC   V c  (+)  V out  (+)  Output is 180° out of phase with input +V CC RBRB RCRC V out V in Q1Q1 C1C1 IBIB ICIC IEIE

 Positive Half Cycle  V in  (+)  V b  (+)   V be   I b, I c, I e   V RC   V c  (+)  V out  (+)  Negative Half Cycle  V in  (-)  V b  (+)   V be   I b, I c, I e   V RC   V c  (+)  V out  (+)  Output is 180° out of phase with input V C / V out VBVB V in t t V E / GND