ME 6405 Student Lecture: Transistors Ryan Akin Xin
ME 6405 Student Lecture: Transistors Ryan Akin Xin Chen Will Dahlin Thursday October 6, 2011 Georgia Institute of Technology Presentation Outline 1 Introduction to Transistors 2 Transistor Types and Checks 3
Bipolar Junction Transistors 4 Field Effect and Power Transistors 5 Transistor Part Numbers and Catal Ryan Akin Ryan Akin Xin Chen Will Dahlin Will Dahlin
Introduction Transistors to Definition & Fundamental Need Brief History Transistor Role in Modern Electronics Two Basic Transistor Functions Doping process and its effects on function Transistors Transistors of various type
& size BJT (PNP) Electrical Diagram Representation First Transistor Used in all modern FET Transistor BJT Transistor Model, 1947 electronics transistor a semiconductor device that amplifies, oscillates, or switches the flow of current between two terminals by varying the current or voltage between one of the terminals and a third. (www.dictionary.com) www.coltecnica.com Basic Purpose
 To electronically switch (no moving parts) a signal on or off (high/low)  To amplify signals Role in Modern Electronics Basic building blocks for all modern electronics Microprocessors, Microcontrollers, Motor Digital Logic Computers, Digital watches, PC & Cell Controllers Microprocesso Headphones Circuits, Cell Phones. Phones r
Reason for Transistors Early 20 century, vacuum tube were used as signal Invention: th amplifiers & switches. Vacuum Tube Radios vacuum tube* ENIAC : 17, 468 vacuum tubes large, fragile, resulted in extremely
Use of energy inefficient, and expensive electronics. Evolution of electronics required device that was small, light weight, robust, reliable, cheap to manufacture, energy efficient *Vacuum tube advantages: operation at higher voltages (10K region vs. 1K region of transistors); high power, high frequency operation (over-the-air TV broadcasting) better suited for vacuum tubes; and silicon transistors more vulnerable to electromagnetic pulses than vacuum tubes Invention In 1947, John Bardeen, Walter Brattain, and William Schockly, researchers at Bell Lab, invented Transistor. They found Transistor Effect: when electrical contacts were applied to a crystal of germanium,
the output power was larger than the input. John Bardeen, Walter Brattain, and William Schockly Awarded the Nobel Prize in physics (1956) Revolutionized portability and efficiency of electronic devices First model of Transistor, 1947 Infinite possibilities V
mV ground Transistor Manufacturing Doping: Process of introducing impure elements (dopants) into Process semiconductor wafers to form regions of differing electrical conductivity. Doping impurities into a puresemiconductor will increase conductivity. Doping results in an N-Type or P-Type semiconductor. High-Temp Furnace Pure Wafers Ion Implanter Wafer
Refineme nt Doped Wafers Effect of Doping on SemiConductors P-Type Semiconductors : Positively charged Semiconductor Dopant Material: Boron, Aluminum, Gallium Effect of Dopant: Creates holes (positive charges where electrons have been removed) in lattice structure Effect of Doping on SemiConductors N-Type Semiconductors : Negatively charged Semiconductor Dopant Material: Phosphorous, Arsenic, Antimony (Sb) Effect of Dopant: Added unbound electrons create negative charge in lattice structure
Remember: Dopant is added to same piece of semiconductor material Resulting Material: Single, solid material called P-N Electrical Switching on P-N Applying Junction External Voltage of Forward Biasing polarity facilitates motion of free electrons of Reverse Biasing polarity impedes motion of free electrons Forward Biasing Circuit is On Current is Flowing Reverse Biasing Circuit
is Off Current not Flowing Finally combining all concepts Semiconductor -> Doping -> P-N Junction -> Depletion Region One P-N Junction can control current flow via an external voltage Two P-N junctions (bipolar junction transistor, BJT) can control current flow and amplify the current flow. Also, if a resistor is attached to the output, the resulting voltage output is much greater than the applied voltage, due to amplified current. Example at end. Presentation Outline 1 2 Introduction to Transistors
Ryan Akin Transistor Types and Checks Ryan Akin 3 Bipolar Junction Transistors 4 Field Effect and Power Transistors 5 Transistor Part Numbers and Catal Xin Chen Will Dahlin
Will Dahlin Transistor Checks Types and Types and Categorization of Transistors Meter Check of Unknown Transistor Transistor Categories and Types Transistor are categorized by Semiconductor material: germanium, silicon, gallium arsenide, etc. Structure: BJT, FET, IGFET (MOSFET), IGBT Polarity: NPN, PNP (BJTs); N-channel, P-channel (FETs)
Maximum power rating: low, medium, high Maximum operating frequency: low, medium, high Application: switch, audio, high voltage, etc. Physical packaging: through hole, surface mount, ball grid array, etc. Amplification factor, Various Types of Transistor: http://en.wikipedia.org/wiki/Category:Transistor_typ es Various Types of Transistors Bipolar Junction Transistor (BJT) Field Effect Transistors (FET) Power Transistors Meter check of a transistor Bipolar transistors are constructed of a three-layer semiconductor sandwich, either PNP or NPN. As such, transistors register as two diodes connected back-to-back when tested with a multimeter's resistance or diode check function
Meter check of a transistor For PNP Transistors 1. Set multimeter to Ohmmeter Ohm Scale. 2. Connect the Negative Probe (Black) to Emitter and the Positive Probe (Red) to the Base(R=R1). 3. Now invert the probe connections to the Emitter for the Red Probe and to the Base for Black. R = OL. If this works, your Emitter-Base junction is OK. 4. Now test the Base-Collector junction. Connect the Red probe to the Base and the Black probe to the Collector (R=R2). 5. Invert the probes again, Black to the Base and the Red probe to the Collector. R = OL. If this works, your Base-Collector junction is Ok. 6. Connect the probes to the Emitter and Collector (probes may be inverted), R = OLindicates a working transistor. Meter check of a transistor For NPN Transistors
1. Set multimeter to Ohmmeter Ohm Scale. 2. Connect the Negative Probe (Black) to Base and the Positive Probe (Red) to the Emitter.(R=R 1). 3. Now invert the probe connections to the Base for the Red Probe and to the Emitter for Black. R = OL. If this works, then your Emitter-Base junction is OK. 4. Now test the Base-Collector junction. Connect the Black probe to the Base and the Red probe to the Collector(R=R 2). 5. Invert the probes again, Red to the Base and the Black probe to the Collector. R = OL. If this works, then your Base-Collector junction is Ok. 6. Connect the probes to the Emitter and Collector (probes may be inverted), R OL indicates a working transistor. Meter check of a transistor Detecting defective Transistors 1. If their is no resistance between any of the pairs during test (R = 0) for all the steps, then the transistor is shorted. 2. If for all the steps R = OL, then the
transistor is open. OL resistance is greater than the meter can read Presentation Outline 1 2 Introduction to Transistors Ryan Akin Transistor Types and Checks Ryan Akin 3 Bipolar Junction Transistors
4 Field Effect and Power Transistors 5 Transistor Part Numbers and Catal Xin Chen Will Dahlin Will Dahlin BJT introduction
BJT = Bipolar Junction Transistor A BJT consists of two back-toback p-n junctions. The three regions are the emitter(E),base(B),and collector(C). The middle region, the base is very thin. Since the base is thin, most carriers from emitter injected into base diffuse into collector. BJT schematic
NPN: BE forward biased BC reverse biased PNP: BE reverse biased BC forward biased NPN PNP BJT Transistor Operation http://www.learnabout-electronics.org/bipolar_junction_t ransistors_05.php
BJT formulae NPN Current control i E iC i B i C i B V V E V CE V C V E
BE V is the amplification factor and ranges from 20 to 200 It is dependent on temperature and voltage B BJT formulae NPN Emitter is more heavily doped than the collector. Therefore, VC > VB > VE for NPN transistor BJT formulae NPN
iC iE iB (1 )iE iC iB 1 is the fraction of electrons that diffuse across the narrow base region 1 is the fraction of electrons that recombine with holes in the base region to create base current BJT Characteristic Curves Transfer Characteristic The graph of ICE / IBE shown (right) is called the Transfer Characteristic The slope of the graph shows the Characteristic curves (graphs) can be drawn to show other parameters of a transistor, and are used both to detail the performance of a particular device and as an aid to the
design of amplifiers. BJT Characteristic Curves Input Characteristic The Input Characteristic is the base emitter current IBE against base emitter voltage VBE(IBE/VBE) shows the input Conductance of the transistor. The steepness of this particular curve when the V BE is above 1 volt shows that the input conductance is very high, and there is a large increase in current (in practice, usually enough to destroy the transistor!) for a very small increase in VBE. Therefore the input RESISTANCE must be low. BJT Characteristic Curves Output Characteristic The slope gives the value of output conductance (and by implication output resistance). The near horizontal parts of the graph lines show that a change in collector emitter voltage VCE has almost no effect
on collector current in this region, just the effect to be expected if the transistor output had a large value resistor in series with it. Therefore the graph shows that the output resistance of the transistor is high. BJT operating regions Operating Region Cut Off Parameters VBE < Vcut-in VCE > Vsupply IB = IC = 0 Mode Switch OFF
Linear VBE = Vcut-in Vsat < VCE < Vsupply IC = *IB Amplification Saturated VBE = Vcut-in, VCE < Vsat IB > IC,max, IC,max > 0 Switch ON The Transistor as A Switch While there are limitations as to what we can switch on and off,
transistor switches offer lower cost and substantial reliability over conventional mechanical relays. The secret to making a transistor switch work properly is to get the transistor in a saturation state The Transistor as A Amplifier From exercise 3 Turns on/off coils digitally The Transistor as A Amplifier Transistor Connections Because an amplifier must have two input and two output terminals, a transistor used as an amplifier must have one of its three terminals common to both input and output as shown on the right. The choice of which terminal is used as the common connection has a marked effect on the performance of
the amplifier. There are three connection modes: Comm0n Emitter Mode Common Collector Mode Common Base Mode The Transistor as A Amplifier Summary of the three types transistor connection Common Common Parameter Common Base Emitter Collector Voltage gain Av
High (about 100) Unity (1) Medium (1050) Current Gain High (50 - 800) High (50 -800) Less than unity (<1) Input Impedance Medium (about
3 to 5k) High (several k) Low (about 50R) Output Impedance Medium, Approx = Load resistor value Low (a few ohms) High (about 1M)
Several Comments about Transistor Bipolar transistor consists of two PN junctions, with two types: NPN and PNP BJT is a current control device. The ratio of currents leads to one of the most important parameters of a transistor, which is its current gain, often referred to as its Beta. IC IB BJT itself does not generate extra energy for amplifying, it just uses small current change to control big current change, which comes from the power supply. Presentation Outline
1 2 Introduction to Transistors Ryan Akin Transistor Types and Checks Ryan Akin 3 Bipolar Junction Transistors 4 Field Effect and Power Transistors 5 Transistor Part Numbers and Catal
Xin Chen Will Dahlin Will Dahlin Power Transistors Concerned with delivering high power Used in high voltage and high current application In general Fabrication process different in order to: Dissipate more heat Avoid breakdown Different types: Power BJTs, power MOSFETS, etc. What makes a Field-Effect Transistor?
FETs have three main parts Drain Source Gate The body has contacts at the ends: the drain and source Gate surrounds the body and can induce a channel by use of an electric field FET Input voltage controls output current Gate Drain Source
BJT Input current controls output current Base Collector Emitter Controls flow of current Current goes out here Current comes in here What is a Field-Effect Transistor (FET)? Semiconductor device that depends on electric field to control the current Performs same functions as a BJT; amplifier, switch, etc. Relies on PNP or NPN junctions to allow
current flow However, mechanism that controls current is different from the BJT Remember the BJT is bipolar. The FET is sometimes called a unipolar transistor One type of charge carrier How does a FET work? Flow of current is similar to water flow through a garden hose Pinch the hose (decrease current channel width) to decrease flow Open the hose (increase channel width) to increase flow
Also, the pressure differential from the front and back of the hose (synonymous with the voltage from drain to source) effects the flow JFET Animation Types of Field-Effect Transistors Type Function Junction Field-Effect Transistor (JFET) Metal-Oxide-Semiconductor FET (MOSFET)
Insulated Gate Bipolar Transistor (IGBT) Similar to MOSFET, but different main channel Organic Field-Effect Transistor (OFET) Uses organic semiconductor in its channel Nanoparticle Organic Memory FET (NOMFET) MOSFET Uses reversed biased p-n junction to separate gate from body Uses insulator (usu. SiO2) between gate and body Combines the organic transistor and gold nanoparticles
IGBT JFET A single channel of single doped SC material with terminals at end Gate surrounds channel with doping that is opposite of the channel, making the PNP or NPN type Uses reversed biased p-n junction to separate gate from body n-channel JFET p-channel JFET
Characteristics and Applications of FETs JFETs Simplest type of FET easy to make High input impedance and resistance Low Capacitance Slower speed in switching Uses? Displacement sensor High input impedance amplifier Low-noise amplifier Analog switch MOSFET Similar to JFET p-channel
A single channel of single doped SC material with terminals at end Gate surrounds channel with doping that is opposite of the channel, making the PNP or NPN type BUT, the MOSFET uses an insulator to separate gate from body, while JFET uses a reverse-bias p-n junction n-channel MOSFET enhanced mode MOSFET
depleted mode How does a MOSFET work? No Voltage to Gate Source Voltage to Gate Drain Source Drain n n Simplified Notation
No current flow Short allows current flow MOSFET FETs vary voltage to control current. This illustrates how that works MOSFET drain current vs. drain-to-source voltage for several values of VGS Vth; the boundary between linear (Ohmic) and saturation (active) modes is indicated by the upward curving parabola. Characteristics and Applications of FETs MOSFETs
Oxide layer prevents DC current from flowing through gate Reduces power consumption High input impedance Rapid switching More noise than JFET Uses? Again, switches and amplifiers in general The MOSFET is used in digital CMOS logic, which uses p- and n-channel MOSFETs as building blocks To aid in negating effects that cause discharge of batteries Use of MOSFET in battery protection circuit Presentation Outline
1 2 Introduction to Transistors Ryan Akin Transistor Types and Checks Ryan Akin 3 Bipolar Junction Transistors 4 Field Effect and Power Transistors 5 Transistor Part Numbers and Catal
Xin Chen Will Dahlin Will Dahlin Transistor Part Numbers and Catalog How to choose and appropriate transistor Reading part numbers Numerous Standards JIS, JEDEC, Pro Electro Dependent on manufacturer and customer Transistor Catalog ZTX 652/653 Datasheet
If in doubt, meter check Presentation Summary 1 Introduction to Transistors 2 Transistor Types and Checks Ryan Akin 3 Bipolar Junction Transistors Xin Chen
Ryan Akin Qualitative explanation of the what & how behind transistors General application and history of transistors Physics behind transistors : Doping Process, Effect on Semiconductors, & Formation of P-N Jun Electrical Properties of P-N Junction & using P-N to control / ampli Categorized by type, ratings, structure Meter check of unknown transistor Introduction & Formulae Explain function and characteristics of common emitter transistor Describe BJT operating regions Applications of BJTs Presentation Summary 4
Field Effect and Power Transistors Will Dahlin Definition and Applications Use of electric field to change the output current JFETs and MOSFETs are most common, and accomplish similar goals as BJTs Used for switches, amplification, applications for protecting electronics 5 Transistor Part Numbers and Catalog Part numbers can be arbitrary Transistor Catalog and Datasheet Will Dahlin Example Problem Ryan Akin
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