© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-1 Electronics Principles & Applications Eighth Edition Chapter 5 Transistors Charles A. Schuler

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-2 Amplification Transistors Characteristic Curves Transistor Testing Other Transistor Types Transistors as Switches INTRODUCTION

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-3 Amplifier Out In Gain = In Out

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-4 N P N NPN Transistor Structure The collector is lightly doped. C The base is thin and is lightly doped. B The emitter is heavily doped. E

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-5 The C-B junction is reverse biased. N P N NPN Transistor Bias C B E No current flows.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-6 The B-E junction is forward biased. N P N NPN Transistor Bias C B E Current flows.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-7 When both junctions are biased.... N P N NPN Transistor Bias C B E Current flows everywhere. Most of the emitter carriers diffuse through the thin base region since they are attracted by the collector. Note that I B is smaller than I E or I C. ICIC IBIB IEIE

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-8 N P N C B E Although I B is smaller it controls I E and I C. ICIC IBIB IEIE Note: when the switch opens, all currents go to zero. Gain is something small controlling something large (I B is small).

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-9 Transistor structure and bias quiz The heaviest doping is found in the ___________ region. emitter The thinnest of all three regions is called the ____________. base The collector-base junction is ___________ biased. reverse The base-emitter junction is ____________ biased. forward The majority of the emitter carriers flow to the ___________. collector

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-10 N P C B E I C = 99 mA I B = 1 mA I E = 100 mA  = ICIC IBIB The current gain from base to collector is called  99 mA 1 mA = 99

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-11 N P C B E I C = 99 mA I B = 1 mA I E = 100 mA I E = I B + I C 99 mA = 1 mA + = 100 mA Kirchhoff’s current law:

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-12 C B E I C = 99 mA I B = 1 mA I E = 100 mA In a PNP transistor, holes flow from emitter to collector. Notice the PNP bias voltages.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-13 Transistor currents quiz  is the ratio of collector current to ______ current. base The sum of the base and collector currents is the __________ current. emitter In NPN transistors, the flow from emitter to collector is composed of _______. electrons In PNP transistors, the flow from emitter to collector is composed of _______. holes Both NPN and PNP transistors show __________ gain. current

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-14 Emitter NPN schematic symbol Base Collector Memory aid: NPN means Not Pointing iN. E B C

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-15 Collector Base Emitter PNP schematic symbol E B C

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-16 IBIB ICIC V CE B C E This circuit is used to collect I C versus V CE data for several values of I B.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V CE in Volts I C in mA When graphed, the data provide an NPN collector family of curves. 20  A 0  A 100  A 80  A 60  A 40  A

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V CE in Volts I C in mA 20  A 0  A 100  A 80  A 60  A 40  A  = ICIC IBIB =  A 6 mA 100  A 14 mA = 140 This type of gain is called  dc or h FE.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V CE in Volts I C in mA 20  A 0  A 100  A 80  A 60  A 40  A  ac = Another type of gain is called  ac or h fe. ICIC IBIB =  A 2.5 mA

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V CE in Volts I C in mA 20  A 0  A 100  A 80  A 60  A 40  A IBIB With these values of I B : The C-E model is a resistor. C E

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V CE in Volts I C in mA 20  A 0  A 100  A 80  A 60  A 40  A IBIB When I B >> 100  A V CE  0 The model is a closed switch.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V CE in Volts I C in mA 20  A 0  A 100  A 80  A 60  A 40  A IBIB When I B = 0 I C = 0 The model is an open switch.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-23 Transistor operating conditions quiz When I B is large and V CE  0, the transistor acts as a ___________ switch. closed When I B = 0 and I C = 0, the transistor acts as an ___________ switch. open When I B > 0 and V CE > 0, the transistor acts as a ___________. resistor Two current gain measures are  dc and __________.  ac The symbol h fe is the same as _________.  ac

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill The E-B junction is forward biased by the ohmmeter. V mA NPN E B C 

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill The C-E resistance is very high. V mA NPN E B C 

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill The meter reading is < 100 k  due to gain. V mA NPN E B C 100 k  

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-27 Current Out Current In Current Amplifier The BJT is current controlled.

Transistors BJTsFETs JFETsMOSFETs NPN PNP Depletion Mode Enhancement Mode N-Channel P-Channel D D D D D D G G G G G G S SSS SS C C E E B B BJTs are current controlled and FETs are voltage controlled. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-28

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-29 Current OutVoltage In Voltage Amplifier The JFET is a voltage controlled amplifier.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-30 Drain Source Drain Source Gate Structure of an N-channel JFET P-type substrate P N-channel The channel has carriers so it conducts from source to drain.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-31 Drain Source Drain Source Gate P N-channel P-type substrate A negative gate voltage can push the carriers from the channel and turn the JFET off.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V DS in Volts I D in mA -4 V -5 V 0 V -1 V -2 V -3 V V GS N-channel JFET drain family of characteristic curves This is known as a depletion-mode device.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-33 n Source Gate Drain V DD p n It’s possible to make enhancement type field effect transistors as well. G S D V GG Gate bias enhances the channel and turns the device on. Metal oxide insulator N-channel MOSFET

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V DS in Volts I D in mA 1 V 0 V 5 V 4 V 3 V 2 V V GS Enhancement mode MOSFET drain family of characteristic curves Drain Source Gate

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-35 The IGBT (insulated gate bipolar transistor) Operation and structure similar to a MOSFET Voltage controlled (like the MOSFET) Has one more junction than a MOSFET Hole injection reduces the collector resistance Faster turn off than BJTs but not as fast as MOSFETS R CE = 8.33 m 

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-36 Courtesy of Powerex, Inc. Three major power device technologies hole injection Extra junction

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-37 Typical IGBT driver circuit IGBT Typically +15 V for turn on Typically - 5 to -15 V for turn off Control signal

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-38 Powerex IGBT module structure Powerex high voltage IGBT package

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-39 Base 2 Base 1 Emitter The unijunction transistor fires when its emitter voltage reaches V P. VPVP Emitter current Emitter voltage Then, the emitter voltage drops due to its negative resistance characteristic. The UJT is not useful as an amplifier. It is used in timing and control applications.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-40 Other transistor types quiz BJTs are __________ -controlled amplifiers. current FETs are __________ -controlled amplifiers. voltage JFETs operate in the _________ mode. depletion MOSFETs operate in the __________ mode. enhancement UJTs are not useful as __________. amplifiers IGBTs are __________ -controlled amplifiers. voltage

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-41 How do transistor switches work? Can be viewed as solid state relays: they are either ON or they are OFF. BJT switches are characterized by: high base current (or no base current) low resistance from collector to emitter (or very high resistance) low collector dissipation P C = V CE x I C P C = 0 x I C = 0 W (or P C = V CE x 0 = 0 W)

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-42 LOAD DRIVER The driver output is zero volts, I B = 0 and I LOAD = 0 The driver output is positive, I B > 0 and the load is onThe driver output is zero volts, I B = 0 and the load is off R CE    R CE  0  R CE    NPN SWITCH

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-43 LOAD DRIVER The driver output is off (high Z): the resistor pulls the base voltage up so that V BE = 0 PNP SWITCH The driver output goes low: the voltage drop across the resistor makes V BE negative The driver output is off (high Z): the resistor pulls the base voltage up so that V BE = 0 LOAD

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-44 PNP SWITCH WITH NPN DRIVER LOAD

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-45 NPN SWITCH WITH PNP DRIVER (NEGATIVE POWER SUPPLY) LOAD V BE  -0.7 V V BE  +0.7 V V BE  0 V

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-46 A B C D ABCD STEPPER MOTOR Enhancement mode power MOSFETs used as switches

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-47 LOAD DRIVER This circuit is often used when the driver amplitude is not great enough to saturate the MOSFET.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-48 The next slide shows a different type of transistor switch. It does not have a digital output; it has an analog input and output. It does have a digital input for controlling on and off. Thus, these switches can be used to connect or disconnect analog signals. Some are bidirectional left to right or right to left. Digital on/off input

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-49 The signal source is a sine wave. The output is switched on and off by the control.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-50 When the control input (pin 6) is at logic 0, the input signal applied to the COM terminal (pin 1) is routed to the NC (normally closed) terminal (pin 2) and when the control input is logic 1, the input signal is connected to the NO (normally open) terminal (pin 8). The MAX4649 integrated circuit acts as a static (no moving parts) SPDT (single-pole-double-throw) relay. It is an example of a mixed-signal integrated circuit. Mixed signal ICs have both digital and analog features and are covered in more detail in subsequent chapters. Control input (logic 0 or 1) Input signal Output signal The MAX4649 is an integrated circuit (IC) analog switch.

© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 5-51 REVIEW Amplification Transistors Characteristic Curves Transistor Testing Other Transistor Types Transistors as Switches