Transcript Slide 1
ME 6405 Mechatronics In Order of Presentation: Jonathan Jobe David Malphurs Isaac Penny October 11, 2005 ME 6405 Transistors 0000 0001 Contents Brief History Properties of Transistors Types of Transistors Characteristics and Applications Engineering Selection October 11, 2005 ME 6405 Transistors 0000 0010 History Vacuum Tube 1879 Edison Invents Light Bulb 1883 Edison found that he could detect electrons flowing through the vacuum from the lighted filament to a metal plate mounted inside the bulb. “Edison Effect” John Fleming implements Edison Effect as first diode. 1906 Lee DeForest introduced a third electrode called the grid into the vacuum tube. The resulting triode could be used as both an amplifier and a switch. October 11, 2005 ME 6405 Transistors 0000 0011 Predecessors Diode October 11, 2005 Triode ME 6405 Transistors 0000 0100 First Transistors Bell Labs 1947 Invented First Transistor Application: replace vacuum tubes Smaller, more durable, no warm up Made of Germanium Current Transistors Silicon based October 11, 2005 Doped with phosphorus (n-type) Doped with boron (p-type) ME 6405 Transistors 0000 0101 The PN Junction Forward Biasing The external Voltage lowers the potential barrier at the junction, allowing the electrons to flow. Reverse Biasing The external voltage raises the potential barrier at the junction, preventing electrons from flowing. October 11, 2005 ME 6405 Transistors 0000 0110 Transistor Types BJT Bipolar Junction Transistor FET Field Effect Transistor JFET MOSFET (Metal Oxide Semiconducting FET) October 11, 2005 (Junction FET) ME 6405 Transistors 0000 0111 BJTs 2 types NPN (most common) When IB≠0, VCE forward biased & VBC NPN bipolar junction transistor reverse biased PNP When IB≠0, VCE reverse biased & VBC forward biased PNP bipolar junction transistor October 11, 2005 ME 6405 Transistors 0000 1000 npn-B J T Voltage Characteristic Cutoff: Base-Emitter starts to conduct with VBE=0.6V Saturation: Increasing IB causes IC to rise exponentially. Active: IC I B Breakdown: Ic approaches infinity due to breakdown at both junctions October 11, 2005 ME 6405 Transistors 0000 1001 B J T Operational Characteristics Operation IB or VCE Region Char. Cutoff IB = Very small Saturation VCE = Small Active Linear Breakdown October 11, 2005 VCE & VBE Junctions Reverse & Reverse Forward & Forward VCE = Reverse & Moderate Forward VCE = Large Beyond Limits ME 6405 Transistors Mode Open Switch Closed Switch Linear Amplifier Overload 0000 1010 Equations of npn-B J T s Definitions VBE VB VE VCE VC VE Kirchoff’s Current Law IE IB Ic In Active region IC IB October 11, 2005 Common values for ß are 20 to 200 ME 6405 Transistors 0000 1011 Point of Operation The existence of RC means that IC and VCE are no longer independent. VCE = Vcc – IC*RC After solving for IC, VCC VCE IC RC RC October 11, 2005 ME 6405 Transistors 0000 1100 Point of Operation Load-line constraint IC VCC VCE RC RC Selecting VBB and VCC, we can find the operating point, or Q point. IB = (VBB-VBE)/RB Q point for IB=100μA October 11, 2005 ME 6405 Transistors 0000 1101 B J T resistor sizing ß and IC,max are specified by the catalog We need to choose Values for RB and RC to keep IC and IB within specifications IB IC VCC RC IC VBB VBB RB IB IC October 11, 2005 ME 6405 Transistors 0000 1110 Field Effect Transistors (FET) Three Types of Field Effect Transistors MOSFET (metal-oxide-semiconductor field-effect transistors) Enhancement mode IDS α VGS Depletion mode IDS α 1/VGS JFET (Junction Field-effect transistors) Available in n or p Channel n-Channel activated by VGS > 0 for MOSFET and VGS < 0 for JFET p-Channel activated by VGS < 0 for MOSFET and VGS > 0 for JFET Most Common Types n-Channel Enhancement Mode MOSFET (NMOS) n-Channel JFET October 11, 2005 ME 6405 Transistors 0000 1111 FET Architecture Enhanced MOSFET Conducting Region Depleted MOSFET JFET Nonconducting Region Analogous BJT Terminals Nonconducting Region October 11, 2005 ME 6405 Transistors BJT FET Base Gate Collector Drain Emitter Source 0001 0000 NMOS Voltage Characteristic VDS = Constant VGS < Vth IDS=0 I DS I DSSHORT VGS > Vth : 0 < VDS < VPinch off VGS 1 VTH Active Region IDS controlled by VGS VDS > VPinch off Saturation Region IDS constant Active Region Saturation Region VDS > VBreakdown IDS approaches IDSShort Should be avoided October 11, 2005 ME 6405 Transistors VPinchoff 0001 0001 2 Junction Field Effect Transistor Difference from NMOS VGS > Vth IDS=0 I DS I DSSHORT VGS < -Vth : 0 < VDS < VPinch off Active Region IDS controlled by VGS Active Region VGS 1 VTH 2 Saturation Region VDS > VPinch off Saturation Region IDS constant VDS > VBreakdown IDSShort October 11, 2005avoided IDS approaches Should be ME 6405 Transistors VPinchoff 0001 0010 Transistor Selection October 11, 2005 ME 6405 Transistors 0001 0011 Applications of Transistors Switch Voltage Amplifier Current Amplifier October 11, 2005 ME 6405 Transistors 0001 0100 Transistor as a Switch Many times you just need to switch a signal on or off Ex. Digital Logic, LED’s, PWM Relays can perform this same function They can usually handle higher currents than can transistors Not Solid State, so shorter life and less durable Slower activation time October 11, 2005 ME 6405 Transistors 0001 0101 Transistor as a Voltage Amplifier Other times you want to amplify an analog signal Ex. Sensor input, audio, Op-amps can perform the same function Higher gains Can’t handle nearly as much current. Thus Op-amps are better for signal amplification, while Transistors are better for power amplification. October 11, 2005 ME 6405 Transistors 0001 0110 Transistor as a Current Amplifier Other times you want to amplify an analog signal Ex. Sensor input, audio, Op-amps can perform the same function Higher gains Can’t handle nearly as much current. October 11, 2005 Thus Op-amps are better for signal amplification, while Transistors are better for power amplification. ME 6405 Transistors 0001 0111 Example Problem Refer to your first handout October 11, 2005 ME 6405 Transistors 0001 1000 Questions Refer to your second handout Candy!! October 11, 2005 ME 6405 Transistors 0001 1001