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Transistors

ME 4447/6405 Student Lecture. Justin Chow Jacob Huang Daniel Soledad. Transistors. Overview. History Properties Types BJT JFET MOSFET Applications. Daniel Soledad. Introduction. Transistor History “Transistor” is combination of “transconductance” and “variable resistor”

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Transistors

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  1. ME 4447/6405 Student Lecture Justin Chow Jacob Huang Daniel Soledad Transistors

  2. Overview • History • Properties • Types • BJT • JFET • MOSFET • Applications Daniel Soledad

  3. Introduction • Transistor History • “Transistor” is combination of “transconductance” and “variable resistor” • How Transistors Are Made • Vacuum tubes • Inefficient, fragile, bulky, generated a lot of heat • First Transistors • Semiconductors – Bell Labs 1947

  4. Introduction • Packaging • Surface Mount or Through Hole • Usually 3 or 4 terminal device • Can be packaged into ICs • General Applications • Amplification /Regulation • Switches

  5. General Operation • Current Controlled • i.e: BJT • The output current is proportional to input current • Voltage Controlled • i.e.: JFET, MOSFET • The output current is proportional to input voltage

  6. BJT Transistor Justin Chow • Bipolar Junction Transistor • 3 semiconductor layers sandwiched together • Comes in two flavors NPN BJT PNP BJT

  7. BJT Transistor • Diodes Forward Biased Reverse Biased current flows no current flows when VPN > .6-.7V

  8. emitter base collector Electron Flow BJT Transistor • BJT Basics (NPN) • BE Forward Biased • BC Reversed Biased • β=IB / Ic ≈ 100 • IE = IB + IC

  9. BJT Transistor • Things to remember • PNP, biasing opposite • Conventional current vs electron flow • A small input current controls a much larger output current.

  10. BJT Transistor Operating Regions

  11. BJT Transistor Operating Regions

  12. Application: Switching • From 3rd Exercise • Turns on/off coils digitally

  13. BJT Transistor β=100 Common Emitter Amplifier

  14. BJT Transistor • IB = (Vin − VB) / 10000Ω = (Vin − 0.7) / 10000Ω • IC = β(Vin − 0.7) / 10000Ω • Vout=10000*(Vin-0.7)/1000 • When VCE = 0.2V • IC = 9.8 / 1000Ω = 9.8mA • IB = IC / β = 0.098mA • Vin − 0.7 = (0.098mA)(10000Ω) • Vin = 1.68V or greater. Common Emitter Amplifier

  15. BJT Transistor • Power Dissipation • PBJT = VCE * iCE • Should be below the rated transistor power • Important for heat dissipation as well

  16. Darlington Transistors Increased Gain β = β1 * β2 VBE = VBE1 + VBE2 Slower Switching 2N6282

  17. FET Transistors Analogous to BJT Transistors Output is controlled by input voltage rather than by current 4 Pins vs. 3

  18. FET Transistors FET (Field Effect Transistors) MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) JFET (Junction Field-Effect Transistor) MESFET HEMT MODFET Most common are the n-channel MOSFET or JFET Jacob Huang

  19. FET Transistors – Circuit Symbols In practice the body and source leads are almost always connected Most packages have these leads already connected D D D B G G B G S S S MOSFET JFET

  20. MOSFET Metal-Oxide Semiconductor F.E.T. A.K.A. Insulated-Gate FET (IGFET) 2 Modes: Enhancement/Depletion

  21. Depletion Mode • N-Channel • + Vgs -> More electrons -> More Current • - Vgs -> Less electrons -> Less current • P-Channel – Reversed • Different from BJT

  22. Characteristic Curves for D-type D G B S Current flow

  23. Enhancement Mode • N-Channel • VGS > Vth -> Turns on device • VGS < VTH -> No Current • P-Channel • Reversed • Only E-type used now

  24. Modes of Operation D G B S Current flow

  25. Characteristic Curve for E-type D G B S Current flow

  26. Power MOSFET • Used in high-power applications • Heat Sink • Vertical layout • Not Planar like other transistors

  27. Junction gate FET Reverse Bias VGS => Reduces channel size => Reduced Current Defaults “on”

  28. JFET as Switch Vgs = 0 “on” |Vgs|> |Vp| “off” Vp = Pinch-off or Cut-off Voltage

  29. JFET Properties • Internal Capacitance • Bi-directional • Cut-off voltage is varying for each JFET • 0.3V – 10V • N-Channel – Negative VGS • P-Channel – Positive VGS • Do not Forward Bias JFET – burn out

  30. JFET Characteristic Curve

  31. Comparison

  32. CMOS Complementary MOS Used in Logic Gates P-channel (PMOS) to high N-channel (NMOS) to low HIGH usually +5 V LOW usually ground Q is high when A = 0, Q is low when A = 1

  33. References Spring 2007/2008 Slides http://www.made-in-china.com/image/2f0j00ZhaTKREnIQkfM/IC-Transistor.jpg http://en.wikipedia.org/wiki/JFET http://en.wikipedia.org/wiki/MOSFET http://en.wikipedia.org/wiki/Bipolar_junction_transistor http://www.allaboutcircuits.com/vol_3/chpt_2/8.html http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/images/basic-bjt.gif&imgrefurl=http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt_theory.html http://www.allaboutcircuits.com/vol_3/chpt_2/6.html http://web.engr.oregonstate.edu/~traylor/ece112/lectures/bjt_reg_of_op.pdf http://hades.mech.northwestern.edu/wiki/index.php/Diodes_and_Transistors#Common_Emitter_Amplifier_Circuit http://en.wikipedia.org/wiki/Darlington_transistor http://www.allaboutcircuits.com/vol_3/chpt_6/2.html http://www.allaboutcircuits.com/vol_3/chpt_4/2.html http://www.designers-guide.org/Forum/YaBB.pl?num=1162476437/4 http://en.wikipedia.org/wiki/CMOS

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