1 / 30

MALVINO & BATES

MALVINO & BATES. ELECTRONIC PRINCIPLES. SEVENTH EDITION. Chapter. 6. Bipolar Junction Transistors. Topics Covered in Chapter 6. Unbiased transistor Biased transistor Transistor currents The CE connection The base curve. Topics Covered in Chapter 6 (Continued). Collector curves

alisa-obrien
Download Presentation

MALVINO & BATES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MALVINO & BATES ELECTRONIC PRINCIPLES SEVENTH EDITION

  2. Chapter 6 Bipolar Junction Transistors

  3. Topics Covered in Chapter 6 • Unbiased transistor • Biased transistor • Transistor currents • The CE connection • The base curve

  4. Topics Covered in Chapter 6(Continued) • Collector curves • Transistor approximations • Reading data sheets • Surface mount transistors • Troubleshooting

  5. Unbiased transistor • Three doped regions: emitter, base, and collector • Two pn junctions: emitter-base and base-collector • NPN or PNP • Silicon or germanium

  6. The bipolar junction transistor has 3 doped regions. N COLLECTOR (medium doping) P BASE (light doping) N EMITTER (heavy doping)

  7. Biased transistor • Forward bias the emitter diode • Reverse bias the collector diode

  8. In a properly biased NPN transistor, the emitterelectrons diffuse into the base and then go on to the collector. RC N VCE RB P VCC N VBE VBB

  9. Transistor currents • The ratio of collector current to base current is current gain (βdc or hFE) • Current gain is typically 100 to 300

  10. IC IC IB IB IE IE IC IC bdc = adc = IB IE Conventional flow Electron flow IE = IC + IB IC @ IE IB << IC

  11. The CE connection • The emitter is grounded or common • The base-emitter acts like a diode • The base-collector acts like a current source that is equal to βdc times the base current

  12. The common emitter connection has two loops: the base loop and the collector loop. RC collector loop RB VCE VCC base loop VBE VBB

  13. Subscript notation • When the subscripts are the same, the voltage represents a source (VCC). • When the subscripts are different, the voltage is between two points (VCE). • Single subscripts are used for node voltages with ground serving as the reference (VC).

  14. Base curve • Graph similar to that of a diode • Diode approximations are used for analysis (typically - ideal or second)

  15. The base circuit is usually analyzed with the same approximation used for diodes. VBB - VBE RC IB = RB VCE VCC RB VBE VBB

  16. 100 mA 80 mA 60 mA 40 mA 20 mA 0 mA A graph of IC versus VCE (Note that each new value of IB presents a new curve.) 14 12 10 IC in mA 8 6 4 2 6 16 2 4 10 12 0 14 18 8 VCE in Volts This set of curves is also called a family of curves.

  17. Regions of operation • Active - - - used for linear amplification • Cutoff - - - used in switching applications • Saturation - - - used in switching applications • Breakdown - - - can destroy the transistor and should be avoided

  18. Transistor circuit approximations • First: treat the base-emitter diode as ideal and use bIB to determine IC. Use for troubleshooting. • Second: correct for VBE and use bIB to determine IC. • Third (and higher): correct for bulk resistance and other effects. Usually accomplished by computer simulation. Use for design work.

  19. The second approximation: bdcIB VBE = 0.7 V VCE

  20. VBB - VBE IB = RB 5 V - 0.7 V = 43 mA IB = RC 100 kW 100 kW VCC RB VBE = 0.7 V 5 V VBB

  21. IC = bdc IB IC = 100 x 43 mA = 4.3 mA RC 100 kW bdc = 100 VCC RB IB = 43 mA 5 V VBB

  22. VRC = IC x RC VRC = 4.3 mA x 1 kW = 4.3 V 1 kW RC IC = 4.3 mA 100 kW 12 V VCC RB IB = 43 mA 5 V VBB

  23. IC = 4.3 mA VCE = VCC - VRC VCE = 12 V - 4.3 V = 7.7 V 1 kW RC VCE 100 kW 12 V VCC RB IB = 43 mA 5 V VBB

  24. Reading transistor data sheets • Maximum ratings on voltage, current, and power • Power transistors dissipate more than 1watt • Temperature can change the value of a transistor’s characteristics

  25. Typical Breakdown Ratings • VCBO = 60 V • VCEO = 40 V • VEBO = 6 V • Note: these are reverse breakdown ratings with one transistor leg open (e.g. VCBO is voltage collector to base with emitter open)

  26. A graphic view of collector breakdown 14 12 10 IC in mA 8 6 4 2 0 50 VCE in Volts

  27. Typical Maximum Ratings • IC = 200 mA dc • PD = 250 mW (for TA = 60 oC) • PD = 350 mW (for TA = 25 oC) • PD = 1 W (for TC = 60 oC)

  28. Data sheet hFE “On Characteristics” IC in mA hFE(min) hFE(max) 0.1 40 ___ 1 70 ___ 10 100 300 50 60 ___ 100 30 ___

  29. Surface-mount transistors • A variety of package styles (three-terminal gull-wing is typical) • Some SMTs can dissipate1 watt or more • Some SMTs house multiple transistors

  30. Troubleshooting • Look for gross voltage errors. • First approximation and mental estimates will usually suffice. • Resistors generally don’t short but circuit boards can. • Circuit boards can and do open. • Junctions can and do short. • Junctions can and do open.

More Related