MALVINO BATES Electronic PRINCIPLES SEVENTH EDITION Copyright

Chapter Bipolar Junction Transistors Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for

Topics Covered in Chapter 6 • • • Unbiased transistor Biased transistor Transistor currents The CE connection The base curve Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Topics Covered in Chapter 6 (Continued) • • • Collector curves Transistor approximations Reading data sheets Surface mount transistors Troubleshooting Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Unbiased transistor • Three doped regions: emitter, base, and collector • Two pn junctions: emitter-base and basecollector • NPN or PNP • Silicon or germanium Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

The bipolar junction transistor has 3 doped regions. N COLLECTOR (medium doping) P BASE (light doping) N EMITTER (heavy doping) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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

In a properly biased NPN transistor, the emitter electrons diffuse into the base and then go on to the collector. RC N VCE RB VBB P VBE N Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. VCC

Transistor currents • The ratio of collector current to base current is current gain (βdc or h. FE) • Current gain is typically 100 to 300 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

IC IB IE IE Conventional flow IC @ IE IE = I C +

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

The common emitter connection has two loops: the base loop and the collector loop V RB RC CE base loop VBB VBE Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. VCC

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). Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Base curve • Graph similar to that of a diode • Diode approximations are used for analysis (typically - ideal or second) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

The base circuit is usually analyzed with the same approximation used for diodes. IB = VBB - VBE RC RB VCE VCC RB VBE Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

A graph of IC versus VCE (Note that each new value of IB presents a new curve. ) 100 m. A 14 12 10 IC in m. A 8 6 4 2 80 m. A 60 m. A 40 m. A 20 m. A 0 2 4 6 8 10 12 14 16 18 0 m. A VCE in Volts This set of curves is also called a family of curves. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Transistor circuit approximations • First: treat the base-emitter diode as ideal and use b. IB to determine IC. Use for troubleshooting. • Second: correct for VBE and use b. IB to determine IC. • Third (and higher): correct for bulk resistance and other effects. Usually accomplished by computer simulation. Use for design work. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

The second approximation: VBE = 0. 7 V bdc. IB Copyright © The Mc.

VR = I C x RC C VR = 4. 3 m. A x 1 k. W = 4. 3 V C 100 k. W 1 k. W IC = 4. 3 m. A 12 V RB IB = 43 m. A VBB RC 5 V Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. VCC

VCE = VCC - VR C IC = 4. 3 m. A VCE = 12 V - 4. 3 V = 7. 7 V 100 k. W 1 k. W VCE 12 V RB IB = 43 m. A VBB RC 5 V Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. VCC

Reading transistor data sheets • Maximum ratings on voltage, current, and power • Power transistors dissipate more than 1 watt • Temperature can change the value of a transistor’s characteristics Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

A graphic view of collector breakdown 14 12 10 IC in m. A 8

Typical Maximum Ratings • • IC = PD = 200 m. A dc o 250 m. W (for TA = 60 C) 350 m. W (for TA = 25 o. C) o 1 W (for TC = 60 C) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Data sheet h. FE “On Characteristics” IC in m. A 0. 1 1 10 50 100 h. FE(min) 40 h. FE(max) ___ 70 100 60 30 ___ 300 ___ Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Surface-mount transistors • A variety of package styles (threeterminal gull-wing is typical) • Some SMTs can dissipate 1 watt or more • Some SMTs house multiple transistors Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

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. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.