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MALVINO & BATES Electronic PRINCIPLES SEVENTH EDITION Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter Bipolar Junction Transistors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6 Topics Covered in Chapter 6 • • • • • Unbiased transistor Biased transistor Transistor currents The CE connection The base curve Copyright © The McGraw-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 McGraw-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 McGraw-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 McGraw-Hill Companies, Inc. Permission required for reproduction or display. Biased transistor • Forward bias the emitter diode • Reverse bias the collector diode Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. In a properly biased NPN transistor, the emitter electrons diffuse into the base and then go on to the collector. RC N VCE RB P VBB VBE N Copyright © The McGraw-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 hFE) • Current gain is typically 100 to 300 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. IC IC IB IB IE IE Conventional flow IC @ IE I E = IC + I B adc = Electron flow IC IE bdc = IB << IC IC IB Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 McGraw-Hill Companies, Inc. Permission required for reproduction or display. The common emitter connection has two loops: the base loop and the collector loop. RC collector loop V RB CE VCC base loop VBB VBE Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 McGraw-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 McGraw-Hill Companies, Inc. Permission required for reproduction or display. The base circuit is usually analyzed with the same approximation used for diodes. VBB - VBE IB = RC RB VCE VCC RB VBB VBE Copyright © The McGraw-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 mA 14 12 10 IC in mA 8 6 4 2 80 mA 60 mA 40 mA 20 mA 0 2 4 6 8 10 12 14 16 18 0 mA VCE in Volts This set of curves is also called a family of curves. Copyright © The McGraw-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 McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The second approximation: VBE = 0.7 V bdcIB Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. VCE VBB - VBE IB = IB = RB 5 V - 0.7 V = 43 mA 100 kW RC 100 kW VCC RB VBB 5V VBE = 0.7 V Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. IC = bdc IB IC = 100 x 43 mA = 4.3 mA 100 kW RC bdc = 100 RB IB = 43 mA VBB 5V Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. VCC VRC = IC x RC VRC = 4.3 mA x 1 kW = 4.3 V 100 kW 1 kW IC = 4.3 mA 12 V RB IB = 43 mA VBB RC 5V Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. VCC VCE = VCC - VRC IC = 4.3 mA VCE = 12 V - 4.3 V = 7.7 V 100 kW 1 kW VCE 12 V RB IB = 43 mA VBB RC 5V Copyright © The McGraw-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 McGraw-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 McGraw-Hill Companies, Inc. Permission required for reproduction or display. A graphic view of collector breakdown 14 12 10 IC in mA 8 6 4 2 0 50 VCE in Volts Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Typical Maximum Ratings • • • • IC = PD = PD = PD = 200 mA dc o 250 mW (for TA = 60 C) 350 mW (for TA = 25 oC) 1W (for TC = 60 oC) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Data sheet hFE “On Characteristics” IC in mA hFE(min) 0.1 1 10 50 100 40 70 100 60 30 hFE(max) ___ ___ 300 ___ ___ Copyright © The McGraw-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 McGraw-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 McGraw-Hill Companies, Inc. Permission required for reproduction or display.