Electronic Principles 7 th Edition Albert Malvino & David J Bates
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Transcript of Electronic Principles 7 th Edition Albert Malvino & David J Bates
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Electronic Principles7th Edition
Albert Malvino & David J Bates
Rizwan H. Alad & Vasim A. Vohra
Ref. Books
1) Electronic devices and circuit theory – Robert Boylestad2) Basic Electronics – A. P. Godse & U. A. Bakshi
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Part 1 Syllabus
• Chap. 6 Bipolar Junction Transistors
• Chap. 7 Transistor Fundamentals
• Chap. 8 Transistor Biasing
• Chap. 9 Transistor AC Models
• Chap. 10 Voltage Amplifiers
• Chap. 11 CC and CB Amplifiers
• Chap. 12 Power Amplifiers
• Chap. 23 Oscillators
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Transistor
• Three doped regions
• Emitter, Base and Collector
• Base region is much thinner as compared to the collector and emitter
• npn and pnp
• Emitter is heavily doped, Base is lightly and collector is intermediate
• Collector regions is physically largest
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Before Diffusion After Diffusion
Each of Dep. Layer barrier potential app. 0.7 V at 25o C
Unbiased transistor is like two back-to-back diodes
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Bipolar Junction Transistors
• A bipolar transistor essentially consists of a pair of PN Junction diodes that are joined back-to-back.
• There are therefore two kinds of BJT, the NPN and PNP varieties.
• The three layers of the sandwich are conventionally called the Collector, Base, and Emitter.
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NPN Bipolar Junction Transistor•One N-P (Base Collector) diode one P-N (Base Emitter) diode
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PNP Bipolar Junction Transistor•One P-N (Base Collector) diode one N-P (Base Emitter) diode
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Analogy with Transistor :Fluid-jet operated Valve
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*The Biased Transistor •Heavily doped emitter inject free electrons into the base•Lightly doped base pass electrons on to the collector•Collector collects or gathers electrons from the base
Biasing method – Emitter junction FB Collector junction RB
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Summary • Forward biased emitter diode, forcing the free electrons in the emitter to enter the base
• Thin and lightly doped base diffuse electrons into collector
• Collector, through RC and into the positive terminal of VCC
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Figure 5.3 Current flow in an npn transistor biased to operate in the active mode. (Reverse current components due to drift of thermally generated minority carriers are not shown.)
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Transistor Currents
• IE – Largest emitter current
• Emitter electrons flow to the collector, IC ≈ IE
• IB ≤ 0.01 IC
• KCL, IE = IC + IB
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BJT and •From the previous figure IE = IB + IC
•Define dc = IC / IE
• DC alpha is slightly less than 1
• Low power transistor αdc > 0.99 and High power transistor αdc > 0.95
•Define dc = IC / IB - known as a current gain
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BJT and
•Then dc = IC / (IE –IC) = dc /(1- dc)
•Assignment – Derive dc = dc /(1+ dc)
•Then IC = dc IE & IB = (1-dc) IE
Solved Example 6.1, 6.2, 6.3
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NPN BJT Current flow
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The CE connection
• CE, CC and CB• CE because emitter is
common to both VBB and VCC
• Left loop – Base loop• Right loop – collector loop
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The CE connection
• Base Loop, VBB source and RB – current limiting resistor
• Changing VBB or RB, change base current and IB Change than IC change
• IB controls IC
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Notation
Double Subscripts
• Voltage source – VBB and VCC
• VBE – voltage between points B and E
• VCE – voltage between points C and E
Single Subscripts
• Used for Node voltages
• VB – voltage between base and ground
• VC and VE
• VCE = VC – VE
• VCB and VBE
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The Base Curve / Input Characteristics
• Graph IB versus VBE
• Like ordinary diode• Ohm’s low to Base loop
• Ideal diode VBE = 0 and second app. VBE = 0.7 V
I
B
BEBBB R
VVI
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Collector Curve / output Characteristics
• Graph IC versus VCE
• Ohm’s low to Collector loop
• Fixed value of based current, vary VCC and measure IC and VCE
I
C
CECCC R
VVI
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Transistor Characteristics
Input Characteristics Output Characteristics
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Active Region, Constant collector current
• After collector diode reverse biased, it collect all the electrons that reach its deplation layer
• Further increased VCE cannot increased IC
• Collector can collect only those free electrons that emitter injects
• VCE > VCE(max), collector diode break down
• Power Dissipation PD = VCEIC
• PD < PD(max)
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Operating Region of Transistor
• Active region, middle region – normal operation of transistor
Emitter diode – FB and Collector diode – RB• Breakdown region – transistor will be destroyed
• Saturation region – rising part of curve, VCE between zero and few tenth of volt
Collector diode has insufficient positive voltage to collect all the free electrons injected into the base
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Operating Region of Transistor
• Cut off region – IB = 0 but still small collector current
Because collector diode RB – Reverse minority carrier + Surface leakage current
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BJT Operating Regions
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Analogy with Transistor in Active Region: Fluid-jet operated Valve
In active region this stopper does not really havenoticeable effect on the flow rate
Emitter Base Junction – FB Collector Base Junction – RB
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Analogy with Transistor CutoffFluid-jet operated Valve
Emitter Base Junction – RB Collector Base Junction – RB
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Analogy with Transistor SaturationFluid-jet operated Valve
The valve is wide open; changing valve position a little bit does not have much influence on the flow rate.
E-B Junction – FB C-B Junction – FB
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