Lecture15-DiodeModelsSmalSignalZener

Lecture15-DiodeModelsSmalSignalZener - ECE 3040 - Dr. Alan...

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Unformatted text preview: ECE 3040 - Dr. Alan Doolittle Georgia Tech Lecture 15 P-N Junction Diodes: Part 5 Large signal (complete model) and small signal (limited use) models of a Diode Reading: Jaeger 3.4-3.14, 13.4, Notes ECE 3040 - Dr. Alan Doolittle Georgia Tech Diode Applications: 1/2 Wave Rectifier R Load v d i d v s +- t V Load v s-v Load =v d +- I d =-I o v Load = -I o R Load ECE 3040 - Dr. Alan Doolittle Georgia Tech Diode Applications: Peak Detector C Load v d i d v s +- t V Load v s-v Load =v d +- ECE 3040 - Dr. Alan Doolittle Georgia Tech Diode Applications: 1/2 Wave Rectifier with an RC Load R Load i d v s +- t V Load +- C Load ECE 3040 - Dr. Alan Doolittle Georgia Tech Diode Applications: LED or a Laser Diode R=1000 ohms V=9V V A I V 1 =IR Light Emission under forward Bias Diode made from a direct bandgap semiconductor. Note: These devices may not be a simple p-n type diode, but behave electrically identical to a p-n junction diode. Majority Carriers that are injected to the oppposite side of the diode under forward bias become minority carriers and recombine. In a direct bandgap material, this recombination can result in the creation of photons. In a real device, special areas are used to trap electrons and holes to increase the rate at which they recombine. These areas are called quantum wells. Light F N P-qV A Quantum well made from smaller bandgap material Electron Current Hole Current-type l 0.5 Ga 0.5 As N-type Al 0.5 Ga 0.5 As GaAs ECE 3040 - Dr. Alan Doolittle Georgia Tech Models used for analysis of Diode Circuits Mathematical Model (previously developed) Graphical Analysis Ideal diode Model Treat the diode as an ideal switch Constant Voltage Drop Model Treat as an ideal switch plus a battery Large signal Model (model used by SPICE transient analysis) multi-components generally applicable Small Signal Model (model used by SPICE AC analysis) easier math valid only for limited conditions-ie small signals ECE 3040 - Dr. Alan Doolittle Georgia Tech Diode Circuits: Graphical Solution R=1000 ohms V=9V V A I V 1 =IR Load Line I=0 -> V A =9V V A =0V -> I=9V/1000 ohms Intersection of the two curves gives the DC operational voltage and currents To solve the problem graphically, we need to find the IV curve for the resistor: V D I D ECE 3040 - Dr. Alan Doolittle Georgia Tech Diode Circuits: Other Models Besides the direct mathematical solution and the graphical solution, we can use 2 other models to approximate circuit solutions: 1.) Ideal Diode Model: a) The voltage across the diode is zero for forward bias. b) The slope of the current voltage curve is infinite for forward bias. c) The current across the diode is zero for reverse bias. V I Circuit Symbol ECE 3040 - Dr. Alan Doolittle Georgia Tech Diode Circuits: Other Models 2.) Constant Voltage Drop (CVD) Model: a) The voltage across the diode is a non-zero value for forward bias. Normally this is taken as 0.6 or 0.7 volts....
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This note was uploaded on 08/23/2011 for the course ECE 3040 taught by Professor Doolittle during the Spring '11 term at University of Florida.

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Lecture15-DiodeModelsSmalSignalZener - ECE 3040 - Dr. Alan...

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