# 8 Diodes - ECE 110 M.-C. Brunet i Diode or pn junction. It...

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ECE 110 M.-C. Brunet Diodes Handout 8 Diode or pn – junction. It is a semiconductor component. + + + + + -- - - i + v - Current flows more easily in one direction . Circuit symbol i + v - “biasing” the diode ( v is the bias): v > 0 (diode is ‘forward-biased’) current i > 0 v < 0 (diode is ‘reverse-biased’) current i < 0 very small Orientation of diode in a circuit is M.-C. BRUNET ECE 110 UIUC 8.1 important. (See lab)

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ECE 110 M.-C. Brunet Diodes Handout 8 IV Characteristics of the pn junction The IV is non-linear!! i + v - i = I s (e qV/ k t –1) Where : El t i h 1 6 10 9 q: Electric charge = 1.6 x 10 -19 C k : Boltzmann constant = 1.38 x 10 -23 m 2 kg / s 2 .K T: Temperature in Kelvin (K) I s : Saturation current small! 10 -8 ~10 -14 Approximation : At ‘room temperature’ T = 300K q/ k T = 38.5 i = I (e 38.5 V -1) s Diode orientation is important!! + - 2V 1 k Ω i 1 + - 2V 1 k Ω i 2 M.-C. BRUNET ECE 110 UIUC 8.2 i 1 = i 2 !! IV Graph i (ma) i - + v V (volts) 0.7v for Silicon 0.3v for Germanium ~ ~ M.-C. BRUNET ECE 110 UIUC 8.3 Question : Is a diode a load or a source?
ECE 110 M.-C. Brunet Diodes Handout 8

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ECE 110 M.-C. Brunet Diodes Handout 8 Example 1 : i D = + - 5V 1 k i D + - v D v D = + - 5V 1 k i D + - v D Graphical Solution (mA) i D M.-C. BRUNET ECE 110 UIUC 8.4 v D Example 2 : 2V 1 k Ω 2 k Ω - v 2 + i 2 i 3 + - i 1 + - v 1 M.-C. BRUNET ECE 110 UIUC 8.5
ECE 110 M.-C. Brunet Diodes Handout 8 Use an approximate IV graph. Will produce an approximate solution. i + v - i i The large signal model v v 1 The diode is OFF Replace the diode by Solve the circuit and then check that 2 The diode is ON Replace the diode by M.-C. BRUNET ECE 110 UIUC 8.6 Solve the circuit and then check that Back to Example 1 : Assume Von = 0.7v 1 k Ω Solution using the model + - 5V i D + - v D Is the diode ON or OFF? Try all cases to see which one works. (mA) If the diode is OFF Draw the linear model used in each case (i.e. assumption), solve, and validate.

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## This note was uploaded on 09/16/2009 for the course ECE 110 taught by Professor Haken during the Spring '08 term at University of Illinois at Urbana–Champaign.

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8 Diodes - ECE 110 M.-C. Brunet i Diode or pn junction. It...

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