l07_kvs_diode_full.pdf

7/27/2019 L07_kvs_diode_full.pdf

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B

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PN Junction Diode

P N

Inside a PN junction at equilibrium (zero applied voltage), there

is built-in voltage with N region being positive and P-region

negative.

+ +

+ +

+ +

The built-in voltage (also called potential barrier) prevents

electrons and holes to give rise to current. 10


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Breakdown

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Analysis using non-linear diode model is not easy

R

VO= ? (1)S OV I R V = +

VS DOV

I

expSTn V

=

Iln( 1) (3)O TV nV = +

I

S

S

I

S T

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VO= ?

1K{exp ( ) 1}D S

T

Vi I

V=

D2V

152 10

/ 26

SI A

V k T q m V

=

=

a t T 300K=

ssume O

VO = 0.5 VO = 0.707VO = 0.711

IR

= I = 1.5 x 10-3 I = 1.293 x 10-3I = 1.289 x 10-3

1)IIln( S+= TO nVV

VO = 0.711 VO = 0.707VO = 0.707

CONVERGENCE 21


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Analysis using a non-lineardiode model is relatively difficult and

time consuming.

It also does not give a symbolic expression that can provide

insi ht and hel in the desi n of the circuit.

Need SIMPLER and LINEAR Device Models

f

V > V

V < V

open circuit

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Even Simpler Diode Models

V > 0

V < 0

I

V=

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E l


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10VExample

n t e currentthrough the diode

using ideal diode

D 5K5K2mAmodel

Is the diode forward biased? Not Sure!!

Assume that it is forward biased

Carry out analysis and then check if current through the diode is inappropriate direction.

If not, diode is reverse biased and we carry out the analysis

again!! 34


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10V


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10V

2mA

Assume reverse bias

10V V +5 5

mk k

+ + =

5K2mA 4K

1==

5K

2

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l07_kvs_diode_full.pdf

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