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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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