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Lecture 24
Basic Diode Concepts
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Diodes
1. Understand diode operation and select diodes
for various applications.
2. Analyze nonlinear circuits using the graphical
load-line technique.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
3. Analyze and design simple voltage-regulator
circuits.
4. Solve circuits using the ideal-diode model and
piecewise-linear models.
5. Understand various rectifier and wave shaping
circuits.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Fluid Analogy
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Diode-Fluid Analogy
Pivot
Seat
Flapper
Schematic diagram of a flapper valve
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Thermionic Diode
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Galena (Sulphide Ore of Lead)
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Cat’s Whisker
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Semiconductor Diode
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
P-Type and N-Type Materials
http://www.ineer.org/Events/ICEE1999/Proceedings/papers/334/334.htm
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
P-N Junction
http://www.ineer.org/Events/ICEE1999/Proceedings/papers/334/334.htm
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Carrier Recombination
http://www.ineer.org/Events/ICEE1999/Proceedings/papers/334/334.htm
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Depletion Layer
http://www.ineer.org/Events/ICEE1999/Proceedings/papers/334/334.htm
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
I-V Characteristic
“On”
“Off”
Reverse
Breakdown
Non-linear I-V
Characteristic
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Shockley Equation
  vD
iD  I s exp 
  nVT
 
  1
 
kT
VT 
q
n = Emission coefficient (1<n<2)
k = 1.38 × 10–23 J/K is Boltzmann’s constant and
q = 1.60 × 10–19 C is the magnitude of the
electrical charge of an electron. At a temperature
of 300 K, we have
VT  26 mV
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Shockley Equation
  vD
iD  I s exp 
  nVT
 
  1
 
 vD
iD  I s exp 
 nVT

 for v D  VT

kT
VT 
 26 mV
q
iD   I s for vD  -VT until reaching reverse breakdown
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Zener Diodes
Diodes that are intended to operate in the
breakdown region are called Zener diodes.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Zener Diodes
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of Diode
Circuits
VSS  Ri D  v D
Assume VSS and R are known. Find iD and vD
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of Diode
Circuits
VSS  Ri D  v D
VSS  Ri D  v D
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of Diode
Circuits V  2V
ss
R  1k
2  1000 i D  v D
iD  0  v D  2
v D  0  iD 
2V
 2mA
1000 
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Load-Line Analysis of Diode
Circuits V  10V
ss
R  10 k
10  10 ,000 iD  v D
10V
 1mA
10 ,000 
i D  0  v D  10 (offscale )
v D  0  iD 
v D  2  iD 
8V
 0.8mA
10 ,000
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Ideal Diode Model
The ideal diode acts as a short
circuit for forward currents
and as an open circuit with
reverse voltage applied.
iD > 0 vD < 0  diode is in the “on” state
vD < 0 ID = 0  diode is in the “off” state
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
1. Assume a state for each diode, either on (i.e., a
short circuit) or off (i.e., an open circuit). For n
diodes there are 2n possible combinations of
diode states.
2. Analyze the circuit to determine the current
through the diodes assumed to be on and the
voltage across the diodes assumed to be off.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
3. Check to see if the result is consistent with the
assumed state for each diode. Current must flow
in the forward direction for diodes assumed to
be on. Furthermore, the voltage across the
diodes assumed to be off must be positive at the
cathode (i.e., reverse bias).
4. If the results are consistent with the assumed
states, the analysis is finished. Otherwise, return
to step 1 and choose a different combination of
diode states.
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
Assume D1 off and D2 on:
vD1= 7V
D1 would
be on!
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
Assume D1 off and D2 off:
Both diodes should be on!
vD1= 10V
vD2= 3V
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
Assume D1 on and D2 on:
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
i1
i2
i3
10V  3V
i1 
 1.75 mA
4 K
3V
i3 
 0.5 mA
6 K
i1  i2  i3  i2  i3  i1  0.5 mA  1.75 mA  1.25 mA
Not consistent with direction of current through D2!
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
Assume D1 on and D2 off:
6V
This works!
vD1= -3V
iD1=1mA
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
D1 off
D1 on
D1 would be
on!
iD


This
works!
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
D2 on
Current is going
the wrong way
through the
diode!
D2 off
VD consistent
with D2 off

iD

ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
D3 on
D3 off
D4 on
D4 on
D3 on
D3 off
D4 off
D4 off
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
V
6.67 mA
D3 on
-1.67 mA
D4 on
V
V  (10)

 5m A
2k
1k
V  2V  20  10
3V  10
V
 10
 i1  1.67m A i2  6.67m A
3
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
+-
D3 on
10V
-+
D4 off
20V
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
Not consistent
with 5 mA
current source!
D3 off
D4 off
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.
Assumed States for Analysis of
Ideal-Diode Circuits
+5V
D3 off
+-
D4 on
V
5mA
v  5  10  0
v  5
ELECTRICAL ENGINEERING: PRINCIPLES AND APPLICATIONS, Fourth Edition, by Allan R. Hambley, ©2008 Pearson Education, Inc.