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‫بسم هللا الرحمن الرحيم‬
The Islamic University of Gaza
Faculty of Engineering
Electrical Engineering Department
POWER ELECTRONICS
EELE 5450 — Fall 2009-2010
Instructor: Eng.Moayed N. EL Mobaied
Lecture 3
Chapter Two
Power Semiconductor Diodes
Power diodes have large power-, voltage-, currenthandling capabilities than that of ordinary signal diodes.
Chapter Two
Power Diodes symbol and type of packaging
Chapter Two
Diode Characteristics
Chapter Two
V-I characteristics
Forward-biased region
Reverse biased region
Breakdown region
Chapter Two
I D  I S (e
VT 
Vd
n VT
 1)
Shockley’s equation
Kt
q
N=1,2( Germanium, Silicon) practically 1.1—1.8
VT= Thermal voltage
IS= Saturation current
k  is Boltzman' s cons tan t  1.38 * 1023 j / k
T  is the absoultetemperature in kelvins  237  thetem in C 
q  is the magnitudeof electronic ch arg e  1.6 * 1019 C
Chapter Two
Shockley diode equation
Chapter Two
Forward-bias VD>0
Chapter Two
Reverse-bias VD<0
Chapter Two
Reverse Recovery Characteristics
trr  ta  tb
(2.5)
2QRR
di / dt
(2.10)
trr 
Tb/Ta is the softness factor (SF)
I RR 
2QRR
trr
I RR  2QRR
di
dt
(2.8)
(2.11)
Chapter Two
Power Diode Types
Ideally, a diode should have no reverse recovery time,
However, the manufacturing cost of such diode will increase.
The power diodes can be classified into three categories:
Standard or general-purpose diodes
Fast-recovery diodes
Schottky diodes
Chapter Two
Standard or general-purpose diodes
Reverse recovery time= 25 us (relatively high).
Used in Low-speed applications.
Current rating : From less than 1 Ampere to several
thousands of Amperes.
Voltage rating 50 v to 5 kV.
Chapter Two
Fast-Recovery Diodes
Reverse recovery time< 5 us ( Low).
Used in DC-DC and DC-AC converter circuit (high
speed applications).
Current rating : From less than 1 Ampere to several
hundreds of Amperes.
Voltage rating 50 v to 3 kV.
Platinum or gold.
Chapter Two
Schottky Diodes
No minority carriers .
Recovered charge is much less than P-n junction diodes.
Used in high current and low voltage dc power supplies.
Current rating : From 1 Ampere to 300 Amperes.
Voltage rating <100 V.
Chapter Two
The reverse recovery time of a diode is trr=3us and
the rate of fall of the diode current is di/dt=30 A/us
Determine
(a) the storage charge Qrr
(b) Peak reverse current Irr
End of Lecture **** Eng.moayed