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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 * 1023 j / k T is the absoultetemperature in kelvins 237 thetem in C q is the magnitudeof electronic ch arg e 1.6 * 1019 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