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POWER ELECTRONICS

بسم الله 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 6. Chapter Three. Thyristors.

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POWER ELECTRONICS

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  1. بسم الله 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 6

  2. Chapter Three Thyristors Two Transistor Model of Thyristors When Driving IB2 using IG and IC1 then α1 + α2 1 then IE will increase Via IA And positive feedback will occur. Thus SCR will turn –on.

  3. Chapter Three • (α1 + α2 >= 1) This condition will turn on the SCR and it will happen when: • If the temperature of the device is very high ,the leakage current through it will increases, and this increase in current causes the alphas to increase. • When the voltage between anode and cathode exceed VBO (break down of J2). • If there is gate current IG.

  4. Chapter Three SCR transient characteristics

  5. Chapter Three SCR Trigger circuits • Firing angle circuits involves three considerations: • Choice of a suitable circuit which will supply the firing signal under the required circuit conditions. • Maximum voltage and current. • Minimum voltage and current. Less trigger current is required at high temp. Less trigger current is required when VAK is high. Sharp pulse is required in senstive applications.

  6. Chapter Three SCR turn-off circuits (Commutating circuits) • AC state. • DC state. • Positive cycle in AC state. Circuit (b) is seldom used except at low power levels. Many methods for these switch circuits will be discuss in chapter 8 End of Lecture **** Eng.moayed

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