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POWER ELECTRONICS Instructor: Eng.Moayed N. EL Mobaied The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department بسم الله.

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Presentation on theme: "POWER ELECTRONICS Instructor: Eng.Moayed N. EL Mobaied The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department بسم الله."— Presentation transcript:

1 POWER ELECTRONICS Instructor: Eng.Moayed N. EL Mobaied The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department بسم الله الرحمن الرحيم EELE 5450 — Fall Lecture 5

2 Chapter Three Thyristors The SCR (Silicon-controlled rectifier) is the most important member of the family of power semiconductor devices.

3 Chapter Three Applications

4 Chapter Three Thyristors family There are other power semiconductor devices of the thyristor family which share the latching characteristics of the SCR. Triac. Bidirectional diode switch. Silicon controlled switch. Silicon unilateral and bilateral switches( SUS,SBS). Light activated devices Like LASCR and LASCS. Complementary SCRs. Programmable unijunction transistors( PUT).

5 Chapter Three Thyristor (SCR) A Thyristor (SCR) is a four-layer semiconductor device of pnpn structure with three pn junctions. It has three terminals :Anode,Cathode, Gate. When the anode voltage is made positive with respect to the cathode, the junction J 1 and J 3 are forward biased. The junction J 2 is reverse biased, and small leakage current flows from anode to cathode. ( Forward blocking off-state) I D If the anode-to cathode voltage V ak is increased to a sufficiently large value, the reverse-biased junction J 2 will break. This is known as avalanche breakdown and the corresponding voltage is called forward breakdown voltage V BO. Since the other junctions J1 and J3 are already forward biased, there will be free movement of carriers across all three junction, resulting in a large forward anode current. The device will be in a conducting state or on-state.

6 Chapter Three SCR (V-I characteristics) The voltage drop would be due to the ohmic drop in the four layers and it is small, Typically, 1V. In the on-state, the anode current is limited by an external impedance or a resistor, R L. The anode current must be more than a value known as latching current I L, in order to maintain the required amount of the carrier flow across the junction. If the forward anode current is reduced below a level known as the holding current I H, thyristor will be in blocking state. When Cathode is positive with respect to anode (reverse blocking state) I R

7 Chapter Three IG effects End of Lecture **** Eng.moayed


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