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Industrial Electronics and, Control, Unit-1, Introduction to SCR, Faculty- Meenakshi Rastogi, Lecturer Electrical Engineering Department, Government Polytechnic Lucknow
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COURSE CONTENT1.1 Power diode characteristics, application of general purpose diode,, fast recovery diode and Schottky diode, use in R, RL series circuit., 1.2 Construction and working principles of an SCR, two transistor, analogy and characteristics of SCR, 1.3 SCR specifications and rating, 1.4 Construction, working principles and V-I characteristics of DIAC,, TRIAC and Quadriac, 1.5 Basic idea about the selection of heat sinks for SCR and TRIACS, 1.6 Methods of triggering a Thyristor. Study of triggering circuits, Meenakshi_EE_GPL
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Junction Diodes, , Space change density the electric field and the electric potential in side a p-n junction under (a) thermal equilibrium condition, (b) reverse, Meenakshi_EE_GPL, biased condition,, (c) forward biased condition
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Power Diode, β’ A power diode is a type of diode that is commonly used in power, electronics circuits. Just like a regular diode, a power diode has twoterminals and conducts current in one direction. A power diode varies, in construction from a standard diode to enable this higher current, rating., , Meenakshi_EE_GPL
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Volt-Amp (i-v) Characteristics, πΉπππ€πππ ππ’πππππ‘, πΌπΉ =, πΌπΉ = Is exp, , ππ, ππ, , β1, , Is = Reverse saturation current ( Amps), v = Applied forward voltage across the device (volts), q = Change of an electron, k = Boltzmanβs constant, T = Temperature in Kelvin, , Meenakshi_EE_GPL
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Power Diode, , Diagram of a power Diode; (a) circuit symbol (b) photograph; (c) schematic cross section., , Meenakshi_EE_GPL
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Characteristics of Power Diodes, 1-Power Diode under Reverse Bias Conditions, β’, , Reverse bias i-v characteristics of a power Diode, , Electric field strength in reverse biased power Diodes;, (a) Non-punch through type; (b) punch through type., , Meenakshi_EE_GPL
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Power Diode under Forward Bias Condition, , (a) Excess free carrier density distribution; (b) i-v characteristics., Meenakshi_EE_GPL
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Switching Characteristics of Power Diodes, β’ Power Diodes take finite time to make transition from reverse bias to forward, bias condition (switch ON) and vice versa (switch OFF)., β’ Behavior of the diode current and voltage during these switching periods are, important due to the following reasons., 1., Severe over voltage / over current may be caused by a diode, switching at different points in the circuit using the diode., 2., Voltage and current exist simultaneously during switching operation, of a diode. Therefore, every switching of the diode is associated, with some energy loss. At high switching frequency this may, contribute significantly to the overall power loss in the diode., , Meenakshi_EE_GPL
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Characteristics difference-Power diode and, Signal diode, , Meenakshi_EE_GPL
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Forward Recovery Characteristics, , Forward current and voltage waveforms of a power diode during Turn On operation., Meenakshi_EE_GPL
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Reverse Recovery Time, β’ The charge carriers (holes & electrons) require a certain time to recombine with, opposite charges and to be neutralized; this time is called the reverse recovery, time π‘ππ of the diode., β’ For fast recovery π‘3 βͺ π‘2 βΎ π‘2 = π‘ππ βΎ π‘ππ =, , 2πππ, ππ, ππ‘, , β’ The fast decay of negative current creates an inductive drop that adds with, the reverse blocking voltage ππ
as illustrate in Fig.3., β’ There are two types of reverse recovery characteristics of junction diodes: Soft, recovery and Fast recovery where, the softness factor, SF is the ratio of π‘2 /π‘3 ., , Meenakshi_EE_GPL
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Application of General Purpose Diode, β’ These diodes have high reverse recovery time of about 25 microsecs (Β΅sec)., β’ This kind diodes have high reverse recovery time. It will be in the range of, 25ΞΌs., β’ The diode current rating will be from 1A to several thousand amperes., β’ The voltage rating will be from 50V to 5kV., β’ Battery charging circuits,, β’ Uninterruptible Power Supplies(UPS) and electrical traction, DC power, supplies etc., β’ Uncontrolled power rectification, β’ For low frequency application up to 1kHz., Meenakshi_EE_GPL
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Application of Fast Recovery Diode, β’ As the name indicates, these diodes have very low reverse recovery, time. It will be less than 5ΞΌs., β’ They are mainly used in switching circuits like choppers, commutation, circuits, switching mode power supplies etc., β’ The current rating of the diode will be from 1A to several hundreds, amperes., β’ The voltage rating will be from 50V to 3kV., , Meenakshi_EE_GPL
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Application of Schottky Diode, β’ In high frequency switching circuits like SMPS, the Schottky diodes are, used (in those applications we canβt use the general purpose diodes)., β’ In this type of diodes, instead of P-N junction ( semiconductor to, semiconductor) metal to semiconductor junctions used., β’ The Schottky diodes have very fast recovery time and low forward, voltage drop., β’ The current flow will be done by only majority carriers., β’ freewheeling in SCR circuits because of low recovery loss, lower, junction temperature and reduced di/dt, Meenakshi_EE_GPL
