EE 330 Lect 22 Fall 2011

EE 330 Lect 22 Fall 2011 - EE 330 Lecture 22 Thyristors SCR...

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EE 330 Lecture 22 Thyristors SCR Triac
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Enhancement and Depletion MOS Devices • Enhancement Mode n-channel devices V T > 0 • Enhancement Mode p-channel devices V T < 0 • Depletion Mode n-channel devices V T < 0 • Depletion Mode p-channel devices V T > 0 Review from Last Lecture
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The JFET S D G GS P DSS DS D GS P DS GS P DS GS P 2 P 2 GS DSS GS P DS GS P P 0 V V 2I V I V -V - V V V V < V -V V2 V I 1- V V V < V -V V     D D S S G G n-channel p-channel p-channel JFET Square-law model of n-channel JFET Functionally identical to the square-law model of MOSFET Parameters I DSS and V P characterize the device I DSS proportional to W/L where W and L are width and length of n+ diff V P is negative for n-channel device, positive for p-channel device thus JFET is depletion mode device Must not forward bias GS junction by over about 300mV or excessive base current will flow Widely used as input stage for bipolar op amps Review from Last Lecture
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The SCR Silicon Controlled Rectifier • Widely used to switch large resistive or inductive loads • Widely used in the power electronics field • Widely used in consumer electronic to interface between logic and power Anode Cathode Gate G C A p p n n G G G A A A C C C Symbols Consider first how this 4-layer 3-junction device operates Usually made by diffusions in silicon Review from Last Lecture
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Operation of the SCR I F V F I G =0 BGF1 V I H I F V F I G =I G1 >0 BGF0 V I H The Ideal SCR G A C V F V G I F I G I H is very small I G1 is small (but not too small)   , F F G I = f V V   , F F G called the SCR model As for MOSFET, Diode, and BJT, several models for SCR can be developed Review from Last Lecture
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Operation of the SCR Operation with the actual SCR V CC V G R L V F I F I F V F I G4 >I G3 >I G2 >I G1 =0 V BRR CC L V R BGF0 V CC V I H To turn on, must make I G large enough to have single intersection point Review from Last Lecture
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SCR Terminology V CC V G R L V F I F I F V F I G =0 V BRR CC L V R BGF0 V I H I L • Trigger parameters (V GT and I GT ) highly temperature dependent • Want gate “sensitive” but not too sensitive (to avoid undesired triggering) • SCRs can switch very large currents but power dissipation is large • Heat sinks widely used to manage power • Trigger parameters affected by both environment and application • Trigger parameters generally dependent upon VF • Exceeding V BRR will usually destroy the device • Exceeding V BGF0 will destroy some devices • Lack of electronic turn-off unattractive in some applications
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EE 330 Lect 22 Fall 2011 - EE 330 Lecture 22 Thyristors SCR...

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