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Title: 1.1 Silicon Crystal Structure Author: Blyang Last modified by: tking Created Date: 3/28/2000 4:44:02 PM Document presentation format: On-screen Show
Title: ANNOUNCEMENTS 1 Lecture 28
  • For Problem 2 of HW9, use A 10-7 cm2
  • The Term Project will be posted online today
  • Due on Friday, April 27
  • You may work with one partner
  • The PNPN thyristor
  • Reading Chapter 13
  • 2 The Silicon Controlled Rectifier (Thyristor)
  • The SCR is a PNPN device
  • Used in high-power switching applications
  • 3 SCR Operation
  • The SCR can be modeled as 2 interconnected BJTs
  • 4 Forward blocking state
  • Few holes injected into N region
  • Thermal R-G current only
  • 5 Conducting State
  • Holes injected into N
  • Due to wide N-P depletion region, holes are swept into P, turning on PNP device
  • This turns on NPN device
  • This regenerative effect maintains conduction even at low voltage, down to a minimum holding current.
  • 6 Quantitative Analysis
  • We can write
  • Normally, (a1a2) lt1
  • However, as VAK ?, base width narrowing causes (a1a2) ?1, IAK?
  • 7 (No Transcript)
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