1. Spring 2007EE130 Lecture 28, Slide 1 Lecture #28 ANNOUNCEMENTS For Problem 2 of HW#9, use A = 10 -7 cm 2 The Term Project will be posted online today –Due on Friday, April 27 –You may work with one partner OUTLINE The PNPN thyristor Reading: Chapter 13

2. Spring 2007EE130 Lecture 28, Slide 2 The Silicon Controlled Rectifier (Thyristor) The SCR is a PNPN device –Used in high-power switching applications

3. Spring 2007EE130 Lecture 28, Slide 3 The SCR can be modeled as 2 interconnected BJTs SCR Operation

4. Spring 2007EE130 Lecture 28, Slide 4 Forward blocking state Few holes injected into N region Thermal R-G current only

5. Spring 2007EE130 Lecture 28, Slide 5 Conducting State 1.Holes injected into N 2.Due to wide N-P depletion region, holes are swept into P, turning on PNP device 3.This turns on NPN device This regenerative effect maintains conduction even at low voltage, down to a minimum “holding current”.

6. Spring 2007EE130 Lecture 28, Slide 6 Quantitative Analysis We can write: Normally, (  1 +  2 ) <1 However, as V AK , base width narrowing causes (  1 +  2 )  1, I AK 