Prelim%202%20solutions_2008

Prelim%202%20solutions_2008 - MAE 3780 MECHATRONICS FALL...

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MAE 3780 MECHATRONICS FALL 2008 1 PRELIM 2 SOULUTIONS 1. (15 points) First, let’s consider BJTs. They consist of two p-n junctions back-to-back. Before the BJT is saturated, the BE junction is forward biased and the BC junction is reverse biased. This means that a large current can flow from collector to emitter, but not the other way around. The BJT becomes saturated when V BC increases (or, alternatively, V CE decreases for a constant V BE ). Once V BC increases to the offset voltage of the BC junction, the BC junction also becomes forward biased. At this point, the currents through each junction begin to cancel out, and the overall current from collector to emitter decreases. Additionally, V CE reaches its minimum value of V CEsat . In summary, the conditions for saturation are: V BE = V γ , V CE = V CEsat , and i C < β i B . Now, let’s consider MOSFETs. They consist of two n-type regions (drain and source) separated by a p-type region (bulk). An n-type channel forms when V GS and V GD are greater than a threshold voltage V T , allowing current to conduct from drain to source. The MOSFET becomes
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Prelim%202%20solutions_2008 - MAE 3780 MECHATRONICS FALL...

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