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Unformatted text preview: C t 7
Problemttl hap er
ro . 7.1 Discuss the current components in the npn. Electrons are injected from
emitter to base; most injected
electrons are collected (2), but some recombine (1). The
resulting loss of holes in the
base is supplied by the base
current (4), which also supplies
holes for injection into the
emitter (5). PVDHe/m #2—
Prob. 7.2 Sketch band diagrams for npn and pnp BJTs at equilibrium and normal
bias. pnp "‘1’" E: T Equilibrium l
Er Normal bias 70 Pmblm #3 For the diode connections shown, sketch 6p in the base. Which is the best ‘ Prob. 7. Z.
diode .9
61) I I; I! <'
‘ Pu (a) 13 = Ic , 13 = 0. Since V is
large, the collector is strongly
reverse biased, Ape = p,..
Since 13 = 1c, ApE = —Apc
= p" from Eq.(734). The area
under 5p(:cn) is zero. 6?
APE
aApE
3n
0 W5
(c) Since 10 = 0, Apc = aApg from
Eq.(734b). I
6?
W H
In
0 Wb (b) ch = 0, thus Ape = 0. Notice
that this is the narrowbase
diode distribution. 0 W5 (d) V55 = Vca = V. Thus Ape = A1); Connection (1)) gives the best diode since the stored charge is least; (a) is not
a good diode since the current is small and symmetrical about V = 0. 84 Problem. # if is reverse biased with 0.6 V. The band diagram must be drawn to scale Your band diagram shnuld include: the fenmi levels the local vacuum level the depletion charge (+ or ) in the forbidden band
C the conduction band edge the valence band edge 06V 1.0 ...
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 Spring '08
 Keyhani

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