Download 971 Quiz 01

1. (25 points)
For a PN junction diode with N A  1017 cm 3 in the p region
and N D  1014 cm3 in the N region, in the thermal equilibrium,
ni  1.5  1010 cm 3 at 300oK.
(a) Find the minority and majority carriers concentration in the P
region. (3 points)
(b) Find the minority and majority carriers concentration in the N
region. (3 points)
(c) Under the open circuit condition, explains the diffusion current
and drift current direction. (4 points)
(d) Under the forward biasing, sketch the steady-state minority
carrier concentration. (10 points)
(e) Sketch the Voltage-Current characteristic curve of a diode.(5
points)
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2.(15 points) Consider the following voltage doubler circuit .(3 points for
each)
A
B
C

10 V

D
E
F
(a) The circuit needs how long to produce a stable voltage for every
capacitor if the source frequency is 60HZ.
(b) Find VAE (t )  ? and V AE is DC or AC?
(c) This circuit can transfer a low DC voltage to a high DC voltage.
(d) How many type of DC voltage we can get in this circuit?
(e) Find the PIV of the each diode.
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3.(25 points) Consider the following DC power supply circuit. Let the
transformer output voltage 10V. The right side figure shows the Zener
diode v  i characteristics.
IZ
110
V / 12V
110/10V
R
8V
RL
C
0.7V
10mA
(a) Sketch a 10V 60Hz Ac voltage signal.
(b) Determine the current-limiting resistance R such that the load
current can vary over the range 20mA  I L  200mA .
(c) Find C such that the ripple voltage is no larger than 3V, determine
the maximum voltage drop of C.
(d) Determine the average current and the peak inverse voltage for
each diode. (hint: I D 
VP
VP
(1  
) ).
R
2Vr
(e) Determine the maximum power dissipated in Zener diode and the
current-limiting resistance R .
3
VZ
4. (15 points) For the following ideal diode circuit,
R1  5 K
R2  10 K
V   5V
V   5V
9V
t
 4V
(a) Find the transfer curve vo v.s. v i .(10 points)
(b) Find the output signal, for the above input signal. (5 points)
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5. (30 points) True and false (3 points for each)
(a) In active mode, the emitter in an NPN transistor injects holes into
the transistor, so the emitter must be at lower potential than the
other two pins of the transistor.
(b) The following diode logic circuit can realize a OR gate.
(c) An NPN transistor if BE and BC junction under the forward biasing,
then
I E  I S e
(VBE
VT
)
in which  
 1
and

 is defined as
  IC I .
B
(d) When a transistor is used as a switch it must be either OFF or fully
ON. In the fully ON state the voltage VBE across the transistor is
almost zero and the transistor is said to be saturated. In this case
the both junction of transistor should be under the forward bias
and the collector current IC  I B .
(e) A Zener diode is generally operated for current between
I Z (min) and I Z (max) .
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(f) A zener diode is usually used to filter the ripple of a rectifier.
(g) In the depletion region of a PN junction, the positive charge will
appear in the N-type side
(h) If we introduce some 3-valence atom into a Si-semiconductor, the
majority carriers of this adopted semiconductor are holes and it
usual denoted by nno . .
(i) If the reverse bias increases, the PN junction capacitance will
increase since the depletion width increased.
(j) In a PNP transistor in the active region of operation the base
current is due to holes injected into the emitter from base.
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