Introduction to Electronic Devices and Circuit Theory
Test 1
Name: ___________________________
ID # : ___________________________
Do All Questions
Section A (10 Mrks)
1. A pn junction is formed by
(a) the recombination of electrons and holes
(b) ionization
(c) the boundary of a p-type and an n-type material
(d) the collision of a proton and a neutron
2. The depletion region consists of
(a) nothing but minority carriers
(b) positive and negative ions
(c) no majority carriers
(d) answers (b) and (c)
3. The difference between an insulator and a semiconductor is
(a) a wider energy gap between the valence band and the conduction band
(b) the number of free electrons
(c) the atomic structure
(d) answers (a), (b), and (c)
___/03/2023
4. To forward-bias a diode,
(a) an external voltage is applied that is positive at the anode and negative at the cathode
(b) an external voltage is applied that is negative at the anode and positive at the cathode
(c) an external voltage is applied that is positive at the p region and negative at the n region
(d) answers (a) and (c)
5. A diode is normally operated in
(a) reverse breakdown
(b) the forward-bias region
(c) the reverse-bias region
(d) either (b) or (c)
6. The V-I curve for a diode shows
(a) the voltage across the diode for a given current
(b) the amount of current for a given bias voltage
(c) the power dissipation
(d) none of these
7. An LED
(a) emits light when reverse-biased
(b) senses light when reverse-biased
(c) emits light when forward-biased
(d) acts as a variable resistance
8. A diode that has a negative resistance characteristic is the
(a) Schottky diode
(b) tunnel diode
(c) laser diode
(d) hot-carrier diode
9. The cathode of a zener diode in a voltage regulator is normally
(a) more positive than the anode
(b) more negative than the anode
(c) at +0.7 V
(d) grounded
10. The three terminals of a bipolar junction transistor are called
(a) p, n, p
(b) n, p, n
(c) input, output, ground
(d) base, emitter, collector
Section B (20 Mrks)
1
The process of adding impurities to a semiconductor crystal is known as
doping
2
3
4
Germanium has four valence electrons.
Silicon has five valence electrons.
Holes drift to the negative end of voltage source.
5
Materials with eight (8) valence electrons tend to be unstable.
6
Silicon does not semi-conduct unless it is doped or heated.
7
N-type materials have free electrons available to support current flow.
8
Good conductors such as copper, contain a large number of charge carriers.
9
10
A silicon crystal is built by ionic bonding.
It is easy to move valence electrons in conductors.
11
Hole current is opposite to electron current.
12
13
Forward bias expands the depletion region.
A junction diode is doped with both P- and N- type impurities.
14
Heat energy can break covalent bonds so that semiconductors are better
conductors at higher temperatures.
15
16
Reverse bias collapses the depletion region and turns on the diode.
A reverse biased diode may show a little leakage current because of minority
carrier action.
17
18
The current carriers in conductors such as copper are holes.
An N-type semiconductor shows a few holes, the holes are minority carriers.
19
20
Holes are current carriers and are assigned as positive charge.
A free electron in a P-type crystal is called a majority carrier.
Section C (70 Mrks)
QUESTION #1
a. Determine the static or dc resistance of the commercially available diode in the finger below
at :
I.
A forward current( ID) of 2 mA
(3 mks)
II.
A forward current ( ID) of 9 mA
(3 mks)
III.
A reverse voltage (Vd) of -40 V
(3 mks)
Fig 1
b. Find the piecewise-linear equivalent circuit for the diode in fig 1 above. Use a straight
line segment that intersects the horizontal axis at 0.7 V.
(8 mks)
c. Define load line as it relates to diodes.
(3 mks)
QUESTION #2
a) Draw the output waveform, Vo, for the clamping networks for the square wave with a
max. input of 5V.
(3 mks)
b) You are to use an oscilloscope to measure the output waveform at RL. Draw the
expected waveform for a square wave input of 10v peak
(4 mks)
c) Explain what happens in the circuit when the diode in the figure above is forward
bias.
(3 mks)
QUESTION #3
a) The rectifier circuit below was taken from a low voltage power supply. The circuit
has 60 V rms at the secondary of the transformer and has a load resister of 1.5 KΩ
i.
Draw the output wave form across RL for ideal diodes.
(4 mks)
ii.
If the diodes are ideal, what is the dc voltage available at the load?
(4 mks)
iii.
If silicon diodes are employed, what is the dc voltage available at the load?
(4 mks)
iv.
Determine the required PIV rating for each Si diode.
v.
Find the max current through each diode during conduction.
(4 mks)
(4 mks)
QUESTION #4
a. State the difference between clipping and clamping
(4 mks)
b. Draw and label the simplest clipping and clamping circuit.
(6 mks)
c. Draw the output wave form across RL for the following circuits. The input is 24v
peak for both circuits and VBB is 0.7V.
(10 mks)
cct 1.
cct 2