SUBJECT NAME: Analogue Electronics 1
CODE: TETE3691 [Tutorials, Questions and Answers]
24th March, 2023
Instructions: Attempt all Questions
1) Discuss the Thermal Runaway concept of Bipolar Junction Transistors
2) What is the DC Alpha of a Transistor
3) Using appropriate diagrammatic illustrations, describe three (3) major configurations of a typical PNP transistors.
4) Describe four basic guides involved in analyzing Bipolar Junction Transistor circuits:
5) Explain Transistor Biasing and State the transistor Biasing Rule
6) Describe the forward reverse biasing concept.
7) You recently secure an internship with a popular organisation in Namibia, specialized in various types of electronic
component design and coupling located in KARA REGION of Namibia. Coincidentally on your resumption you are
lucky to be part of a project that requires the use of Light Emitting Diodes (LEDs). List at least five (5) applications of
this component.
8) A half-wave rectifier using silicon diode has a secondary emf of 14.14 V (rms) with a resistance of 0.2 Ω. The
diode has a forward resistance of 0.05 Ω and a threshold voltage of 0.7 V. If load resistance is 10 Ω, determine (i)
dc load current (ii) dc load voltage (iii) voltage regulation and (iv) efficiency.
9) Using the original circuit for a silicon diode in Figure A. (a) Illustrate the following by drawing a new
circuit;
i. first diode approximation
ii. second diode approximation
iii. third diode approximation respectively
Figure A: Original Circuit for diode approximation
(b) Use the corresponding new circuit(s) in questions 9(a) to solve for the following:
(i) load voltage and current using the first diode approximation
(ii) load voltage and current using the second diode approximation
(iii) load voltage and current using the third diode approximation
10) A 1-φ, full-wave rectifier supplies power to a 1 k W load. The ac voltage applied to the diode is 300-0-300 V
(rms). If diode resistance is 25 W and that of the transformer secondary negligible, determine“
(i) average load current, (ii) average value of load voltage,
(iii) rms value of ripple, (iv) efficiency.
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11) Figure Q3 represents a new design for a brand-new product of an electronic organisation. The design
consists of the power supply stage using a bridge rectifier with no capacitor. The circuit supplies 18 volt DC
(average) to a Load resistor at a current of 10A. The primary voltage is 220Vac at a frequency 50Hz.
Calculate the:
i. Peak output voltage
ii. Peak secondary voltage
iii. Secondary voltage (RMS)
iv. Peak inverse voltage
v. Transformer MIN
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Answer
12) Show the voltage waveforms across each half of the secondary windings and across RL when a 100V peak sin
wave is applied to the primary winding in Figure Q12. Also, find the minimum PIV rating the diodes should have?
Figure Q12
Answer: (a) The transformer turns ration n = 0.5. The total peak secondary voltage is
Vp(sec) = nVp(pri) = 0.5(100 V) = 50 V
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There is a 25 V peak across each half of the secondary with respect to ground. The output load voltage has
a peak value of 25 V, less the 0.7 V drop across the diode. The waveforms are shown figure Q12.1.
Figure Q12.1
(b) Each diode must have a minimum PIV rating of:
PIV = 2Vp(out) + 0.7 V = 2(24.3 V) + 0.7 V = 49.3 V
13) Design and draw the circuit diagram of a power supply which delivers 18Vdc at 2A to a load resistance using
centre tapped transformer with capacitor. The power supply should operate from 220 V domestic power source at
a frequency 50Hz. The design must include switch and fuse. (Take ripple voltage as 9.09V).
a) Draw the design circuit diagram
b) Peak output Voltage
c) The capacitor value.
d) Secondary Voltage
e) Peak secondary Voltage (rms)(i.e V1(pk) &V2(pk))
f) Diode peak inverse voltage (PIV)
g) Transformer size
h) Fuse rating of twice the line current of the primary voltage.
i) Sketch the output waveform of the rectifier before and after the capacitor.
Show all calculations clearly and indicate the calculated values on your drawing.
Answer
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a)
Vdc = Vout(pk) Vout(pk) = 18 +
b)
2
9.09
2
= 22.55 Vp ✓
CVripple = It
C=
c)
𝑉𝑟𝑖𝑝𝑝𝑙𝑒
2 ×0.01
=
9.09
2200µF ✓
Secondary Voltage = 22.55 + 0.7 = 23.25V ✓
d) Peak secondary Voltage (rms)
V1(pk) = V2(pk) = 1.414 ×
e)
23.25
2
PIV = (2 x 23.25V) – 0.7V
= 45.8V ✓
f)
Transformer size
16.44 x 2 =32.88VA✓
g)
Fuse rating
=2 ×
h)
14)
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32.88
220
= 𝟐𝟗𝟗𝒎𝑨 ✓
= 𝟏𝟔. 𝟒𝟒𝑽 ✓
15) What kind of semiconductor is produced if germanium is doped with (a) arsenic, and (b) gallium?
(i) Germanium has four valence electrons. If germanium doped with arsenic (five valence electrons), four are
used in bonding and one electron will be left for conduction. This produces an n-type material.
(ii) If germanium is doped with gallium (three valence electrons), all three electrons are used in bonding,
leaving one hole for conduction. This results in a p-type material.
16) Explain the concept of Hall effect in semiconductor materials
17) In the circuit of Fig. 20, find (i) IE, (ii) IB, (iii) IC and (iv) VCE. Neglect VBE and take β = 100.
18) In the CC circuit of Fig. 23, find (a) IB , (b) IE , (c) VCE , (d) VE and (e) VB. Take β = 49 and VBE = 0.7 V
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19) Explain the concept of Breakdown Voltage Rating, VBR
20) What is Average Forward-Current Rating, IO or Avalanche breakdown
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