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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 201 1 /1 2
Module Title: ANALOGUE ELECTRONICS 2
Module Code: ELTR
School: Mechanical, Electrical & Process Engineering
Programme Titles: Bachelor of Engineering in Electronic Engineering, Year 1 Bachelor of Engineering in Electronic Systems Engineering, Year 1
Programme Codes: EELXE_7_Y EELES_8_Y
External Examiner(s): Dr A. Donnellan Mr I. Kennedy Internal Examiner: Mr M. O’Gorman
Instructions: Answer Question 1 and TWO other questions. Question 1 (worth 40 marks) is compulsory. Questions 2, 3, and 4 are each worth 30 marks.
Duration: 2 Hours
Sitting: Summer 201 2
Requirements for this examination: N/A
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you are attempting the correct examination paper. If in doubt please contact an Invigilator.
COMPULSORY QUESTION
Q. 1 (a) Show how the maximum power dissipation curve for a transistor may be drawn on the transistor’s output characteristics. [7 Marks] Illustrate the direction of curve displacement if the ambient operating temperature of the device is to be increased. [3 Marks] (b) Sketch typical output characteristics for a common emitter transistor and illustrate the region where the transistor is said to be saturated. [7 Marks] What bias condition exists at the collector-base junction ( VCB ) when a transistor operates in the saturated region? [3 marks] (c) (i) Define the current ratios and as applied to a bipolar junction transistor. [4 marks] (ii) Determine , , and the base current, IB for a transistor where IC = 4.80mA and IE = 4.86mA. [6 marks] (d) Explain why the output voltage of a common emitter transistor amplifier is
180 ^ out of phase with the input voltage.^ [10 marks]
CHOOSE TWO QUESTIONS FROM Q.2, Q.3, OR Q.4.
Q. 2 (a) Draw the circuit diagram of a simple zener diode voltage regulator and briefly explain how the circuit minimises the effects of load current variations on the load voltage. [10 Marks] (b) A zener diode has a reverse breakdown voltage of 10 V and after this may be
considered to be a linear resistance of 25 .
Draw the circuit diagram and calculate the value of series resistor required for a simple voltage regulating circuit, using the diode above, which is to maintain
12 V across a constant 600 load from a nominal 15 V supply. [12 Marks]
(c) Determine the maximum variation that can be tolerated in the nominal 15 V supply if the 12 V load voltage is not to vary by more than 10%. [8 Marks]
Q.4 The output characteristics of an NPN transistor are tabulated below, and are assumed to be linear over the given range:
BASE
CURRENT
COLLECTOR CURRENT mA FOR
COLLECTOR VOLTAGES OF,
A 1 V 10 V
The transistor, which has an ac input resistance of 950, is to be used in the common emitter mode with a resistive load of 1.25k and a supply voltage of 10V.
(a) Plot the output characteristics and draw the load-line on graph paper. [15 marks]
(b) Calculate the ac current gain and voltage gain when a 60A peak-to-peak input current varies sinusoidally about a mean value of 50A. [10 marks]
(c) State how a reduction in load resistance would affect the ac voltage gain. [5 marks]
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