EX-504-A Industrial Electronics - Dec 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aDraw the block diagram of on-line uninterrupted power supply and explain the function of each block.
   How to answer

   • Block diagram of on-line UPS: rectifier/charger, battery, inverter, static bypass switch, load.
   • Normal mode: mains via rectifier-inverter supplies load and charges battery.
   • Mains failure: battery via inverter supplies uninterrupted power without transfer time.
2. 7 Marks
   bWhat do you mean by active power line condition? Explain by drawing appropriate diagram.
   How to answer

   • Definition of active power line conditioning / active power line conditioner.
   • Purpose: correct voltage sag, swell, harmonics, power factor.
   • Diagram showing series/shunt active filter with control and waveforms.
3. 7 Marks
   aExplain how a full bridge regulator is derived from a buck regulator.
   How to answer

   • Basic buck regulator topology: switch, diode, L-C filter.
   • Extension to full-bridge: four switches forming bridge with transformer/isolation.
   • Switching sequence giving step-down and polarity reversal to derive full-bridge operation.
4. 7 Marks
   bA buck regulator has an input voltage of 110 volt, the average load voltage is 60 volt, and the average load current is 30 ampere. The switching frequency is 25 kHz. The peak to peak ripple inductor current is 1.2 ampere. Calculate the value of the inductor and load current.
   How to answer

   • Duty ratio $D = V_o/V_{in} = 60/110$.
   • Inductor formula $L = V_o(1-D)/(f \cdot \Delta I_L)$.
   • Substitute $f=25\,kHz$, $\Delta I_L=1.2\,A$ to get $L$ and discuss load $R=V_o/I_o$.
5. 7 Marks
   aDiscuss the transistor model of SCR and derive the expression for anode current in terms of current gain.
   How to answer

   • Two-transistor (p-n-p and n-p-n) model of SCR structure.
   • Current relations with gains alpha1, alpha2.
   • Derivation of $I_A = (\alpha_1 I_G + I_{CBO1}+I_{CBO2})/(1-(\alpha_1+\alpha_2))$ and latching condition.
6. 7 Marks
   bDraw and explain the static characteristics of a SCR.
   How to answer

   • V-I axes: anode voltage vs anode current with gate current as parameter.
   • Forward blocking, forward conduction, reverse blocking regions.
   • Breakover voltage, holding and latching current marking.
7. 7 Marks
   aExplain the transistor model of the IGBT and draw its V-I characteristics.
   How to answer

   • IGBT structure as MOSFET-driven BJT Darlington/cascade model.
   • Equivalent circuit with MOSFET and p-n-p transistor.
   • V-I output characteristics: transfer and output curves with saturation/active regions.
8. 7 Marks
   bDescribe the electronic crowbar protection employed for power transistor from over current.
   How to answer

   • Need for overcurrent protection of power transistor.
   • Crowbar principle: sense overcurrent and short supply to blow fuse.
   • Circuit with SCR/thyristor crowbar, sensing and triggering operation.
9. 7 Marks
   aHow does an operational amplifier work as a comparator?
   How to answer

   • Op-amp without feedback as high-gain comparator.
   • Reference vs input comparison giving +Vsat/-Vsat.
   • Zero-crossing and level detector operation with waveforms.
10. 7 Marks
    bDiscuss the following terms related with operational amplifier:

    1. i)CMRR
    2. ii)Slew rate
    3. iii)Gain
    How to answer

    • CMRR: differential vs common-mode gain ratio.
    • Slew rate: maximum output voltage rate $dV/dt$.
    • Gain: open-loop and closed-loop voltage gain definitions.
11. 7 Marks
    aExplain any three standard PLC communication protocols.
    How to answer

    • Select three e.g. Modbus, Profibus, Ethernet/IP, Profinet.
    • Topology, medium and master-slave/client-server working.
    • Application in PLC networking.
12. 7 Marks
    bExplain program mode, run mode and test mode in PLC.
    How to answer

    • Program mode: editing/downloading allowed, outputs disabled.
    • Run mode: normal execution and I/O update.
    • Test mode: program execution with forced I/O for debugging.
13. 7 Marks
    aDiscuss the functional block diagram of PLC.
    How to answer

    • Main blocks: CPU, memory, input/output modules, power supply, programming device.
    • Signal flow from field inputs through processor to outputs.
    • Scan cycle explanation.
14. 7 Marks
    bHow PLC interface with power electronics control to make a modern automated system?
    How to answer

    • PLC digital/analog outputs driving power electronic converters.
    • Isolation, signal conditioning and gate drive interface.
    • Example of automated drive/motor control system.
15. 14 Marks
    Write short notes on any two of the following :

    1. a)SMPS
    2. b)Wien Bridge Oscillator
    3. c)Power MOSFET
    4. d)Event Driven device
    How to answer

    • For any two: definition, block diagram/circuit, working principle.
    • Key features, advantages and typical applications.
    • Relevant waveforms/characteristics where applicable.