Industrial Electronics (4331103) - Winter 2023 Solution

Question 1(a) [3 marks]

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Draw symbol and construction of SCR. Also write down applications of SCR.

Answer:

Symbol and Construction of SCR:

Construction:

graph TD
    A[Anode] --- P1[P-Layer]
    P1 --- N1[N-Layer]
    N1 --- P2[P-Layer]
    P2 --- N2[N-Layer]
    N2 --- K[Cathode]
    G[Gate] --- P2

Applications of SCR:

• Power control: AC/DC power regulators
• Motor drives: Speed control of motors
• Lighting control: Dimmer circuits
• Inverters: DC to AC conversion

Mnemonic: “PALS” - Power control, Appliance control, Lighting systems, Speed regulators

Question 1(b) [4 marks]

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State full form of (i) SCS (ii) LASCR (iii) MCT (iv) PUT.

Answer:

Mnemonic: “SLaMP” - Silicon controlled switch, Light activated SCR, MOS controlled thyristor, Programmable UJT

Question 1(c) [7 marks]

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Draw and explain V-I characteristics of TRIAC. Also write down applications of TRIAC.

Answer:

V-I Characteristics of TRIAC:

graph LR
    subgraph "V-I Characteristics"
    style V-I fill:#f9f9f9,stroke:#333,stroke-width:1px

    MT2((MT2)) --- O[O]
    O --- MT1((MT1))
    
    V1[V] --- I1[I]
    
    G[Gate Triggering]
    
    quad1[I quadrant] --- quad3[III quadrant]
    breakover1[Breakover voltage +Vbo] --- breakover2[Breakover voltage -Vbo]
    
    holding1[Holding current +Ih] --- holding2[Holding current -Ih]
    end

TRIAC V-I characteristics explanation:

• Bidirectional device: Conducts in both directions
• Quadrant operation: Works in 1st and 3rd quadrants
• Breakover voltage: Starts conducting when voltage exceeds ±Vbo
• Holding current: Minimum current to maintain conduction state
• Gate triggering: Can be triggered with positive/negative gate voltage

Applications of TRIAC:

• AC power control: Lamp dimmers, heater controls
• Motor speed control: AC motor regulators
• Fan regulators: Domestic fan speed control
• Light dimmers: Adjustable lighting systems

Mnemonic: “HALF” - Heaters, AC controls, Lighting systems, Fan regulators

Question 1(c) OR [7 marks]

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Explain construction and working of IGBT in detail.

Answer:

IGBT Construction and Working:

graph TD
    G[Gate] --- E[Emitter]
    E --- N+[N+ Layer]
    N+ --- P[P Layer]
    P --- N-[N- Drift Region]
    N- --- N+B[N+ Buffer Layer]
    N+B --- C[Collector]

Construction details:

• Three-terminal device: Gate, Emitter, Collector
• Multilayer structure: N+, P, N-, N+ buffer, P+ substrate
• Hybrid device: Combines MOSFET input with BJT output characteristics

Working principle:

• Gate control: Positive voltage at gate forms inversion layer in P-region
• Channel formation: Electrons flow from N+ emitter to N- drift region
• Conductivity modulation: P-N- junction injects holes, lowering resistance
• Turn-off process: Removing gate voltage stops electron flow

Advantages of IGBT:

• High input impedance: Easy voltage control
• Low conduction losses: Efficient power handling
• Fast switching: Good for high-frequency applications

Mnemonic: “GIVE” - Gate controlled, Input high impedance, Voltage driven, Efficient conduction

Question 2(a) [3 marks]

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Discuss relaxation oscillator circuit using UJT.

Answer:

UJT Relaxation Oscillator:

graph TD
    VCC[VCC] --- R1[R1] --- E[Emitter]
    E --- C[Capacitor] --- GND[GND]
    E --- UJT[UJT]
    UJT --- B1[Base 1] --- R2[R2] --- GND
    UJT --- B2[Base 2] --- R3[R3] --- VCC
    B1 --- Output[Output]

Working principle:

• Capacitor charging: C charges through R1 until reaching UJT firing voltage
• UJT fires: When emitter voltage reaches peak point voltage
• Discharge cycle: Capacitor discharges through emitter-base1 junction
• Oscillation: Process repeats creating sawtooth waveform

Mnemonic: “CROP” - Capacitor charges, Reaches threshold, Oscillates, Produces sawtooth

Question 2(b) [4 marks]

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Discuss the triggering methods of SCR.

Answer:

Key points:

• Gate triggering: Most common method
• Light triggering: Used in opto-isolators
• dv/dt triggering: Often undesirable, requiring snubber circuits

Mnemonic: “GLTDB” - Gate, Light, Thermal, dv/dt, Breakover

Question 2(c) [7 marks]

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Explain class A type commutation method.

Answer:

Class A Commutation (Self-commutation by LC circuit):

graph LR
    DC_Source[DC Source] --- SCR[SCR] --- Load[Load]
    SCR --- L[Inductor] --- C[Capacitor]
    C --- SW[Switch] --- DC_Source

Working principle:

• Initial state: SCR conducting, capacitor charged with polarity (+) on right
• Commutation start: When switch SW closed
• Resonant circuit: LC circuit forms resonant path
• Reverse current: Capacitor discharge creates reverse current through SCR
• Turn-off: SCR turns off when current falls below holding current
• Recharging: Capacitor recharges with opposite polarity

Applications:

• Inverter circuits: DC to AC conversion
• Chopper circuits: DC to DC conversion

Mnemonic: “SCCRRT” - Switch closes, Capacitor discharges, Current reverses, SCR turns off, Recharging begins, Turn-off complete

Question 2(a) OR [3 marks]

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State full form of GTO and draw the structure of GTO.

Answer:

Full form of GTO: Gate Turn-Off Thyristor

Structure of GTO:

graph TD
    A[Anode] --- P1[P+ Anode Layer]
    P1 --- N[N Base Layer]
    N --- P2[P Base Layer]
    P2 --- N2[N+ Cathode Layer]
    N2 --- K[Cathode]
    G[Gate] --- P2

Mnemonic: “PANG” - P-anode, And, N-base, Gate-controlled thyristor

Question 2(b) OR [4 marks]

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Discuss the design and requirement of snubber circuit for SCR.

Answer:

Snubber Circuit for SCR:

graph LR
    SCR[SCR] --- R[Resistor] --- C[Capacitor]
    C --- SCR

Design requirements:

• Resistor selection: Limits discharge current of capacitor
• Capacitor selection: Controls rate of voltage rise (dv/dt)
• RC time constant: Determines response time

Purpose of snubber circuit:

• dv/dt protection: Prevents false triggering due to rapid voltage changes
• Voltage spike suppression: Absorbs inductive voltage spikes
• Transient protection: Protects SCR during switching

Mnemonic: “RAPE” - Resistor And capacitor Protect against Excessive voltage rise

Question 2(c) OR [7 marks]

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Explain class C type commutation method.

Answer:

Class C Commutation (Complementary commutation):

graph LR
    DC_Source[DC Source] --- SCR1[SCR1] --- Load1[Load 1]
    DC_Source --- SCR2[SCR2] --- Load2[Load 2]
    SCR1 --- SCR2

Working principle:

• Initial state: SCR1 conducting, SCR2 off
• Commutation start: SCR2 is triggered
• Load transfer: Current transfers from SCR1 to SCR2
• Voltage reversal: Voltage across SCR1 becomes negative
• Turn-off: SCR1 turns off as current falls below holding current
• Alternating operation: SCR1 and SCR2 conduct alternatively

Applications:

• Inverter circuits: Used in bridge inverters
• Dual load systems: Where alternate operation is required

Mnemonic: “TACTOR” - Triggering Alternate SCRs Creates Turn-Off and Reversal

Question 3(a) [3 marks]

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State the advantages of poly-phase rectifier over single phase rectifier.

Answer:

Mnemonic: “HELPS” - Higher efficiency, Even output, Lower ripple, Power handling better, Smaller filter

Question 3(b) [4 marks]

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Draw and explain the circuit of single phase Half Wave rectifier. Draw the waveforms.

Answer:

Single Phase Half Wave Rectifier:

graph LR
    AC[AC Supply] --- D[Diode] --- R[Load Resistor]
    R --- AC

Waveform:

Working principle:

• Forward bias: Diode conducts during positive half-cycle
• Reverse bias: Diode blocks current during negative half-cycle
• Output: Pulsating DC with high ripple factor
• Frequency: Output frequency same as input frequency

Mnemonic: “PROF” - Positive half conducts, Reverse half blocks, Output is pulsating, Frequency unchanged

Question 3(c) [7 marks]

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List all types of Inverters. Out of that explain single phase full bridge Inverter.

Answer:

Types of Inverters:

1. Based on circuit: Series, Parallel, Bridge
2. Based on phases: Single-phase, Three-phase
3. Based on output: Square wave, Modified sine wave, Pure sine wave
4. Based on commutation: SCR-based, Transistor-based

Single Phase Full Bridge Inverter:

graph TD
    DC[DC Source] --- S1[Switch S1] --- S2[Switch S2] --- DC
    S1 --- Load[Load] --- S3[Switch S3]
    S2 --- Load
    S3 --- S4[Switch S4] --- DC

Working principle:

• First half-cycle: S1 and S4 ON, S2 and S3 OFF
• Second half-cycle: S2 and S3 ON, S1 and S4 OFF
• Output waveform: AC square wave across load
• Control method: Gate signals to switches with 180° phase shift

Advantages:

• Higher output power: Twice the output of half bridge
• Better voltage utilization: Full DC bus voltage across load
• Lower current rating: Each switch carries only load current

Mnemonic: “SOAP” - Switches Operate Alternately in Pairs

Question 3(a) OR [3 marks]

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Compare UPS and SMPS.

Answer:

Mnemonic: “BBOSS” - Backup Battery Only in UPS, Small Size in SMPS

Question 3(b) OR [4 marks]

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Draw and explain the circuit of three phase Half Wave rectifier. Draw the waveforms.

Answer:

Three Phase Half Wave Rectifier:

graph LR
    R[R Phase] --- D1[Diode D1] --- Load[Load]
    Y[Y Phase] --- D2[Diode D2] --- Load
    B[B Phase] --- D3[Diode D3] --- Load
    Load --- N[Neutral]

Waveform:

Working principle:

• Conduction sequence: Each diode conducts when its phase voltage is highest
• Conduction angle: Each diode conducts for 120°
• Output ripple: 3 pulses per cycle, lower ripple than single phase
• Ripple frequency: 3 times the input frequency

Mnemonic: “CROP” - Conduction of 120°, Ripple reduced, Output smoother, Pulses tripled

Question 3(c) OR [7 marks]

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Define chopper. With the help of circuit diagram explain class D chopper.

Answer:

Definition of Chopper: A chopper is a DC to DC converter that converts fixed DC input voltage to variable DC output voltage using high-frequency switching.

Class D Chopper (Two-quadrant chopper):

graph LR
    VS[DC Source] --- S1[Switch S1] --- L[Inductor]
    L --- Load[Load] --- VS
    Load --- D1[Diode D1] --- S1
    Load --- S2[Switch S2] --- D2[Diode D2] --- VS

Working principle:

• First quadrant operation (forward motoring):

  • S1 ON, S2 OFF: Energy flows from source to load
  • S1 OFF, S2 OFF: Current freewheels through D2

• Second quadrant operation (forward regeneration):

  • S1 OFF, S2 ON: Energy flows from load to source
  • S1 OFF, S2 OFF: Current freewheels through D1

Applications:

• DC motor drives: Providing forward motoring and regenerative braking
• Battery charging: Controlling charging current
• Renewable energy: Interfacing with solar panels

Mnemonic: “FRED” - Forward motoring, Regenerative braking, Energy flow control, Dual quadrant operation

Question 4(a) [3 marks]

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Describe the use of SCR as a static switch.

Answer:

SCR as Static Switch:

graph LR
    VS[Supply] --- SCR[SCR] --- Load[Load]
    GC[Gate Control] --- SCR

Key features:

• No moving parts: Purely electronic switching
• Fast switching: Microsecond response time
• High reliability: Longer lifetime than mechanical switches
• Controlled turn-on: Precise control via gate signal

Advantages over mechanical switches:

• No arcing: No contact bounce or wear
• Silent operation: No mechanical noise
• EMI reduction: Less electromagnetic interference

Mnemonic: “FANS” - Fast switching, Arc-free operation, No mechanical wear, Silent operation

Question 4(b) [4 marks]

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Draw the circuit diagram of A.C. Power control using DIAC and TRIAC and explain its working.

Answer:

AC Power Control using DIAC and TRIAC:

graph LR
    AC[AC Supply] --- TRIAC[TRIAC] --- Load[Load]
    AC --- R[Resistor] --- C[Capacitor] --- DIAC[DIAC] --- G[TRIAC Gate]
    G --- TRIAC

Working principle:

• RC network: Controls firing angle by delaying gate pulse
• Capacitor charging: C charges through R during each half-cycle
• DIAC breakdown: When capacitor voltage reaches DIAC breakover voltage
• TRIAC triggering: DIAC conducts and triggers TRIAC
• Power control: Varying R changes firing angle and thus power delivered

Applications:

• Light dimmers: Controlling brightness of lamps
• Fan speed control: Regulating fan speed
• Heater control: Adjusting heating elements

Mnemonic: “CRAFT” - Capacitor charges, Reaches breakover, Activates DIAC, Fires TRIAC, Transfers power

Question 4(c) [7 marks]

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Explain the working principle of induction heating also write the applications of induction heating.

Answer:

Working Principle of Induction Heating:

graph TD
    Power[AC Power Supply] --- Inv[High Frequency Inverter]
    Inv --- Coil[Induction Coil]
    Coil --- Workpiece[Metal Workpiece]

    subgraph "Physical Process"
    Coil -.- Magnetic[Alternating Magnetic Field]
    Magnetic -.- Eddy[Eddy Currents]
    Eddy -.- Heat[Heat Generation]
    end

Working principle:

• High-frequency current: Passes through induction coil
• Electromagnetic induction: Creates alternating magnetic field
• Eddy currents: Induced in workpiece
• Resistance heating: Eddy currents generate heat due to resistance
• Skin effect: Heat concentrated near surface
• Non-contact heating: No physical contact between coil and workpiece

Applications of Induction Heating:

• Metal heat treatment: Hardening, annealing, tempering
• Metal melting: Foundry operations
• Welding and brazing: Joining metal components
• Forging: Heating before forming
• Domestic cooking: Induction cooktops
• Semiconductor processing: Crystal growth

Mnemonic: “MASTER” - Magnetic field, Alternating current, Surface heating, Temperature control, Eddy currents, Resistance heating

Question 4(a) OR [3 marks]

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Explain working of photo relay circuit using LDR.

Answer:

Photo Relay Circuit using LDR:

graph LR
    VS[Supply] --- R1[Resistor R1] --- LDR[LDR]
    LDR --- GND[Ground]
    R1 --- B[Transistor Base]
    VS --- RC[Collector Resistor] --- C[Transistor Collector]
    C --- Relay[Relay Coil] --- GND
    E[Transistor Emitter] --- GND

Working principle:

• Light-dependent resistor: Resistance decreases with increasing light
• Voltage divider: LDR and R1 form voltage divider
• Transistor switching: Base voltage controls transistor conduction
• Relay operation: Transistor drives relay coil
• Threshold adjustment: Can be set using variable resistor

Applications:

• Automatic street lighting: Turns on lights at dusk
• Day/night switching: Controls devices based on ambient light
• Security systems: Light-activated alarms

Mnemonic: “LARK” - Light controls, Activates transistor, Relay switches, Keeps circuit automated

Question 4(b) OR [4 marks]

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Explain the operation of timer circuit using 555 timer IC.

Answer:

555 Timer Circuit (Monostable):

graph TD
    VCC[+VCC] --- R[Resistor R] --- D8[Pin 8 VCC]
    D8 --- D4[Pin 4 Reset]
    D8 --- D7[Pin 7 Discharge]
    R --- D7
    D7 --- C[Capacitor C] --- GND[Ground]
    Trigger[Trigger Input] --- D2[Pin 2 Trigger]
    D3[Pin 3 Output] --- Output[Output]
    D1[Pin 1 GND] --- GND
    D5[Pin 5 Control] --- CC[Control Capacitor] --- GND
    D6[Pin 6 Threshold] --- D7

Working principle:

• Trigger input: Active low trigger at pin 2
• Timing components: R and C determine timing period (T = 1.1RC)
• Output high: When triggered, output goes high
• Capacitor charging: C charges through R
• Threshold detection: When voltage reaches 2/3 VCC, output goes low
• Timer reset: Circuit can be reset using pin 4

Applications:

• Delay circuits: Creating time delays
• Pulse generation: Generating precise pulses
• Timing control: Sequential timing operations

Mnemonic: “TRACT” - Trigger activates, Resistor-capacitor timing, Accurate delay, Capacitor charges, Threshold detection

Question 4(c) OR [7 marks]

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Explain the working principle of dielectric heating also write the applications of dielectric heating.

Answer:

Working Principle of Dielectric Heating:

graph TD
    RF[RF Generator] --- Electrodes[Electrodes]

    subgraph "Material Between Electrodes"
    Electrodes --- Electric[Alternating Electric Field]
    Electric --- Dipoles[Molecular Dipoles]
    Dipoles --- Oscillation[Dipole Oscillation]
    Oscillation --- Friction[Molecular Friction]
    Friction --- Heat[Heat Generation]
    end

Working principle:

• High-frequency electric field: Applied between electrodes
• Dielectric material: Placed between electrodes
• Molecular polarization: Dipoles align with electric field
• Field oscillation: Rapid reversal of field direction
• Molecular friction: Dipoles rotate rapidly causing friction
• Volumetric heating: Heat generated throughout material
• Frequency range: Typically 10-100 MHz

Applications of Dielectric Heating:

• Food processing: Baking, drying, pasteurization
• Wood industry: Gluing, drying timber
• Textile drying: Removing moisture from fabrics
• Plastic welding: Joining thermoplastics
• Medical applications: Therapeutic diathermy
• Paper industry: Drying paper products

Mnemonic: “DIPOLE” - Dielectric material, Intense electric field, Polarization of molecules, Oscillation causes, Linkage of heat, Even heating throughout

Question 5(a) [3 marks]

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Define AC drive. State applications of AC drives.

Answer:

Definition of AC Drive: An AC drive is an electronic device that controls the speed, torque, and direction of an AC motor by varying the frequency and voltage supplied to the motor.

Applications of AC Drives:

Mnemonic: “PITCHW” - Pumps, Industrial machinery, Textile machines, Conveyor systems, HVAC systems, Water treatment

Question 5(b) [4 marks]

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Draw and explain any one method for speed control of DC shunt motor.

Answer:

Armature Voltage Control Method for DC Shunt Motor:

graph TD
    AC[AC Supply] --- B[Bridge Rectifier]
    B --- SCR[SCR] --- A[Armature]
    A --- B
    AC --- F[Field Circuit]
    F --- Field[Field Winding]
    GC[Gate Control] --- SCR

Working principle:

• Constant field current: Field supply maintained constant
• Variable armature voltage: Controlled by SCR
• Speed equation: N ∝ (Vₐ - IₐRₐ)/Φ
• Speed control: By changing armature voltage Vₐ
• Torque control: Armature current controls torque

Advantages:

• Wide speed range: Can achieve speeds below and above base speed
• Smooth control: Continuous speed adjustment
• High efficiency: Low power loss in control circuit

Mnemonic: “SAVE” - SCR controls, Armature voltage varies, Velocity changes, Efficient operation

Question 5(c) [7 marks]

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Draw the block diagram of PLC and explain the function of each block.

Answer:

PLC Block Diagram:

graph TD
    PS[Power Supply] --- CPU[Central Processing Unit]
    CPU --- MEM[Memory]
    CPU --- INP[Input Module]
    CPU --- OUT[Output Module]
    CPU --- COM[Communication Module]
    INP --- Input[Input Devices]
    OUT --- Output[Output Devices]
    COM --- Network[Network/HMI]
    PROG[Programming Device] --- COM

Functions of each block:

Advantages of PLC:

• Reliability: Solid-state components with high MTBF
• Flexibility: Easily reprogrammable for different applications
• Communication: Network capabilities for distributed control
• Diagnostics: Built-in diagnostics and troubleshooting

Mnemonic: “PRIME-C” - Power supply, RAM/ROM memory, Input module, Microprocessor (CPU), Execution of program, Communication interface

Question 5(a) OR [3 marks]

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State the applications of stepper motor.

Answer:

Mnemonic: “POMAC” - Positioning systems, Office equipment, Medical devices, Automotive controls, Consumer electronics

Question 5(b) OR [4 marks]

#

Draw and explain the circuit to control speed of a DC series motor.

Answer:

Speed Control of DC Series Motor using SCR:

graph TD
    AC[AC Supply] --- B[Bridge Rectifier]
    B --- SCR[SCR] --- A[Armature]
    A --- SF[Series Field]
    SF --- B
    GC[Gate Control] --- SCR

Working principle:

• Series connection: Field winding in series with armature
• SCR control: Phase-controlled SCR regulates average voltage
• Speed equation: N ∝ (V - I(Ra+Rf))/IΦ
• Speed-torque relation: Non-linear relationship
• Application: Used when high starting torque required

Advantages:

• High starting torque: Ideal for traction applications
• Simple control: Basic circuit design
• Cost-effective: Fewer components than other methods

Mnemonic: “SCAT” - Series connection, Current controls flux, Average voltage controlled by SCR, Torque highest at low speeds

Question 5(c) OR [7 marks]

#

Discuss the BLDC motor in brief.

Answer:

BLDC Motor (Brushless DC Motor):

graph TD
    subgraph "BLDC Motor Construction"
    Stator[Stator with Windings]
    Rotor[Rotor with Permanent Magnets]
    Hall[Hall Sensors]
    end

    subgraph "Control System"
    Controller[Electronic Controller]
    Driver[Power Driver]
    Feedback[Position Feedback]
    end
    
    Controller --- Driver
    Driver --- Stator
    Hall --- Feedback
    Feedback --- Controller

Construction:

• Stator: Contains windings (typically 3-phase)
• Rotor: Permanent magnets on rotor
• Position sensing: Hall effect sensors or encoders
• Controller: Electronic commutation controller

Working principle:

• Electronic commutation: Replaces mechanical brushes
• Sequencing: Controller energizes stator coils in sequence
• Position feedback: Hall sensors determine rotor position
• Phase energizing: Proper phase energized based on rotor position

Advantages:

• High efficiency: No brush friction losses
• Low maintenance: No brush wear
• Longer lifespan: Reliable operation
• Better speed-torque characteristics: Flat curve
• Low noise: Quiet operation
• Better heat dissipation: Windings on stator

Applications:

• Computer cooling fans: CPU/GPU coolers
• Hard disk drives: Spindle motors
• Electric vehicles: Propulsion systems
• Drones: Propeller motors
• Home appliances: Washing machines, refrigerators
• Industrial automation: Precision control systems

Mnemonic: “COPPER” - Commutation electronic, Operation efficient, Permanent magnets, Position sensors, Electronic control, Reliable performance