Question 1(a) [3 marks]

Draw the construction of SCR and explain it.

Answer: SCR (Silicon Controlled Rectifier) is a four-layer PNPN semiconductor device with three terminals: Anode, Cathode, and Gate.

Diagram:

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

P-N-P-N Layers: Four alternating semiconductor layers
Gate Terminal: Controls turn-on of the device
Current Flow: Anode to cathode when triggered

Mnemonic: "Silicon Controls Rectification" - SCR controls current flow in one direction only when triggered.

Question 1(b) [4 marks]

Draw construction of TRIAC and explain it.

Answer: TRIAC (Triode for Alternating Current) is a bidirectional three-terminal semiconductor device that conducts in both directions when triggered.

Diagram:

graph LR
    MT1[Main Terminal 1] --- N1[N-layer]
    N1 --- P1[P-layer]
    P1 --- N2[N-layer]
    N2 --- P2[P-layer]
    P2 --- N3[N-layer]
    N3 --- MT2[Main Terminal 2]
    G[Gate] --- P1

Bidirectional Operation: Conducts in both directions when triggered
Gate Control: Single gate controls conduction in both directions
Equivalent Circuit: Acts like two SCRs connected in anti-parallel
AC Applications: Widely used for AC power control applications

Mnemonic: "TRI-direction AC controller" - Controls current in both directions in AC circuits.

Question 1(c) [7 marks]

Describe construction & working of Opto-Isolators, Opto-TRIAC, Opto-SCR, and Opto-transistor. And list their applications.

Answer: Opto-isolators use light to transfer electrical signals between isolated circuits.

Diagram:

graph LR
    subgraph Input
        LED[LED]
    end
    subgraph Output
        PD[Photo Detector]
    end
    LED -- "Light" --> PD
    style Input fill:#f9f,stroke:#333
    style Output fill:#bbf,stroke:#333

Device	Construction	Working	Applications
Opto-Isolator	LED + Photodetector	LED emits light when input current flows; photodetector activates output circuit	Signal isolation, Medical equipment, Industrial controls
Opto-TRIAC	LED + Photo-TRIAC	LED triggers the TRIAC through light; provides electrical isolation	AC power control, Solid state relays, Motor controls
Opto-SCR	LED + Photo-SCR	LED emits light to trigger SCR; provides high isolation	DC switching, Industrial controls, High voltage isolation
Opto-transistor	LED + Photo-transistor	LED light controls base current of phototransistor	Encoders, Level detection, Position sensing

Electrical Isolation: Complete separation between input and output
Noise Immunity: High resistance to electrical noise
Speed: Response times in microseconds range

Mnemonic: "LOST" - Light Operates Semiconductor Terminals in all opto-devices.

Question 1(c) OR [7 marks]

Describe Explain working of SCR using two transistor analogies. List the various industrial applications of SCR.

Answer: SCR can be modeled as two interconnected transistors: PNP (T1) and NPN (T2).

Diagram:

graph TD
    A[Anode] --- E1[Emitter T1]
    B1[Base T1] --- C2[Collector T2]
    C1[Collector T1] --- B2[Base T2]
    E2[Emitter T2] --- K[Cathode]
    G[Gate] --- B2

Working Principle:

Step	Operation
Initial State	Both transistors are OFF
Gate Triggering	Current injected into gate (B2 of T2)
Regenerative Action	T2 turns ON → T1 base gets current → T1 turns ON → More current to T2 base
Latching	Self-sustaining current flow continues even if gate signal is removed

Industrial Applications of SCR:

Power Control: AC/DC motor speed control
Switching: Static switches, solid-state relays
Inverters: DC to AC conversion
Protection: Overvoltage protection circuits
Lighting: Light dimmers, illumination control

Mnemonic: "POWER" - Power control, Overvoltage protection, Welding machines, Electronic converters, Regulated supplies.

Question 2(a) [3 marks]

Define Triggering in SCR and explain any two triggering techniques.

Answer: Triggering is the process of turning ON an SCR by applying appropriate signal to its gate terminal.

Two Triggering Techniques:

Technique	Description
Gate Triggering	Direct current pulse applied to gate-cathode circuit
Light Triggering	Photons striking junction provide energy for conduction

Gate Triggering: Most common method using electrical pulse
Light Triggering: Uses photosensitive semiconductor properties

Mnemonic: "GET" - Gate Electrical Triggering is the most common method.

Question 2(b) [4 marks]

Write the differences between forced commutation and natural commutation.

Answer:

Parameter	Forced Commutation	Natural Commutation
Definition	External circuitry forces SCR to turn OFF	SCR turns OFF naturally when current falls below holding value
Application	DC circuits	AC circuits
Components	Requires additional components (capacitors, inductors)	No additional components needed
Complexity	Complex circuit design	Simple circuit design
Energy	External energy needed for turn-off	No external energy needed

Forced Commutation: Actively turns OFF SCR using external circuit
Natural Commutation: SCR turns OFF when AC current crosses zero

Mnemonic: "FACE" - Forced Active Commutation requires External components.

Question 2(c) [7 marks]

Design the snubber circuit for SCR.

Answer: Snubber circuit protects SCR from high dV/dt and limits rate of voltage rise.

Diagram:

graph LR
    A[Anode] --- R[Resistance]
    R --- C[Capacitance]
    C --- K[Cathode]
    A --- SCR[SCR]
    SCR --- K

Design Steps:

Step	Calculation
1. Calculate dV/dt rating	From datasheet (V/μs)
2. Determine R value	R = V₁/IL where V₁ is supply voltage and IL is load current
3. Determine C value	C = 1/(R × (dV/dt)max)
4. RC time constant	τ = R × C (should be greater than SCR turn-off time)

Resistance R: Limits discharge current of capacitor
Capacitance C: Absorbs transient energy and limits dV/dt
Protection: Prevents false triggering and damage
Power Rating: R must have sufficient power rating

Mnemonic: "RCSS" - Resistance-Capacitance Saves Silicon from Stress.

Question 2(a) OR [3 marks]

Define commutation and Explain class-E commutation for SCR.

Answer: Commutation is the process of turning OFF an SCR by reducing its anode current below the holding current level.

Class-E Commutation:

Diagram:

graph LR
    S[Supply] --- L[Load]
    L --- SCR[SCR]
    L --- C[Capacitor]
    C --- A[Auxiliary SCR]
    A --- S

Auxiliary SCR: Controls the commutation process
Resonant Circuit: Forms LC resonant circuit
Operation: Auxiliary SCR triggers capacitor discharge to reverse-bias main SCR
Application: Used in inverters and choppers

Mnemonic: "ACE" - Auxiliary Capacitor Extinguishes conduction.

Question 2(b) OR [4 marks]

Explain Triggering of Thyristor.

Answer:

Triggering Method	Working Principle
Gate Triggering	Electrical pulse applied between gate and cathode
Temperature Triggering	Junction temperature increases to cause turn-on
Light Triggering	Photons create electron-hole pairs at junctions
dV/dt Triggering	Rapid voltage rise causes capacitive current flow
Forward Voltage Triggering	Exceeding breakover voltage causes avalanche conduction

Gate Triggering: Most common and controllable method
Parameter Control: Pulse width, amplitude, and rise time
Gate Sensitivity: Varies with temperature
Protection: Required against unwanted triggering

Mnemonic: "VITAL" - Voltage, Illumination, Temperature And Level are all triggering methods.

Question 2(c) OR [7 marks]

Explain methods to protect SCR against over voltage and current in details.

Answer:

Overvoltage Protection:

Diagram:

graph LR
    S[Supply] --- F[Fuse]
    F --- V[Varistor]
    V --- SCR[SCR]
    SCR --- L[Load]
    V --- RC[RC Snubber]
    RC --- SCR

Protection Method	Working Principle
RC Snubber Circuit	Limits rate of rise of voltage (dV/dt)
Voltage Clamping	Using Zener diodes or MOVs to limit maximum voltage
Crowbar Protection	Deliberate short-circuit when voltage exceeds threshold

Overcurrent Protection:

Diagram:

graph LR
    S[Supply] --- F[Fuse/Circuit Breaker]
    F --- R[Current Limiting Resistor]
    R --- SCR[SCR]
    SCR --- L[Load]

Protection Method	Working Principle
Fuses/Circuit Breakers	Disconnects circuit during fault conditions
Current Limiting Reactors	Limits fault current magnitude
Electronic Current Limiting	Sensing and control circuits limit current

Coordination: Protection devices must work in coordination
Response Time: Critical for effective protection
Multiple Layers: For critical applications, several methods are combined

Mnemonic: "SCOPE" - Snubbers, Clamps, Overload sensors, Protectors, and Electronic limiters.

Question 3(a) [3 marks]

List the differences between single phase rectifier and poly phase rectifier.

Answer:

Parameter	Single Phase Rectifier	Poly Phase Rectifier
Input	Single phase AC supply	Multiple phase (usually 3-phase) AC supply
Output Ripple	Higher ripple content	Lower ripple content
Efficiency	Lower efficiency	Higher efficiency
Power Rating	Suitable for low power applications	Suitable for high power applications
Transformer Utilization	Lower utilization factor	Higher utilization factor

Ripple Factor: Single phase has higher ripple compared to poly phase
Form Factor: Better in poly phase systems
Size/Weight: Poly phase systems have better power/weight ratio

Mnemonic: "PERCH" - Poly phase has Efficiency, Ripple improvement, Capacity, and Higher ratings.

Question 3(b) [4 marks]

Draw the circuit diagram of three phases Half Wave Rectifier and explain its Working.

Answer: Three-phase half-wave rectifier converts three-phase AC into pulsating DC using three diodes.

Diagram:

graph TD
    A[Phase A] --- D1[Diode 1]
    B[Phase B] --- D2[Diode 2]
    C[Phase C] --- D3[Diode 3]
    D1 --- O[Output +]
    D2 --- O
    D3 --- O
    N[Neutral] --- ON[Output -]

Working:

Each diode conducts when its phase voltage is most positive
Conduction angle of each diode is 120°
Ripple frequency is 3 times the input frequency
Average output voltage = 3Vm/2π (where Vm is peak phase voltage)
Ripple factor = 0.17 (much lower than single-phase half-wave)

Mnemonic: "THREE-D" - THREE Diodes conducting sequentially.

Question 3(c) [7 marks]

Describe the working of UPS & SMPS with the help of block diagram.

Answer:

UPS (Uninterruptible Power Supply):

Diagram:

graph LR
    AC[AC Input] --- R[Rectifier]
    R --- BC[Battery Charger]
    BC --- B[Battery]
    B --- I[Inverter]
    R --- I
    I --- F[Filter]
    F --- L[Load]
    AC -.Bypass.-> L

Block	Function
Rectifier	Converts AC to DC for battery charging and inverter
Battery	Stores energy for backup during power failure
Inverter	Converts DC to AC for powering load
Filter	Smooths output waveform
Bypass	Provides direct AC during maintenance

SMPS (Switched Mode Power Supply):

Diagram:

graph LR
    AC[AC Input] --- R[Rectifier & Filter]
    R --- SW[High Frequency Switch]
    SW --- T[HF Transformer]
    T --- RF[Rectifier & Filter]
    RF --- L[Load]
    FB[Feedback] --- SW
    RF --- FB

Block	Function
Rectifier & Filter	Converts AC to unregulated DC
High Frequency Switch	Chops DC into high-frequency pulses
HF Transformer	Provides isolation and voltage transformation
Output Rectifier & Filter	Converts high-frequency AC to smooth DC
Feedback Circuit	Regulates output voltage by controlling switch

UPS Efficiency: 80-90%, provides backup power
SMPS Efficiency: 70-90%, much smaller than linear supplies
Regulation: Both provide regulated output voltage

Mnemonic: "BRIEF" - Battery backup, Rectification, Inversion, Efficient switching, Feedback control.

Question 3(a) OR [3 marks]

Explain the Principle & working of Chopper circuits.

Answer: Chopper is a DC-to-DC converter that converts fixed DC input voltage to variable DC output voltage.

Diagram:

graph LR
    DC[DC Source] --- S[Switch/SCR]
    S --- L[Load]
    L --- DC

Principle:

Switch (typically SCR, MOSFET, or IGBT) rapidly connects and disconnects source to load
Output voltage controlled by duty cycle (ON time / total time)
Average output voltage = Input voltage × Duty cycle
Time Ratio Control: Varies duty cycle, keeping frequency constant
Frequency Modulation: Varies frequency, keeping ON time constant
Applications: DC motor control, battery-powered vehicles

Mnemonic: "CHOP" - Control High-speed Operation with Pulses.

Question 3(b) OR [4 marks]

Compare single-phase and Poly-phase rectifier circuits.

Answer:

Parameter	Single-Phase Rectifier	Poly-Phase Rectifier
Supply	Single-phase AC	Three or more phase AC
Output Waveform	More pulsating	Smoother (less pulsating)
Ripple Content	Higher (0.48 for full wave)	Lower (0.042 for 3-phase full wave)
Filtering	More filtering required	Less filtering required
Power Handling	Limited power handling	Higher power handling
Transformer Utilization	0.812 (full wave)	0.955 (3-phase full wave)
Efficiency	Lower	Higher
Size	Smaller for same power	More compact for high power

Harmonic Content: Lower in poly-phase systems
TUF (Transformer Utilization Factor): Higher in poly-phase systems
Cost-Effectiveness: Poly-phase more economical for high power

Mnemonic: "PERIPHERY" - Poly-phase Efficiency Ripple Improvement Power Handling Economy Rating Yield.

Question 3(c) OR [7 marks]

Describe the working of solar Photovoltaic (PV) based power generation with the help of block diagram.

Answer: Solar PV power generation converts sunlight directly into electricity using semiconductor materials.

Diagram:

graph LR
    Sun((Sunlight)) --- PV[PV Array]
    PV --- CC[Charge Controller]
    CC --- B[Battery Bank]
    B --- I[Inverter]
    I --- L[AC Load]
    B --- DCL[DC Load]
    I --- G[Grid Connection]

Component	Function
PV Array	Converts solar energy to DC electricity through photovoltaic effect
Charge Controller	Regulates battery charging and prevents overcharging
Battery Bank	Stores energy for use during night or cloudy conditions
Inverter	Converts DC to AC for powering AC loads
Grid Connection	Optional connection for feeding excess power to grid

Working Principle:

Photovoltaic Effect: Photons from sunlight knock electrons free in semiconductor
Cell Structure: P-N junction creates electric field
Voltage Generation: Typical cell produces 0.5-0.6V DC
Array Configuration: Series-parallel connections for desired voltage/current
Efficiency: Typically 15-22% for commercial panels
Applications: Residential, commercial, industrial power generation

Mnemonic: "SOLAR" - Semiconductors Oriented Light-to-electricity Array Regulation.

Question 4(a) [3 marks]

List the advantages of static switch.

Answer:

Advantages of Static Switch
No moving parts - higher reliability
Silent operation
Fast switching response (microseconds)
Longer operational life
No contact bounce or arcing
Compact size
Compatible with digital control systems
Lower maintenance requirements

Reliability: No mechanical wear and tear
Speed: Much faster than mechanical switches
Isolation: Can provide electrical isolation

Mnemonic: "SAFE" - Speed, Arc-free, Fast response, Endurance.

Question 4(b) [4 marks]

Draw the circuit diagram of A.C. Power control using DIAC-TRIAC and Explain it.

Answer: DIAC-TRIAC circuit provides smooth AC power control for resistive and inductive loads.

Diagram:

graph LR
    AC[AC Supply] --- L[Load]
    L --- T[TRIAC]
    T --- AC
    AC --- R1[Resistor R1]
    R1 --- C[Capacitor C]
    C --- D[DIAC]
    D --- G[TRIAC Gate]
    G --- T
    R2[Variable Resistor R2] --- C
    R2 --- T

Working:

Variable resistor R2 controls charging rate of capacitor C
When capacitor voltage reaches DIAC breakover voltage, DIAC conducts
DIAC delivers trigger pulse to TRIAC gate
TRIAC conducts for remainder of half-cycle
Process repeats for both half-cycles
Phase Control: Controls power by varying firing angle
Applications: Light dimmers, heater controls, motor speed control
Power Range: Can control from near-zero to full power

Mnemonic: "DIRECT" - DIAC Initiates Regulated Energy Control in TRIAC.

Question 4(c) [7 marks]

Describe function of DC power control circuit using SCR with UJT in triggering circuit.

Answer: UJT-triggered SCR circuit provides precise control of DC power to the load.

Diagram:

graph LR
    DC[DC Source] --- L[Load]
    L --- SCR[SCR]
    SCR --- DC
    DC --- R1[Resistor R1]
    R1 --- R2[Variable Resistor R2]
    R2 --- C[Capacitor C]
    C --- E[UJT Emitter]
    B1[UJT Base 1] --- R3[Resistor R3]
    B2[UJT Base 2] --- R4[Resistor R4]
    R3 --- DC
    R4 --- G[SCR Gate]
    G --- SCR
    E --- B1
    E --- B2

Working Principle:

Stage	Operation
Charging	R1 and R2 control charging rate of capacitor C
UJT Firing	When capacitor voltage reaches UJT firing level, UJT conducts
Pulse Generation	UJT generates sharp trigger pulse across R4
SCR Triggering	Pulse triggers SCR gate, turning SCR ON
Power Control	Variable resistor R2 adjusts timing, controlling average power

Precise Control: UJT provides stable, predictable triggering
Applications: Battery chargers, DC motor speed control, temperature control
Advantages: Low cost, high reliability, good temperature stability
Control Range: Wide range from near-zero to full power

Mnemonic: "SCRUP" - SCR Using Pulse from UJT for Power control.

Question 4(a) OR [3 marks]

Enlist applications of dielectric heating.

Answer:

Applications of Dielectric Heating
Plastic welding and sealing
Wood gluing and curing
Food processing (pre-cooking, defrosting)
Textile drying and processing
Paper and board drying
Pharmaceutical products drying
Medical applications (hyperthermia treatment)
Rubber vulcanization

Material Requirements: Works best with poor conductors that have polar molecules
Frequency Range: Typically 10-100 MHz
Advantages: Uniform heating, faster processing, energy efficiency

Mnemonic: "POWER" - Plastics, Organics, Wood, Edibles, and Rubber processing.

Question 4(b) OR [4 marks]

Draw and explain three stage IC555 timer circuit.

Answer: Three-stage IC555 timer circuit provides sequential timing operations.

Diagram:

graph LR
    subgraph "Timer 1"
        IC1[555 Timer] 
    end
    subgraph "Timer 2"
        IC2[555 Timer]
    end
    subgraph "Timer 3"
        IC3[555 Timer]
    end
    TR[Trigger Input] --> IC1
    IC1 --> O1[Output 1]
    O1 --> IC2
    IC2 --> O2[Output 2]
    O2 --> IC3
    IC3 --> O3[Output 3]

Working:

First timer activated by external trigger
Output of first timer triggers second timer
Output of second timer triggers third timer
Each timer can be independently adjusted
Applications: Industrial sequencing, process control, animation effects
Timing Range: Microseconds to hours with proper component selection
Features: Stable timing, immune to supply variations
Advantages: Simple design, reliable operation, low cost

Mnemonic: "THREE-SET" - THREE Stage Electronic Timers in sequence.

Question 4(c) OR [7 marks]

Describe the working principle of Induction heating. And List merits-demerits of Induction heating.

Answer: Induction heating uses electromagnetic induction to heat electrically conductive materials.

Diagram:

graph LR
    PS[Power Supply] --> INV[Inverter]
    INV --> LC[Matching Circuit]
    LC --> WC[Work Coil]
    WC --> W[Workpiece]
    FC[Feedback Control] --> INV

Working Principle:

High frequency AC in work coil creates alternating magnetic field
Magnetic field induces eddy currents in workpiece
Eddy currents generate heat due to material resistance
Heating occurs within the workpiece, not from external source

Merits	Demerits
Rapid heating	High initial equipment cost
Energy efficient (80-90%)	Limited to electrically conductive materials
Precise temperature control	Requires high-frequency power supply
Clean process with no combustion	Complex coil design for specific applications
Localized heating possible	High power requirements
Consistent, repeatable results	Requires water cooling systems
Environmentally friendly	Electromagnetic interference issues
Improved working conditions	Limited penetration depth

Frequency Range: 1 kHz to 1 MHz depending on application
Applications: Heat treatment, melting, brazing, soldering

Mnemonic: "EDDY" - Electromagnetic Device Develops Yield of heat.

Question 5(a) [3 marks]

Draw & explain solid state circuit to control dc shunt motor speed.

Answer: Solid-state circuit for DC shunt motor speed control uses SCR to control armature voltage.

Diagram:

graph LR
    AC[AC Supply] --- BR[Bridge Rectifier]
    BR --- SCR[SCR]
    SCR --- A[Armature]
    A --- BR
    BR --- F[Field Winding]
    F --- BR
    RC[Firing Circuit] --- SCR

Armature Voltage Control: SCR controls voltage to armature
Field Winding: Connected directly to DC supply
Speed Control: By varying SCR firing angle
Advantages: Smooth control, high efficiency, compact size

Mnemonic: "SAFE" - SCR Armature Firing for Efficient control.

Question 5(b) [4 marks]

Explain working principle of stepper motor.

Answer: Stepper motor converts electrical pulses into discrete mechanical movements.

Diagram:

graph TD
    subgraph "Stepper Motor"
        R[Rotor]
        S1[Stator Winding 1]
        S2[Stator Winding 2]
        S3[Stator Winding 3]
        S4[Stator Winding 4]
    end

Working Principle:

Energizing stator windings in sequence creates rotating magnetic field
Permanent magnet rotor aligns with magnetic field
Each pulse creates rotation by exact "step" angle
Step angle determined by motor construction (typically 1.8° or 0.9°)

Type	Characteristics
Variable Reluctance	No permanent magnet, relies on magnetic reluctance
Permanent Magnet	Uses permanent magnet rotor
Hybrid	Combines features of both types

Precise Positioning: Movement in exact increment steps
Open-Loop Control: No feedback needed for position control
Holding Torque: Maintains position when energized

Mnemonic: "STEP" - Sequential Triggering Enables Precise positioning.

Question 5(c) [7 marks]

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

Answer: Programmable Logic Controller (PLC) is a digital computer used for automation of industrial processes.

Diagram:

graph TD
    PS[Power Supply] --- CPU[Central Processing Unit]
    I[Input Modules] --- CPU
    CPU --- O[Output Modules]
    M[Memory] --- CPU
    P[Programming Device] --- CPU
    C[Communication Module] --- CPU

Block	Function
Power Supply	Converts main AC to DC for internal use
CPU	Executes program, processes data, manages operations
Input Modules	Interface with sensors, switches, and field devices
Output Modules	Control actuators, motors, valves, and indicators
Memory	Stores program and data (ROM, RAM, EEPROM)
Programming Device	External computer or terminal for programming
Communication Module	Interfaces with other PLCs, SCADA, HMI

Scan Cycle: Input scanning → Program execution → Output updating
Advantages: Reliability, flexibility, modular design, easy troubleshooting
Applications: Manufacturing automation, process control, material handling
Programming: Ladder logic, function block diagram, structured text

Mnemonic: "PILOT" - Processing Inputs and Logic for Outputs with Timing control.

Question 5(a) OR [3 marks]

Draw and explain the construction of DC servo motor.

Answer: DC servo motor is designed for precise position and speed control.

Diagram:

graph TD
    subgraph "DC Servo Motor"
        A[Armature]
        F[Field Winding]
        S[Shaft]
        FB[Feedback Device]
    end

Components:

Armature: Low inertia for quick response
Field System: Provides magnetic field (permanent magnets in modern motors)
Commutator & Brushes: Electrical connection to rotating armature
Feedback Device: Position sensor (encoder/resolver/tachometer)
Housing: Contains bearings and mounting provisions
High Torque-to-Inertia Ratio: Allows quick starts and stops
Linear Torque-Speed Characteristics: Enables precise control
Low Electrical Time Constant: Fast response to control signals

Mnemonic: "SAFE" - Sensitive Armature with Feedback for Exactness.

Question 5(b) OR [4 marks]

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

Answer: DC series motor speed control circuit using SCR.

Diagram:

graph LR
    AC[AC Supply] --- BR[Bridge Rectifier]
    BR --- SCR[SCR]
    SCR --- S[Series Field]
    S --- A[Armature]
    A --- BR
    FC[Firing Circuit] --- SCR
    P[Potentiometer] --- FC

Working:

Bridge rectifier converts AC to DC
SCR controls average voltage to motor
Firing angle controlled by potentiometer
Series field and armature current is the same
Speed varies inversely with voltage at low loads
Armature Voltage Control: Primary method for speed control
Torque Characteristics: High starting torque maintained
Speed Range: Typically 3:1 for stable operation

Mnemonic: "SCRAM" - SCR Controls Rectified Armature and Motor speed.

Question 5(c) OR [7 marks]

Explain construction, working of Stepper motor Give and its applications

Answer: Stepper motor is an electromechanical device that converts electrical pulses into discrete mechanical movements.

Construction:

Diagram:

graph TD
    subgraph "Stepper Motor"
        R[Rotor - Permanent Magnet]
        S[Stator - Electromagnetic Coils]
        SH[Shaft]
    end

Component	Description
Stator	Contains multiple coil windings arranged in phases
Rotor	Permanent magnet or soft iron (reluctance type)
Bearings	Support shaft and allow rotation
Housing	Mechanical structure holding all components
Leads	Electrical connections to stator windings

Working Principle:

Digital pulses energize stator windings in sequence
Magnetic field rotates in steps around stator
Rotor follows magnetic field in precise angular steps
Direction controlled by sequence of energization
Speed controlled by pulse frequency

Types of Stepper Motors:

Type	Characteristics
Variable Reluctance	No permanent magnet, high speed, low torque
Permanent Magnet	Simpler design, moderate torque, lower resolution
Hybrid	Combines both designs, high resolution, good torque

Applications:

CNC machines and 3D printers
Robotics and automation
Camera lens focusing mechanisms
Precision positioning systems
Medical equipment
Office equipment (printers, scanners)
Automotive applications (headlight positioning)
Small consumer devices

Mnemonic: "REACT" - Rotation Exactly At Controlled Timing.