About this previous year paper
SECTION A – Short Answer Type Questions (2 Marks each)
(a) Differentiate Between Normal and Power MOSFET.
| Feature | Normal MOSFET | Power MOSFET |
|---|---|---|
| Voltage/Current Rating | Low current and voltage | High current and voltage |
| Application | Used in signal-level and low-power circuits | Used in switching regulators, converters, and motor drives |
| Structure | Planar construction | Vertical construction for high power handling |
| Switching Speed | Very high | Moderate to high |
| On-State Resistance (Rds(on)) | Higher | Very low, improves efficiency |
Conclusion:
Power MOSFETs are specially designed to handle high power and voltage in industrial circuits while maintaining good switching speed and thermal performance.
(b) What is a Transducer?
A transducer is a device that converts one form of energy into another, especially non-electrical quantities into electrical signals for measurement or control.
Types of Transducers:
Active Transducers: Generate their own electrical output (e.g., thermocouple, piezoelectric sensor).
Passive Transducers: Require external power for signal conversion (e.g., LVDT, strain gauge).
Applications:
Used in automation, robotics, pressure and temperature measurement, and industrial process control.
SECTION B – Long Answer Type Questions (10 Marks each)
(a) Describe the Structure and Working of an IGBT with Neat Diagram.
Structure:
An Insulated Gate Bipolar Transistor (IGBT) combines the characteristics of MOSFET (high input impedance) and BJT (low on-state voltage drop).
It has four layers (P+, N−, P, N+) forming a PNPN structure controlled by an insulated gate.
Working Principle:
When gate voltage (Vge) > threshold, electrons flow through MOSFET channel from emitter to collector, turning the device ON.
The BJT section amplifies current, reducing conduction losses.
When gate voltage = 0, channel closes, and device turns OFF.
Advantages:
High current and voltage capacity. Low switching losses.
Simple gate drive requirements.
Applications:
Used in inverters, SMPS, induction heating, and motor drives.
(b) What is SMPS? Explain Its Block Diagram and Working.
Definition:
SMPS (Switched Mode Power Supply) converts electrical power efficiently using high-frequency switching devices like MOSFETs or IGBTs.
Block Diagram:
AC Input & Rectifier: Converts AC to DC. Filter: Removes ripples.
Switching Section: Converts DC to high-frequency AC. Transformer: Provides isolation and voltage conversion.
Rectifier & Filter: Converts HF AC back to smooth DC output.
Feedback Control: Maintains stable output voltage.
Advantages:
High efficiency (up to 90%). Compact size and lightweight. Wide input voltage range.
Applications: Computers, communication devices, industrial control circuits.
SECTION C – Very Long Answer Type Questions (10 Marks each)
(a) Describe the Switching Characteristics of a Power Transistor.
Switching Characteristics:
A power transistor acts as an electronic switch in converter and inverter circuits. Its switching process has
three intervals:
Turn-On Process:
Delay time (td): Time for base current to rise.
Rise time (tr): Time for collector current to reach maximum and voltage to fall.
Turn-Off Process:
Storage time (ts): Time to remove stored charge from base.
Fall time (tf): Collector current falls to zero.
Graph:
A plot of collector current (Ic) and collector-emitter voltage (Vce) against time shows the switching delays.
Importance:
Determines switching frequency and efficiency.
Affects power losses and heat dissipation.
Conclusion:
Fast-switching transistors improve performance in high-speed switching circuits like SMPS and converters.
(b) Define Different Types of Industrial Robots and Their Applications.
Definition:
An industrial robot is an automatically controlled, reprogrammable, multipurpose manipulator used in manufacturing and industrial processes.
Types of Industrial Robots:
Cartesian Robots: Linear motion along X, Y, Z axes.
Used in CNC machines and pick-and-place operations.
Cylindrical Robots:
Rotary motion at the base and linear motion along the arm.
Used for assembly and handling operations.
SCARA Robots (Selective Compliance Assembly Robot Arm):
Ideal for assembly and material handling. High speed with horizontal reach.
Articulated Robots:
Multi-jointed arms with rotary joints. Used for welding, painting, and inspection.
Delta (Parallel) Robots:
Lightweight arms for high-speed tasks like packaging.
Applications:
Automotive welding and painting. Electronics assembly.
Material handling and quality inspection.
Conclusion:
Industrial robots improve efficiency, precision, safety, and productivity in automation systems.