Electronic Engineering Review – AC Theory, ICs, Power Control, Transducers & Instrumentation

80 question-and-answer flashcards summarising key concepts from AC theory, filters, integrated circuits, ESD, transducers, thyristors, control systems, and digital instrumentation.

What does the ‘selectivity’ of a radio receiver describe?

Its ability to discriminate between signals of different frequencies.

Define a low-pass filter in one sentence.

A circuit that presents low reactance to low-frequency signals and attenuates high-frequency signals.

What percentage of its final value does a current reach after one time constant in an RL or RC circuit?

63.2 % of its final value.

What is a harmonic of a waveform?

A frequency component that is an integer multiple of the fundamental frequency.

Give a concise definition of bandwidth.

The range of frequencies selected within a continuous spectrum.

How is the Q-factor of a resonant circuit defined?

The ratio of the reactance of the inductor or capacitor to its equivalent resistance.

Why is an RC differentiator called a high-pass filter?

Its series capacitor offers high reactance at low frequencies and passes high-frequency components.

List two practical uses of an RC differentiator.

Producing trigger spikes for timing circuits and acting as a DID controller/high-pass filter in signal processing.

State two applications of an RL differentiator.

Time-delay generation and separation of horizontal sync pulses in TV receivers.

Why is an RC integrator regarded as a low-pass filter?

Because it attenuates high-frequency components while passing low-frequency (average) values.

Name two electronic functions that employ RC integrators.

Analogue-to-digital converters and wave-shaping circuits.

Which waveform contains both odd and even harmonics?

A saw-tooth waveform.

Square waves contain which harmonics?

Only odd harmonics, of amplitude 1/π times the fundamental for the nth harmonic.

Explain the key difference between symmetrical and asymmetrical waveforms.

Symmetrical waveforms have equal positive and negative half-cycles; asymmetrical ones do not.

What three factors determine the capacitance of a capacitor?

Plate area, plate separation, and dielectric constant.

What are coupling capacitors used for in amplifiers?

Blocking DC while allowing AC signals to pass between stages.

Why are square waves useful for circuit testing?

They are easily distorted by faults, so distortion quickly reveals errors and their type.

At what phase angle is a series RL circuit purely resistive?

0 degrees (when inductive reactance is zero or cancelled).

What is static electricity?

An electrical charge caused by an imbalance of electrons on a material’s surface.

Give two common applications of integrated circuits in automobiles.

Climate-control systems and anti-lock braking systems.

Why are surface-mount IC packages considered fragile?

Their small leads and high lead density are easily damaged during handling or soldering.

Describe the current path during the positive half-cycle in a single-phase bridge rectifier.

Diodes D1 and D2 conduct in series, while D3 and D4 are reverse-biased, so current flows through the load in one direction.

How many diodes are used in a three-phase bridge rectifier?

Six diodes.

State one advantage and one disadvantage of an IC voltage regulator.

Advantage: built-in protection and low noise. Disadvantage: limited to low power (≈ < 10 W).

What output voltage does a 7805 regulator provide?

5 V DC.

Identify the three pins of a 7812 regulator.

Pin 1 – Input, Pin 2 – Ground, Pin 3 – +12 V Output.

Give two advantages of switching regulators over linear regulators.

Much higher efficiency and smaller/lighter components.

What are the three standard ESD failure models?

Human Body Model (HBM), Machine Model (MM), and Charged Device Model (CDM).

List two handling precautions for CMOS ICs.

Wear a grounded wrist-strap and ensure all test equipment is earthed.

Why must unused CMOS inputs be tied to Vdd or Vss?

Floating gates can accumulate charge and cause unpredictable switching or damage.

Define a transducer in one sentence.

A device that converts one form of energy into another measurable form.

Differentiate between active and passive transducers.

Active transducers generate their own output (e.g. thermocouple), while passive transducers need external power (e.g. strain gauge).

What does potentiometer ‘resolution’ mean?

The smallest detectable change in resistance ratio per wiper movement.

State the basic operating principle of a strain gauge.

Resistance changes proportionally with mechanical strain due to dimensional changes in the conductor.

What are NTC and PTC in thermistors?

Negative and Positive Temperature Coefficient types, where resistance decreases or increases with temperature respectively.

List four key criteria for selecting a transducer.

Sensitivity, accuracy, environmental compatibility, and range.

What does LVDT stand for and what does it sense?

Linear Variable Differential Transformer; it senses linear displacement.

How is the magnitude of LVDT output related to core displacement?

Output voltage is proportional to the difference between the induced voltages of the two secondary windings, hence to displacement.

State one application of a current transducer.

Motor control feedback for speed or torque regulation.

How does a light-dependent resistor (LDR) behave with increasing light?

Its resistance decreases as light intensity increases.

What two components form a precise light-switch using an LDR?

The LDR in a voltage divider and an operational-amplifier comparator driving a relay.

Name two ESD-protection networks used for CMOS gates.

Double-diode clamps and resistor-diode (RC) snubber networks.

Give the typical trigger and conduction angle definitions for thyristors.

Trigger angle – period the thyristor is off before gating; conduction angle – period it conducts after gating.

List three methods to turn an SCR on.

Gate triggering, forward voltage breakover, and light triggering (LASCR).

List three ways to turn an SCR off.

Natural commutation at AC zero crossing, forced commutation circuits, or reducing anode current below holding current.

How does a TRIAC differ functionally from an SCR?

A TRIAC conducts in both directions and can be triggered by positive or negative gate pulses; an SCR conducts in one direction only.

What is meant by ‘dv/dt triggering’ of a thyristor?

Rapidly rising anode voltage causes capacitive current into the gate region, unintentionally turning the device on.

Which phase-control circuit uses two SCRs in inverse parallel?

Full-wave AC phase control (back-to-back SCRs).

Why is an open-loop control system considered less accurate?

It lacks feedback, so it cannot correct for load or environmental changes.

Describe the error-correction action in a closed-loop system.

A comparator subtracts feedback from the reference, and the controller adjusts the plant until the error approaches zero.

What role does a DIAC play in a simple TRIAC dimmer?

It provides a break-over trigger pulse to the TRIAC once the capacitor reaches the DIAC’s switching voltage.

Give one household application of closed-loop phase control.

Fan speed regulation using TRIAC plus tachometer feedback.

Define an analogue signal.

A continuously varying electrical quantity representing a physical variable.

Define a digital signal in one phrase.

A signal that assumes discrete voltage levels, typically representing logic 0 and 1.

Why are analogue signals converted to digital before measurement storage?

Digital form offers low noise susceptibility, higher accuracy/resolution, fast processing, and easy storage/transfer.

State two advantages of a digital voltmeter over an analogue meter.

Greater accuracy with digital read-out and the ability to store or transmit data electronically.

What does a sample-and-hold circuit do in an ADC front-end?

Captures and stores the analogue voltage momentarily so the ADC can convert a stable value.

Name the five common ADC architectures used in measuring instruments.

Ramp, Integrating (voltage-to-frequency), Dual Slope, Successive Approximation, and Flash.

Which ADC type employs a binary search algorithm?

The Successive Approximation Register (SAR) ADC.

What is the primary advantage of a dual-slope ADC?

Excellent noise rejection and accuracy independent of component tolerances.

Explain the basic operation of a frequency counter.

Counts cycles of the input signal during a precise time gate generated by an internal reference clock, then displays frequency.

What function does a Schmitt trigger serve in a frequency counter’s input?

It squares and cleans the incoming waveform, producing crisp digital transitions for accurate counting.

In a staircase (ramp) voltmeter, what event stops the clock to the counter?

When the DAC’s ramp voltage equals the unknown input, the comparator output changes state and halts counting.

During SAR conversion, what happens if the trial DAC voltage Vr is greater than the unknown Vu?

The tested bit is reset to 0 and the algorithm proceeds to the next lower bit.

Give one reason MOSFET-based CMOS circuits use less power than bipolar circuits.

Quiescent (static) current is nearly zero because only leakage currents flow when gates are not switching.

True or False: ‘Voltage pulses that exceed 15 V on CMOS inputs are safely clamped by protection diodes.’

True.

What is the main disadvantage of linear regulators compared with switching regulators?

Low efficiency due to series pass element dissipating excess power as heat.

Name two parameters improved by using a closed-loop control system.

Accuracy and disturbance rejection.

Which transducer would you choose to measure angular displacement accurately?

A rotational potentiometer or an LVDT configured for rotation.

Provide two industrial uses for Wheatstone bridge circuits.

Precision temperature measurement with thermistors and strain-gauge based load/pressure sensors.

How does an infrared detector pair consisting of LED and photodiode generate an alarm?

Interruption of the IR beam stops photodiode current, changing amplifier output which de-energises or energises a relay that triggers an alarm.

What is the typical logic-high voltage used in the digital signal example from the notes?

5 V represents logic 1.

Why is robustness listed as an advantage of analogue devices?

They often tolerate voltage/current overloads better than delicate digital circuits.

Which package type is best suited for high pin-count microprocessors but occupies more board area?

Pin Grid Array (PGA).

State one mechanical factor that affects potentiometer resolution.

The total number of resistive turns/tracks relative to one wiper movement.

What causes thermal runaway turn-off in an SCR?

Excess heating reduces device impedance, increasing current until the device turns off or fails.

Explain natural commutation for an SCR in AC circuits.

At every current zero crossing of the AC waveform, anode current falls below holding value, turning the SCR off.

How does a series RC snubber aid TRIAC commutation?

It limits dv/dt and provides a transient path, helping the TRIAC switch off at current zero.

Why can’t high-power (>10 W) IC regulators be monolithically fabricated easily?

Heat dissipation and large pass elements exceed what a single silicon die can handle.

Which two logic levels does a PAM (Pulse Amplitude Modulated) signal vary between?

It varies analogue amplitude levels at discrete sampling instants, not fixed logic levels; amplitude represents the sampled value.

Which transducer category does an LDR fall into: active or passive?

Passive; it requires bias to produce a usable output.

Give one advantage of an integrating-type ADC in noise environments.

Averaging during integration attenuates periodic noise components, improving measurement accuracy.

What device combination forms the basic element of an opto-isolator?

An infrared LED and a phototransistor housed together with optical coupling.

State the operating principle of a tachogenerator in a feedback loop.

It produces a voltage proportional to rotational speed, which is compared with a reference to control motor drive.

Why do MOSFET gates appear ‘floating’ if not tied to a defined potential?

The gate is insulated by oxide, so it forms a tiny capacitor that can hold charge indefinitely, leading to undefined states.

How does capacitive discharge commutation turn a TRIAC off?

A charged capacitor produces a reverse current when discharged through the TRIAC, forcing current below holding value.

List two applications of optical fibre in electronics.

Medical endoscopes/cameras and high-speed communication links.

What is ‘trigger angle’ in an SCR dimmer circuit?

The delay angle from the start of the AC half-cycle to the gate pulse; equal to firing angle α.

In control terminology, what is a ‘set-point’?

The desired target value for the controlled variable.

Explain why linear voltage regulators have low output ripple.

Series pass transistor operates in linear region, providing constant attenuation of input variations and high PSRR.

Give two disadvantages of switching regulators.

Complex design and higher component cost (inductors, control ICs).

What component inside a CMOS IC most often fails first during an ESD event?

The thin gate oxide of MOSFETs.

How do ‘double-diode clamps’ protect CMOS inputs?

Forward-biased diodes to Vdd and Vss limit the positive and negative voltage excursions to about ±0.7 V beyond the rails.

What is the main control element in a series linear regulator?

A pass transistor (often a PNP or P-channel device) placed in series with the load.

How is converter efficiency defined for regulators?

Output power divided by input power, expressed as a percentage.

Which ADC architecture is inherently the fastest?

Flash ADC.

True or False: An LDR exhibits higher resistance in darkness than in bright light.

True.

Which circuit element in a voltage-to-frequency converter defines output frequency proportionality?

The integrator’s capacitor charge/discharge rate controlled by the input voltage.

Why must an open-loop motor controller rely on human intervention for precision?

There is no automatic feedback to correct speed or position deviations.

Give one reason to use a Wheatstone bridge with a thermistor.

It converts small resistance changes into measurable voltage changes with high sensitivity.