EASA Part-66 Module 04 — Electronic Fundamentals

In a forward-biased silicon PN-junction diode, approximately what voltage must be exceeded across the junction before significant conduction begins?

• A0.3 V
• B1.4 V
• C0.7 V
• D5.0 V

A single diode used as a half-wave rectifier is supplied with a 50 Hz sine wave. What is the ripple frequency of the rectified output?

• A25 Hz
• B50 Hz
• C100 Hz
• D150 Hz

How many diodes are required to build a single-phase full-wave bridge rectifier?

• A1
• B2
• C6
• D4

A Zener diode is normally operated in which condition to provide voltage regulation?

• AForward biased above 0.7 V
• BReverse biased in the breakdown region
• CUnbiased
• DReverse biased well below its Zener voltage

In a series voltage-regulator circuit using a Zener diode, what is the function of the series resistor placed between the supply and the Zener?

• ACannot raise the Zener breakdown voltage above its rating
• BLimits Zener current and drops surplus supply voltage
• CRectification needs diodes, not a series resistor alone
• DThe load sits across the Zener, not the series resistor

A light-emitting diode (LED) emits light when it is:

• AReverse biased near breakdown
• BOperated with no current
• CForward biased and conducting
• DHeated above 100 degrees C

Which semiconductor device is a four-layer (PNPN) device that, once triggered into conduction by a gate pulse, continues to conduct until the anode current falls below the holding current?

• AA Zener is a two-terminal regulator, not a gated latch
• BThyristor (silicon controlled rectifier)
• CA varactor is a voltage-variable capacitor, not a latch
• DA Schottky diode is a fast rectifier with no gate terminal

A varactor (varicap) diode is used in circuits because, when reverse biased, it behaves as a:

• AVoltage reference
• BConstant-current source
• CVoltage-variable capacitor
• DLight detector in this case

Compared with a standard silicon PN rectifier diode, a Schottky diode is characterised by:

• AHigher forward drop and slower switching than Schottky
• BSchottky diodes are two-terminal devices with no gate
• CSchottky diodes have relatively high reverse leakage
• DLower forward drop and faster switching than silicon PN

In a diode clamping (DC restorer) circuit, the function performed is to:

• ARemoving peaks above a level describes a clipper/limiter
• BSmooth DC conversion needs rectification plus filtering
• CShifts the DC level without changing waveform shape
• DFrequency doubling is not a clamping circuit function

A diode clipper (limiter) circuit is used to:

• AAdd a DC offset to a waveform
• BLimit the amplitude of a waveform to a set level
• CIncrease the signal power
• DStore charge for smoothing

In a half-wave rectifier with a reservoir (smoothing) capacitor, increasing the capacitance value will:

• AIncrease the ripple voltage
• BHave no effect on ripple
• CDecrease the ripple voltage
• DChange the ripple frequency to 100 Hz

The peak inverse voltage (PIV) rating of a rectifier diode specifies the maximum:

• AForward current it can pass
• BSwitching frequency
• CPower it can dissipate
• DReverse voltage it can withstand without breakdown

A photodiode is normally operated reverse biased so that its reverse leakage current:

• AIncreases with incident light intensity
• BPhotodiode current varies with light; it is not fixed
• CLight increases reverse current; it does not drive it to zero
• DA fixed reference voltage is a Zener function, not photodiode

When testing a good diode with an ohmmeter, you should measure:

• ALow resistance one way and high resistance the other way
• BHigh resistance in both directions
• CLow resistance in both directions
• DExactly zero ohms one way in this case

A varistor (voltage-dependent resistor) is commonly fitted across a load to:

• AA Zener holds a fixed reference voltage, not surge clamping
• BClamps transients by sharply lowering resistance at high voltage
• CA varistor is bidirectional and does not rectify AC
• DVaristors suppress spikes; they do not add capacitance

In an NPN bipolar transistor operating as an amplifier, the base-emitter junction and the base-collector junction are respectively:

• AForward biased and reverse biased
• BBoth junctions reverse biased is cut-off, not amplification
• CBoth junctions forward biased is saturation, not linear gain
• DReverse/forward order describes inverse-active, not normal amp

Which bipolar transistor amplifier configuration provides voltage gain together with current gain, and inverts the signal (180 degrees phase shift) between input and output?

• ACommon emitter
• BCommon base
• CCommon collector (emitter follower)
• DCommon gate

The common-collector (emitter-follower) configuration is mainly used because it provides:

• AHigh input impedance and low output impedance (buffer)
• BEmitter follower voltage gain is near unity, not high
• CThe emitter follower does not invert the input signal
• DEmitter follower gives positive current gain, not negative

A Class A amplifier is biased so that the transistor conducts for:

• AConduction for 180 degrees describes Class B operation
• BThe full 360 degrees of the input cycle
• CConduction under 180 degrees describes Class C operation
• DConducting only at peaks is not a standard amplifier class

In a Class B push-pull amplifier, each transistor conducts for approximately 180 degrees. The main distortion introduced by this arrangement is:

• AHarmonic distortion at high frequency
• BThermal runaway distortion for this application
• CCrossover distortion near the zero-crossing
• DPhase distortion from the transformer

In a transistor amplifier, the emitter bypass (decoupling) capacitor is fitted across the emitter resistor to:

• ADC bias is set by resistors, not the bypass capacitor
• BBypasses the emitter resistor for AC to restore gain
• CCollector bias comes from the supply network, not the bypass cap
• DThis cap bypasses emitter AC; supply ripple uses other filters

Applying negative feedback to an amplifier generally results in:

• ALower gain but better stability, bandwidth and lower distortion
• BNegative feedback lowers gain and reduces distortion
• CNegative feedback widens bandwidth while lowering gain
• DNegative feedback changes gain, bandwidth and distortion

An oscillator circuit differs from an amplifier in that an oscillator:

• AUses positive feedback to self-sustain output without input
• BNegative feedback stabilises amplifiers; it does not oscillate
• CTransistors are commonly used as the active device in oscillators
• DAn oscillator generates its own AC; no external input needed

An astable multivibrator is a circuit that:

• ANo stable state; free-runs to produce a square wave
• BTwo stable states needing a trigger is a bistable (flip-flop)
• COne stable plus one quasi-stable state is a monostable
• DStoring one bit describes a bistable flip-flop, not astable

A bistable multivibrator (flip-flop) is characterised by:

• ANo stable states
• BTwo stable states, changing only when triggered
• COne stable state
• DThree stable states

A monostable (one-shot) multivibrator, when triggered, produces:

• AContinuous square waves come from an astable multivibrator
• BA monostable outputs a rectangular pulse, not a sine wave
• CTwo stable outputs describe a bistable flip-flop circuit
• DOne output pulse of fixed width, then returns to stable state

In a multistage cascaded amplifier, the overall voltage gain is found by:

• AAdding the individual stage gains
• BTaking the lowest stage gain
• CMultiplying the individual stage gains
• DDividing the first gain by the last

In an NPN transistor, conventional current flows into the collector and out of the emitter. The relationship between the currents is:

• AIE = IC - IB
• BIC = IE + IB
• CIB = IC + IE
• DIE = IC + IB

The current gain of a transistor in common-emitter configuration is the parameter known as:

• Aalpha (about 0.98)
• Bbeta or hFE (often 20 to 800)
• Cgm (transconductance)
• Dthe Q factor in this case

A field-effect transistor (FET) differs fundamentally from a bipolar transistor because the FET is:

• AVoltage-controlled with very high input impedance
• BCurrent control is a bipolar transistor property, not FET
• CFETs are commonly silicon; material is not the key difference
• DFETs amplify well and are widely used as switches

Thermal runaway in a bipolar transistor occurs because:

• ABase current does not fall to zero in thermal runaway
• BThe device heats, not cools, as collector current rises
• CRunaway is driven by forward conduction, not reverse bias
• DRising temperature increases IC, which raises temperature further

An operational amplifier (op-amp) configured with no feedback (open loop) has:

• AUnity gain in this context
• BNegative input impedance
• CZero gain in this circuit
• DVery high voltage gain

An op-amp connected as a voltage follower (buffer) provides:

• AA follower does not invert and has unity, not high, gain
• BFollower gain is fixed at unity, not set by resistor ratio
• CA voltage follower introduces no deliberate 90-degree shift
• DUnity gain with high input Z and low output Z

For an inverting op-amp amplifier with input resistor Rin = 10 kilohm and feedback resistor Rf = 100 kilohm, the voltage gain is:

• A+10
• B+0.1
• C-10
• D-0.1

An op-amp used as a comparator with no feedback will produce an output that is:

• ASaturates to a supply rail depending on which input is larger
• BWithout feedback the op-amp saturates, not linearly copies input
• CComparator output swings to a rail, not a constant zero
• DSquare wave output needs repeated threshold crossings

An op-amp integrator circuit is created by placing which components in the inverting amplifier positions?

• AResistors in both positions give a plain inverting amplifier
• BInput capacitor with feedback resistor forms a differentiator
• CInput resistor and feedback capacitor in inverting positions
• DCapacitors in both positions do not form a standard integrator

In digital logic, an AND gate produces a logic 1 output only when:

• AAll inputs are at logic 1
• BAny input is at logic 1
• CAll inputs are at logic 0
• DThe inputs differ