ELEX 2

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A string of series connected thyristors needs equalizing circuit to

to ensure proper voltage division

An input signal is needed for an oscillator to start.

False

Whenever a totem pole TTL output goes LOW to HIGH, a high amplitude current spike is drawn from the Vcc supply. How is the effect corrected to a digital circuit?

By connecting a radio frequency capacitor from Vcc to ground

The output frequency of a cycloconverter can be changed by changing the firing angle.

False

Which of the following is widely used in digital computers?

MOSFET

Main Utility of SCR

Gate Triggering

A floating TTL input may be defined as

unused input that is not connected.

In Jone Chopper, the commutating element :

a capacitor and a auto transformer

Which of the following logic families has the highest maximum clock frequency?

AS-TTL

The leads of a transistor are typically made of _____

Aluminum

Why is the fan out of CMOS gates frequency dependent?

The input gates of the FETs are predominantly capacitive, and as the signal frequency increases, thereby limiting the number of loads that may he attached to the output of the driving gate.

The symbol for figure is for

Shockly Diode

The term bipolar reflects the fact that ____ and ____ participate in the injection process into oppositely polarized material.

holes, electrons

Which of the following may be described as most commonly used semiconductor material?

Silicon

What is the relationship between the series and parallel resonant of a quartz crystal?

Parallel resonant frequency is approximately 1 kHz higher than series resonant frequency.

For a phase shift oscillator, the gain of the amplifier stage must be greater than ____

A certain oscillator has a tap on the inductor in the tank circuit. This oscillator is probably

Hartley oscillator

When a dc chopper feeds an RLE load, the load current during steady state operation

varies between maximum and minimum values

The output of a certain voltage divider is 12 with no load. When a load is connected, the output voltage,

decreases

The voltage across a zener diode

is constant in reverse direction

The parallel resonance, the impedance of a crystal is

maximum

The series resonance, the impedance of a crystal is

minimum

The feedback signal in a(n) ____ oscillator is derived from an inductive voltage divider in the LC circuit.

Hartley

The load circuit of a single phase full bridge inverter

may be any type of load

The bipolar TTL logic family that was developed to increase switching speed by preventing transistor saturation:

emitter-coupled logic (ECL) and transistor-transistor logic (TTL)

The duty cycle of a step down chopper is

Ton/(Ton + Toff)

A rectifier is fed by a transformer. The rms voltage and current at secondary of transformer are Vs and Is. Output dc power is (Vdc) (Idc) and output ac power is (Vrms) (Irms). Transformer utilization factor TUF is

Vdc Idc/(Vs Is)

Which of the following oscillators is (are) tuned circuit?

All of the above

In a 3 phase full wave regulator feeding a star connected resistance load, firing angle is 75°. Then number it thyristors conducting at one time is

The common collector configuration has a ____ input impedance and a _____ ouput impedance.

high, low

The minimum gate current which can turn on SCR is called

Trigger Current

The base current is the ____ of the emitter and collector current.

difference

Forward dv/dt rating of an SCR is

the maximum rate of rise of anode voltage which will not trigger the SCR if gate signal is applied.

A LASCR

4 semiconductor layers and 3 junctions.

can be used in controlled heating, excitation systems of alternators, speed control of motors and HVDC

Thyristor

In order to start up, a feedback oscillator requires

positive feedback greater than 1

The efficiency of a chopper circuit is about

80% or more

When a single phase dual converter is operating in circulating current mode

one converter is always working as rectifier and other as inverter.

The saturation region, the collector base junction is _____-biased and the base emitter junction is _____-biased for a transistor.

forward, forward

There is (are) _____ in the internal construction of a TO-92 package

All of the above

Which of the following is correct for a BJT

B = a/(1 - a)

What is the ratio of the output impedance with series feedback to that without feedback?

1 + BA

A 3 phase dual converter consists of

two 3 phase full converters connected in antiparallel

The number ot thyristors in a single phase fully controlled bridge rectifier

What is the minimum frequency at which a crystal will oscillate

Fundamental

As compared to a pn junction diode

a Schottky diode has lower cut in voltage wnd higher reverse current

A single phase semiconverter is feeding a highly inductive load and has a freewheeling diode across the load. The waveshape of input current is

rectangular

Which of the following improvements is (are) a result of the negative in a circuit?

All of the above

The method of triggering SCS

application of positive pulse at cathode gate or negative pulse at anode gate.

The circuit in figure is

Complementary Commutation

The outer layers of a transistor are ____ sandwiched layer.

much larger than

When SCR is reverse biased

two junction are reverse biased and one junction is forward biased

All amplifiers should have at least ____ terminals with ____ terminal(s) controlling the flow between ____ other terminals

3, 1, 2

A surge voltage has ___ magnitude and ____ duration

very high, very small

In a 3 phase bridge inverter wirh 120° mode of operation the number of thyristors conducting at one time are

When an SCR is in forward blocking mode, the applied voltage

appears across only one junction

The Nyquist plot combines the two Bode plots of gain versus frequency and phase shift versus frequency on a single plot.

True

The step function (per step) of a curve tracer reveals the scale for ____

base current Ib

What is increase in switching speed between 74LS series TTL wnd 74HC/HCT (High Speed CMOS)

Which of the following may be described as donor impurity?

Antimony

The total number of leads in SCR, DIAC, and TRIAC respectively are ____

3, 2, 3

If the frequency is less than the damped frequency in a series inverter

the distortion of output voltage waveform is high

Class A and Class B chopper

Class A chopper operates in first quadrant and Class B chopper operates in second quadrant

In disc mounting of SCR

SCR is clamped between two disc shaped heat sink

One condition for positive feedback is that the phase shift around the feedback loop must be ___

0°

Which of the logic families listed below allows the highest operating frequency?

ECL

An OL indication of an advanced digital meter indicates _____ while checking a transistor.

reverse bias

What causes low power Schottky TTL to use less power than the 74XX Series TTL?

A larger value resistor

In a single phase full wave ac regulator the firing angle during both half cycle are equal

True

In a full bridge circuit supplying an RLC under damped circuit

the waveshape of output voltage is square but the waveshape of load current is nearly sinusoidal.

Which of the following is an example of propagation below cutoff?

Evanescent Wave

Which of the following is (are) th determining factor(s) of the stability of a feedback amplifier?

Both A and the phase shift between input and output signals.

The depletion layers around pn junction in JFET consist of

immobile charges

The circuit in figure is

Self Commutation

The number of leads in DIAC are

The silicon is preferred over germanium in manufacture of semiconductor devices. Forbidden gap in silicon is

more than that in germanium

Typical values of voltage amplification for common base configurations vary from ______ and the current gain is always ____

50 to 300, less than 1

A crowbar is generally needed for protection under fault conditions

True

Light triggering is very suitable for _____ and has the advantage of complete ____ of gate current.

HVDC transmission, electrical isolation

The twin T oscillator produces a ____ response.

bandstop

The effect of source inductance in a 3 phase fully controlled bridge converter is to

decrease the output voltage

What is the typical value of quality factor for crystal oscillatore?

20,000

What must be done to interface CMOS battery to TTL?

As long as the cmos supply voltage is 5 v, they can be interfaced; however, the fan-out of the CMOS is limited to two TTL gates.

Which statement is false as regards holes?

Holes exist in conductors as well as semiconductors.

The total number of leads in SUS, SBS, and SCS respectively are

3, 3, 4

The number of diodes used in a half wave rectifier are _____

Which of the following logic families has the shortest propagation delay?

AS-TTL

In a modified series inverter

the output frequency can be even higher than the frequency of damped oscillation.

A schottky diode is used along with switching BJT

reducing the switching time

The magnitude of the base current is typically on the order _____ as compared to ____ for the emitter.

µA, mA

The number of diodes in a full wave rectifier using center tapped transformer rectifier is _____

In a single phase half wave ac regulator feeding a resistive load, the rms load current

is always positive

From which instant is the turn off time of a thyristor defined

when anode current becomes zero.

Typical values of di/dt (A/µsec) and dv/dt (V)µsec) an SCR are in range of

25 to 500

A class B chopper operates in third quadrant

False

In the IC phase shift oscillator, what should the ratio of feedback Rf to R1 be?

Greater than -29

A single phase cycloconverter with center tapped input transformer requires

4 thyristors

What are major differences between the 5400 and 7400 series of ICs?

The 5409 series are military grade and allow for a wider range of supply voltages and temperatures.

Which of the following is required for oscillation?

Both BA > 1 and the phase shift around the feedback network must be 180°.

100

The feedback signal in a(n) ____ oscillator derived from a capacitive voltage divider in the circuit.

Colpitts

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