Practice Test Questions

Industrial Electrons

V_CBO refers to…

collector to base breakdown voltage.

V_CEO refers to…

collector to emitter breakdown voltage.

f_T refers to…

gain-bandwidth product.

The frequency at which the gain of a transistor drops to unity is called it’s…

gain-bandwidth product or f_T.

If a data sheet refers to MAX P_D it is reffering to…

maximum power dissipation.

The formula to calculate the dynamic resistance of the base-emitter junction is…

r’_e = 25mV / I_E

A transistor switch should be in one of what two conditions…

saturation and cut-off.

A NPN transistor always behaves exactly like two diodes joined node to node. (T/F)

False.

Normally, the collector-base junction of a transistor is reversed-biased. (T/F)

True.

To get collector current, the base-collector junction must be forward-biased. (T/F)

False.

The emitter injects minority carriers into the base. (T/F)

True.

The injection of minority carriers into the base is controlled by the base-emitter voltage. (T/F)

True.

Base current is due to a small percentage of minority carriers combining with majority carriers. (T/F)

True.

Transistors having the same part number will have approximately the same value for current gain. (T/F)

False.

At saturation, collector current is limited by the base current. (T/F)

False.

Collector-emitter current is effectively zero at cut-off. (T/F)

True.

When measured with an Ohm-meter, the collector-base drop us typically less that the emitter-base drop. (T/F)

True.

The current gain of a transistor will decrease above some signal frequency. (T/F)

True.

The input resistance of a transistor is constant. (T/F)

False.

The dynamic resistance of a PN junction depends on the current going through it. (T/F)

True.

When a transistor is fully on, and its current is limited by the load resistance, it is:

in saturation.

The B of a transistor is defined as:

collector current divided by base current.

A transistor can be used as:

a switch and an amplifier.

Another term for B is:

h_FE.

When the transistor is a one-transistor amplifier conducts during all parts of the signal, it is:

class A.

When the transistor in a one-transistor amplifier conducts during half of the singal, it is:

class B.

The Q-point of a transistor refers to its:

bias point.

Gain means that, for the signal being amplified:

output power is greater than input power.

Given a transistor with a fixed amount of base current, when V_CE increases, I_C will:

stay the same.

A transistor amplifier is inverting when:

the output signal goes up when the input signal goes down.

When a transistor is in cut-off:

collector current is zero.

What can you say about a transistor if I_C = 100mA when V_BE = 0V:

it has failed shorted.

What can you say about a transistor if I_C = 0mA when V_BE = 0.7V:

it has failed open.

If V_BE is measured to be 2.7V on an NPN transistor:

the base-emitter junction is open.

Q-point instability is caused by

beta.

As a transistor warms up, the value of its beta

increases.

In voltage divider biasing, the voltage divider is used to fix the DC _____ voltage.

base

In voltage divider biasing, the emitter resistor is used to fix the DC _____ current.

emitter

When analyzing the biasing in an RC coupled multi-stage amplifier, the coupling capacitors are considered to be _____ circuited.

open

In voltage divider biasing, bypassing the emitter resistor will cause the gain to ______.

increase

In voltage divider biasing, bypassing the emitter resistor will cause distortion to _______.

increase

In voltage divider biasing, bypassing the emitter resistor will cause Z_IN to _______.

decrease

The text says that the main advantage of using voltage-mode feedback is its stability to operate with a _______ supply voltage.

low

In a 2-stage amplifier, the load on the first stage is the _______ of the second stage.

input impedance

The actual value of a transistor’s beta can be 50% higher or lower than the typical value given on its date sheet. (T/F)

True.

Transistor beta increases with temperature. (T/F)

True.

Variations in beta have no effect on Q-point. (T/F)

False.

Placing a resistor in series with the emitter will help stabilize the Q-point. (T/F)

True.

Placing a resistor in series with the emitter will reduce distortion. (T/F)

True.

Bypassing the emitter resistor with a capacitor will increase voltage gain. (T/F)

True.

Placing a resistor in series with the emitter will increase voltage gain. (T/F)

False.

A voltage-mode feedback biased amplifier will neither saturate nor cutt off for any values of R_B and R_C. (T/F)

True.

A voltage-mode feedback biased amplifier has a high voltage gain. (T/F)

True.

If the coupling capacitors in a multi-stage amplifier are too small, then gain is lost at higher signal. (T/F)

False.

For a 2-stage bipolar transistor amplifier to be direct coupled, one transistor must be NPN and the other must be PNP. (T/F)

True.

The input impedance of a transistor amplifier stage is higher if the emitter resistor is bypassed with a capacitor. (T/F)

False.

When voltage divider baising is used, the Q-point becomes essentially independant of beta as long as beta is above some minimum value. (T/F)

True.

Multistage, RC coupled amplifiers can amplify DC signals. (T/F)

False.

In a 2-stage amplifier, the load seen by the first stage is the input impedance of the second stage. (T/F)

True.

Which of these DC parameters are kept essentially constant by voltage divider biasing?

Base voltage

Voltage divider biasing uses a resistor in series with the emitter to:

keep DC emitter current constant

Voltage gain for an unbypassed voltage divider biased amplifier stage is in the range:

2 to 10

Voltage gain for a fully bypassed voltage divider biased amplifier stage is in the range:

50 to 500

Voltage gain for a split-emitter biased amplifier stage is in the range:

5 to 50

The value of V_CE in a voltage-mode feedback biased transistor is:

approximately 2 volts

In addition to V_CC, an emitter-biased NPN transistor typically requires:

a seperate negative voltage supply (V_EE)

The number of ______ determines the atom’s atomic number.

protons

The outtermost shell or band of an atom is called the ______ band.

valence

Silicon atoms are held together by _______ bonding.

covalent

Pure silicon is called _______ material.

intrinsic

Adding a few atoms of impurities to pure silicon is called ______.

Doping

________ (A.K.A _______) atoms are used to make N-type material.

Pentavelent, donor

________ (A.K.A _______) atoms are used to make P-type material.

Trivalent, accepter

In P material, _____ carry the current.

holes

In N material, _______ carry the current.

electrons

A depletion regain contains no _____ carriers.

charge

A depletion region becomes wider in a _______ -biased PN junction.

reverse

The practical diode model contains an ideal diode in series with a ________.

battery

The complete/detailed diode model requires a ______ and ______.

battery, resistor

Real diodes have a small amount of reverse ______ current.

leakage

The _____ diode model is good for analyzing low-voltage circuits.

practical

The ______ diode model does not contain a battery.

ideal

The _____ diode model includes reverse leakage current.

complete/detailed

The ______ potential must be overcome to forward bias a PN junction.

barrier

One type of diode that has only a 0.3V forward drop is a ______ diode.

germanium/Schottky

The _____ material is the cathode in a PN junction diode.

N-type

The arrow in the diode symbol shows the direction of ______ current flow.

conventional

A depletion region forms in a _____ -biased PN junction.

reverse

Adding a few atoms of gallium or arsenic to silicon is called _____.

doping

An LED can have a foward drop in the range of _____ volts.

1.5V - 3V

The arrow in the diode schematic symbol points in the direction of electron flow. (T/F)

False

The key property of a diode is to let current flow through it in one direction only. (T/F)

True

To forward bias a diode, the anode must be positive with respect to the cathode. (T/F)

True

A device is called a semiconductor when current can flow through it only one way. (T/F)

Flase

The most common use for a diode is to change AC into DC. (T/F)

True

In addition to silicon, diodes also are commonly made from carbon. (T/F)

False

N-type material has more negative charge than positive charge. (T/F)

False

The atoms in crystal materual are held together with covalent bonds. (T/F)

True

Covalent bonds are relatively weak. (T/F)

False

The practical diode model contains a battery. (T/F)

True