Solid State 1 Final Review

The only correct way to turn on an SCR:

Gate turn on

What line is drawn between the two extremes of operation on a characteristic curve?

Load line

What are the two types of transistors?

NPN and PNP transistors

Vce of a low power transistor in its off state is:

equal to supply voltage

What are the four types of filters?

- Capacitive filters - L-Section resistive filters - L-Section inductive filters - Pi-Section filters

List four ways the output of any rectifier can be affected.

- Filters - Regulators - Voltage dividers - Voltage multipliers

What are the three basic types of rectifier configurations used in single phase DC power supplies?

- Half-wave - Full-wave - Full-wave bridge

Describe the types of thermistors.

- PTC: Positive temperature coefficient, an increase in temperature causes the resistance to increase - NTC: Negative temperature coefficient, an increase in temperature causes the resistance to decrease

What are the 3 sections (elements) of a Pi-Section filter?

- Shunt input capacitor (C1) - Series inductor/choke (L1) - Shunt output capacitor (C2)

What are the major parts of most DC power supplies?

- Transformer - Rectifier - Filter - Voltage regulator - Voltage divider

The gain of a transistor allows

- the transistor to multiply the small base current into a larger collector current - a small base current to drive a transistor into saturation - a small base current to control a larger collector current

How much voltage is usually dropped across a silicon diode?

0.6 V

What type of voltage do the following instruments read? 1) DC voltmeter 2) AC voltmeter 3) Oscilloscope 4) Multimeter

1) Actual voltage 2) Root-mean-square (effective) voltage (Vrms) 3) Peak to peak voltage 4) DC/AC meter

When an SCR is turned ON, the anode-to-cathode voltage (VAK) is approximately:

1.0 VDC

In a voltage divider network with a variable resistor at the SCR gate of a full wave circuit, the conduction angle can be varied from approximately ______ to _______ for each half cycle, or from _______ to ________ for each cycle.

180, 90 360, 180

How many leads do transistors have extending from the base?

2 or 3. If 2, the connection to the collector is through the case

At what temperature is the power of a transistor rated?

25 degrees C

The full wave circuit, with the RC-diode network at the gate, has a phase control range from approximately: - 180 to 90 degrees for one whole cycle - 180 to 90 degrees for one whole cycle - 360 to 180 degrees for one whole cycle - 360 to 0 degrees for one whole cycle

360 to 180 degrees for one whole cycle

What is a hybrid circuit?

A circuit that mixes mechanical devices (relays) and electrical devices (SCR)

What is a rectifier?

A device that converts AC power into DC power by allowing electrons to flow in only one direction

What is a transducer?

A device that converts various forms of energy into electrical energy.

What should be placed across the relay coil of a relay that is used with a transistor?

A diode

Describe a diode characteristic curve and explain its use.

A diode characteristic curve is a curve on a graph that shows the relationship between voltage and current for a typical diode. It indicated the response of a diode when subjected to different forward and reverse bias voltages.

What is guided wave radar?

A level measuring detector consisting of a cable or rod as a wave carrier extending from an emitter down to the bottom of a vessel and electronics to measure the transit time.

What is a pulsed radar level sensor?

A level measuring sensor consisting of a radar generator that directs an intermittent pulse with a constant frequency toward the surface of the material in a vessel.

What is a frequency modulated continuous wave (FMCW) radar?

A level measuring sensor consisting of an oscillator that emits a continuous microwave signal that repeatedly varies its frequency between a minimum and maximum value, a receiver that detects the signal, and electronics that measure the frequency difference between the signal and echo.

What is a semiconductor?

A material that has the electrical conductivity characteristics between that of a conductor and an insulator.

What is a zener diode?

A semi-conductor device used as a voltage regulator.

How do the two types of regulators operate?

A series regulator has a variable resistance that automatically changes as output voltage changes, and the circuit must be manually operated. A shunt regulator combined with the resistance of a power supply or with an additional resistor forms a voltage divider

What is used to determine the different voltage and possible current combinations in a transistor?

A set of operating characteristic curves that are provided by the manufacturer

What is forward blocking current?

A small amount of forward leakage current when an SCR is forward-biased

What is a smoke switch? (smoke detector)

A switch that detects a set amount of smoke by smoldering or burning material and activates a set of electrical contacts. They are used as early warning devices in fire detection.

What is a gas switch? (gas detector)

A switch that detects a set amount of specified gas and activates a set of electrical contacts.

What is an ultrasonic sensor?

A transducer that can detect the presence of an object by emitting and recieving high-frequency sound waves.

What is a Hall effect sensor.

A transducer that detects the proximity of a magnetic field.

What is a piezoelectric sensor?

A transducer that operates based on the interaction between the deformation of certain materials and an electric charge.

How are transistors referenced?

A transistor outline number/TO number. The number represents the size and shape of a transistor

What is a thermistor?

A type of transducer that acts as a temperature-sensitive resistor.

What is a voltage divider and when is it used?

A voltage divider is a circuit that provides several different voltages for several different loads. They're used in a power supply when it's necessary to provide voltages for several different loads.

What are voltage multipliers and how do they work?

A voltage multiplier is a circuit designed to apply higher voltages than the AC source voltage without using a transformer. Two capacitors are allowed to be charged individually from a 100 VAC source. During the positive half cycle, diode D1 is forward biased and allows capacitor C1 to be charged to 100 VDC. During the negative cycle, diode D2 is forward biased and allows capacitor C2 to be charged to 100VDC. 200 VDC would be read across the two capacitors.

How is a transistor tested to determine if it is an NPN or PNP?

An NPN will show forward bias when the positive lead of a DMM is on the base, and the negative lead on either the emitter or collector. A PNP will show reverse bias when the positive lead of a DMM is on the base, and the negative lead is on either the emitter or collector

What is a rectifier?

An electrical circuit that changes AC into DC

What is a carrier?

An electron in a material that allows the conduction of electricity (free electron)

You can determine the anode current in an SCR from the:

Anode resistor value and anode resistor voltage

The three terminals of an SCR are called:

Anode, Cathode, Gate

Name the three electrodes of an SCR.

Anode, Cathode, and Gate

Material that is sandwiched by the two outer sections of a transistor form:

Base junction

How could it be determined that a transistor junction is open?

Base-emitter junction open: Both resistance readings high Collector-base junction open: High resistance reading in both directions Collector-emitter junction open: Cannot be determined

What is Vbe?

Base-emitter voltage drop

_____________ can be used to protect transistors in addition to heat sinking.

Bias stabilization circuits

What is Vbb?

Bias voltage applied to the base-emitter circuit

The only junction of an SCR that measures like a normal diode is:

Cathode-gate junction

Explain thermal instability.

Change in bias due to heat

How is beta determined mathematically?

Change of collector current divided by change of base current

What type of tests can be done on a diode using a DMM?

Checking the polarity, checking for opens, and checking for shorts.

Prevents voltage in one part of a circuit from exceeding the voltage in another part and protects transistors from high voltage surges:

Clamping diode (used when transistors control inductive loads)

What is cold and hot resistance?

Cold and hot resistance refer to the operating resistance of a thermistor at temperature extremes. Cold resistance is measured at 25 C, or room temperature. Hot resistance is the resistance of a heated thermistor.

What is Vcb?

Collector-base voltage drop

What is Vce?

Collector-emitter voltage drop

Explain why current gain is used to describe the operation of a transistor.

Current changes are more dramatic in a transistor then voltage changes

How does current flow through a diode in reference to the anode and cathode?

Current flows from the cathode to anode

How does an SCR most often used?

DC switch

As the average voltage across a DC motor decreases, the speed of the motor __________.

Decreases

How can the PIV and current rating of a diode be increased?

Diodes are connected in series for a higher PIV rating, and in parallel for a higher current rating.

Which of the following statements about a full wave bridge rectifier is true? - All diodes conduct together for alternate phases of the input voltage. - Diodes conduct in pairs - each pair conducts during one half of an input cycle. - Diodes conduct in pairs - each pair conducts during alternate cycles of the input voltage. - A bridge configuration is the only way to achieve full wave rectification

Diodes conduct in pairs - each pair conducts during alternate cycles of the input voltage.

What is pulsating DC?

Direct current that varies in amplitude but does not change polarity

Explain direct and diffused modes.

Direct mode: a method of ultrasonic sensor operation in which the emitter and receiver are placed opposite of each other so that the sound waves from the emitter are received directly by the receiver. Diffused mode: a method of ultrasonic sensor operation in which the emitter and receiver are housed in the same enclosure. In diffused mode, the emitter sends out a sound wave and the receiver listens for the sound wave echo bouncing off an object.

Terminals of a transistor are labeled:

E, B, C

What are the three most common types of base bias stabilization circuits?

Emitter feedback, Collect-feedback, and Combination bias

What are the three main parts of a transistor?

Emitter, base, and collector

Powers at the load in a full wave circuit is significantly __________ than that in a half wave circuit.

Greater

What is the simplest form of a rectifier circuit?

Half wave rectifier

Describe toxic gas detectors.

Hazardous atmosphere detector used to measure toxic gases or vapors that are not combustible but are harmful to people.

What type of circuit can be used to provide a time delay in an SCR circuit?

Hybrid circuit SCR can be used in circuits to provide time delay for motor control, photo enlargers, and other timed or delayed functions.

How is a semi-conductor doped?

Impurities are added to the crystal structure of semiconductors, allowing electrons to flow more freely

What devices could be connected together to form an SCR equivalent circuit?

Interconnected PNP and NPN transistors

What is the main function of a DC power supply?

It converts AC power into DC power

What is peak voltage?

Maximum value of an alternating voltage that is reached on the positive or negative half cycle of a sine wave

What is the difference between N-type material and P-type material?

N-type material's electrons flow from negative to positive through the crystal when voltage is applied. P-type material's hole flow is from positive to negative, while the electrons outside the P-type material flow from negative to positive

If the gate voltage is decreased after the SCR turns on, anode current (Ia) will:

Not change

For an SCR to turn OFF, the gate has:

Nothing to do with the SCR turn-off

What are the two operating states on an SCR?

ON or OFF

What special precautions should be observed when installing diodes?

Observe voltage specifications Make sure diode is properly rated Do not overload diodes Double check circuits, polarities, component sizes and wiring Stud mounted diodes must be fastened properly and securely to their heat sinks Do not overtighten stud-mounted diodes

In what region is a transistor when it is on and when it is off?

On = Saturation region Off = Cutoff region

Emitter-base junction of a transistor conducts:

Only one direction

Explain how thermistors are tested.

Place the thermistor in ice water, record the resistance and temperature. Place the thermistor in hot (not boiling) water and record the resistance and temperature. Compare the hot/cold readings with the manufacturer spec sheet.

How is an SCR turned off?

Reduce voltage across the SCR to a value too low to maintain the holding current

What is a maximum power dissipation curve?

Represents the maximum power that a transistor can handle under normal ambient temperature.

What is the function of the filter section in a DC power supply?

Smoothes the pulsating DC to make it more consistent

What is added across the SCR terminals to protect the SCR when static turn on is a problem?

Snubber circuit

Method of turning on an SCR when a fast-rising voltage is applied across the terminals of a triac:

Static turn on

What is ripple voltage?

The amount of varying voltage present in a DC power supply

What is the critical factor in determining current flow through a transistor?

The base current is a critical factor because the forward biased junction has a very low resistance and could be destroyed by large current flow

What is the bias configuration for the normal operation of any transistor?

The base-emitter junction must always be forward biased and the collector-base must always be reverse biased. The external voltage (bias voltage) is connected so that the positive terminal connects to the P-type material (base), and the negative terminal connects to the N-type material (emitter)

Define phase control.

The control of the time relationship between two events when dealing with voltage and current. In this case, it is the time relationship between the trigger pulse and the point in the conducting cycle when the pulse occurs

What is the piezoelectric effect?

The electrical polarization of some materials when mechanically strained.

What effect does the RC time constant have on a DC output?

The extent to which the capacitor discharges during the negative half cycle depends on the RC time constant of the resistance-capacitance combination. Therefore, an average direct output voltage is obtained.

What effect does gate current have on the level of breakover voltage?

The gate current is used to reduce the level of breakover voltage necessary for the SCR to conduct or fire.

Which electrode on an SCR is the control point for the SCR?

The gate serves as the control point for the SCR

Define the power capacity of a diode.

The maximum current at which a diode may operate in a normal environment.

What is peak inverse voltage? (PIV)

The maximum reverse bias voltage that a diode can withstand without breaking down and allowing electron flow.

How is the physical size of an SCR affected by an increase in current rating?

The size of an SCR increases with an increase in current rating

What is piezoelectricity?

The voltage generated from the application of pressure.

In transistor operation, what is the function of a heat sink?

Thermal protection

Turning on an SCR when heat levels exceed the limit of the SCR (typically 230 F/ 110 C)

Thermal turn on

Why are diodes unique?

They allow electrons to flow in only one direction. (electron flow is - to +)

How are zener diodes rated?

They are rated at a specific voltage, which is based on a specific test current.

How are zener diodes tested?

They are tested with an oscilloscope while they are operating in a circuit.

How can the leads of a transistor be identified?

They can be identified by lead spacing or an index pin

What are the disadvantages of capacitive filters?

They tend to produce surge currents, which over time can damage fuses and diodes in a circuit

Adding a capacitor at the gate of a full wave circuit does not change the conduction angle significantly. (True or False)

True

Phase control works equally well for both resistive load and an inductive load. (True or False)

True

Power decreases as the conduction angle decreases. (True or False)

True

How many layers of P-type and N-type material does an SCR have?

Two PN junctions joined together PNPN

What is used for AC switching?

Two SCRs

What is the Vce of a transistor that is switched OFF?

Vce equals approximately the Vcc (applied voltage)

What is reverse bias?

Voltage applied with opposite polarity that allows a diode to act as an insulator. Negative voltage is applied to the anode and positive to the cathode, causing no electrons to flow. (high resistance)

What is forward bias?

Voltage applied with polarity that allows a diode to act as a conductor. Electrons flow from the cathode to the anode when forward biased. (low resistance)

Turning on an SCR when the voltage across the SCR terminals exceeds the maximum voltage rating of the device:

Voltage breakover turn on

What is the most common use for a zener diode?

Voltage regulators

What effect does a filter have on a PIV?

When a filter is added, the PIV becomes much higher.

What two events can cause an SCR to conduct in the forward direction?

When the forward breakover voltage is reached, or if a small forward bias voltage is applied to the gate

A transistor in its non-saturated conducting state has:

a forward biased base-emitter junction, and a reverse biased base collector junction

The amount of percent ripple in a filtered rectifier circuit is inversely proportional to ___________. - the amount of filter capacitance in the circuit - the load resistance - all of the above - none of the above

all of the above

A decrease in the ripple content of a filtered output rectifier circuit can be caused by ___________. - a decrease in line frequency - a decrease in the value of filter capacitance - an increase in the line frequency - the addition of a smoothing diode

an increase in the line frequency

For an NPN transistor, the base emitter junction is forward biased when:

base voltage is positive with respect to the emitter

If the diode in a positive half wave rectifier circuit has insufficient reverse resistance, then _________. - less current flows when the diode is forward biased - current can flow in the negative direction - the efficiency of the rectifier increases - the circuit acts as a negative half wave rectifier

current can flow in the negative direction

The output ripple frequency of a full wave rectifier is ___________. - double the input frequency - the same as the input frequency - half of the input frequency - 200 Hz

double the input frequency

In a full wave bridge rectifier circuit configuration, ___________. - only negative input alternations are passed - only positive input alternations are passed - both input alternations are passed at the same time - each input alternation is passed in turn

each input alternation is passed in turn

In a full-wave phase control circuit, power is delivered to the load - continuously - for the positive half cycle - for the time during the positive half cycle when the SCR is triggered - for the time during both half cycles when the SCR is triggered

for the time during both half cycles when the SCR is triggered

In a transistor, collector current will flow through a load when the base-emitter junction is:

forward biased

For an SCR to turn on, the:

gate has to be more positive than the cathode

Removing the load from a filtered rectifier circuit will cause its output voltage to ___________. - decrease to zero - increase to its maximum value - decrease to its minimum value - reverse its AC polarity - there would be no effect on circuit operation - AC would appear across RL - the output would reverse its polarity

increase to its maximum value

When a transistor is forward biased, the base-to-emitter voltage:

is constant

In a half wave rectifier circuit, the output voltage pulse width (diode conduction time) __________. - is greater than one half of the input cycle time - is equal to one half of the input cycle time - is slightly less than one half of the input cycle time - depends on the amplitude of the ac input signal

is slightly less than one half of the input cycle time

The base-emitter junction of an NPN transistor will conduct milliamps of current if the:

junction is forward biased

The Vce voltage drop of a low power plastic transistor in saturation is:

less than one volt

One way to turn off an SCR is to make the anode voltage:

lower than the gate voltage

What tool can be used to determine the type of an unidentified transistor?

multimeter

A doubled collector supply voltage of a transistor results in:

no change in collector current

The transistor base-emitter junction can withstand reverse voltages:

of several volts

If the amount of filter capacitance in a rectifier circuit is increased, the __________. - percent ripple increases - DC output voltage decreases - load percent increases - percent ripple decreases

percent ripple decreases

The sawtooth ripple waveform is a filtered rectifier circuit is caused by the _____________. - rapid charging and slow discharging of the filter capacitor - slow charging and rapid discharging of the filter capacitor - rapid charging and discharging of the filter capacitor - slow charging and discharging of the filter capacitor

rapid charging and slow discharging of the filter capacitor

The base-collector junction of a transistor must be _______ for operation in the linear region.

reverse biased

When replacing the resistor divider network with an RC-diode network at the gate of the SCR, ________ - the minimum conduction angle can be greatly decreased - the phase control range doesn't drastically change - the output voltage changes - the maximum conduction angle greatly increases

the phase control range doesn't drastically change

Current gain is equal to the collector current divided by the base current (true or false)

true

Phase retard is caused by delaying the anode voltage to and SCR. (true or false)

true

When the base-emitter junction of a transistor is reverse biased, the amount of base current will be:

zero, except for leakage current

A small change in the base current of a transistor results in:

a large change of collector current

An SCR is a type of:

thyristor