A

Abbreviation for "ampere" a unit of electrical current.

A.C

Abbreviation for "Alternating Current".

A.C/D.C

Equipment that will operate on either an A.C or D.C power source.

A.C generator

Device used to transform mechanical energy into A.C electrical power.

A.C power supply

Power supply that delivers an A.C voltage.

A.C voltage

A voltage in which the polarity alternates.

Alternator

Name for an A.C generator.

Ammeter

A meter used to measure current.

Ampere

Unit of electrical current.

Apparent power

Power attained in an A.C circuit as a product of effective voltage and current which reach their peak at different times.

Autotransformer

A single winding transformer where the output is taken from taps on the winding.

Battery

A D.C voltage source containing two or more cells that convert chemical energy to electrical energy.

Bleeder current

A current drawn continuously from a source. Bleeder current is used to stabilize the output voltage of a source.

Breakdown voltage

Voltage at which the breakdown of a dielectric or insulator occurs.

Bridge rectifier

A circuit using four diodes to provide full wave rectification. Converts an A.C voltage to a pulsating D.C voltage.

Cable

Group of two or more insulated wires.

Capacitance

The ability of a capacitor to store an electrical charge. The basic unit of capacitance is the Farad.

Capacitor

An electronic component having capacitive reactance.

Cell

Single unit used to convert chemical energy into a D.C electrical voltage.

Center tap

Midway connection between the two ends of a winding.

Charge

Quantity of electrical energy.

Charge current

Current that flows to charge a capacitor or battery when voltage is applied.

Chassis

Metal box or frame into which components are mounted.

Chassis ground

Connection to a chassis.

Choke

Inductor used to oppose the flow of alternating current.

Circuit

Interconnection of components to provide an electrical path between two or more components.

Circuit breaker

A protective device used to open a circuit when current exceeds a maximum value. In effect a reusable fuse.

Contact

Current carrying part of a switch, relay or connector.

Core

Magnetic material within a coil used to concentrate the magnetic field.

Current

Measured in amperes, it is the flow of electrons through a conductor. Also know as electron flow.

Current-limiting resistor

Resistor in the path of current flow to control the amount of current drawn by a device.

D.C

Abbreviation for "direct current".

D.C load line

A graph representing all possible combinations of voltage and current for a given load resistor in an amplifier.

D.C offset

The change in input voltage required to produce a zero output voltage when no signal is applied to an amplifier.

D.C power supply

Any source of D.C power for electrical equipment.

Dead short

Short circuit having zero resistance.

Device

A component or part.

Diode

A two terminal device that conducts in only one direction.

Direct current

Current that flows in only one direction.

Discharge

Release of energy stored in either a battery or a capacitor.

Electromagnet

A coil of wire usually wound on a soft iron or steel core. When current is passed through the coil a magnetic field is generated. The core provides an easy path for the magnetic lines of force. This concentrates the field in the core.

Electromagnetic induction

Voltage produced in a coil due to relative motion between the coil and magnetic lines of force.

Electromotive force

(E.M.F) Force that causes the motion of electrons due to potential difference between two points. (voltage)

Electrostatic

Related to static electric charge.

Energized

Being electrically connected to a voltage source so the device is activated.

Energy

Capacity to do work.

Equivalent resistance

Total resistance of all the individual resistances in a circuit.

Farad

The basic unit of capacitance.

Feedback

A portion of the output signal of an amplifier which is connected back to the input of the same amplifier.

Ferrite

A powdered, compressed and sintered magnetic material having high resistivity. The high resistance makes eddy current losses low at high frequencies.

Ferrite bead

Ferrite composition in the form of a bead. Running a wire through the bead increases the inductance of the wire.

Ferrite-core inductor

An inductor wound on a ferrite core.

Ferrites

Compound composed of iron oxide, a metallic oxide and ceramic. The metal oxides include zinc, nickel, cobalt or iron.

Ferrous

Composed of and or containing iron. A ferrous metal exhibits magnetic characteristics as opposed to non-ferrous material.

Full wave rectifier

Rectifier that makes use of the full A.C wave in both the positive and negative half cycles.

Fuse

A protective device in the current path that melts or breaks when current exceeds a predetermined maximum value.

Generator

Device used to convert mechanical energy to electrical energy.

Ground

An intentional or accidental conducting path between an electrical system or circuit and the earth or some conducting body acting in place of the earth. A ground is often used as the common wiring point or reference in a circuit.

Henry

The basic unit of inductance.

HERTZ

(Hz.) Unit of frequency. One hertz is equal to one cycle per second.

I.C

Abbreviation for "integrated circuit".

I.C voltage regulator

Three terminal device used to hold the output voltage of a power supply constant over a wide range of load variations.

Impedance

(Z) Measured in Ohms it is the total opposition to the flow of current offered by a circuit. Impedance consists of the vector sum of resistance and reactance.

Induced voltage

Voltage generated in a conductor when subjected to a moving magnetic field.

Inductance

Property of a circuit to oppose a change in current. The moving magnetic field produced by a change in current causes an induced voltage to oppose the original change.

Inductive circuit

Circuit having greater inductive reactance than capacitive reactance.

Inductor

Length of conductor used to introduce inductance into a circuit. The conductor is usually wound into a coil to concentrate the magnetic lines of force and maximize the inductance. While any conductor has inductance, in common usage the term inductor usually refers to a coil.

Joule

The unit of work and energy.

Kilo

Metric prefix for 1000. (103)

Kilovolt-ampere

1000 volts at 1 ampere.

Kilowatt-hour

1000 watts for 1 hour.

Kilowatt-hour meter

A meter used by electric utility companies to measure the amount of electric power used by a customer.

Kirchhoff"s current law

The sum of the currents flowing into a point in a circuit is equal to the sum of the currents flowing out of that same point.

Kirchhoff"s voltage law

The algebraic sum of the voltage drops in a closed path circuit is equal to the algebraic sum of the source voltages applied.

Lamp

Device that produces light.

Lead-acid cell

Cell made up of lead plates immersed in a sulphuric acid electrolyte. An automobile battery usually consists of six lead-acid cells.

Leakage

Small undesirable flow of current through an insulator or dielectric.

L.E.D

Abbreviation for "light emitting diode."

Lenz's law

The current induced in a circuit due to a change in the magnetic field is so directed as to oppose the flux, or to exert a mechanical force to oppose the motion.

Limiter

Circuit or device that prevents some portion of its input from reaching the output. A clipper.

Line regulation

The ability of a voltage regulator to maintain a constant voltage when the regulator input voltage varies.

Load

A source drives a load. Whatever component or piece of equipment is connected to a source and draws current from a source is a load on that source.

Load current

Current drawn from a source by a load.

Load impedance

Vector sum of reactance and resistance in a load.

Loading effect

Large load impedance will draw a small load current and so loading of the source is small. (light load). A small load impedance will draw a large load current from the source. (heavy load).

Load regulation

The ability of a voltage regulator to maintain a constant output voltage under varying load currents.

Load resistance

Resistance of a load.

Loss

Term used to describe a decrease in power.

Magnetic circuit breaker

Circuit breaker that is tripped or activated by use of an electromagnet.

Magnetic core

Material that exists in the center of the magnetic coil to either physically support the windings (non-magnetic material) or to concentrate the magnetic flux (magnetic material).

Magnetic field

Magnetic lines of force traveling from the north pole to the south pole of a magnet.

Magnetizing force

Also called magnetic field strength. It is the magnetomotive force per unit length at any given point in a magnetic circuit.

Maximum power transfer

A theorem that states that maximum power will be transferred from source to load when input impedance of the load equals the output impedance of the source.

Maxwell

Unit of magnetic flux. One maxwell equals one magnetic line of force.

Metal film resistor

A resistor in which a film of metal oxide or alloy is deposited on an insulating substrate.

Metal oxide resistor

A metal film resistor in which an oxide of metal (such as tin) is deposited as a film onto the substrate.

Meter

Any electrical or electronic measuring device. In the metric system, it is the unit of length equal to 39.37 inches.

Meter resistance

D.C resistance of the meter's armature coil.

MOSFET

Abbreviation for "metal oxide field effect transistor" also known as an "insulated gate field effect transistor). A field effect transistor in which the insulating layer between the gate electrode and the channel is a metal oxide layer.

Multimeter

Electronic test equipment that can perform multiple tasks. Typically one capable of measuring voltage, current and resistance. More sophisticated modern digital multimeters also measure capacitance, inductance, current gain of transistors and/or anything else that can be measured electronically.

Mutual inductance

Ability of one inductor's lines of force to link with another inductor.

Negative

Terminal that has an excess of electrons.

Negative feedback

A feedback signal 180° out of phase with an amplifier input signal. Used to increase amplifier stability, bandwidth and input impedance. Also reduces distortion.

Negative ground

A system where the negative terminal of the source is connected to the system's metal chassis.

Neutral

A terminal, point or object with balanced charges. Neither positive or negative.

Neutral wire

The conductor of a polyphase circuit or a single-phase three wire circuit that is intended to have a ground potential. The potential difference between the neutral and each of the other conductors are approximately equal in magnitude and equally spaced in phase.

Nickel-cadmium cell

A secondary cell that uses a nickel oxide positive electrode and a cadmium negative electrode.

Normally closed

Designation which states that the contacts of a switch or relay are closed or connected when at rest. When activated, the contacts open or separated.

Normally open

Designation which states that the contacts of a switch or relay are normally open or not connected. When activated the contacts close or become connected.

Ohm

Unit of resistance symbolized by the Greek capital letter omega (W).

Ohmmeter

Device used to measure electrical resistance.

Ohm's law

Relationship between voltage, current and resistance. Ohm's law states that current in a resistance varies in direct proportion to voltage applied and inversely proportional to resistance.

Output

Terminal at which a component, circuit or piece of equipment delivers current, voltage or power.

Output power

Amount of power a component, circuit or system can deliver to a load.

Overload

Condition that occurs when the load is greater than the system was designed to handle. (Load resistance too small, load current too high.) Overload results in waveform distortion and/or overheating.

Overload protection

Protective device such as a fuse or circuit breaker that automatically disconnects a load when current exceeds a predetermined value.

Parallel

Circuit having two or more paths for current flow. Also called shunt.

Peak

Maximum or highest amplitude level.

Peak inverse voltage

(P.I.V) The maximum rated value of an A.C voltage acting in the direction opposite to that in which a device is designed to pass current.

Peak to peak

Difference between the maximum positive and maximum negative values of an A.C waveform.

Percent of regulation

The change in output voltage that occurs between no-load and full-load in a D.C voltage source. Dividing this change by the full-load value and multiplying the result by 100 gives percent regulation.

Percent of ripple

The ratio of the effective R.M.S value of ripple voltage to the average value of the total voltage. Expressed as a percentage.

Phase

Angular relationship between two waves.

Phase angle

Phase difference between two or more waves, normally expressed in degrees.

Phase shift

Change in phase of a wave form between two points, expressed as degrees of lead or lag.

Pi

Value representing the ratio between the circumference and diameter of a circle and equal to approximately 3.142.

Positive

Polarity of point that attracts electrons as opposed to negative which supplies electrons.

Positive charge

A charge that exists in a body that has fewer electrons than protons.

Positive ground

A system whereby the positive terminal of the source is connected to the system's conducting chassis.

Potential difference

Voltage difference between two points which will cause current to flow in a closed circuit.

Potentiometer

A variable resistor with three terminals. Mechanical turning of a shaft can be used to produce variable resistance and potential. Example: A volume control is usually a potentiometer.

Power

Amount of energy converted by a circuit or component in a unit of time, normally seconds. Measured in units of watts. (joules/second).

Power derating factor

A transistor rating that tells how much the maximum allowable value of PD decreased for each 1°C rise in ambient temperature.

Power dissipation

Amount of heat energy generated by a device in one second when current flows through it.

Power factor

Ratio of actual power to apparent power.

Power loss

Ratio of power absorbed to power delivered.

Power supply

Electrical equipment used to deliver either A.C or D.C voltage.

Pulse

Rise and fall of some quantity (usually voltage) for a period of time.

Quiescent

At rest. For an amplifier the term is used to describe a condition with no active input signal.

Reactive power

Also called imaginary power or watt less power. It is the power value in "volt amps" obtained from the product of source voltage and source current in a reactive circuit.

Rectification

Process that converts alternating current to direct current.

Rectifier

Diode circuit that converts alternating current into pulsating direct current.

Reed relay

Relay consisting of two thin magnetic strips within a glass envelope. When a coil around the envelope is energized, the relay,s contacts snap together making a connection between leads attached to the reed strips.

Regulated power supply

Power supply that maintains a constant output voltage under changing load conditions.

Relay

Electromechanical device that opens or closes contacts when a current is passed through a coil.

Reluctance

Resistance to the flow of magnetic lines of force.

Resistance

Symbolized "R" and measured in Ohms. Opposition to current flow and dissipation of energy in the form of heat.

Resistive power

Amount of power dissipated as heat in a circuit containing resistive and reactive components. True power as opposed to reactive power.

Resistivity

Measure of a material's resistance to current flow.

Resistor

Component made of material that opposes flow of current and therefore has some value of resistance.

Reverse breakdown voltage

Amount of reverse bias that will cause a P.N junction to break down and conduct in the reverse direction.

Reverse current

Current through a diode when reverse biased. An extremely small current also referred to as leakage.

Reverse saturation current

Reverse current through a diode caused by thermal activity. This current is not affected by the amount of reverse bias on the component, but does vary with temperature.

Ripple frequency

Frequency of the ripple present in the output of a D.C source.

Ripple voltage

The small variations in D.C voltage that remain after filtering in a power supply.

R.M.S

Abbreviation for "root mean square".

R.M.S value

R.M.S value of an A.C sine wave is 0.707 times the peak value. This is the effective value of an A.C sine wave. The R.M.S value of a sine wave is the value of a D.C voltage that would produce the same amount of heat in a heating element.

Saturation

Condition in which a further increase in one variable produces no further increase in the resultant effect. In a bipolar junction transistor, the condition when the emitter to collector voltage is less than the emitter to base voltage. This condition puts forward bias on the base to collector junction.

Schematic diagram

Illustration of an electrical or electronic circuit with the components represented by their symbols.

Schottky diode

High speed diode that has very little junction capacitance. Also known as a "hot-carrier diode" or a "surface-barrier diode."

Scientific notation

Numbers entered as a number from one to ten multiplied by a power of ten. Example: 8765 = 8.765 × 103.

Secondary

Output winding of a transformer. Winding that is connected to a load.

Secondary cell

Electrolytic cell used to store electricity. Once discharged may be restored by recharging by putting current through the cell in the direction opposite to that of discharge current.

Self inductance

Property that causes a counter electromotive force to be produced in a conductor when the magnetic field expands or collapses with a change of current.

Semiconductor

An element which is neither a good conductor or a good insulator, but rather lies somewhere between the two. Characterized by a valence shell containing four electrons. Silicon, germanium and carbon are the semiconductors most frequently used in electronics.

Series circuit

Circuit in which the components are connected end to end so that current has only one path to follow through the circuit.

Short circuit

Also called a short. Low resistance connection between two points in a circuit typically causing excessive current.

Shunt resistor

Resistor connected in parallel or in shunt with another component or circuit.

Signal

Electrical quantity that conveys information.

Signal to noise ratio

Ratio of the magnitude of the signal to the magnitude of noise usually expressed in decibels.

Silicon-controlled rectifier

(S.C.R) Three terminal active device that acts as a gated diode. The gate terminal is used to turn the device on allowing current to pass from cathode to anode.

Sine

Sine of an angle of a right angle triangle is equal to the opposite side divided by the hypotenuse.

Sine wave

Wave whose amplitude is the sine of a linear function of time. It is plotted on a graph that plots amplitude against time or radial degrees relative to the angular rotation of an alternator.

Sinusoidal

Varying in proportion to the sine of an angle or time function. A.C voltage in which the instantaneous value is equal to the sine of the phase angle times the peak value.

Slew rate

The maximum rate at which the output voltage of an op-amp can change.

Slow acting relay

Slow operating relay that when energized may not pull up the armature for several seconds.

Slow-blow fuse

Fuse that can withstand a heavy current (up to ten times its rated value) for a small period of time before it opens.

Software

Program of instructions that directs the operation of a computer.

Solder

Metallic alloy used to join two metal surfaces.

Soldering

Process of joining two metallic surfaces to make an electrical contact by melting solder (usually tin and lead) across them.

Solid state

Pertaining to circuits where signals pass through solid semiconductor material such as transistors and diodes as opposed to vacuum tubes where signals pass through a vacuum.

Spark

Momentary discharge of electrical energy due to ionization of air or other dielectric material separating two charges.

Square wave

Wave that alternates between two fixed values for an equal amount of time.

Static

Crackling noise heard on AM radio receivers. Caused by electric storms or electric devices.

Step-down transformer

Transformer in which the output A.C voltage is less than the input A.C voltage.

Step-up transformer

Transformer in which the output A.C voltage is greater than the input A.C voltage.

Supply voltage

Voltage provided by a power source.

Switch

Electrical device having two states, on (closed) or off (open). Ideally having zero impedance when closed and infinite impedance when open.

Tantalum capacitor

Electrolytic capacitor having a tantalum foil anode. Able to have a large capacity in a small package.

Technician

Expert in troubleshooting circuit and system malfunctions. Along with a thorough knowledge of test equipment and how to use it to diagnose problems, the technician is also familiar with how to repair or replace faulty components. Technicians basically translate theory into action.

Tesla

(T) Unit of magnetic flux density. (1 tesla = 1 Wb/m2).

Thermal relay

Relay activated by a heating element.

Thermal runaway

Problem that can develop in an amplifier when an increase in temperature causes an increase in collector current. The increase in collector current causes a further increase in temperature and so on. Unless the circuit is designed to prevent this condition, the device can be driven into saturation.

Thermistor

Temperature sensitive semiconductor that has a negative temperature coefficient of resistance. As temperature increases, resistance decreases.

Three phase supply

A.C supply that consists of three A.C voltages 120° out of phase with each other.

Threshold voltage

For an enhancement MOSFET, the minimum gate source voltage required for conduction of source drain current.

Thyristor

A term used to classify all four layer semiconductor devices. S.C.Rs and triacs are examples of thyristors.

Time constant

(t) Time required for a capacitor in an R.C circuit to charge to 63% of the remaining potential across the circuit. Also time required for current to reach 63% of maximum value in an R.L circuit. Time constant of an R.C circuit is the product of R and C. Time constant of an R.L circuit is equal to inductance divided by resistance.

Toroidal coil

Coil wound on a doughnut shaped core.

Transformer

Inductor with two or more windings. Through mutual inductance, current in one winding called a primary will induce current into the other windings called secondaries.

Transformer coupling

Also called inductive coupling. Coupling of two circuits by means of mutual inductance provided by a transformer.

Transistor

Term derived from "transfer resistor." Semiconductor device that can be used as an amplifier or as an electronic switch.

Troubleshooting

Systematic approach to locating the cause of a fault in an electronic circuit or system.

Ultrasonic

Signals that are just above the frequency range of human hearing of approximately 20 kHz.

V.A

Abbreviation for "volt ampere".

Variable capacitor

Capacitor whose capacitance can be change by varying the effective area of the plates or the distance between the plates.

Variable resistor

Resistor whose resistance can be changed by turning a shaft. See also "potentiometer and rheostat."

Virtual ground

Point in a circuit that is always at approximately ground potential. Often a ground for voltage, but not for current.

Volt

Unit of potential difference or electromotive force. One volt is the potential difference needed to produce one ampere of current through a resistance of one Ohm.

Voltage

(V) Term used to designate electrical pressure or force that causes current to flow.

Voltage divider

Fixed or variable series resistor network connected across a voltage to obtain a desired fraction of that voltage.

Voltage drop

Voltage or difference in potential developed across a component due to current flow.

Voltage feedback

Feedback configuration where a portion of the output voltage is fed back to the input of an amplifier.

Voltage follower

Operational amplifier circuit characterized by a high input impedance, low output impedance and unity voltage gain. Used as a buffer between a source and a low impedance load.

Voltage rating

Maximum voltage a component can withstand without breaking down.

Voltage regulator

Device or circuit that maintains constant output voltage (within certain limits) in spite of changing line voltage and/or load current.

Volt-ampere

Unit of apparent power in an A.C circuit containing capacitive or inductive reactance. Apparent power is the product of source voltage and current.

Voltmeter

Instrument used to measure difference in potential between two points.

Zener diode

Semiconductor diode in which reverse breakdown voltage current causes the diode to develop a constant voltage. Used as a clamp for voltage regulation.