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- Alternating current (ac): An electrical current that periodically changes
in magnitude and in direction of the current.
- Alternation: Either half of a cycle of alternating current. It is the
time period during which the current increases from zero to its maximum
value (in either direction) and decreases to zero.
- Alternator (or ac generator): An electromechanical device which transforms
mechanical energy into electrical energy- an alternating current.
Very early users called this a dynamo.
- Ammeter: An instrument for measuring ac or DC electrical current in a
circuit. Unless magnetically coupled, it must be placed in the current
path so the flow is through the meter.
- Ammeter shunt: A low-resistance conductor that is used to increase the
range of an ammeter. It is shunted (placed in parallel) across the
ammeter movement and carries the majority of the current.
- Ampere (A): The unit of measurement for electrical current in coulombs
(6.25 x 1018 electrons) per second. One ampere results in a circuit
that has one ohm resistance when one volt is applied to the circuit. See
Ohm's law.
- Amplification: See Gain.
- Amplifier: An electrical circuit designed to increase the current, voltage,
or power of an applied signal.
- Analog-to-Digital Conversion or Converter (ADC or A/D): The process of
converting a sampled analog signal to a digital code that represents
the amplitude of the original signal sample.
- Audio and audio frequency (AF): The range of frequencies normally heard
by the human ear.
- Typically, about 20 to 20, 000 Hz.
- Beta (/3): The current gain of a transistor when connected in a common
emitter circuit.
- Bias: In an electronic circuit, a voltage or current applied to an active
device (transistor, diode, etc.) to set the steady-state operating
point of the circuit.
- Binary Coded Decimal (BCD): A binary numbering system in which any decimal
digit is represented by a group of 4 bits. Each digit in a multi-digit
number continues to be identified by its 4-bit group.
- Binary digit (Bit): A digit in the binary number system whose value can
be either l or 0. Bipolar: A semiconductor device having both majority
and minority carriers.
- Bit: See Binary digit.
- Block diagram: A system diagram which shows the relationship between
the main functional units of the system represented by blocks.
- Breakdown: The condition for a reverse-biased semiconductor junction
when its high resistance, under the reverse bias, suddenly decreases,
causing excessive current. Not necessarily destructive.
- Bridge rectifier: A full-wave rectifier in which the rectifier diodes
are connected in a bridge circuit to allow current to the load during
both the positive and negative alternation of the supply voltage.
- Capacitance (C): The capability to store charge in an electrostatic field.
It can be expressed as equal to the charge Q in coulombs that is
stored divided by the voltage E in volts that supplied the charge.
- Capacitance tends to oppose any change in voltage.
- The unit is farads.
- Capacitive reactance (Xe): The opposition that a capacitor offers to
a time changing signal or supplied voltage. Its value is Xe = _l_ 2rrfc
Capacitor IC): A device made up of two metallic plates separated by
a dielectric or insulating material. Used to store electrical energy in
the electrostatic field between the plates.
- Cathode (K): The negative electrode of a semiconductor diode.
- Charge (Q): A measurable quantity of electrical energy representing the
electrostatic forces between atomic particles. Electrons have a negative
charge.
- Choke: An inductance which is designed to pass large amounts of DC current.
It usually is used in power supply filters to help reduce ripple;
although, there are inductances called rf chokes (rlc) which prevent rf
from feeding to a circuit.
- Circuit: A complete path that allows electrical current from one terminal
of a voltage source to the other terminal.
- Circuit breaker: An electromagnetic switch used as a protective device.
It breaks a circuit if the current exceeds a specified value.
- Clock or Clock generator: An electronic circuit that generates accurate
and precisely controlled,' regularly occurring, synchronizing or
timing signals called clock signals.
- Clock rate: The frequency of oscillation of the master clock, or oscillator,
in a system.
- Coil: The component that is formed when several turns of wire are wound
on a cylindrical form or on a metal core.
- Collector (C): The element in a transistor that collects the moving electrons
or holes, and from which the output usually is obtained. Analogous
to the plate of a triode vacuum tube.
- Color code: A system in which colors are used to identify the value of
electronic components, or other variables, such as component tolerance.
- Component: The individual parts that make up a circuit, a function, a
subsystem or a total piece of equipment.
- Conductor: A substance through which electrons flow with relative ease.
- Contactor: A special relay for switching heavy currents at power line
voltages.
- Continuity: A continuous electrical path.
- Controlled rectifier: A four-layer semiconductor device in which conduction
is triggered ON by gate current and OFF by reducing the anode -voltage
below a critical value.
- Coulomb (C): The unit of electrical charge, made up of a quantity of
6.25 x 10^18 electrons.
- Current (I): The flow of electrons, measured in amperes. One ampere results
when one volt is impressed on a circuit that has a resistance of
one ohm.
- Decibel (db): The standard unit for expressing the ratio between powers
P1 and P2• db = 10log1J>i/ P 2, one tenth of a bel. Dielectric:
The non-conducting material used to separate the plates of a capacitor
or for insulating electric contacts.
- Digital signal: A signal whose level has only discrete values, like on
or off, 1 or 0, + 5v or +0.2v.
- Digital to Analog Conversion (or Converter) (DAC or DIA): A circuit that
accepts digital input signals and converts them to an analog output
signal.
- Diode: A device which has two terminals and has a high resistance to
current in one direction and a low resistance to current in the other
direction.
- Direct Current (DC, de): Current in a circuit in one direction only.
- Drain: The element in field-effect transistor which is roughly analogous
to the collector of a bipolar transistor.
- Effective value: The value of ac current that will produce the same heating
effect in a load resistor as the corresponding value of DC current.
- Electricity: A form of energy produced by the flow of electrons through
materials and devices under the influence of an electromotive force
produced electrostatically, mechanically, chemically or thermally.
- Electrolytic capacitor: A capacitor whose electrodes are immersed in
a wet electrolyte or dry paste.
- Electromotive force (E): The force which causes an electrical current
in a circuit when there is a difference in potential. Synonym for voltage.
- Electron: The basic atomic particle having a negative charge that rotates
around a positively charged nucleus of an atom. · Electrostatic field:
The electrical field or force surrounding objects that have an electrical
charge.
- Emitter (E): The semiconductor material in a transistor that emits carriers
into the base region when the emitter-base junction is forward biased.
- Error: Any deviation of a computed, measured, or observed value from
the correct value.
- Farad (F): The basic unit for capacitance. A capacitor has a value of
one farad when it has stored one coulomb of charge with one volt across
it.
- Field coil: An electromagnet formed from a coil of insulated wire wound
around a soft iron core.
- Commonly used in motors and generators.
- Field-Effect Transistor (FET): A 3-terminal semiconductor device where
current is from source to drain due to a conducting channel fanned
by a voltage field between the gate and the source.
- Filament: The heated element in an incandescent lamp or vacuum tube.
- Filter: A circuit element or group of components which passes signals
of certain frequencies while blocking signals of other frequencies.
- Fluorescent: The ability to emit light when struck by electrons or other
radiation.
- Forward resistance: The resistance of a forward biased junction when
there is current through the semiconductor p-n junction.
- Forward voltage (or bias): A voltage applied across a semiconductor junction
in order to permit forward current through the junction and the device.
- Frequency (F or f): The number of complete cycles of a periodic waveform
during one second.
- Gain (G): I. Any increase in the current, voltage or power level of a
signal. 2. The ratio of output to input signal level of an amplifier.
- Ground (or Grounded): 1. The common return path for electric current
in electronic equipment. Called electrical ground. 2. A reference point
connected to or assumed to be at zero potential with respect to the
earth.
- Henry (H or h): The unit of inductance. The inductance of a coil of wire
in henries is a function of the coils size, the number of turns of
wire and the type core material.
- Hertz {Hz): One cycle per second.
- Impedance (Z): In a circuit, the opposition that circuit elements present
alternating current. The impedance includes both resistance and reactance.
- Inductance (L): The capability of a coil to store energy in a magnetic
field surrounding it which results in a property that tends to oppose
any change in the existing current in the coil.
- Inductive reactance (X): The opposition that an inductance offers when
there is an ac or pulsating DC in a circuit. XL = 2 pi fL. Input impedance:
The impedance seen by a source when a device or circuit is connected
across the source.
- Integrated circuit (IC): A complex semiconductor structure that contains
all the circuit components for a high functional density analog or
digital circuit interconnected together on a single chip of silicon.. Junction:
The region separating two layers in a semiconductor material, e.g.
a p-n junction.
- Junction transistor: A PNP or NPN transistor formed from three alternate
regions of pan n type material. The alternate materials are formed
by diffusion or ion implantation.
- Leakage (or Leakage current): The undesired flow of electricity around
or through a device or circuit.
- In the case of semiconductors, it is the current across a reverse biased
semiconductor junction.
- Linear amplifier: A class A amplifier whose output signal is directly
proportional to the input signal.
- The output is an exact reproduction of the input except for the increased
gain.
- Load: Any component, circuit, subsystem or system that consumes power
delivered to it by a source of power.
- Loop: A closed path around which there is a current or signal.
- Magnetic Field: The force field surrounding a magnet.
- Magnetic lines of force: The imaginary lines called flux lines used to
indicate the directions of the magnetic forces in a magnetic field.
- Megohm {MD): A million ohms. Sometimes abbreviated meg.
- Microampere (µA): One millionth of an ampere.
- Microfarad (µId, MFD, or mid): One millionth of a farad.
- Milliampere (mA): One thousandth of an ampere.
- Millihenry (mH): One thousandth of a henry.
- Milliwatt (mW): One thousandth of a watt.
- NPN Transistor: A bipolar transistor with a p-type base sandwiched between
an n-type emitter, and an n-type collector.
- N-type semiconductor material (N): A semiconductor material in which
the majority carriers are electrons, and there is an excess of electrons
over holes.
- Ohm (omega): The unit of electrical resistance. A circuit component has
a resistance of one ohm when one volt applied to the component produces
a current of one ampere.
- Ohms-per-volt: The sensitivity rating for a voltmeter. Also expresses
the impedance (resistance) presented to a circuit by the meter when
a voltage measurement is made.
- Open circuit: An incomplete path for current.
- Operating point: The steady state or no signal operating point of a circuit
or active device.
- Operational amplifier (OP AMP): A high-gain analog amplifier with two
inputs and one output.
- Oscillation: A sustained condition of continuous operation where the
circuit outputs a constant signal at a frequency determined by circuit
constants and as a result of positive or regenerative feedback.
- Pi {n): The mathematical constant which is equal to the ratio of the
circumference of a circle to its diameter. Approximately 3.14.
- Picofarad (pf): A unit of capacitance that is 1 x 10-12 farads or one
millionth of a millionth of a farad.
- Piezoelectric: A crystal property which causes a voltage to be developed
across the crystal when mechanical stress is applied, or vice-versa.
- PNP Transistor: A bipolar transistor with an n-type base sandwiched between
a p-type emitter and a p type collector.
- Polarity: The description of whether a voltage is positive or negative
with respect to some reference point.
- Potential difference: The voltage difference between two points, calculated
algebraically.
- Power (P): The time rate of doing work.
- Power (reactive): The product of the voltage and current in a reactive
circuit measured in volt amperes (apparent power). Power {real): The
power dissipated in the purely resistive components of a circuit measured
in watts.
- Power supply: A defined unit that is the source of electrical power for
a device, circuit, subsystem or system.
- P-type semiconductor material (P): A semiconductor material in which
holes are the majority carriers and there is a deficiency of electrons.
- Reactance (X): The opposition that a pure inductance or a pure capacitance
provides to current in an ac circuit.
- Rectification: The process of converting alternating current into pulsating
direct current.
- Relay: A device in which a set of contacts is opened or closed by a mechanical
force supplied by turning on current in an electromagnet. The contacts
are isolated from the electromagnet.
- Resistance (R): A characteristic of a material that opposes the flow
of electrons. It results in loss of energy in a circuit dissipated
as heat.
- Resistor (R): A circuit component that provides resistance to current
in the circuit.
- Reverse current: The current when a semiconductor junction is reverse
biased.
- Root-Mean-Square (RMS): See effective value. The Rlv1S value of an ac
sinusoidal waveform is 0.707 of the peak amplitude of the sine wave.
- Semiconductor: One of the materials falling between metals as good conductors
and insulators as poor conductors in the periodic chart of the elements.
- Shunt: A parallel circuit branch, see Ammeter shunt.
- Signal: In electronics, the information contained in electrical quantities
of voltage or current that forms the input, timing, or output of
a device, circuit, or system.
- Silicon Controlled Rectifier (SCR): A semiconductor diode in which current
through a third element, called the gate, controls turn-on, and the
anode-to cathode voltage controls turn-off.
- Sine (sinusoidal) wave: A waveform whose amplitude at any time through
a rotation of an angle from 0° to 360c is a function of the sine of
an angle.
- Step-down transformer: A transformer in which the secondary winding has
fewer turns than the primary.
- Step-up transformer: A transformer in which the secondary winding has
more turns than the primary.
- Transformer: A set of coils wound on an iron core in which a magnetic
field couples energy between two or more coils or windings.
- Transistor: A three-terminal semiconductor device used in circuits to
amplify electrical signals or to perform as a switch to provide digital
functions.
- Turns ratio: The ratio of secondary winding turns to primary winding
turns of a transformer.
- Vector: A line representing the magnitude and time phase of some quantity,
plotted on rectangular or polar coordinates.
- Voltage (or Volt): The unit of electromotive force that causes current
when included in a closed circuit. One volt causes a current of one
ampere through a resistance of one ohm.
- Voltage drop: The difference in potential between two points caused by
a current through an impedance or resistance.
- Watt (W): The unit of electrical power in joules per second, equal to
the voltage drop (in volts) times the current (in amperes) in a resistive
circuit.
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