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thyristor
A term used to classify all four layer semiconductor devices. SCRs and triacs are examples of thyristors.
time constant
(t) Time required for a capacitor in an RC 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 RL circuit. Time constant of an RC circuit is the product of R and C. Time constant of an RL circuit is equal to inductance divided by resistance.
time division multiplexing
(TDM) Transmission of two or more signals on the same path, but at different times.
time-domain analysis
A method of representing a waveform by plotting amplitude over time.
toggle switch
Spring loaded switch that is put in one of two positions either on or off.
tolerance
Permissible deviation from a specified value normally expressed as a percentage.
TO package
Cylindrical, ****l can type of package of some semiconductor components.
toroidal coil
Coil wound on a doughnut shaped core.
transconductance
Also called mutual conductance. Ratio of a change in output current to the change in input voltage that caused it.
transducer
Device that converts energy from one form to another.
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.
transmission
Sending of information.
transmission line
Conducting line used to transmit signal energy between two points.
transmitter
Equipment used to achieve transmission.
triac
Bidirectional gate controlled thyristor similar to an SCR, but capable of conducting in both directions. Provides full wave control of AC power.
triangular wave
A repeating wave that has equal positive going and negative going ramps. The ramps have linear rates of change with time.
trigger
Pulse used to initiate a circuit action.
triggering
Initiation of an action in a circuit which then functions for a predetermined time. Example: The duration of one sweep in a cathode ray tube.
trimmer
Small value variable capacitor, resistor or inductor used to fine tune a larger value.
trivalent element
One having three valence electrons. Used as an impurity in semiconductor material to produce p-type material. Most commonly used trivalent elements are: Aluminum, Gallium and Boron.
troubleshooting
Systematic approach to locating the cause of a fault in an electronic circuit or system.
tuned circuit
Circuit that can have its component values adjusted so that it responds to one selected frequency and rejects all others.
tunnel diode
Heavily doped junction diode that has negative resistance in the forward direction of its operating range.
turn-off time
Sum of storage time and fall time.
turn-on time
Sum of delay time and rise time.
turns ratio
Ratio of the number of turns in the secondary winding of a transformer to the number of turns in the primary winding.
two phase
Two repeating waveforms having a phase difference of 90°
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U
UHF
Abbreviation for "ultra high frequency.
uncharged
Material having atoms with the same number of electrons in orbit as the number of protons in the nucleus. Having no electrical charge.
unijunction transistor
Three terminal device that acts as a diode with its own internal voltage divider biasing circuit.
unity gain frequency
Frequency of operation for a device where the gain of the component drops to unity.
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V
VA
Abbreviation for "volt ampere"
vacuum tube
Electron tube evacuated to such a degree that its electrical characteristics are essentially unaffected by the presence of residual gas or vapor. Have been essentially replaced by transistors for amplification and rectification. Cathode ray tubes are still used as display devices.
valence ****l
The outermost electron ****l for a given atom. The number of electrons in this ****l determines the conductivity of the atom.
varactor diode
PN junction diode with a high junction capacitance when reverse biased. Most often used as a voltage controlled capacitor. The varactor is also called: varicap, tuning diode and epicap.
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."
VCR
Abbreviation for "video cassette recorder."
vector
Quantity having both magnitude and direction. Normally represented by a line. Length of the line indicates magnitude and orientation indicates direction.
vector diagram
Arrangement of vectors showing phase relationships between two or more AC quantities of the same frequency.
vertical MOS
Enhancement type MOSFET designed to handle much greater values of drain current than standard E-MOSFET.
very high frequency
(VHF) Electromagnetic frequency band from 30 MHz to 300 MHz.
very low frequency
(VLF) Frequency band from 3 kHz to 30 kHz.
video
Relating to any picture or visual information. From the latin word meaning "I see."
video amplifier
Amplifier having one or mare stages designed to amplify video signals.
virtual ground
Point in a circuit that is always at approximately ground potential. Often a ground for voltage, but not for current.
voice coil
Coil attached to the diaphragm of a moving coil loudspeaker. The coil is moved through an air gap between magnetic pole pieces.
voice synthesizer
Synthesizer that can simulate speech by stringing together phonemes.
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 amplifier
Amplifier designed to build up signal voltage. By design amplifiers can have a large voltage gain or a large current gain or a large power gain. Voltage amplifiers are designed to maximize voltage gain often at the expense of current gain or power gain.
voltage controlled oscillator
Oscillator whose output frequency depends on an input control voltage.
voltage divider
Fixed or variable series resistor network connected across a voltage to obtain a desired fraction of that voltage.
voltage divider biasing
Biasing method used with amplifiers in which two series resistors connected across a source. The junction of the two biasing resistors provides correct bias voltage for the 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 gain
Also called voltage amplification. Ratio of amplifier output voltage to input voltage usually expressed in decibels.
voltage multiplier
Rectifier circuit using diodes and capacitors to produce a DC output voltage that is some multiple of the peak value of AC input voltage. Cost effective way of producing higher DC voltages. Voltage doublers and voltage triplers are examples.
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.
voltage source
Circuit or device that supplies voltage to a load.
volt-ampere
Unit of apparent power in an AC 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.
volume
Magnitude or power level of audio frequency. Measured in volume units (VU).
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