Page 187 - Electrical Engineering Dictionary

current density vector field the field stantial voltage across the fuse following the
(commonly denoted J) that is related to the melting of the fuse element.
electric field intensity vector field by the con-
ductivity of the medium that the fields are lo-
current mirror a configuration of two
cated in. One of the quantities found on the
matched transistors in which the output is a
right side of Ampere’s Law. The units are
current that is ideally equal to the input cur-
(amperes/square meter).
rent. In the case of a BJT current mirror,
the collector of the first transistor is forced
current distribution factor in economic
to carry the input current. This establishes
dispatch studies, the proportion of a power
a corresponding base-emitter voltage, which
line’s total current which is contributed by a
is applied to the second transistor. If the two
particular generating plant.
devices are matched, then the collector cur-
rent of the second transistor will equal that of
current fed inverter an inverter in which
the first transistor, thus “mirroring” the input
the current is switched instead of the voltage
current. This is a commonly used configura-
to create AC current from a DC source. A
tion in integrated circuits, which can take ad-
large inductor is used to maintain a nearly
vantage of the inherent matching available by
constant current on the DC side which is then
fabricating the two transistors in close prox-
directed to the load in an alternating fashion
imity to each other.
by the use of switching elements.
current feedback op-amp an op-amp in current regulator a device used to con-
which the output voltage is controlled by the trol the magnitude and phase of the current
current in the input stage, rather than the in DC, AC or other electrical variable speed
voltage. The advantage of the current feed- drives. May use different control strategies
back op-amp is that (to first order) its closed- like hysteresis current control or ramp com-
loop performance is not subject to the gain- parison current control.
bandwidth tradeoff that affects voltage feed-
back op-amps.
current source amplifier the most com-
mon group of amplifiers is made up of cur-
current gain short-circuit current gain
rent sourcing amplifiers, in which the active
that helps describe the physical operation of
device acts as a modulated current source.
the transistor. The current gain is the di-
All class A, B, A-B, and C amplifiers fit into
mensionless ratio of the peak RF output cur-
thisgeneralgroup. Parameterssuchasdevice
rent (I out.pk ) to the peak incident RF current
characteristics, quiescent bias point, RF load
(I incident.pk ). Hence, current gain, G I is
line, and amplitude and waveform of the ap-
plied signal should be included with the class
I out.pk
G I = definition, thus defining the major contribu-
I incident.pk
tors to the physical actions taking place in
one of these amplifiers.
current limiting the output current is lim-
ited to a preset level even under a shorted
current source inverter See current fed
output condition. This can be accomplished
inverter.
by reducing the output voltage to prevent the
current limit from being exceeded.
current source region region of the I-
current limiting fuse a fuse that limits V curve(s) of a device in which the output
the level of fault current from that which is current is relatively constant (slope near zero)
available. It operates by developing a sub- for changing output voltage.

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2000 by CRC Press LLC