current density vector field
the field
(commonly denoted
J ) that is related to the
electric field intensity vector field by the con-
ductivity of the medium that the fields are lo-
cated in. One of the quantities found on the
right side of Ampere’s Law. The units are
(amperes/square meter).
current distribution factor
in economic
dispatch studies, the proportion of a power
line’s total current which is contributed by a
particular generating plant.
current fed inverter
an inverter in which
the current is switched instead of the voltage
to create AC current from a DC source. A
large inductor is used to maintain a nearly
constant current on the DC side which is then
directed to the load in an alternating fashion
by the use of switching elements.
current feedback op-amp
an op-amp in
which the output voltage is controlled by the
current in the input stage, rather than the
voltage. The advantage of the current feed-
back op-amp is that (to first order) its closed-
loop performance is not subject to the gain-
bandwidth tradeoff that affects voltage feed-
back op-amps.
current gain
short-circuit current gain
that helps describe the physical operation of
the transistor. The current gain is the di-
mensionless ratio of the peak RF output cur-
rent (
I
out.pk
) to the peak incident RF current
(
I
incident.pk
). Hence, current gain,
G
I
is
G
I
=
I
out.pk
I
incident.pk
current limiting
the output current is lim-
ited to a preset level even under a shorted
output condition. This can be accomplished
by reducing the output voltage to prevent the
current limit from being exceeded.
current limiting fuse
a fuse that limits
the level of fault current from that which is
available. It operates by developing a sub-
stantial voltage across the fuse following the
melting of the fuse element.
current mirror
a configuration of two
matched transistors in which the output is a
current that is ideally equal to the input cur-
rent. In the case of a BJT current mirror,
the collector of the first transistor is forced
to carry the input current. This establishes
a corresponding base-emitter voltage, which
is applied to the second transistor. If the two
devices are matched, then the collector cur-
rent of the second transistor will equal that of
the first transistor, thus “mirroring” the input
current. This is a commonly used configura-
tion in integrated circuits, which can take ad-
vantage of the inherent matching available by
fabricating the two transistors in close prox-
imity to each other.
current regulator
a device used to con-
trol the magnitude and phase of the current
in DC, AC or other electrical variable speed
drives. May use different control strategies
like hysteresis current control or ramp com-
parison current control.
current source amplifier
the most com-
mon group of amplifiers is made up of cur-
rent sourcing amplifiers, in which the active
device acts as a modulated current source.
All class A, B, A-B, and C amplifiers fit into
this general group. Parameters such as device
characteristics, quiescent bias point, RF load
line, and amplitude and waveform of the ap-
plied signal should be included with the class
definition, thus defining the major contribu-
tors to the physical actions taking place in
one of these amplifiers.
current source inverter
See
current fed
inverter
.
current source region
region of the I-
V curve(s) of a device in which the output
current is relatively constant (slope near zero)
for changing output voltage.
c
2000 by CRC Press LLC