U.S. patent application number 09/782122 was filed with the patent office on 2001-08-09 for active current limiter.
Invention is credited to Falk, Victor A., Galecki, Steven M..
Application Number | 20010012192 09/782122 |
Document ID | / |
Family ID | 27085461 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012192 |
Kind Code |
A1 |
Galecki, Steven M. ; et
al. |
August 9, 2001 |
Active current limiter
Abstract
A communication power distribution system including a single
power regulator which feeds a plurality of transmission lines
current limited by corresponding active current limiters.
Inventors: |
Galecki, Steven M.; (Mentor,
OH) ; Falk, Victor A.; (Westlake, OH) |
Correspondence
Address: |
David B. Cochran, Esq.
JONES, DAY, REAVIS & POGUE
North Point
901 Lakeside Avenue
Cleveland
OH
44114
US
|
Family ID: |
27085461 |
Appl. No.: |
09/782122 |
Filed: |
February 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09782122 |
Feb 13, 2001 |
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09480797 |
Jan 10, 2000 |
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6215633 |
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09480797 |
Jan 10, 2000 |
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08997443 |
Dec 23, 1997 |
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08997443 |
Dec 23, 1997 |
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08607239 |
Feb 26, 1996 |
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5706157 |
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Current U.S.
Class: |
361/93.9 ;
361/111; 361/119 |
Current CPC
Class: |
H04M 19/001 20130101;
H04M 3/18 20130101 |
Class at
Publication: |
361/93.9 ;
361/111; 361/119 |
International
Class: |
H02H 009/08 |
Claims
Having thus described the invention, it is now claimed:
1. A communication power distribution system comprising: a single
power regulator configured to supply a predetermined regulated
power over a first set of a plurality of transmission lines; a
plurality of active current limiters, at least one of the plurality
in operative connection with one of the first set of plurality of
transmission lines; a second set of a plurality of transmission
lines, at least one of the plurality in operative connection with
said at least one of the active current limiters; and, a plurality
of optical network units, at least one of the plurality in
operative connection with one of the second set of transmission
lines.
2. The communication power distribution system according to claim 1
wherein an IGBT is used as a switch of the active current
limiters.
3. The communication power distribution system according to claim 1
further including a single housing holding the active current
limiters and the single power regulator.
4. The communication power distribution system according to claim
1, wherein the first and second set of transmission lines are
comprised of at least one of optical fibers, coaxial cable, and
2-wired twisted pairs.
5. The power distribution system according to claim 2 wherein the
power is distributed in a star configuration.
6. The power distribution system according to claim 1 wherein the
active current limiters include thermal protection.
7. The power distribution system according to claim 2 wherein the
active current limiters include thermal protection.
8. A communication power distribution system comprising: a central
office which generates system operating parameters; a host digital
terminal in operative connection with the central office,
configured to receive the system operating instructions from the
central office; a plurality of optical network units, each arranged
to receive control signals from the host digital -terminal; and a
local power hub in operative connection with the host digital
terminal to receive control signals from the host digital terminal
and in operative connection with each of the optical network units
over individual transmission lines for carrying power to the
optical network units, the local power hub including a single power
regulator with a plurality of output lines, at least some of the
output lines having an associated current limiting circuit used to
current limit its associated output line, the output of the active
current limiters connected to associated ones of the transmission
lines.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/480,797 filed Jan. 10, 2000, which is a
continuation of U.S. patent application Ser. No. 08/997,443 filed
on Dec. 23, 1997, which is a continuation of Ser. No. 08/607,239,
filed on Feb. 26, 1996, now U.S. Pat. No. 5,706,157.
BACKGROUND OF THE INVENTION
[0002] This invention pertains to the art of power and signal
distribution and, more particularly, to a communication power
distribution system with current limiting capabilities.
[0003] The invention is particularly applicable to controlling
fiber-to-the-curb distribution of power and transmission of signals
from a central office to a desired destination in accordance with
existing electric code requirements. However, it is to be
appreciated that the application has broader applications and may
be advantageously employed in other power distribution environments
and uses.
[0004] In supplying power to end users such as homes, businesses,
etc., electrical safety considerations need to be addressed. The
National Electric Safety Code allows the distribution of power on a
"utility right of way." The term "utility right of way" as used in
this context is meant to define the geographic area where utility
companies have the right to run power lines, prior to entry into
homes, businesses, etc. When this distributed power is led off the
"utility right of way", into a home, business, etc. other
regulations take effect, such as those set forth in the National
Electric Code (see for example table 725-31B, National Electric
Code, 1993 Edition).
[0005] One type of communication power distribution system is set
forth in FIG. 1, which illustrates a typical set-up of a
fiber-to-the-curb distribution system. Optical fiber, OF, connects
the central office, CO, to the host digital terminal, EDT. The
central office is a main switching location and the host digital
terminal is an intermediate device which provides remote switching
capabilities. Optical fiber, OF, is also used to connect the host
digital terminal, EDT, to individual optical network units, ONU.
Each optical network unit, ONU, supplies individual lines to a
number of users. In this example configuration, an ONU which
supplies 12 lines will be used to service four end users (i.e. 3
lines per end user). It is to be appreciated, however, that while
in this example 3 lines are provided for an end user, different
numbers of lines may be provided.
[0006] The local power hub, LPE, supplies power to each of the
optical network units, ONUs, via conductors such as 2-pair wire,
W.
[0007] In the example of FIG. 1, the LPE is on the "utility right
of way", and the ONUs supplied by the LPH are of f the "utility
right of way". Therefore, the output of the LPU must be within
parameters set forth in existing code regulations. However, once
the distribution system leaves the "utility right of way" other
code regulations must be followed.
[0008] Prior art systems such as that shown in FIG. 2 have achieved
the required power distribution by relying on individual power
supplies, PS, to feed each ONU with limited power. Such a system
increases the physical size of the local power hub and also
increases the cost by requiring a plurality of individual power
supplies.
[0009] The present invention contemplates a new and improved power
distribution system which utilizes a bulk rectifier, and limits
power by use of active current limit devices in order to overcome
the above-referenced problems and others, and to provide an
economically feasible installation.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, a communication
power distribution system is provided which includes a bulk
rectifier at a local power hub used to distribute power to a
plurality of optical network units. At least one of the lines from
the local power hub being connected to an active current limiting
device.
[0011] A principal advantage of the invention is providing an
economical communication power distribution system where the cost
of a bulk rectifier is distributed over several optical network
units.
[0012] Another advantage of the invention is realized by the use of
active current limiters to provide active control up to a maximum
limit.
[0013] Still other advantages and benefits of the invention will
become apparent to those skilled in the art upon a reading and
understanding of the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention may take physical form in certain parts and
arrangements of parts, a preferred embodiment of which will be
described in detail in the specification and illustrated in the
accompanying drawings which form a part hereof, and wherein:
[0015] FIG. 1 is an illustration of a typical fiber-to-the-curb
configuration;
[0016] FIG. 2 is an expanded view of a section of FIG. 1 wherein
the local power hub depicts a prior art use of a plurality of power
supplies individually connected to optical network units;
[0017] FIG. 3 is an embodiment of the subject invention wherein a
local power hub includes a bulk rectifier having individual lines
from the rectifier associated with active current limiters;
[0018] FIG. 4 is a block diagram showing protection circuits in one
of the active current limiters between a local power hub and an
optical network unit;
[0019] FIG. 5 is a detailed schematic of an active current limiter
according to the present invention;
[0020] FIGS. 6A-6D are time versus voltage and current graphs of
the active current limiter with over-current protection according
to the present invention;
[0021] FIG. 7 is a schematic of another embodiment of an active
current limiter; and
[0022] FIG. 8 is a graph comparing active versus non-active current
limiter action.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] Referring now to the drawings wherein the showings are for
purposes of illustrating the preferred embodiment of the invention
only and not for purposes of limiting same, FIG. 3 illustrates a
fiber-to-the-curb "star" distribution system from a local power
hub, LPH, to a plurality of optical network units,
ONU.sub.1-ONU.sub.3. Within the local power hub is a bulk rectifier
10. Leading from rectifier 10 are a plurality of rectifier output
lines 12. A plurality of active current limiters 14 located within
the LPH are each connected to a corresponding one of the rectifier
output lines 12. Leading from the current limiters 14 are
distribution lines 16 extending f rpm the LPH module and connected
to individual optical network units, ONU.sub.1-ONU.sub.3. Each of
the distribution lines 16 carry current limited power to the
individual optical network units, ONU.sub.1-ONU.sub.3. Host digital
terminal, HDT, distributes and receives signals to and from the
ONUS over optical fiber lines 18.
[0024] Through such a distribution arrangement each local power
hub, LPH, in a distribution system needs to contain only a single
bulk rectifier system 10. By providing active current limiting to
the individual distribution lines a compact precise system is
designed which increases the ease of configuring the distribution
system, and distributes the cost of the bulk rectifier 10 over a
plurality of optical network units, ONUs.
[0025] The local power hub, LPH, performs four functions. First, it
generates a DC voltage to provide power to the ONUs. Next it
distributes the power to the different ONUs. Third, it isolates the
ONUs from faults such as over-voltage stresses and over-current
conditions that any other of the ONUs may experience. Finally it
sends alarms and other telemetric information back to the host
digital terminal, HDT.
[0026] A concern of such communication power distribution systems
is that a short circuit on one of the ONU lines will disrupt the
power (and, therefore, the service) of other ONUs connected to the
local power hub, LPH. Therefore, the configuration of the local
power hub, LPE, of the subject invention acts to localize any
problems at an ONU to the particular ONU with the problem.
[0027] It is to be appreciated that whereas in FIG. 3 the bulk
rectifier 10 and the active current limiters 14 are found within
the local power hub LPH, in certain environments it may be
desirable to provide these elements in a different arrangement. For
example, the active current limiter can be placed outside of the
LPH in a closer physical proximity to or even within the same
housing as the ONUs they are supplying. Still further, while FIG. 3
shows a "star" configuration, the subject invention can be
implemented in other arrangements as well.
[0028] Active current limiter 14 used in the embodiments can be
constructed in a plurality of arrangements. In one particular
arrangement active current limiter 14 is configured to address at
least three (3) fault conditions. In the first fault condition an
unwanted one (1) amp load is, for instance, applied to one of power
limiter modules PL_-PL_, when this occurs current limiter 14 needs
to limit the current to less than one (1) amp within sixty seconds.
The second fault condition concerns an external AC line cross.
Current limiter 14 needs to reduce the current within 200 ms with a
5 amp load applied. This protection reflects the capability of
polymer positive temperature coefficient resistors. The third fault
condition occurs after a lightening strike on the line between the
ONUs and the LPH. The lightening strike will trigger primary
over-voltage protection. The over-voltage protection creates a low
impedance to ground and shunts the current surge from the
lightening to ground. The lightening surge decays within
microseconds, but the over-voltage protection will remain on, and
shunt the power supply from the LPH to ground, effecting the other
ONUs until active current limiter circuit 14 reacts.
[0029] FIG. 4 sets forth a block diagram depicting the protection
circuits between the local power hub, LPH, and the optical network
unit, ONUs. Using these protection circuits the above three fault
conditions can be controlled.
[0030] Active current limiter 14, which is an over-current
protector, not only protects against external line faults and
surges, but also allows power supplies of the ONUs to start. Since
the power supplies may have relatively large capacitors (up to 4
SO.mu.F.), active current limiter 14 is required to charge these
capacitors while limiting the average load current to 74 OmA.
[0031] The maximum voltage which will be seen by current limiter 14
depends on the primary over-voltage protection used. The primary
over-voltage protection is located in a separate plug-in module and
may consist of a solid state device (V.sub.max=400V), a gas
discharge tube (V.sub.max=750V), or even a carbon block
(V.sub.max=1,000V).
[0032] The active current limiter 14 can be divided into six
sections, a power switch, current sensing area, control bias, gate
alarm, alarm out and reverse current protection. One embodiment of
such an over-current protection circuit i.e. active current limiter
14 is depicted in FIG. 5. While FIG. 5 does not show an error
alarm, an additional MOSFET, with its gate connected to the gate of
IGBT, can be used to provide a high impedance status signal.
Connecting an indication light to the MOSFET drain to ground would
therefore provide an `on` indication. Active current limiter 14 of
FIG. 5 reacts to short circuits in less than 10 ms and resets in 11
ms, averaging less than 740 m.k of current passing through it
during a fault condition. The power switch of current limiter 14,
is. implemented as an IGBT. For this IGBT the minimum breakdown
voltage rating is the same as the maximum over-voltage protection
ating of 1,000V.
[0033] Current sensing is accomplished by a low inductance resistor
R1. This resistor allows each of the ONUs' capacitors to charge.
The current signal is filtered by a variable time constant filter
consisting of P.11, P.9, Cl and D4. When the load current is less
than 1 amp, the filtered time constant is 20 ms. When the load
current is greater than 1 amp, the filter time constant decreases
to 10 ms. The faster time constant lowers the average current and
power on the IGBT for larger currents.
[0034] Comparator U4 turns off the IGBT quickly whenever very high
current passes through the IGET. This action prevents the IGBT from
overheating when it leaves the linear region. The threshold of U4
should, therefore, occur at some point below the saturated current
level of the IGBT. P.2, P.S and P.4 and a zener clamp voltage from
diode D1 determine the threshold voltage on comparator U4.
Capacitor C2 is used to reduce the noise on the threshold voltage.
Resistor Rt provides positive feedback for comparator U4 when the
comparator is to switch.
[0035] Data gathered from a current limiter as described above,
with 4.37V threshold for fast turn-off, includes:
1 (t.sub.oo/ms Il.sub.oad/amps 65.30 0.8 20.73 1.0 7.88 1.5 4.59
2.0 3.18 2.5 2.44 3.0 2.01 3.5 1.70 4.0 1.26 5.0 1.034 6.0 0.853
7.0 0.766 8.0 0.029 8.4
[0036] FIGS. 6A-6D provide graphs of data for the active current
limiter of FIG. 5, wherein channel 1 is gate voltage (Vgs)i channel
2 is a current load (I.about.), channel 3 is the voltage across
capacitor, and channel 4 is the voltage across the current
limiter.
[0037] FIG. 7 discloses an alternative current limiter circuit for
a fiber-in-the-loop configuration (FITL). While this circuit is
similar to that of FIG. 5 it is configured to limit heating
occurring in the circuit and to provide secondary current
protection.
[0038] Returning attention to the circuit depicted in FIG. 5, the
on-time of the IGBT, t.sub.on, can be calculated as, 1 t on = - T *
ln ( 1 - V threshold R 1 .times. I on )
[0039] where, T is a filter time constant, I.sub.on is current
through the sense resistor R1, and V.sub.threshold is the reference
voltage determined by the resistor divider string R6 and R7. The
average current can then be calculated as: 2 I ave = - I on .times.
t on t on .times. t reset
[0040] The reset time of the circuit is less than the filter time
constant, so comparator U3 resets the filter whenever the IGBT is
of if.
[0041] Comparator U2 changes state whenever the voltage on the
filter capacitor, C1, exceeds the threshold voltage. Capacitor Cfb
provides positive AC feedback to insure proper switching. The
threshold voltage is determined by a resistor divider string (R6
and R7) and power supply which in this example is taken to be 135V.
The following relationship determines the DC load current: 3 I
load_min = V ps * R7 R7 + R6 + V offset _ U2 R1
[0042] Variations in the source voltage, resistor divider string,
comparator offset and the sense resistor determine the minimum
guaranteed load current which may be calculated by: 4 I load_min =
I load_max * 100 - 2 * R1 - 2 * RS - ps 100 * [ 1 - 2 * V off _ at2
V ps * R7 R7 + R6 ]
[0043] where,
[0044] I.sub.load.sub..sub.--.sub.min: Guaranteed maximum DC load
current; 0.63A
[0045] I.sub.load.sub..sub.--.sub.max: Maximum current allowed out
of LPH; 100 VA/135V=0.741A
[0046] */ri: Percent tolerance error of sense resistor over
temperature and devices; 1.5%
[0047] */.sub.rs: Percent ratio mismatch between R6 and R7 over
temperature and devices; 0.5%
[0048] */.sub.ps Percent variation of 135 Volt power supply; 6%
[0049] V.sub.off.sub..sub.--.sub.u2: Maximum offset voltage of
comparator U2;. 9 mV
[0050] The voltage drop across the load and external wiring will
depend upon current as well as the "on" voltage of the IGBT and the
source power supply, and may be described as:
V.sub.load=V.sub.ps-V.sub.on.sub..sub.---
.sub.IGBT-I.sub.load*R1.
[0051] The minimum load voltage will be 125 volts and the minimum
guaranteed power to the load and external wiring will be 80VA.
[0052] The current sense resistor RI also limits the peak current
through the IGBT. As the load current increases, the voltage across
R1 increases. Since the voltage on the gate of the IGBT stays the
same, the gate-emitter voltage on the IGBT decreases. In this
arrangement the saturation current through IGBT is related to the
gate-emitter voltage. The value of P.1 is selected to limit the
current through IGBT to 12 amps.
[0053] With continuing reference to FIG. 5, control of the gate of
IGBT switch is now set forth. Resistor .R8 and comparator U1. are
used to turn off the gate of IGBT. Comparator U1, an open collector
comparator, pulls the gate low whenever its positive input goes
below a threshold voltage. Resistor P.10 pulls up the gate to the
potential on the 16V zener D1. The lower the value of resistor
P.10, the faster IGBT turns on and the sense circuit detects a
short. The faster IGBT turns on, the larger the current required to
flow through M2. Diode D3 clamps the voltage on the gate to the
zener's potential where diode D3 is used to protect the gate from
voltages coupled across the collector-gate capacitance.
[0054] The positive input of comparator U1 switches to a low
voltage whenever comparator U2 senses a fault. When the fault
clears, an RC network determines how long the gate stays off. The
reset time should be less than 16 .Gms but greater than 8.33 ms
which allows the circuit to synchronize with any 60 Hz fault
conditions. The circuit restarts during reverse current conditions
and turn-off of the circuit will occur when forward current flows
through the IGBT, i.e. at a low-voltage low-current condition. The
above described arrangement will minimize the power dissipated by
the IGBT during a situation of high-voltage line cross.
[0055] Rt, CT, R2, R4 and C2., determine the reset time of the
gate, i.e. t.sub.reset The simplest method of varying the reset
time is by varying Ct, whereby the reset time, is increased by
increasing the value of Ct. In the same manner to decrease the
reset time, the value of Ct is decreased. It is to be appreciated
that the other components in the network also affect the amount of
positive feedback for U4.
[0056] The control bias of the subject circuit is provided by M2,
P.3, and D1. D1 is a 16 volt zener diode that clamps the Vcc
voltage for the comparator and the IGBT gate to 16 volts. 142 is a
500 volt depletion mode transistor that acts as a current source.
Using this current source provides a clean start-up of the circuit.
However, it is to be appreciated that it would be possible to also
use a bias resistor in place of the current source.
[0057] R3 determines the amount of current flowing through 142,
wherein the minimum current flowing through 142 must supply the
comparators, resistor voltage divider, and resistor pull-ups during
a low threshold voltage condition. A comparator which may be used
is the LP339, which requires no more than 100 microamps bias
current. The other resistors all have high impedances to minimize
the current drain through the depletion mode transistor. By
minimizing 142 the current drain through 142 minimizes the heat
generated from the control section.
[0058] The subject circuit of FIG. 5 is also provided with reverse
current/voltage protection. This portion of the circuit includes
diode D2 which is a 1,000 volt diode used to protect against
over-current situations in case of a reverse current. If the
current should flow in the reverse direction, D2 limits the voltage
across the circuit to one volt. The local power hub, LPH, would
then absorb all the reverse current. If it is desired that no
reverse current flow into the local power hub, then D2 is connected
(by itself) to -130V instead of a negative input position.
[0059] In configuring the current limiter 14 for use in the subject
invention, it is important to also take thermal conditions into
consideration. The power dissipated by the circuit is crucial for
two reasons: the heating of the devices on the circuit and the heat
load presented to the rest of the system.
[0060] The thermal impedance of the devices to air will be
approximately 14.3.degree. C./watts, and depend upon the air flow
across the circuit. If the circuit dissipates 1.4 watts, the
temperature of the device will increase from an ambient temperature
of 65.degree. C. to 85.degree. C. Most devices used are rated for a
maximum of 85.degree. C. The circuit shown in FIG. 5 has the IGBT
dissipating 0.9 watts, the sense resistor P.1 dissipating 0.3 watt,
and the control section dissipating 0.2 watt.
[0061] The heat load of one circuit to the entire local power hub,
LPH, system may not be overly significant, however, the LPH may
have up to one hundred of these protector modules. That number of
modules can impose a significant heat load, therefore heating of
each protector module must be minimized.
[0062] It should be noted that the current limiter 14 may
experience troubles starting up the capacitive loads expected in
the external ONU's power supply. The circuit cannot distinguish
between a capacitor placed close to the LPH and an external short.
The circuit must protect itself in case of a short circuit and will
turn off quickly when the current through the switch exceeds eight
(8) amps. The short duration of current may not be enough to charge
the capacitors on the ONUs.
[0063] For currents less than eight (8) amps, the over-current
protection circuit will average approximately 0.74A into the load.
Capacitor loads must not discharge completely while the protection
circuit is in the reset mode. This will allow the protection
circuit to "ratchet" the voltage across the capacitor up.
[0064] By using one of the current limiters disclosed in FIGS. 5 or
7, active current limiting is achieved. This results in the ability
to provide accurate control of current out to a defined limit. On
the other hand, non-active current limiters begin to lose control
of the current prior to the predetermined limit; this difference is
depicted in FIG. 9. By use of active current limiters 14 a precise
power distribution system using a single bulk rectifier is
developed.
[0065] The invention has been described with reference to the
preferred embodiment. Obviously, modifications and alterations will
occur to others upon a reading and understanding of this
specification. It is intended to include all such modifications and
alterations insofar as they come within the scope of the appended
claims or the equivalents thereof.
* * * * *