U.S. patent application number 11/433221 was filed with the patent office on 2007-11-15 for system and method for high voltage protection of powered devices.
This patent application is currently assigned to Silicon Laboratories, Inc.. Invention is credited to Russell J. Apfel.
Application Number | 20070263332 11/433221 |
Document ID | / |
Family ID | 38684869 |
Filed Date | 2007-11-15 |
United States Patent
Application |
20070263332 |
Kind Code |
A1 |
Apfel; Russell J. |
November 15, 2007 |
System and method for high voltage protection of powered
devices
Abstract
An integrated circuit includes a rectifier circuit, at least one
low power element, and a power protection element. The rectifier
circuit includes two inputs to receive an input power supply and
includes two outputs to provide a rectified power supply related to
the input power supply. The low-power circuit element is coupled
between the two outputs. The power protection element is coupled
between the two output terminals. In a first mode of operation, the
power protection element presents a high impedance to the two
output terminals. In a second mode of operation, the power
protection element has a first power protection characteristic. In
a third mode of operation, the power protection element has a
second power protection characteristic. The power protection
element is adapted to shut down the low-power circuit element when
in the third mode of operation.
Inventors: |
Apfel; Russell J.; (Austin,
TX) |
Correspondence
Address: |
TOLER SCHAFFER, LLP
8500 BLUFFSTONE COVE
SUITE A201
AUSTIN
TX
78759
US
|
Assignee: |
Silicon Laboratories, Inc.
Austin
TX
|
Family ID: |
38684869 |
Appl. No.: |
11/433221 |
Filed: |
May 11, 2006 |
Current U.S.
Class: |
361/90 |
Current CPC
Class: |
H02H 9/041 20130101 |
Class at
Publication: |
361/090 |
International
Class: |
H02H 3/20 20060101
H02H003/20 |
Claims
1. An integrated circuit comprising: a rectifier circuit having two
inputs to receive an input power supply and having two outputs to
provide a rectified power supply related to the input power supply;
at least one low-power circuit element coupled between the two
outputs; and a power protection element coupled between the two
output terminals, wherein, in a first mode of operation, the power
protection element presents a high impedance to the two output
terminals, in a second mode of operation, the power protection
element has a first power protection characteristic, and in a third
mode of operation, the power protection element has a second power
protection characteristic, the power protection element to shut
down the at least one low-power circuit element when in the third
mode of operation.
2. The integrated circuit of claim 1, wherein the power protection
element comprises an over-voltage threshold component to detect an
over-voltage condition and a switch coupled to the over-voltage
threshold component to clamp the rectified power supply to a
voltage level that is below a threshold voltage level.
3. The integrated circuit of claim 1, wherein the power protection
element comprises two switches adapted to activate asynchronously
in response to a signal to clamp the rectified power supply to a
reduced voltage level.
4. The integrated circuit of claim 1, wherein the power protection
element comprises a silicon controlled rectifier.
5. The integrated circuit of claim 1, wherein the power protection
element further comprises active logic to generate a fault
protection signal provided to the at least one low-power circuit
element when in the third mode of operation.
6. The integrated circuit of claim 5, wherein the fault protection
signal comprises a shut down signal to deactivate the at least one
low-power circuit element.
7. The integrated circuit of claim 1, wherein the power protection
element is at a higher voltage in the second mode of operation than
in the third mode of operation.
8. The integrated circuit of claim 7, wherein in the second mode of
operation, the higher voltage is greater than 55 volts and wherein
the power protection element has a current level less than one
Ampere.
9. The integrated circuit of claim 7, wherein in the third mode of
operation, the power protection element has a voltage level less
than ten volts and a current level greater than half an Ampere.
10. The integrated circuit of claim 7, wherein the power protection
element changes from the second mode of operation to the first mode
of operation after a current level of the power protection element
falls below a threshold current level.
11. The integrated circuit of claim 1, wherein the second power
protection characteristic comprises a lower impedance than the
first power protection characteristic.
12. A method comprising: receiving an input voltage supply at a
pair of terminals; detecting an over-voltage condition related to
the input voltage supply using an over-voltage protection element;
and concurrently shunting the input voltage supply between the pair
of terminals and generating a shut off signal to associated
circuitry in response to the over-voltage condition using the
over-voltage protection element.
13. The method of claim 12, wherein detecting an over-voltage
condition comprises: detecting a voltage at a silicon controlled
rectifier of an integrated circuit, the integrated circuit having
at least one low-voltage component; and maintaining a first
transistor and a second transistor in an off state when the voltage
is less than a voltage protection threshold.
14. The method of claim 13, wherein shunting the input voltage
supply comprises: activating the first transistor and the second
transistor to shunt the voltage to a lower voltage level when the
voltage exceeds the voltage protection threshold; and generating a
fault protection signal to shut off power to the at least one
low-voltage component.
15. The method of claim 14, wherein activating the first transistor
and the second transistor comprises activating the first transistor
before activating the second transistor.
16. The method of claim 12, wherein detecting the over-voltage
condition comprises: receiving an input voltage from a powered
network at an integrated circuit including the over-voltage
protection element; rectifying the input voltage to produce a
rectified voltage; and detecting a voltage level of the rectified
voltage.
17. An integrated circuit comprising: input terminals to receive an
input power supply; at least one low-power circuit element coupled
between the input terminals; and a power protection element coupled
between the input terminals to detect a power characteristic of the
input power supply, the power protection element to shunt excess
power between the input terminals and to shut off power to the at
least one low-power circuit element when the power characteristic
exceeds a threshold power level.
18. The integrated circuit of claim 17, wherein the power
characteristic comprises a voltage level in excess of a threshold
voltage level.
19. The integrated circuit of claim 17, wherein the power
characteristic comprises a current level that is greater than a
threshold current level.
20. The integrated circuit of claim 17, wherein the power
protection element comprises a silicon controlled rectifier
circuit.
21. The integrated circuit of claim 17, wherein the input terminals
comprise a first power supply terminal and a second power supply
terminal and wherein the power protection element comprises: a
resistor having a first terminal coupled to the second power supply
terminal, and a second terminal; a diode circuit having an anode
terminal coupled to the second terminal of the resistor and a
cathode terminal coupled to the first power supply terminal; and a
transistor having a first terminal coupled to the first power
supply terminal, a second terminal coupled to the second power
supply terminal, and a control terminal coupled to the second
terminal of the resistor, the transistor providing a current path
between the first power supply terminal and the second power supply
terminal when active.
22. The integrated circuit of claim 17, wherein the input terminals
are coupled to a powered network.
23. A method comprising: receiving an input power supply at a pair
of terminals, the pair of terminals including a first terminal and
a second terminal; detecting a power level of the input power
supply using a power protection element of an integrated circuit,
the integrated circuit having at least one low-power component;
activating the power protection element to shunt the input power
supply between the first terminal and the second terminal when the
power level exceeds a threshold power level; and substantially
reducing a power supply to the at least one low-power component
when the power level exceeds the threshold power level.
24. The method of claim 23, wherein the power protection element
comprises a first transistor and a second transistor, the first
transistor and the second transistor coupled between the first
terminal and the second terminal, the method further comprising:
maintaining the first transistor and the second transistor in an
off state when the power level is less than the threshold power
level.
25. The method of claim 24, wherein activating the power protection
element comprises activating the first transistor before activating
the second transistor.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application is related to co-pending U.S. patent
application Ser. No. ______ filed on ______, and entitled, "SYSTEM
AND METHOD FOR HIGH VOLTAGE PROTECTION OF ELECTRONIC DEVICES,"
which is incorporated herein by reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure generally relates to Power over
Ethernet powered devices, and more particularly, to over-voltage
protection circuits within Power over Ethernet devices.
BACKGROUND
[0003] Power over Ethernet (PoE) refers to a technique of
transmitting electrical power over twisted-pair cabling, along with
data, to remote devices in an Ethernet network. PoE as standardized
in IEEE 802.3af provides 44 to 57 volts over at least two-pairs of
a four-pair cable at a current of up to 350 mA for a guaranteed
load power of approximately 15.4 watts. It is also possible to
provide power and data over electrical lines, over power buses, and
the like. As used herein, the term "powered network" refers to
system that delivers power and data on a cable, comprised of one or
more wires.
[0004] A powered device is an electronic device that is adapted to
derive power and to receive data from such a powered network via a
cable. A powered device may include a diode bridge to rectify the
power supply, one or more transformer windings to isolate internal
circuitry, a circuit to protect against transient over-voltage
conditions, and other associated circuit components.
[0005] In general, the powered devices (PDs) may be exposed to
transient high voltage conditions, which may include electrostatic
discharge events, transient charges in the cable, and the like. A
transient over-voltage condition refers to a high voltage level on
the cable, which may be greater than a voltage rating of at least
some of the associated circuit components. PoE as standardized in
IEEE 802.3af dictates that PDs should be capable of withstanding
such high voltage transient conditions, without sustaining high
voltage-related damage.
[0006] Conventionally, PDs often include an over-voltage protection
device that is separate from the integrated circuitry within the
PD. In some instances, the over-voltage protection device is a high
voltage transient suppressor, such as a high voltage zener diode. A
typical external over-voltage protection device is a surface mount
transient voltage suppressor that is rated to become active at
voltage levels between 64 Volts and 70 Volts with one milliamp of
current. Such a transient voltage suppressor typically clamps the
supply voltage to a voltage level that is less than the voltage
rating of the associated circuit components. In one particular PoE
PD, the over-voltage protection device clamps the voltage at a
level that is less than 94 Volts for a 4.3 A transient signal.
[0007] Unfortunately, the electrical characteristics, ratings and
tolerance of the over-voltage protection device also determine the
power ratings for other circuit components within the PD. For
example, since 94 Volt transients are possible at 4.3 A, any
coupled circuitry, such as a power regulator circuit and such as
load circuitry, should be rated for a higher power level (e.g. for
higher voltage and higher current levels). Unfortunately, this high
voltage rating increases costs of the circuits and, consequently,
increases PD unit costs.
SUMMARY
[0008] In one embodiment, an integrated circuit includes a
rectifier circuit, at least one low power element, and a power
protection element. The rectifier circuit includes two inputs to
receive an input power supply and includes two outputs to provide a
rectified power supply related to the input power supply. The
low-power circuit element is coupled between the two outputs. The
power protection element is coupled between the two output
terminals. In a first mode of operation, the power protection
element presents a high impedance to the two output terminals. In a
second mode of operation, the power protection element has a first
power protection characteristic. In a third mode of operation, the
power protection element has a second power protection
characteristic. The power protection element is adapted to shut
down the low-power circuit element when in the third mode of
operation.
[0009] In a particular embodiment, the power protection element
includes active logic to generate a fault protection signal
provided to the at least one low-power circuit element when in the
third mode of operation.
[0010] In another embodiment, a method is provided. An input
voltage supply is received at a pair of terminals. An over-voltage
condition related to the input voltage supply is detected using an
over-voltage protection element. Concurrently, the input supply
voltage is shunted between the pair of terminals and a shut off
signal is generated to associated circuitry in response to the
over-voltage condition using the over-voltage protection
element.
[0011] In another embodiment, an integrated circuit includes input
terminals to receive an input power supply, at least one low-power
circuit element coupled between the input terminals, and a power
protection element. The power protection element is coupled between
the input terminals to detect a power characteristic of the input
power supply. The power protection element is adapted to shunt
excess power between the input terminals and is adapted to shut off
power to the at least one low-power circuit element when the power
characteristic exceeds a threshold power level.
[0012] In another embodiment, a method is provided. An input power
supply is received at a pair of terminals, including a first
terminal and a second terminal. A power level of the input power
supply is detected using a power protection element of an
integrated circuit, which has at least one low-power component. The
power protection element is activated to shunt the input power
supply between the first terminal and the second terminal when the
power level exceeds a threshold power level. A power supply to the
at least one low-power component is substantially reduced when the
power level exceeds the threshold power level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a block diagram of a particular illustrative
embodiment of a Power over Ethernet (PoE) system.
[0014] FIG. 2 is an example of PoE wiring interconnections between
power source equipment and a powered device (PD).
[0015] FIG. 3 is a block diagram of a portion of an integrated
circuit that includes an integrated over-voltage fault protection
circuit within a PD.
[0016] FIG. 4 is a block diagram of a portion of an integrated
circuit that includes diode bridges and an integrated over-voltage
fault protection circuit within a PD.
[0017] FIG. 5 is a circuit diagram of an embodiment of an
over-voltage protection circuit within a PD.
[0018] FIG. 6 is a circuit diagram of another embodiment of an
over-voltage protection circuit within a PD.
[0019] FIG. 7 is a graph that illustrates voltage versus current
comparing a traditional zener diode protection device to the
circuits of FIGS. 5 and 6.
[0020] FIG. 8 is a circuit diagram of another embodiment of an
over-voltage protection circuit within a PD.
[0021] FIG. 9 is a graph illustrating voltage versus current
comparing a traditional zener diode protection device to the
circuit of FIG. 8.
[0022] FIG. 10 is a flow diagram of a method of providing
over-voltage fault protection in an integrated circuit.
[0023] FIG. 11 is a flow diagram of an alternative method of
providing over-voltage fault protection in an integrated
circuit.
DETAILED DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a block diagram of system 100 with a power over
Ethernet (PoE) power source equipment (PSE) device 102 and powered
devices. In this particular implementation, the PSE device 102
includes an Ethernet switch 104, a high voltage power supply 106,
and a PoE injector 108. The system 100 also includes PoE powered
devices (PDs) 112, 114 and 116 with respective diode bridges 118,
120, and 122 and with respective over-voltage protection elements
119, 121, and 123. The over-voltage protection elements 119, 121
and 123 may protect against over-voltage fault conditions,
transient conditions, and the like, and may be referred to as
transient protection elements or power protection elements. The PSE
device 102 is communicatively coupled to the PDS 112, 114, and 116
via twisted pair cabling 124, 126, and 128. In general, the system
100 may also include network devices (not shown) that are not
adapted for PoE, which may draw power from a separate power supply,
such as an electrical wall plug.
[0025] The high voltage power supply 106 provides a supply voltage
to the power injector 108. The power injector receives Ethernet
signals from the Ethernet switch 104 and places the Ethernet
signals and at least a portion of the supply voltage onto Ethernet
cables 124, 126 and 128. The PSE 102 can power a number of PDs
depending on the specific implementation. Each powered device 112,
114 and 116 may include one or more diode bridges 118, 120 and 122
respectively. In general, in many applications, such as telephony
and PoE, due to wiring uncertainties, the polarity of the input
supply voltage at the PD cannot be guaranteed. The diode bridges
118, 120 and 122 provide that the correct voltage polarity is
applied to load electronics within the PD or to electronic devices
attached to the PD.
[0026] In general, the term "powered device" and "PD," as used
herein, refers to a device adapted to receive a power supply and to
receive data from the same cable or wiring. In the embodiment
shown, the PDs 112, 114 and 116 are adapted to operate within a PoE
environment. Alternatively, the power sourcing equipment (PSE) may
be any source adapted to transmit power and data over common
wiring. For example, the PSE 102 may be an electrical power
transmission station adapted for high speed broadband data
transmissions over electrical transmission lines. In such an
instance, the data transmissions may use data packets, may use data
frames, may use other data protocols, or any combination thereof.
Nevertheless, the PDs 112, 114, and 116 may be adapted to
communicate using an appropriate protocol, and the active diode
bridges 118, 120 and 122 can be used to provide low loss
rectification of the power supply for the PDs 112, 114, and 116,
respectively.
[0027] The over-voltage protection elements 119, 121, and 123 are
adapted to detect an electrical characteristic of the rectified
voltage supply from the diode bridges 118, 120 and 122,
respectively. When the rectified voltage supply exceeds a threshold
voltage level, the over-voltage protection elements 119, 121, and
123 are activated to limit the rectified voltage supply level. In
one embodiment, the over-voltage protection elements 119, 121, and
123 shunt excess voltage and current between the rectified voltage
supply rails (such as supply voltage terminals 238 and 240 in FIG.
2). In another embodiment, the over-voltage protection elements
119, 121, and 123 shut down associated circuitry, such as load
circuitry, a power regulator, control logic, and the like, to
prevent a damage to such circuitry. In general, the turn-on voltage
of the over-voltage protection element 119, 121, and 123 may be
utilized as a threshold, and high voltage transients that exceed
the threshold voltage level may trigger the over-voltage protection
elements 119, 121, and 123 to shunt the excess voltage and current
between the rectified voltage supply rails and to issue a fault
protection signal to deactivate, to shut off, or to substantially
reduce power to the associated circuitry.
[0028] FIG. 2 is a block diagram illustrating a wire
interconnection between an illustrative PSE device 102 and an
illustrative PD 112. The PSE device 102 and the PD 112 are
connected via Ethernet cable 124. In general, the Ethernet cable
124 is comprised of a plurality of wire pairs 220, 222, 224, and
226. The IEEE 802.3AF standard defines a role for each of the wire
pairs 220, 222, 224 and 226 within the twisted pair wiring 124. Two
of the wire pairs 220 and 222 carry Ethernet packets, and two of
the wire pairs 224 and 226 are spares.
[0029] The PSE device 102 includes a power supply 202, which is
used to power windings of the transformers 204 and 206, which place
power onto the wire pairs 220 and 220 of the twisted pair cable
124. In this implementation, the PSE 102 is coupled to the
transformers 204 and 206 through switches 208 and 210. The switches
208 and 210 may couple the power supply 202 to the transformers 204
and 206 or may couple the power supply 202 directly to wire pairs
224 and 226 (sometimes referred to as the spare pare). At least one
of the wire pairs 220, 232, 224, and 226 may carry power, data, or
any combination thereof.
[0030] The PD 112 includes diode bridges 118, transformers 212 and
214, an over-voltage protection circuit 119, and a PoE
controller/hot swap/switching regulator circuit 230, which provides
power to an output load 232. The diode bridges 118 include diode
bridge 216 and diode bridge 218. Each of the diode bridges 216 and
218 include two inputs for receiving an input voltage supply and
two outputs for providing a rectified voltage supply (Vrect+ and
Vrect-) to the input voltage supply terminals 238 and 240. In
general, the transformers 212 and 214 are connected to wire pairs
220 and 222 to receive data signals and power from the PSE 102. The
transformers 212 and 214 are connected via their respective center
taps 234 and 236 to the inputs of the diode bridge 216. By
connecting to the respective center taps 234 and 236, data can be
extracted from the signal at a common mode of the transformers 212
and 214.
[0031] The wire pairs 224 and 226 are connected to the inputs of
the diode bridge 218. The outputs of the diode bridges 216 and 218
are connected to input voltage supply terminals 238 and 240. The
diode bridges 216 and 218 provide a positive rectified voltage
(Vrect+) onto the input voltage supply terminal 238 and a negative
rectified voltage (Vrect-) onto the input voltage supply terminal
240. The over-voltage protection circuit 119 is connected between
the input voltage supply terminals 238 and 240, to detect an
over-voltage condition and to protect the PoE controller/hot
swap/switching regulator circuit 230 as well as the output load 232
from over-voltage faults. Additionally, the PoE controller/hot
swap/switching regulator circuit 230 is connected between the input
voltage supply terminals 238 and 240. When the supply voltage
levels on the input voltage supply terminals 238 and 240 are within
an expected voltage supply range (such as between 36 and 57 volts),
the PoE controller/hot swap/circuit 230 provides a DC voltage
supply to the output load 232 via the supply terminals 242 and
244.
[0032] During operation, two of the wire pairs, such as wire pairs
220 and 222 or wire pairs 224 and 226, may be used to provide an
input supply voltage to the PD 112. It is typically not known which
of the pairs of wires will be used. Consequently, the PD 112 is
adapted to receive a supply voltage from either set of wire
pairs.
[0033] In one embodiment, the diode bridges 216 and 218 may include
diode bypass elements (diode bypass switches) placed in parallel
with at least one of the diodes within each of the diode bridges
216 and 218. Under certain conditions, a selected one of the diode
bypass elements within one of the diode bridges 216 and 218 may be
activated to provide a current path to bypass the associated diode
within the respective diode bridge 216 or 218. The diode bypass
element reduces the voltage consumption within the diode bridge by
routing current through the bypass element to bypass the associated
diode. From a power perspective, the diode bypass element looks
like a low value resistor when it is active. The bypass current
flows through the diode bypass element as long as the voltage drop
across the bypass element is less than a turn on voltage of the
diode. In one embodiment, the diode bypass element is a field
effect transistor (FET). Since an active FET can sink a large
amount of current at low voltage, the diode can remain inactive. By
applying a transistor bypass to a full diode bridge 208 or 210 to
bypass selected diodes within the diode bridge, the overall power
consumption of the diode bridge is reduced, thereby reducing the
overall load and improving the power efficiency of the PD 112.
Alternatively, the diode bypass element may be a bipolar
transistor.
[0034] In general, if a rectified voltage level provided by the
diode bridge 216 or 218 exceeds a predetermined threshold level,
the over-voltage protection circuit 119 is activated to shunt
excess voltage between the input voltage supply terminals 238 and
240. Additionally, the over-voltage protection circuit 119 may be
adapted to generate an over-voltage fault signal to deactivate, to
shut down, or to substantially reduce a power supply to the PoE
controller/hot swap/switching regulator circuit 230 as well as the
output load 232.
[0035] FIG. 3 is a block diagram of a portion of an integrated
circuit 300 that includes an integrated over-voltage fault
protection circuit 119 that may be used within a PD, such as PD 112
in FIG. 1. The integrated circuit 300 includes the over-voltage
fault protection circuit 119, a controller, hot swap, and switching
regulator 230, and an output load 232. The over-voltage fault
protection circuit 119 may include an over-voltage fault sensor 302
and a controller 304. The over-voltage fault protection circuit 119
is connected to the supply voltage terminal 238 and to the supply
voltage terminal 240 and is communicatively coupled to the
controller, hot swap, and switching regulator 230. The controller,
hot swap, and switching regulator 230 is connected to the power
supply voltage terminals 238 and 240 and provides at least one
regulated voltage supply for driving an output load 232, which may
include low voltage rated circuit components.
[0036] It should be understood that the supply voltage terminal 238
may have a first voltage potential and the supply voltage terminal
240 may have a second voltage potential. The difference between the
first and the second voltage potentials defines an input voltage to
the controller, hot swap, and switching regulator 230 and to the
over-voltage fault protection circuit 119.
[0037] The controller 304 of the over-voltage fault protection
circuit 119 monitors the supply voltage terminals 238 and 240 for
an over-voltage condition using the over-voltage fault sensor 302.
When an over-voltage condition is detected, the over-voltage fault
protection circuit 119 shunts the excess voltage between the supply
voltage terminals 238 and 240. Additionally, the controller 304
generates a fault protection signal to the controller, hot swap,
and switching regulator 230. The fault protection signal may
include a shut off signal to deactivate or substantially reduce a
power supply to the controller, hot swap, and switching regulator
230, so that components of the controller, hot swap, and switching
regulator 230, as well as the output load 232 that is powered from
the regulated voltage supply of the controller, hot swap, and
switching regulator 230, are protected from the over-voltage
condition. In one embodiment, the shut off signal may include an
abrupt decrease in an input supply voltage level on the supply
voltage terminals 238 and 240, which may be caused by activation of
the over-voltage fault protection circuit 119 and which may be
detected by the controller, hot swap, and switching regulator
230.
[0038] For example, in one particular illustrative embodiment, the
controller, hot swap, and switching regulator 230 may include
switches that are active when the supply voltage of the supply
voltage terminals 238 and 240 is appropriate for operation of the
controller, hot swap, and switching regulator 230. The over-voltage
fault protection signal from the controller 304 can deactivate the
switches when an over-voltage condition is detected.
[0039] FIG. 4 is a block diagram of a particular embodiment of a
portion of an integrated circuit 400 that includes diode bridges
118 and an integrated over-voltage fault protection circuit 119
that can be used within a PD. The integrated circuit 400 also
includes the controller, hot swap, and switching regulator 230. The
diode bridges 118 are connected to input supply terminals (such as
wire pairs 222 and 224 in FIG. 2) and to supply voltage terminals
238 and 240. The diode bridges 118 receive an input voltage supply
from the input supply terminals and convert the input voltage
supply to a rectified voltage supply. The diode bridges 118 drive
the input voltage supply onto the supply voltage terminals 238 and
240.
[0040] The over-voltage fault protection circuit 119 is connected
to the supply voltage terminals 238 and 240. The controller 304
monitors a voltage level of the supply voltage terminals 238 and
240 using the over-voltage fault sensor 302. When the voltage level
exceeds an over-voltage threshold, the over-voltage protection
circuit 119 shunts the excess voltage between the supply voltage
terminals 238 and 240. Additionally, the over-voltage protection
circuit 119 may generate an over-voltage fault protection signal to
the controller, hot swap, and switching regulator 230.
[0041] The controller, hot swap, and switching regulator 230 is
connected to the supply voltage terminals 238 and 240 to receive
the rectified input voltage supply. The controller, hot swap, and
switching regulator 230 may generate a regulated supply voltage
(Vreg+ and Vreg-) to drive a circuit load. The regulated supply
voltage may have a lower voltage potential than the rectified input
voltage supply on supply voltage terminals 238 and 240.
[0042] In general, though the controller 304 and the over-voltage
fault sensor 302 are illustrated as part of the over-voltage
protection circuit 119, it should be understood that the controller
304 and the over-voltage fault sensor 302 may be included as part
of the power regulator circuit 230. Alternatively, the controller
304 and the over-voltage fault sensor 302 may be separate circuit
components of the integrated circuit (such as 300 or 400 in FIGS. 3
and 4, respectively). Alternatively, the controller 304 and the
over-voltage fault sensor 302 may be separately arranged on the
integrated circuit or included as part of other components of the
integrated circuit 400, depending on the particular implementation.
In such an instance, the over-voltage protection circuit 119 may
include shunt circuitry to shunt the excess voltage between the
supply voltage terminals 238 and 240, and the controller 304
monitors the voltage level for over-voltage conditions.
[0043] FIG. 5 is a circuit diagram of an embodiment of an
over-voltage protection circuit within a portion of an integrated
circuit 500 for use within a PD. The integrated circuit 500
includes an over-voltage protection circuit 119 and an output load
232. The over-voltage protection circuit 119 and the output load
232 are both connected between the supply voltage terminals 238 and
240. The over-voltage protection circuit 119 includes a plurality
of zener diodes 502, 504, and 506 arranged in series (a zener
stack) between the supply voltage terminals 238 and 240. Each zener
diode 502, 504, and 506 has a characteristic breakdown voltage. The
sum of the breakdown voltages defines a trigger or threshold
voltage level for the over-voltage protection circuit 119. When the
input supply voltage potential between the supply voltage terminals
238 and 240 exceeds the threshold voltage level, the zener diodes
502, 504, and 506 breakdown and shunt the excess voltage between
the supply voltage terminals 238 and 240.
[0044] When the over-voltage fault event is finished, the
over-voltage protection fault circuit 119 stops shunting the excess
voltage and the circuit 500 returns to a normal operating mode.
During this recovery phase, the input supply voltage on the supply
voltage terminals 238 and 240 falls below the over-voltage
threshold defined by the sum of the characteristic breakdown
voltages of the zener diodes 502-506, the zener diodes 502-506 turn
off and stop conducting. The input supply voltage rises to the
operating input level, and downstream circuitry, such as a voltage
regulator or the output load 232, receives the input supply
voltage.
[0045] FIG. 6 is a circuit diagram of another particular embodiment
of an integrated circuit 600 with an over-voltage protection
circuit for use within a PD. The integrated circuit 600 includes an
over-voltage protection circuit 119 and an output load 232. The
over-voltage protection circuit 119 includes a plurality of zener
diodes 602, 604, and 606, an N-channel insulated gate field effect
transistor 608, a resistor 616, and a diode 618. The insulated gate
field effect transistor 608 can be, for example, a metal oxide
semiconductor (MOS) field effect transistor, a poly-oxide field
effect transistor, or any other suitable type of field effect
transistor. The transistor 608 includes a drain terminal 610
connected to the supply voltage terminal 238, a gate terminal 612,
and a source drain terminal connected to the supply voltage
terminal 240. A diode 618 includes a cathode terminal connected to
the supply voltage terminal 240 and an anode terminal connected to
the gate terminal 612. A resistor 616 is connected to the supply
voltage terminal 240 and to the gate terminal 612. The zener diodes
602, 604, and 606 of a zener stack are connected in series between
the gate terminal 612 and the voltage supply terminal 238.
[0046] In general, any number of zener diodes, such as the
illustrated zener diodes 602-606, can be used. Each zener diode
602-606 includes a characteristic breakdown voltage. The sum of the
breakdown voltages of each of the zener diodes defines an
over-voltage threshold. For example, if the threshold over-voltage
condition is 57 volts, nine zener diodes, having characteristic
breakdown voltages of 6.4 volts each, can be arranged in series to
define an over-voltage threshold of approximately 57.6 volts. If
the differential voltage between the voltage supply terminals 238
and 240 exceeds 57.6 volts, the nine zener diodes breakdown and
begin to conduct current between the supply voltage terminals 238
and 240. The voltage increases at the gate terminal 612 of the
field effect transistor 608, which switches on and shunts the input
supply voltage between the voltage supply terminals 238 and
240.
[0047] When the over-voltage fault event is finished, the
over-voltage protection fault circuit 119 stops shunting the excess
voltage and the circuit 600 returns to a normal operating mode.
During this recovery phase, the input supply voltage on the supply
voltage terminals 238 and 240 falls below the over-voltage
threshold defined by the sum of the characteristic breakdown
voltages of the zener diodes, the zener diodes turn off and stop
conducting. The input voltage at the gate terminal 612 falls below
the turn on voltage of the transistor 608, and the transistor turns
off. The input supply voltage rises to the operating input level,
and downstream circuitry, such as a voltage regulator or the output
load 232, receives the input supply voltage.
[0048] FIG. 7 is a graph 700 that illustrates voltage versus
current comparing a traditional zener diode protection device to
the circuits of FIGS. 5 and 6. In conventional over-voltage protect
device, a large zener diode may be connected between the supply
voltage terminals external to the integrated circuitry. The graph
line 702 illustrates such a conventional, external zener diode. The
large external diode of line 702 typically has a large variance in
breakdown voltages, so the turn on voltage may be significantly
higher than the threshold over-voltage level. As shown, the large
external diode of line 702 turns on at a differential voltage of
approximately 67 volts and clamps the input supply voltage to
approximately less than 94 volts for a 4.3 A transient current.
[0049] The graph line 704 illustrates a voltage clamp that may be
provided by the over-voltage protection circuit arrangement of FIG.
5. The breakdown voltage for each diode is lower and the margin of
error in the breakdown voltage is also significantly less. Thus,
the over-voltage protection circuit begins to conduct at just over
57 volts and clamps the input supply voltage to approximately less
than 80 volts for a 4.3 A transient current.
[0050] The graph line 706 illustrates a voltage clamp provided by
the over-voltage protection circuit arrangement of FIG. 6. As in
the arrangement of FIG. 5, the plurality of diodes provide a more
precise turn-on voltage than the conventional, large, external
zener diode. Thus, the over-voltage protection circuit of FIG. 6
turns on at around 58 volts and clamps the input supply voltage to
approximately 67 volts for a 4.3 A transient current.
[0051] FIG. 8 is a circuit diagram of another particular embodiment
of a portion of an integrated circuit 800 with an over-voltage
protection circuit 119 for use within a PD. The over-voltage
protection circuit 119 is a voltage-triggered silicon controlled
regulator (SCR). The over-voltage protection circuit 119 includes a
P-channel bipolar junction transistor 802, an N-channel bipolar
junction transistor 804, resistors 806 and 808, and a zener diode
circuit 810. The transistor 802 includes a drain terminal connected
to the input supply terminal 238, a gate terminal, and a source
terminal. The transistor 804 includes a drain terminal connected to
the gate terminal of the transistor 802, a gate terminal connected
to the source terminal of the transistor 802, and a source terminal
that is connected to the voltage supply terminal 240. The resistor
806 has a first terminal connected to the voltage supply terminal
238 and a second terminal connected to the gate terminal of the
transistor 802. The resistor 808 has a first terminal connected to
the gate terminal of the transistor 804 and a second terminal
connected to the voltage supply terminal 240. The zener diode
circuit 810 includes a cathode terminal connected to the source of
the transistor 802 and an anode terminal connected to the drain
terminal of the transistor 804. The output load 232 or a regulator
circuit can be connected between the voltage supply terminals 238
and 240 in parallel with the over-voltage protection circuit
119.
[0052] In general, the diode circuit 810 defines an over-voltage
threshold for the over-voltage protection circuit 119. When a
voltage differential between the input supply terminals exceeds the
characteristic breakdown voltage of the diode circuit 810, the
diode circuit 810 begins conducting. A voltage on the gate terminal
of the transistor 804 increases and activates the transistor 804,
which pulls down the voltage at the gate terminal of the transistor
802, activating the transistor 802, thereby shunting the current
between the voltage supply terminals 238 and 240. In general, the
transistors 802 and 804 turn on asynchronously, resulting in an
abrupt change in the voltage differential between the voltage
supply terminals 238 and 240 at the point where both transistors
802 and 804 become active.
[0053] In general, in a first mode of operation, the over-voltage
fault protection circuit 119 presents a high impedance to the
supply voltage terminals 238 and 240. In a second mode of
operation, the over-voltage fault protection circuit 119 has a
first over-voltage characteristic. An example of the first
over-voltage characteristic is represented by line 904 in FIG. 9.
In a third mode of operation, the over-voltage fault protection
circuit 119 has a second over-voltage protection characteristic. An
example of the second over-voltage characteristic is represented by
line 906 in FIG. 9. In a particular embodiment, the supply voltage
terminals 238 and 240 provide an input voltage that is at a higher
voltage in the second mode of operation than in the first or the
third modes of operation. For example, in the first mode of
operation, the differential supply voltage between the supply
voltage terminals 238 and 240 may range from zero volts to
approximately 55 volts. In a second mode of operation, the
differential supply voltage may be greater than 55 volts with a
current of up to approximately 1 A. In a third mode of operation,
the supply voltage has a voltage level of less than approximately
10 volts and a current level greater than approximately 0.5 A. In
the second and third modes of operation, the over-voltage fault
protection circuit 119 becomes active, providing a lower impedance
between the supply voltage terminals 238 and 240 than during the
first mode of operation.
[0054] It should be understood that the voltage and current levels
described above are illustrative only. Other voltage and current
levels may also be achieved by adjusting the breakdown voltage of
the diode circuit, for example. A lower breakdown voltage provides
for second and third modes of operation at a lower voltage level.
For example, if the breakdown voltage of the diode circuit is at
approximately 30 volts, then the second mode of operation would be
greater than approximately 30 volts. Similarly, a higher breakdown
voltage provides for a higher voltage level at the second and third
modes of operation.
[0055] When the over-voltage fault event is finished, the
over-voltage protection fault circuit 119 stops shunting the excess
voltage and the circuit 800 returns to a normal operating mode.
During this recovery phase, when the supply voltage on the voltage
supply terminals 238 and 240 falls below the over-voltage threshold
of the diode circuit 810, the diode circuit 810 turns off, causing
the voltage to decrease at the gate terminal of transistor 804 and
to increase rapidly at the gate terminal of the transistor 802. The
transistor 802 turns off in response to the increased voltage at
its gate terminal, and the voltage level at the gate terminal of
the transistor 804 decreases rapidly, turning off the transistor
804. The supply voltage on the voltage supply terminals 238 and 240
is allowed to drive the output load 232.
[0056] It should be understood that, though the diode circuit 810
is illustrated as a single high voltage zener diode with a
breakdown voltage of 62 Volts, the diode circuit 810 can be formed
from a plurality of diodes in series (as shown in FIG. 5), where
each of the plurality of diodes has a small breakdown voltage.
Additionally, it should be understood that, though the transistors
802 and 804 are shows as bipolar junction transistors, other types
of transistors may also be used, such as insulated gate field
effect transistors, metal oxide semiconductor field effect
transistors, or other suitable electronic switches. In one
embodiment, the diode circuit 810 may be a trigger element, and the
transistors 802 and 804 may operate as a switch responsive to the
trigger element.
[0057] The over-voltage protection circuit 119 reduces the
transient voltage seen by the PD and the PD-coupled circuitry. The
power dissipated in the transistors 802 and 804 is much lower than
is dissipated in a large external zener diode, so the reliability
and robustness of the protection is improved. In general, in PD
devices, there may be a large capacitor in the PD between a hot
swap switch (not shown) and the circuit load. This capacitor may be
discharged through the hot swap switch, which is reverse biased
under the over-voltage condition. A controller (such as that shown
in FIGS. 2 and 3) may be used to shut down the hot swap switch to
prevent such a discharge.
[0058] It should be understood that the diode circuit 810 defines a
turn-on threshold for the transistors 802 and 804, and that the
resulting voltage at the gate terminals of the transistors 802 and
804 can be considered control signals. Alternatively, the
transistors 802 and 804 could be activated by a control signal
sent, for example, by a controller or other active circuit element
upon detection of an over-voltage fault condition.
[0059] FIG. 9 is a graph 900 illustrating voltage versus current
comparing a traditional external zener diode protection device to
the circuit of FIG. 8. The graph line 902 is the same as the graph
line 702 in FIG. 7. The large external zener diode turns on at
approximately 67 volts and clamps the input supply voltage to
approximately less than 94 volts for a 4.3 A transient current.
[0060] In contrast, the over-voltage protection circuit of FIG. 8
turns on at approximately 58 volts, and increases to a little over
60 volts up to approximately 1 A of current as illustrated by line
904. As the current continues to rise, the transistor 802 turns on
and the voltage is clamped at a value of less than 10 volts for a
4.3 A transient current as illustrated by line 906.
[0061] FIG. 10 is a flow diagram of a method of providing
over-voltage fault protection in an integrated circuit. An
integrated circuit having a first over-voltage protection element
and at least one low-power element receives a first input voltage
at a first input (block 1000). The integrated circuit receives a
second input voltage at a second input (block 1002). The
over-voltage protection element detects an over-voltage condition
when the input voltage exceeds a threshold voltage level (block
1004). The over-voltage protection element activates a first switch
and a second switch in response to the over-voltage condition to
protect the at least one low-power element (block 1006). The
over-voltage protection element clamps a voltage applied to the at
least one low-power element to a lower voltage level that is below
a voltage rating of the at least one low-power element and/or that
is below a voltage rating of components coupled to the integrated
circuit (block 1008). The over-voltage protection circuit draws
excess current through the first and the second switch (block
1010).
[0062] FIG. 11 is a flow diagram of an alternative method of
providing over-voltage fault protection in an integrated circuit.
An over-voltage protection circuit within an integrated circuit
having at least one low-voltage component detects a voltage (block
1100). The over-voltage protection circuit maintains a first
transistor and a second transistor in an off state when the voltage
is less than a voltage protection threshold (block 1102). The
over-voltage protection circuit activates the first transistor and
the second transistor to clamp the voltage to a lower voltage level
when the voltage exceeds the voltage protection threshold (block
1104). The over-voltage protection circuit generates an
over-voltage protection signal to shut off the at least one
low-voltage component (block 1106).
[0063] It should be understood that the at least one low-voltage
component of the flow diagram of FIG. 11 and the low-power
component of the flow diagram of FIG. 10 may be a circuit load, an
LED, an oscillator, a voltage regulator, or any circuit component
that could be damaged by exposure to an ESD event or other high
voltage event.
[0064] In general, the over-voltage protection circuit 119 defines
voltage handling capabilities of the device, such as the PD. The
over-voltage protection circuit 119 described above can detect the
turn on of the over-voltage detection circuit. Thus, the turn on
can be used as a trigger to turn off or shut down power circuits,
such as the regulator circuit, to prevent high power
dissipation.
[0065] The over-voltage protection device can be implemented using
a low impedance zener diode implemented by an active zener diode,
such as a high voltage zener diode or a zener stack. In one
embodiment, a high voltage transistor may be provided within a
feedback loop, to lower the effective zener impedance and to clamp
the voltage to a much lower voltage level during an over-voltage
fault event.
[0066] It should be understood that the over-voltage protection
circuit may be a transient suppressor circuit that is adapted to
provide protection to the circuit from high voltage transients.
[0067] In general, though the embodiments described above have
focused largely on PoE implementations, it should be understood
that the over-voltage protection circuit or element may be utilized
in other applications where power fault protection is desired. The
above-described embodiments may be employed with other types of
powered networks, where the power supply voltage cabling also
carries data. For example, diode bridges may be used to rectify a
voltage supply from a bus including power and data, and a power
protection element may be utilized to shunt excess current and
voltage between input supply terminals to provide fault protection
to associated circuitry. In some embodiments, the wiring that
couples the powered network to the powered device may include a
plurality of individual wires, such as twisted pair cabling. In
such instances, a pair of individual wires may carry both power and
data. Alternatively, a first pair of the individual wires may carry
data and a second pair of the individual wires may carry a supply
voltage. In another embodiment, the wiring may include a power bus
that carries both power and data. In another embodiment, the wiring
may include a coaxial cable that carries both power and data.
[0068] Additionally, in the above-discussion, the over-voltage
protection element has been described with respect to voltage
potentials. However, it should be understood that the protection
element may also be referred to as a power protection element,
because power is a function of voltage and current. When activated,
the power protection element limits the voltage and shunts current
between the input supply terminals to protect load circuitry from
transient high voltage and high current events.
[0069] The above-disclosed subject matter is to be considered
illustrative, and not restrictive, and the appended claims are
intended to cover all such modifications, enhancements, and other
embodiments, which fall within the true spirit and scope of the
present invention. Thus, to the maximum extent allowed by law, the
scope of the present invention is to be determined by the broadest
permissible interpretation of the following claims and their
equivalents, and shall not be restricted or limited by the
foregoing detailed description.
* * * * *