U.S. patent application number 12/886857 was filed with the patent office on 2011-03-24 for power supply and method for electric lighting device.
This patent application is currently assigned to Secure Manufacturing Pty Ltd.. Invention is credited to Malcolm Alexander Young.
Application Number | 20110068712 12/886857 |
Document ID | / |
Family ID | 43756045 |
Filed Date | 2011-03-24 |
United States Patent
Application |
20110068712 |
Kind Code |
A1 |
Young; Malcolm Alexander |
March 24, 2011 |
POWER SUPPLY AND METHOD FOR ELECTRIC LIGHTING DEVICE
Abstract
Disclosed herein are a power control system (110) and method for
a light emitting diode (LED) lighting device. The system includes a
rectifier (125) to rectify an input voltage, a squaring module
(145) for squaring the rectified input voltage to produce a squared
input voltage value; a filter (155) to filter said squared input
voltage; a first function generator (160) for applying a first
function to determine a light control signal (165); a second
function generator (170) for applying a second function to
determine a conductance factor (175), wherein said first function
and said second function are independent functions of the root mean
square (RMS) value of said input voltage; a multiplier (180) for
multiplying said first multiplier signal with said rectified input
signal to determine a current control signal (185); and a power
supply (190) for determining an input light power to said LED
lighting device and an input load power to a dissipative load
(120), dependent upon said light control signal (165), said current
control signal (185) and said rectified input voltage (140).
Inventors: |
Young; Malcolm Alexander;
(Strathfield, AU) |
Assignee: |
Secure Manufacturing Pty
Ltd.
Belrose
AU
|
Family ID: |
43756045 |
Appl. No.: |
12/886857 |
Filed: |
September 21, 2010 |
Current U.S.
Class: |
315/307 |
Current CPC
Class: |
H05B 45/10 20200101;
H05B 45/12 20200101; H05B 45/37 20200101; H05B 47/18 20200101; H05B
45/385 20200101; H05B 31/50 20130101; Y02B 20/30 20130101 |
Class at
Publication: |
315/307 |
International
Class: |
H05B 37/02 20060101
H05B037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2009 |
AU |
2009904551 |
Claims
1. A power supply system for controlling supply of power to an
electric lighting device, said system comprising: a first function
generator for generating a light control signal, dependent upon a
first mathematical function of a root mean square (RMS) value of a
received input voltage; a second function generator for generating
a current control signal, dependent upon a second mathematical
function establishing a ratio of instantaneous input voltage to
instantaneous input current as a mathematical function of the RMS
value of said received input voltage, wherein said first function
and second function are independent of one another; and a power
supply for presenting a light power signal to said electric
lighting device and for presenting a load power to a dissipative
load, dependent upon said light control signal, said current
control signal, and said received input voltage.
2. The power supply according to claim 1, wherein said ratio of
instantaneous input voltage to instantaneous input current is
substantially constant.
3. The power supply according to claim 1, wherein said ratio of
instantaneous input voltage to instantaneous input current of said
second mathematical function is a scalar multiple of a mathematical
function relating a ratio of the instantaneous voltage and an
instantaneous current to the RMS input voltage of tungsten filament
incandescent lamp.
4. The power supply according to claim 1, wherein said second
mathematical function relating the ratio of the instantaneous
voltage and the instantaneous current to the RMS input voltage is a
power function in which the ratio of the instantaneous voltage and
the instantaneous current is proportional to the RMS value of the
received input voltage raised to a power in the range of -1.0 to
1.0.
5. The power supply according to claim 4, wherein said power is
about 0.4.
6. The power supply according to claim 1, wherein said first
function utilises a break-point function, such that said light
power signal presented to said electric lighting device is: 0, for
input RMS voltages below a first predetermined threshold V1; 50% of
nominal power, for input RMS voltages between a first predetermined
threshold V1 and a second predetermined threshold V2; an amount of
power between 50% and 100% of nominal power, for input RMS voltages
between said second predetermined threshold V2 and a third
predetermined threshold V3; and 100% of nominal power, for input
RMS voltages above said third predetermined threshold.
7. A power control system for a light emitting diode (LED) lighting
device, said system comprising: a first function generator for
utilising a first function to generate a light control signal
dependent upon a received input voltage; a second function
generator for utilising a second function to generate a conductance
factor dependent upon said received input voltage, wherein said
first function and said second function are independent functions
of the root mean square (RMS) value of said input voltage; a
multiplier for determining a current control signal dependent upon
said first multiplier signal and said received input voltage; and a
power supply for generating an input light power to present to said
electric lighting device and an input load power to present to a
dissipative load, dependent upon said light control signal, said
current control signal, and said received input voltage.
8. A method for controlling power supplied to a light emitting
diode (LED) lighting device, said method comprising the steps of:
determining a light control signal dependent upon a received input
voltage and a first function, wherein said first function is a
function of the root mean square (RMS) value of said received input
voltage; determining a conductance factor dependent upon said
received input voltage and a second function, wherein said second
function is a function of the RMS value of said received input
voltage, said first and second functions being independent of one
another; determining a current control signal dependent upon said
conductance factor and said received input voltage; and generating
an input light power to present to said lighting device and an
input load power to present to a dissipative load, dependent upon
said light control signal, said current control signal, and said
received input voltage.
9. The method according to claim 8, wherein said dissipative load
is selected from the group consisting of: a resistor; an active
dissipative device; and a Zener diode.
10. The method according to claim 8, wherein said received input
voltage is derived from a mains power supply.
11. The method according to claim 8, wherein at least one of said
first function and said second function is a break-point
function.
12. The method according to claim 8, wherein said LED lighting
device is selected from the group of lighting devices consisting
of: a road traffic control lantern; a railway signal lantern; and
operating theatre lighting.
13. The method according to claim 8, comprising the further steps
of: rectifying said received input voltage to produce a direct
current input voltage; squaring said direct current input voltage
to determine a squared voltage proportional to the square of the
received input voltage; and filtering said squared voltage to
produce a steady state signal for use in determining said light
control signal, wherein said steady state signal is proportional to
an average of the square of the received input voltage.
14. The method according to claim 13, wherein said squaring
includes the steps of: sampling instantaneous values of said direct
current input voltage; and squaring those instantaneous values.
15. The method according to claim 8, wherein said second function
is a transfer function that produces a power function of the RMS
value of the received input voltage.
16. A power control system for a light emitting diode (LED)
lighting device, said system comprising: a rectifier for rectifying
a received input voltage; a squaring module for squaring said
rectified input voltage to determine a squared voltage value
proportional to the square of the received input voltage; a filter
to filter said squared input voltage and produce a steady state
signal; a first function generator for applying a first function to
the steady state signal to determine a light control signal; a
second function generator for applying a second function to the
steady state signal to determine a conductance factor, wherein said
first function and said second function are independent functions
of the root mean square (RMS) value of said input voltage; a
multiplier for multiplying said conductance factor with said
rectified input signal to determine a current control signal; and a
power supply for producing an input light power to said LED
lighting device and an input load power to a dissipative load,
dependent upon each of said light control signal, said current
control signal, and said rectified input voltage.
17. The power control system according to claim 16, wherein said
system is adapted for use in at least one of a traffic signal
lantern, a railway signal lantern, and an operating theatre
light.
18. A method for controlling power supplied to a light emitting
diode (LED) lighting device, said method comprising the steps of:
rectifying a received input voltage waveform; squaring said
rectified input voltage waveform to determine a squared voltage
value proportional to the square of the received input voltage;
filtering said squared input voltage to produce a steady state
signal; applying a first function to the steady state signal to
determine a light control signal, dependent upon said received
input voltage; applying a second function to the steady state
signal to determine a conductance factor, dependent upon said
received input voltage, wherein said first function and said second
function are independent functions of the root mean square (RMS)
value of said input voltage; multiplying said conductance factor
and said rectified input voltage waveform to determine a current
control signal; and generating an input light power for presenting
to said LED lighting device and an input load power for presenting
to a dissipative load, dependent upon said light control signal,
said current control signal, and said rectified input voltage.
Description
REFERENCE TO RELATED PATENT APPLICATION(S)
[0001] This application claims benefit of Serial No. 2009904551,
filed 21 Sep. 2009 in Australia and which application is
incorporated herein by reference. To the extent appropriate, a
claim of priority is made to the above disclosed application.
TECHNICAL FIELD
[0002] The present invention relates generally to electric lighting
devices and, in particular, to power supplies for electric lighting
devices. The present invention also relates to a method and
apparatus for controlling power supply to an electric lighting
device.
BACKGROUND
[0003] Artificial lighting devices are used to provide light at a
desired intensity and location, and can be fixed, such as street
lights, or mobile, such as hand-held torches. Artificial lights are
used to illuminate dark areas, such as interiors of buildings or
outdoor spaces at night. Illuminating dark areas can be used, for
example, to facilitate navigation, improve security and safety,
extend working and production hours, and increase leisure time.
Examples of artificial lights include street lights, torches,
floodlights, fluorescent light globes, and filament light
globes.
[0004] In some applications, artificial lights are utilised to
provide illumination of a predetermined area, such as a street or
path. Controlling the intensity and/or the direction of light from
an artificial lighting device can also be utilised to create
atmosphere or ambience, such as in a restaurant. Another
application of artificial lighting devices is to focus light in a
predetermined manner to guide and control the movement of people,
vessels, and vehicles. Such lighting devices include, for example,
beacons, warning lights, lighthouses, headlights, tail-lights, and
traffic signal lanterns.
[0005] Traditionally, signal lanterns have used incandescent
filament lamps or quartz halogen lamps as a source of artificial
light. The lamp is fitted at the focus of a parabolic reflector and
the front of the reflector is fitted with a coloured lens that
determines the colour of the signal. More recently, signal lanterns
have been implemented using light emitting diodes (LEDs) as a light
source. The LED lanterns, when compared with lanterns utilising
incandescent filament lamps, have the advantage of lower power
consumption and longer life.
[0006] Current lanterns use light sources that suffer a reduction
in light output as those light sources age. This loss of light,
which is often called lumen depreciation, causes designers to make
lanterns that produce excessive light and consume excessive power
in the early part of the lanterns' lives. The excess light can be
so great as to be harmful and the extra power is just wasted. The
production of excessive light and consumption of excessive power
also reduces the lifetime of the LED.
[0007] For some kinds of LED, especially those used in red and
yellow traffic light signals, the light output depends strongly on
the operating temperature of the LED. The operating temperature is
further affected by the local ambient temperature and by heating
due to solar radiation. This again leads designers to compensate by
applying extra power to the LEDs. Applying extra power to the LEDs
exacerbates the power consumption and lumen depreciation problems.
The combined effect is large and makes the design of red lanterns
particularly problematic. LEDs work most efficiently when cold and
least efficiently when the LEDs are hot, whereas the required light
output is greatest during the day and least during the night.
[0008] In order to reduce the light output of an LED signal lantern
for use at night, it may be necessary to apply less than a standard
voltage to the LED signal lantern. However, typical LED signal
lanterns have poor power factor and are difficult to operate with
less than the standard voltage.
[0009] For the purpose of dimming the light output of a signal
lantern, one approach is to reduce an applied voltage by reducing
the amplitude of the applied alternating current (A.C.) mains
voltage. Alternatively, a second approach uses a method known as
"phase dimming" to dim a signal lantern, by removing part of the
applied mains wave form through the use of a control element, such
as a TRIAC. Both forms of dimming of a signal lantern can give the
same applied root mean square (RMS) voltage. However, LED signal
lanterns commonly produce different amounts of output light when
different methods of dimming are utilised. This is in contrast to
traditional incandescent lanterns, which do not behave in this
manner and generally produce the same amount of output light,
irrespective of the type of dimming method that is utilised.
[0010] An additional problem occurs when it is desired to determine
the number of lanterns connected to a control system by measuring
the total power consumed. This is readily determined when using
incandescent lanterns, as the incandescent lanterns behave in a
consistent manner. Since the relationship between an applied
voltage and the consumed power for a LED signal lantern is commonly
not the same as the voltage power relationship of an incandescent
lantern and, more seriously, the relationship is also dependent on
the applied voltage waveform, it is difficult to use power
consumption as a means for assessing the number of LED lanterns
connected to the control system.
[0011] Thus, a need exists to provide an improved method and system
for controlling power supplied to electric lighting devices.
SUMMARY
[0012] Disclosed herein are a method and a power supply system for
supplying power to a light source in which the output power
delivered to the light source and the ratio of an instantaneous
input voltage to an instantaneous input current are independent
mathematical functions of the root mean square (RMS) value of the
input voltage.
[0013] According to a first aspect of the present disclosure, there
is provided a power supply system for controlling supply of power
to an electric lighting device, said system comprising: a first
function generator for generating a light control signal, dependent
upon a first mathematical function of a root mean square (RMS)
value of a received input voltage; a second function generator for
generating a current control signal, dependent upon a second
mathematical function establishing a ratio of instantaneous input
voltage to instantaneous input current as a mathematical function
of the RMS value of said received input voltage, wherein said first
function and second function are independent of one another; and a
power supply for presenting a light power signal to said electric
lighting device and for presenting a load power to a dissipative
load, dependent upon said light control signal, said current
control signal, and said received input voltage.
[0014] According to a second aspect of the present disclosure,
there is provided a power control system for a light emitting diode
(LED) lighting device, said system comprising: a first function
generator for utilising a first function to generate a light
control signal dependent upon a received input voltage; a second
function generator for utilising a second function to generate a
conductance factor dependent upon said received input voltage,
wherein said first function and said second function are
independent functions of the root mean square (RMS) value of said
input voltage; a multiplier for determining a current control
signal dependent upon said first multiplier signal and said
received input voltage; and a power supply for generating an input
light power to present to said electric lighting device and an
input load power to present to a dissipative load, dependent upon
said light control signal, said current control signal, and said
received input voltage.
[0015] According to a third aspect of the present disclosure, there
is provided a method for controlling power supplied to a light
emitting diode (LED) lighting device, said method comprising the
steps of: determining a light control signal dependent upon a
received input voltage and a first function, wherein said first
function is a function of the root mean square (RMS) value of said
received input voltage; determining a conductance factor dependent
upon said received input voltage and a second function, wherein
said second function is a function of the RMS value of said
received input voltage, said first and second functions being
independent of one another; determining a current control signal
dependent upon said conductance factor and said received input
voltage; and generating an input light power to present to said
lighting device and an input load power to present to a dissipative
load, dependent upon said light control signal, said current
control signal, and said received input voltage.
[0016] According to a fourth aspect of the present disclosure,
there is provided a power control system for a light emitting diode
(LED) lighting device, said system comprising: a rectifier for
rectifying a received input voltage; a squaring module for squaring
said rectified input voltage to determine a squared voltage value
proportional to the square of the received input voltage; a filter
to filter said squared input voltage and produce a steady state
signal; a first function generator for applying a first function to
the steady state signal to determine a light control signal; a
second function generator for applying a second function to the
steady state signal to determine a conductance factor, wherein said
first function and said second function are independent functions
of the root mean square (RMS) value of said input voltage; a
multiplier for multiplying said conductance factor with said
rectified input signal to determine a current control signal; and a
power supply for producing an input light power to said LED
lighting device and an input load power to a dissipative load,
dependent upon each of said light control signal, said current
control signal, and said rectified input voltage.
[0017] According to a fifth aspect of the present disclosure, there
is provided a method for controlling power supplied to a light
emitting diode (LED) lighting device, said method comprising the
steps of: rectifying a received input voltage waveform; squaring
said rectified input voltage waveform to determine a squared
voltage value proportional to the square of the received input
voltage; filtering said squared input voltage to produce a steady
state signal; applying a first function to the steady state signal
to determine a light control signal, dependent upon said received
input voltage; applying a second function to the steady state
signal to determine a conductance factor, dependent upon said
received input voltage, wherein said first function and said second
function are independent functions of the root mean square (RMS)
value of said input voltage; multiplying said conductance factor
and said rectified input voltage waveform to determine a current
control signal; and generating an input light power for presenting
to said LED lighting device and an input load power for presenting
to a dissipative load, dependent upon said light control signal,
said current control signal, and said rectified input voltage.
[0018] According to another aspect of the present disclosure, there
is provided an apparatus for implementing any one of the
aforementioned methods.
[0019] According to another aspect of the present disclosure, there
is provided a computer program product including a computer
readable medium having recorded thereon a computer program for
implementing any one of the methods described above.
[0020] Other aspects of the invention are also disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] At least one embodiment of the present disclosure will now
be described with reference to the drawings, in which:
[0022] FIG. 1 shows a schematic block diagram representation of a
lighting supply system in accordance with the present
disclosure;
[0023] FIGS. 2A to 2C show examples of functions that may be
utilised by embodiments of the present disclosure for controlling
light output of an electric lighting device;
[0024] FIGS. 3A and 3B collectively form a schematic block diagram
representation of an electronic device upon which described
arrangements can be practised;
[0025] FIG. 4 shows a traffic lantern arrangement embodying a power
supply system of the present disclosure;
[0026] FIG. 5 is a flow diagram of a method for controlling power
to an electric lighting device, in accordance with an embodiment of
the present disclosure;
[0027] FIG. 6 is a schematic block diagram representation of an
embodiment of a power supply in accordance with the present
disclosure; and
[0028] FIG. 7 is a schematic block diagram representation of an
embodiment of a power supply in accordance with the present
disclosure.
DETAILED DESCRIPTION
[0029] Where reference is made in any one or more of the
accompanying drawings to steps and/or features that have the same
reference numerals, those steps and/or features have for the
purposes of this description the same function(s) or operation(s),
unless the contrary intention appears.
[0030] The present disclosure provides a method, system, and
computer-implemented method for controlling power applied to an
electric lighting device, by separating and independently
controlling light output of the electric lighting device and power
consumption. In one embodiment, a power control system and method
in accordance with the present disclosure supplies power to a
lighting device according to a first control signal and consumes
power according to a second control signal. If more power is to be
consumed than the amount of power consumed by the lighting device,
then the excess power is dissipated in a dissipative device. Thus,
the system and method manage an input voltage waveform to deliver a
desired power consumption for a lighting arrangement.
[0031] Independently controlling the light output of the electric
lighting device and power consumption enables the power consumption
of the electric lighting device to be closely modelled on the power
consumption of an incandescent lantern. Further, the method and
system of the present disclosure facilitate monitoring of one or
more electric lighting devices and the light output of the electric
lighting device can be controlled by the supply voltage in
accordance with a predetermined function. The predetermined
function may be chosen, for example, by a purchaser of the electric
lighting device and can be implemented without substantially
affecting the power consumption of the lighting device.
[0032] Embodiments of the present disclosure can be utilised, for
example, to control power supplied to road traffic control
lanterns, railway signal lanterns and operating theatre lighting,
especially where monitoring of the lantern power or dimming is
used. In particular, power control systems and methods in
accordance with the present disclosure can be utilised to control
power supplied to LED lighting devices so as to control the light
output from the LED lighting devices while also independently
controlling the overall power consumed by the LED lighting
devices.
[0033] Embodiments of the present disclosure facilitate measuring
power consumption of an electric lighting device, as the consumed
power is related to the supply voltage and is independent of the
supply voltage waveform. Further, embodiments of the present
disclosure enable a light output for an electric lighting device to
be selected with respect to an input mains voltage in a manner
independent from the power consumption characteristic. When
utilising LED light sources, it sometimes arises that a leakage of
power to the input power supply cables can result in the LED light
source being spuriously lit. In applications such as traffic or
railway signal lanterns, spuriously lit light sources can have
disastrous consequences. In embodiments of the present disclosure,
power is consumed while the supplied input voltage is too low to
illuminate the lighting device, so consequently leakage of power to
the input power cables does not easily result in the electric
lighting device being spuriously lit. Thus, in some applications
the system and method of the present disclosure provides a safety
feature.
[0034] FIG. 5 is a flow diagram 500 of a method for controlling
power to an electric lighting device, in accordance with an
embodiment of the present disclosure. The method 500 begins at a
Start step 505 and proceeds to a rectification step 510, in which a
rectifier rectifies an input power supply to convert an alternating
current (A.C.) power supply to a direct current (D.C.) input
voltage. The input power supply may be derived from a mains power
supply, for example. Control passes from step 510 to a squaring
step 515, which squares the rectified power supply received from
step 505 to determine a squared voltage value proportional to the
square of the received input signal. The squaring produces a signal
having an average value that is unaffected by the shape of the
input voltage waveform.
[0035] Control passes from step 515 to a filtering step 520, which
filters the squared voltage value by averaging the squared voltage
values to produce a steady state signal. The filtering may be
implemented, for example, by using a low pass filter. From step
520, control splits to each of a first function step 525 and a
second function step 530. The first function step 520 applies a
first function to the filtered, squared voltage values to determine
a light control signal that is used to control an amount of light
that is to be output from the electric lighting device. Control
passes from step 525 to a power step 540.
[0036] Returning to step 530, the second function step 530 applies
a second function to the filtered, squared voltage values to
determine a conductance factor to be presented to a multiplier. The
conductance factor is used to set the instantaneous current drawn
by the power supply to be proportional to the instantaneous mains
voltage applied. Control passes from step 530 to a multiplying step
535, which multiplies the conductance factor with the rectified
power signal to determine a current control signal, which controls
the instantaneous current drawn by a power supply.
[0037] The first function and second function may be selected
independently of one another. The first function and second
function are independent functions of the same input variable,
being the root mean square (RMS) value of a received input
voltage.
[0038] Control passes from step 535 to the power step 540. The
power step 540 receives the light control signal from the first
function step 525, the current control signal from step 535, and
the rectified input power signal and determines an input light
power that is applied to the electric lighting device to produce a
desired light output. The power step also determines an input load
power that is presented to a dissipative load to dissipate any
excess power, if required. Control passes from step 540 to an End
step 550 and the method terminates.
[0039] FIG. 1 shows a schematic block diagram representation of a
lighting supply system 100 in accordance with the present
disclosure. The lighting supply system 100 includes an input power
supply 105, a power control system 110, a light source 115, and a
dissipative load 120. The power control system 110 receives the
input power supply 105 and produces outputs in the form of: (i) an
input light power 192 that is applied to the light source 115; and
(ii) an input load power 194 that is applied to the dissipative
load 120. In the example shown, the light source 115 is an LED
signal lantern comprising one or more LEDs. Controlling the input
light power 192 directly controls the light output of the light
source 115. Controlling the input power load 194 controls the power
consumption of the lighting supply system 100 in conjunction with
the light source 115 and the dissipative load 120.
[0040] The power control system 110 includes a rectifier 125 that
receives the applied input power supply 105 and produces a
rectified output that is presented to each of a first isolation
diode 130, a second isolation diode 135 and a third isolation diode
140. One implementation of the rectifier 125 utilises a bridge
rectifier comprising four diodes to convert an alternating current
input power supply to a direct current input voltage, as would be
readily understood by a person skilled in the relevant art. The
diodes may be silicon diodes type 1N4004, for example. The first
isolation diode 130, second isolation diode 135, and third
isolation diode 140 are optional and are utilised to prevent
undesirable interactions. The first isolation diode 130, second
isolation diode 135, and third isolation diode 140 may be
implemented using silicon diodes type 1N4004, for example. While
silicon diodes 1N4004 are mentioned as examples above, other diodes
may equally be utilised without departing from the spirit and scope
of the present disclosure.
[0041] The first isolation diode 130 receives the rectified power
output from the rectifier 125 and passes the rectified power output
to a squaring module 145. The input power supply 105 can utilise
input voltages of many different waveforms, including, for example,
sinusoidal waveforms, phase-cut waveforms, triangular waveforms,
and square waveforms. The squaring module 145 squares the rectified
power output and determines a squared voltage value 150 that is
provided to a filter 155. The squared voltage value 150 is
proportional to the square of a received input signal. The squaring
produces a signal having an average value that is unaffected by the
shape of the input voltage waveform. This enables control of the
light output by the light source 115 to be indifferent to the
method of dimming. It is clear that a value proportional to the RMS
value of the input voltage can be simply derived from the output of
the filter 155 by applying a square root function. Such a function
may, for example, form part of subsequent first and second function
generators 160 and 170. If the squaring module is of a kind that
can properly accept inputs of either polarity, the squaring module
may receive an alternating input proportional to the input at 105
without the need for rectification by diodes or bridges.
[0042] In one implementation, the squaring module 145 is
implemented by sampling a number of instantaneous values of the
rectified power output and then squaring those instantaneous values
to determine the squared voltage value 150. The squaring module 145
can be implemented in hardware, firmware, software, or any
combination thereof. In one embodiment, the squaring module 145 is
implemented by using a log-antilog multiplier. An alternative
embodiment utilises a pulse width-pulse height method to implement
the squaring module 145.
[0043] The filter 155 receives the squared voltage 150 and averages
the squared voltage values to produce a steady state signal that is
readily comparable to one or more set values or steady state
values. The output of the filter 155 is proportional to the average
of the square of the voltage of the input power supply 105.
[0044] A tungsten filament lamp has a resistance that changes as
the filament heats up over time; the resistance of a tungsten
filament is low when cool and increases when the filament is hot.
In a signalling application in which a tungsten filament is "on"
for a short time period, any change in the resistance of the
filament is negligible. It is desirable for a LED lighting device
coupled to the power control system 110 to present a load that is
similar to that of a tungsten filament load. This facilitates
retro-fitting of LED lighting devices to existing lighting
arrangements. Further the LED lighting device will appear as a
tungsten filament load to the power supply, but the light output of
the LED lighting device will have a different characteristic
relative to the input voltage. One characteristic of the light
output may be that the light output does not change relative to the
input voltage. That is, the lighting device is either "on" or
"off", and produces a constant light output when "on". The filter
155 simulates the thermal component of a tungsten filament lamp.
Another characteristic uses different output light levels for
different times of day, different seasons, or even combinations
thereof.
[0045] The filter 155 can be implemented using hardware, firmware,
software, or a combination thereof. The filter 155 may be
implemented by utilising, for example, a 2-pole Bessel-type low
pass filter of the Sallen-Key type, made using operational
amplifiers type LM321, or by using switched capacitor techniques.
In such an embodiment, the cutoff frequency could be set to
approximately 15 Hz. The actual filter characteristic implemented
will depend on the particular application and may include, for
example, a Thompson or Butterworth characteristic. The pass band
and stop band characteristics are selected such that the output of
the filter is substantially free from fundamental and harmonic
components of the power line mains frequency. The filter should
preferably not delay low frequency signals excessively. In
particular, the delay should be less than 100 ms, and preferably
less than 50 ms, so that the significance of the information or
status conveyed by the illumination of the light is made visible in
a timely manner and that any variation in the current consumption
of the light is approximately contemporaneous with the variation in
the voltage that caused that variation.
[0046] These constraints determine a range of suitable filter
characteristics that may be used. The filter may also be
implemented using digital computing techniques using well know
finite impulse response (FIR) or infinite impulse response (IIR)
filters. It will be appreciated by a person skilled in the art that
other filters may equally be practised without departing from the
spirit and scope of the present disclosure.
[0047] The squared voltage values output from the filter 155 are
presented to each of a first function generator 160 and a second
function generator 170. The first function generator 160 receives
the squared voltage values, applies a first function to those
squared voltage values, and generates a light control signal 165
that is supplied to a power supply 190. The light control signal
165 controls the amount of light that is to be output from the
light source 115 by controlling the input light power 192 applied
by the power supply 190 to the light source 150. The first function
is selected such that the light output from the light source 115 is
a selected function of the root mean square (RMS) voltage of the
input power supply 105. As indicated above, the output of the
filter 155 is proportional to the average of the square of the
voltage of the input power supply 105. Thus, the output of the
filter 155 can be used in place of the RMS value of the voltage of
the input power supply when the first function generator 160
includes a square root component.
[0048] The second function generator 170 receives the filtered
squared voltage values from filter 155, applies a second function
to those filtered squared voltage values, and generates a first
multiplier input to a multiplier 180 in the form of a conductance
factor 175. The conductance factor 175 is utilised to control the
current drawn by the lighting system 100 and hence its power
consumption
[0049] In particular, the instantaneous current drawn by the power
supply 190 is set to be proportional to the instantaneous mains
voltage applied, so that the power supply 190 appears to be
equivalent to a resistor with a value equal to the ratio of the
applied voltage and current drawn. Since the power supply 190
comprises a substantial portion of the total load presented by the
lighting system 100, the lighting system 100 also appears to be
similarly equivalent to that resistor. In one embodiment, the
second function is a transfer function, wherein an output of the
second function generator 170 is a power function of the input. The
typical power (exponent) would be a small number, about -0.2. This
transfer function can be implemented using analog circuitry by
log-antilog techniques or alternatively by using a method described
by Barrie Gilbert in "Translinear circuits: a proposed
classification," Gilbert, B., Electronics Letters, 11-1, 1975, pp.
14-16 using bipolar transistors and resistors to define the power
function. The second function may equally be implemented by using,
for example, a break-point type function. One embodiment implements
a second function generator 170 that utilises a break-point type
function made using operational amplifiers type LM321 and with
break-points set using Zener diodes.
[0050] The second isolation diode 135 receives the rectified power
output from the rectifier 125 and passes the rectified power output
to the multiplier 180. The multiplier 180 multiplies the
conductance factor 175, provided by the second function generator
170, with the rectified power output received from the second
isolation diode 130 to generate a current control signal 185 that
is presented to the power supply 190. The current control signal
185 is the instantaneous product of the conductance factor 175 and
the signal received from the second diode 135. The current control
signal 185 controls the instantaneous current drawn by the power
supply 190. It will be appreciated that the second function
generator 170 and the multiplier 180 may be implemented as an
integral unit.
[0051] The multiplier 180 receives two inputs, a conductance factor
175 and a voltage factor in the form of the rectified power output
from the second diode 135, and produces a current control signal
185. The current drawn by the lighting device 115 is proportional
to the product of the voltage factor and the conductance factor.
When considered as a resistor, the resistance of the lighting
device 115 is inversely proportional to the conductance factor
(which is dimensionally appropriate). The conductance factor is
derived from the filtered output of the squarer 145 being modified
by the first function generator 170. The most useful functions for
function generator 170 will typically be small negative power
functions.
[0052] Embodiments of the present disclosure may equally utilise a
divider in place of the multiplier 180, and by using a resistance
factor in place of the conductance factor. The resistance factor
would differ from the conductance factor, but still be derived from
the filtered squarer output by choosing a different characteristic
for the first function generator 170. In this case, the most useful
functions for function generator 170 will typically be small
positive power functions.
[0053] One embodiment implements the multiplier 180 as an analog
function using a Barrie cell, which is a common arrangement for
performing a multiplication function. Alternative embodiments can
utilise, for example, log-antilog methods or digital computing
techniques.
[0054] The current control signal 185 is proportional to the
instantaneous mains voltage using a signal from the second
isolation diode 135 and a predetermined function of the filtered
squared signal, as applied by the second function generator 170. By
varying the function implemented by the second function generator
170, the lighting system 100 may be made to behave, with respect to
power consumption, like an incandescent lamp or, alternatively,
like a resistor having a constant value. These two behaviours are
set by choosing a second function applied by the second function
generator 170 such that the conductance factor 175 output from the
second function generator 170 is proportional to 1/sqrt (mains
voltage) to approximate an incandescent lamp or by making the
conductance factor 175 to be constant.
[0055] In one embodiment, the current of an incandescent lamp is
assumed to be proportional to the voltage raised to the 0.5 power.
The conductance of a typical tungsten filament lamp is known to
vary as the -0.4 power of the applied RMS voltage. In one
embodiment, the function generator 170 is configured to generate a
-0.2 power function to simulate this behaviour. The value of -0.2
is made up as a power of 0.5 to obtain the RMS value from the
filtered squared input multiplied by -0.4 to account for the -0.4
power function of the conductance variation with RMS voltage
yielding a total power function of -0.2. The multiplier 180 can be
implemented in hardware, firmware, software, or any combination
thereof. In one embodiment, the multiplier 180 is implemented by
using a log-antilog multiplier. An alternative embodiment utilises
a pulse width-pulse height method to implement the multiplier
180.
[0056] The third isolation diode 140 receives the rectified power
output from the rectifier 125 and passes a rectified power output
195 to the power supply 190. The power supply 190 presents the
input power load 194 to a dissipative load 120 to control the power
consumption of the lighting supply system 100 by dissipating any
excess power. One embodiment implements the dissipative load 120 by
using a resistor, a Zener diode, an active device dissipating
power, a shunt regulator, or a combination thereof.
[0057] FIGS. 6 and 7 are schematic block diagram representations of
two embodiments of the power supply 190 of FIG. 1. FIG. 6 shows a
power supply 600 that includes a comparator 640. The comparator 640
acts as an oscillator driving the gate terminal of a MOSFET 632.
The MOSFET 632, together with a first inductor 602, a first diode
604, and a reservoir capacitor 606, forms a switching power supply
of the flyback kind. The current drawn by the flyback power supply
passes through a current sense resistor 634. The voltage developed
across the current sense resistor 634 has a pulsing waveform. This
voltage signal is filtered by a low pass filter comprising a first
resistor 636 and a second capacitor 644 and is fed to an inverting
input of the comparator 640.
[0058] The comparator 640 is made to oscillate by providing
positive feedback via a second resistor 638. In operation, an input
voltage fed into terminal 648 determines the current drawn by the
flyback power supply, such that the average current passing through
the current sense resistor 634 is made to be equal or substantially
equal to the input voltage applied at terminal 648. It is to be
understood that the value of the second resistor 638 is much
greater than the value of a third resistor 642. In operation, the
flyback power supply receives power from terminal 646,
corresponding to the rectified power output 195 from the third
isolation diode 140 of FIG. 1, and charges the reservoir capacitor
606 to a voltage greater than the voltage present on terminal 646.
Since the flyback power supply current consumption is determined
externally from the flyback power supply, by the voltage present on
terminal 648, the flyback power supply may produce more power than
LED lighting devices 618, 620 can properly consume in the
production of the desired amount of light. The LEDs 618, 620
correspond to the lighting device 115 of FIG. 1. This excess power
is dissipated in a Zener diode 608, corresponding to the
dissipative load 120 of FIG. 1, which is chosen to be of a suitable
size and rating for this purpose.
[0059] The operating current of the LEDs 618, 620 is controlled by
the control voltage presented to terminal 652. The control voltage
determines the collector current in a bipolar transistor 626, which
together with a fourth resistor 628 and an operational amplifier
630 forms a precision current sink. This collector current controls
the collector current in a bipolar transistor 612, which together
with a bipolar transistor 610 forms a current mirror. It is
preferable that transistors 610 and 612 are closely matched and at
the same temperature as each other. Properly matched and thermally
connected current mirror devices are commercially available. The
collector current of transistor 612 can thus be made proportional
to the applied control voltage at terminal 652. The collector
current of transistor 612 passes through a fifth resistor 614
developing a voltage relative to the raw variable rectified voltage
appearing on terminal 646, that is proportional to the applied
input voltage at terminal 652, which is relative to the common
return rail at terminal 650. The voltage across the fifth resistor
614 controls the current through the LEDs 618, 620 using a
transistor 622, a sixth resistor 624 and an operational amplifier
616, which form a controllable precision current sink.
[0060] FIG. 7 shows an alternative implementation of the power
supply 190 of FIG. 1. FIG. 7 shows a power supply 700 that includes
a comparator 740. The comparator 740 acts as an oscillator driving
the gate terminal of a MOSFET 732. The MOSFET 732, together with a
first inductor 702, a first diode 704, and a reservoir capacitor
706, forms a switching power supply of the flyback kind. The
current drawn by the flyback power supply passes through a current
sense resistor 734. The voltage developed across the current sense
resistor 734 has a pulsing waveform. This voltage signal is
filtered by a low pass filter comprising a first resistor 736 and a
second capacitor 744 and is fed to an inverting input of the
comparator 740.
[0061] The comparator 740 is made to oscillate by providing
positive feedback via a second resistor 738. In operation, an input
voltage fed into terminal 748 determines the current drawn by the
flyback power supply, such that the average current passing through
the current sense resistor 734 is made to be equal or substantially
equal to the input voltage applied at terminal 748. It is to be
understood that the value of the second resistor 738 is much
greater than the value of a third resistor 742. In operation, the
flyback power supply receives power from terminal 746,
corresponding to the rectified power output from the third
isolation diode 140 of FIG. 1, and charges the reservoir capacitor
706 to a voltage greater than the voltage present on terminal 746.
Since the flyback power supply current consumption is determined
externally from the flyback power supply, by the voltage present on
terminal 748, the flyback power supply may produce more power than
LED lighting devices 718, 720 can properly consume in the
production of the desired amount of light. The LED lighting devices
718, 720 correspond to the lighting device 115 of FIG. 1. This
excess power is dissipated in a Zener diode 708, which is chosen to
be of a suitable size and rating for this purpose. The Zener diode
708 corresponds to the dissipative load 120 of FIG. 1.
[0062] The operating current of the LEDs 718, 720 is controlled by
the control voltage presented to terminal 752. The control voltage
determines the collector current in a bipolar transistor 726, which
together with a fourth resistor 728 and an operational amplifier
730 forms a precision current sink. This collector current controls
the collector current in a bipolar transistor 712, which together
with a bipolar transistor 710 forms a current mirror. It is
preferable that transistors 710 and 712 are closely matched and at
the same temperature as each other. Properly matched and thermally
connected current mirror devices are commercially available. The
collector current of transistor 712 can thus be made proportional
to the applied control voltage at terminal 752. The collector
current of transistor 712 passes through a fifth resistor 714
developing a voltage relative to the raw variable rectified voltage
appearing on terminal 746, that is proportional to the applied
input voltage at terminal 752, which is relative to the common
return rail at terminal 750. The voltage across the fifth resistor
714 controls the current through the LEDs 718, 720 using a
transistor 722, a sixth resistor 724 and an operational amplifier
716, which form a controllable precision current sink.
[0063] The power supply 700 of FIG. 7 operates similarly to the
power supply 600 of FIG. 6, except that the voltage developed
across the sixth resistor 714 controls the current through LEDs 718
and 720, such that light output from the LEDs 718, 720, as sensed
by a light sensor 756, is set at a value dependent upon the control
voltage at terminal 752. In this embodiment, it is understood that
the light sensor 756, which may be implemented using, for example,
a photodiode, is illuminated by the LEDs 718, 720. Operational
amplifier 754 and resistor 758 convert the current produced by
photodiode 756 to a voltage proportional to that current.
[0064] While FIG. 1 shows the power control system 110 separate
from the light source 115 and the dissipative load 120, it will be
appreciated by a person skilled in the art that other embodiments
may equally be practised in which the power control system 110 is
integral with either one or both of the light source 115 and the
dissipative load 120. The light source 115 and the dissipative load
120 may also be implemented as an integral unit. Further, the
components of the power control system 110 may be implemented as
discrete components, integrated components, or any combination
thereof, without departing from the spirit and scope of the present
disclosure.
[0065] As described above, the first function generator 160 applies
a first function to the squared voltage values to determine a light
control signal 165, wherein the light control signal 165 is
utilised to control the amount of light that is to be output from
the light source 115. The first function implemented by the first
function generator 160 defines a relationship between the amount of
light to be output from the light source 115 and the input voltage
from the input power supply 105. One embodiment utilises a break
point type function, which produces the following outputs: [0066]
(i) 0, for voltages up to 60% of a nominal mains voltage value;
[0067] (ii) 50%, for mains voltages from 60% to 85% of the nominal
mains voltage value; and [0068] (iii) 100%, for mains voltages
greater than 85% of the nominal mains voltage value. It will be
appreciated that the actual break-points used will depend on the
particular application. Various embodiments may equally be
practised using more or fewer break-points. For example, an
alternative embodiment sets the light output to be constant for
mains voltages above 60% of the nominal mains voltage and a further
alternative embodiment sets the light output to be proportional to
the square of the mains voltage value. Alternative embodiments
utilise linear functions or exponential functions, with or without
break-points, for the first function, depending upon the particular
application. The first function generator 160 can be implemented in
hardware, firmware, software, or any combination thereof. One
embodiment implements a first function generator 160 as an analog
function using, for example, log-antilog devices or translinear
techniques. One embodiment implements a first function generator
160 that utilises a break-point type function made using
operational amplifiers type LM321 and with break-points set using
Zener diodes. A further embodiment uses digital computing
techniques.
[0069] FIGS. 2A to 2C show examples of functions that may be
utilised by the first function generator 160 for various
embodiments to control the light output of an LED lighting device
115 coupled to the power control system 110 of FIG. 1. The vertical
axis in each graph shows an intended LED light output as a
percentage of maximum output. This may alternatively refer to LED
current or LED power. The horizontal axis in each graph shows the
filtered output of the squaring module 145 in arbitrary units.
Other characteristics are possible, including smooth continuous
characteristics. Useful characteristics include those that are zero
below some specified input value and are constant above some other
input value. The three graphs shown in FIGS. 2A to 2C illustrate
this useful characteristic. While not illustrated on the graphs of
FIGS. 2A to 2C, the first function generator 160 may optionally
include features to compensate for characteristics of the power
supply to achieve the stated percentages. Where a characteristic
with a step change is used, some degree of hysteresis may also be
applied.
[0070] FIG. 2A shows a graph of a function 200 that may be utilised
by the first function generator 160. The first function 200
establishes a relationship between the light control signal 165 and
the output of the filter 155. The units of the output of the
squaring means are arbitrary. During a first period 210 when the
output of the filter 155 is less than 20, the light control signal
165 is set to 0. During a second period 215 when the output of the
filter 155 is between 20 and 40, the light control signal 165 is
set to 50. During a third period 220, when the output of the filter
155 is between 40 and 60, the light control signal 165 is set to
value between 50 and 100, based on a linear function with respect
to the output of the filter 155. During a fourth period 225, when
the output of the filter 155 is between 60 and 120, the light
control signal 165 is set to 100.
[0071] FIG. 2B shows a graph of a function 230 that may be utilised
by the first function generator 160. The function 230 establishes a
relationship between the light control signal 165 and the output of
the filter 155. The units of the output of the squaring means are
arbitrary. During a first period 235 when the output of the filter
155 is less than 20, the light control signal 165 is set to 0.
During a second period 240 when the output of the filter 155 is
between 20 and 40, the light control signal 165 is set to 50.
During a third period 245, when the output of the filter 155 is
between 60 and 120, the light control signal 165 is set to 100.
[0072] FIG. 2C shows a graph of a function 250 that may be utilised
by the first function generator 160. The function 250 establishes a
relationship between the light control signal 165 and the output of
the filter 155. The units of the output of the squaring means are
arbitrary. During a first period 255 when the output of the filter
155 is less than 20, the light control signal 165 is set to 0.
During a second period 260 when the output of the filter 155 is
between 20 and 40, the light control signal 165 is set to a value
between 50 and 100, based on a linear function with respect to the
output of the filter 155. During a third period 265, when the
output of the filter 155 is between 60 and 120, the light control
signal 165 is set to 100.
[0073] In one implementation, the power supply 190 is a switching
power supply with a shunt-type regulator functioning as the
dissipative load 120 for absorbing excess power. The power supply
190 controls consumption of power fed from the rectifier 125, such
that the instantaneous current drawn is determined by the
conductance factor 175. The power supply 190 applies power to the
lighting source 115 so that the light emitted from the lighting
source 115 is determined by the light control signal 165 output
from the first function generator 160. The power supply optionally
includes short term energy storage, which may be implemented using
reservoir capacitors or the like, so that the lighting source 115
remains continuously lit throughout the whole of the mains cycle.
Any power consumed by the power supply in excess of that required
by the lighting device 115 is lost as heat in the dissipative load
120, which in one embodiment is a Zener diode.
[0074] FIGS. 3A and 3B collectively form a schematic block diagram
of a general purpose electronic device 301 including embedded
components, upon which the power and light control methods
described herein are desirably practised. The electronic device 301
may be, for example, a railway signal lantern, a traffic signal
lantern, a guidance system, or other illumination apparatus, in
which processing resources are limited. Nevertheless, the methods
described herein may also be performed on higher-level devices such
as desktop computers, server computers, and other such devices with
significantly larger processing resources. For example, the power
and light control methods described herein may be performed on a
traffic control server that is coupled to one or more external
lighting devices. Alternatively, the power and light control
methods described herein may be performed on an embedded device
co-located with, or proximate to, a light source and forming a
traffic signal lantern.
[0075] As seen in FIG. 3A, the electronic device 301 comprises an
embedded controller 302. Accordingly, the electronic device 301 may
be referred to as an "embedded device". In the present example, the
controller 302 has a processing unit (or processor) 305 that is
bi-directionally coupled to an internal storage module 309. The
storage module 309 may be formed from non-volatile semiconductor
read only memory (ROM) 360 and semiconductor random access memory
(RAM) 370, as seen in FIG. 3B. The RAM 370 may be volatile,
non-volatile or a combination of volatile and non-volatile
memory.
[0076] The electronic device 301 optionally includes a display
controller 307, which is connected to a video display 314, such as
a liquid crystal display (LCD) panel or the like. The display
controller 307 is configured for displaying graphical images on the
video display 314 in accordance with instructions received from the
embedded controller 302, to which the display controller 307 is
connected.
[0077] The electronic device 301 also includes user input devices
313, which are typically formed by keys, a keypad, DIP switches, or
like controls. In some implementations, the user input devices 313
may include a touch sensitive panel physically associated with the
display 314 to collectively form a touch-screen. Such a
touch-screen may thus operate as one form of graphical user
interface (GUI), as opposed to a prompt or menu driven GUI
typically used with keypad-display combinations. Other forms of
user input devices may also be used, such as a microphone (not
illustrated) for voice commands or a joystick/thumb wheel (not
illustrated) for ease of navigation about menus.
[0078] As seen in FIG. 3A, the electronic device 301 also comprises
a portable memory interface 306, which is coupled to the processor
305 via a connection 319. The portable memory interface 306 allows
a complementary portable memory device 325 to be coupled to the
electronic device 301 to act as a source or destination of data or
to supplement the internal storage module 309. Examples of such
interfaces permit coupling with portable memory devices such as
Universal Serial Bus (USB) memory devices, Secure Digital (SD)
cards, Personal Computer Memory Card International Association
(PCMIA) cards, optical disks and magnetic disks.
[0079] The electronic device 301 also has a communications
interface 308 to permit coupling of the device 301 to a computer or
communications network 320 via a connection 321. The connection 321
may be wired or wireless. For example, the connection 321 may be
radio frequency or optical. An example of a wired connection
includes Ethernet. Further, an example of wireless connection
includes a Bluetooth.TM. type local interconnection, Wi-Fi
(including protocols based on the standards of the IEEE 802.11
family), Infrared Data Association (IrDa), and the like.
[0080] Typically, the electronic device 301 is configured to
perform some special function. The embedded controller 302,
possibly in conjunction with further special function components
310, is provided to perform that special function. For example,
where the device 301 is a digital camera, the components 310 may
represent a lens, focus control and image sensor of the camera.
Where the device 301 is a traffic signal lantern, the components
310 may represent a light sensor, and/or digital and analog inputs
and outputs, and/or components required for communicating with a
server or other traffic signal lanterns. The special function
components 310 are connected to the embedded controller 302. As
another example, the device 301 may be a mobile telephone handset.
In this instance, the components 310 may represent those components
required for communications in a cellular telephone environment.
Where the device 301 is a portable device, the special function
components 310 may represent a number of encoders and decoders of a
type including Joint Photographic Experts Group (JPEG), (Moving
Picture Experts Group) MPEG, MPEG-1 Audio Layer 3 (MP3), and the
like.
[0081] The methods described hereinafter may be implemented using
the embedded controller 302, wherein one or more of the processes
described herein with reference to FIG. 1, FIG. 5, and Tables 1 to
6 may be implemented as one or more software application programs
333 executable within the embedded controller 302. The electronic
device 301 of FIG. 3A implements the described methods. In
particular, with reference to FIG. 3B, the steps of the described
methods are effected by instructions in the software 333 that are
carried out within the controller 302. The software instructions
may be formed as one or more code modules, each for performing one
or more particular tasks. The software may also be divided into two
separate parts, in which a first part and the corresponding code
modules performs the described methods and a second part and the
corresponding code modules manage a user interface between the
first part and the user.
[0082] The software 333 of the embedded controller 302 is typically
stored in the non-volatile ROM 360 of the internal storage module
309. The software 333 stored in the ROM 360 can be updated when
required from a computer readable medium. The software 333 can be
loaded into and executed by the processor 305. In some instances,
the processor 305 may execute software instructions that are
located in RAM 370. Software instructions may be loaded into the
RAM 370 by the processor 305 initiating a copy of one or more code
modules from ROM 360 into RAM 370. Alternatively, the software
instructions of one or more code modules may be pre-installed in a
non-volatile region of RAM 370 by a manufacturer. After one or more
code modules have been located in RAM 370, the processor 305 may
execute software instructions of the one or more code modules.
[0083] The application program 333 is typically pre-installed and
stored in the ROM 360 by a manufacturer, prior to distribution of
the electronic device 301. However, in some instances, the
application programs 333 may be supplied to the user encoded on one
or more CD-ROM (not shown) and read via the portable memory
interface 306 of FIG. 3A prior to storage in the internal storage
module 309 or in the portable memory 325. In another alternative,
the software application program 333 may be read by the processor
305 from the network 320, or loaded into the controller 302 or the
portable storage medium 325 from other computer readable media.
Computer readable storage media refers to any non-transitory
tangible storage medium that participates in providing instructions
and/or data to the controller 302 for execution and/or processing.
Examples of such storage media include floppy disks, magnetic tape,
CD-ROM, a hard disk drive, a ROM or integrated circuit, USB memory,
a magneto-optical disk, flash memory, or a computer readable card
such as a PCMCIA card and the like, whether or not such devices are
internal or external of the device 301. Examples of transitory or
non-tangible computer readable transmission media that may also
participate in the provision of software, application programs,
instructions and/or data to the device 301 include radio or
infra-red transmission channels as well as a network connection to
another computer or networked device, and the Internet or Intranets
including e-mail transmissions and information recorded on Websites
and the like. A computer readable medium having such software or
computer program recorded on it is a computer program product.
[0084] The second part of the application programs 333 and the
corresponding code modules mentioned above may be executed to
implement one or more graphical user interfaces (GUIs) to be
rendered or otherwise represented upon the display 314 of FIG. 3A.
Through manipulation of the user input device 313 (e.g., the
keypad), a user of the device 301 and the application programs 333
may manipulate the interface in a functionally adaptable manner to
provide controlling commands and/or input to the applications
associated with the GUI(s). Other forms of functionally adaptable
user interfaces may also be implemented, such as an audio interface
utilizing speech prompts output via loudspeakers (not illustrated)
and user voice commands input via the microphone (not
illustrated).
[0085] FIG. 3B illustrates in detail the embedded controller 302
having the processor 305 for executing the application programs 333
and the internal storage 309. The internal storage 309 comprises
read only memory (ROM) 360 and random access memory (RAM) 370. The
processor 305 is able to execute the application programs 333
stored in one or both of the connected memories 360 and 370. When
the electronic device 301 is initially powered up, a system program
resident in the ROM 360 is executed. The application program 333
permanently stored in the ROM 360 is sometimes referred to as
"firmware". Execution of the firmware by the processor 305 may
fulfil various functions, including processor management, memory
management, device management, storage management and user
interface.
[0086] The processor 305 typically includes a number of functional
modules including a control unit (CU) 351, an arithmetic logic unit
(ALU) 352 and a local or internal memory comprising a set of
registers 354 which typically contain atomic data elements 356,
357, along with internal buffer or cache memory 355. One or more
internal buses 359 interconnect these functional modules. The
processor 305 typically also has one or more interfaces 358 for
communicating with external devices via system bus 381, using a
connection 361.
[0087] The application program 333 includes a sequence of
instructions 362 though 363 that may include conditional branch and
loop instructions. The program 333 may also include data, which is
used in execution of the program 333. This data may be stored as
part of the instruction or in a separate location 364 within the
ROM 360 or RAM 370.
[0088] In general, the processor 305 is given a set of
instructions, which are executed therein. This set of instructions
may be organised into blocks, which perform specific tasks or
handle specific events that occur in the electronic device 301.
Typically, the application program 333 waits for events and
subsequently executes the block of code associated with that event.
Events may be triggered in response to input from a user, via the
user input devices 313 of FIG. 3A, as detected by the processor
305. Events may also be triggered in response to other sensors and
interfaces in the electronic device 301.
[0089] The execution of a set of the instructions may require
numeric variables to be read and modified. Such numeric variables
are stored in the RAM 370. The disclosed method uses input
variables 371 that are stored in known locations 372, 373 in the
memory 370. The input variables 371 are processed to produce output
variables 377 that are stored in known locations 378, 379 in the
memory 370. Intermediate variables 374 may be stored in additional
memory locations in locations 375, 376 of the memory 370.
Alternatively, some intermediate variables may only exist in the
registers 354 of the processor 305.
[0090] The execution of a sequence of instructions is achieved in
the processor 305 by repeated application of a fetch-execute cycle.
The control unit 351 of the processor 305 maintains a register
called the program counter, which contains the address in ROM 360
or RAM 370 of the next instruction to be executed. At the start of
the fetch execute cycle, the contents of the memory address indexed
by the program counter is loaded into the control unit 351. The
instruction thus loaded controls the subsequent operation of the
processor 305, causing for example, data to be loaded from ROM
memory 360 into processor registers 354, the contents of a register
to be arithmetically combined with the contents of another
register, the contents of a register to be written to the location
stored in another register and so on. At the end of the fetch
execute cycle the program counter is updated to point to the next
instruction in the system program code. Depending on the
instruction just executed this may involve incrementing the address
contained in the program counter or loading the program counter
with a new address in order to achieve a branch operation.
[0091] Each step or sub-process in the processes of the methods
described below is associated with one or more segments of the
application program 333, and is performed by repeated execution of
a fetch-execute cycle in the processor 305 or similar programmatic
operation of other independent processor blocks in the electronic
device 301.
[0092] FIG. 4 shows a cross-section of a traffic signal lantern 400
embodying a lighting supply system in accordance with the present
disclosure. The traffic signal lantern 400 includes an input power
supply 470. The input power supply may be, for example, a mains
power supply. The traffic signal lantern also includes a printed
circuit board 430 to which are coupled a number of electronic
components 480. The electronic components 480 may include, for
example, a microprocessor, resistors, capacitors, transformers,
memory, transistors, and the like. In this example, the electronic
components 480 are utilised to implement the power control system
100 of FIG. 1. In one implementation, the components 480 include
one or more processors and memory units for implementing one or
more of the rectifier 125, the squarer 145, the filter 155, the
first function generator 160, the second function generator 170,
the multiplier 180, and the power supply 190. The power control
system implemented on the printed circuit board 480 receives the
input power supply 470 to control light output by a lighting source
450, which is also coupled to the printed circuit board 480. In
this example, the electronic components 480 include a resistive
load corresponding to the dissipative load 120 of FIG. 1.
[0093] The traffic signal lantern 400 includes a hollow structural
housing 415. An internal surface of the housing 415 defines a
cavity 405. The traffic signal lantern 400 also includes the light
source 450, which in this example is implemented using three LEDs.
Depending on the application, a plurality of LEDs may be utilised
in implementing the light source 450. The plurality of LEDs may be
arranged, for example, in a linear pattern, a rectangular array, or
any regular or irregular configuration to provide a light source
appropriate for the housing 415.
[0094] A first portion 440 of the housing 415 is opaque to visible
light and provides a reflector in the interior of the housing 415.
That is, light that is incident on the first portion 440 from
within the cavity 405 is not able to pass through the first portion
440 and that light is reflected back into the cavity 405. The
reflector may be implemented by virtue of the first portion 440
possessing a different refractive index from the cavity 405,
resulting in internal reflection within the cavity 405.
Alternatively, the first portion may provide the reflector by
virtue of a reflective coating or textured surface applied to the
interior surface of the housing 415 or within the first portion
440. In a further alternative, a reflective coating or textured
surface is applied to an exterior surface of the first portion 440
to reflect light back into the cavity 405.
[0095] The housing 415 further includes a second portion 420 that
is opaque to visible light. The second portion 420 includes a
plurality of apertures that allow light to pass from the cavity 405
on the interior of the housing 415 to the exterior of the housing
415. The second portion 420 may be implemented by using a
perforated plate. Further implementations of the second portion may
equally be practised, such as an inner surface of the second
portion 420 being screen-printed or pad-printed to realise a
predetermined arrangement of apertures. The inner surface of the
second portion 420 is optionally a reflective surface, by virtue of
the second portion 420 possessing a different refractive index from
the cavity, resulting in internal reflection within the cavity.
Alternatively, the second portion 420 may be reflective towards the
cavity 405 by virtue of a reflective coating or textured surface
applied to the interior surface of the housing 415 corresponding to
the second portion 420 or within the second portion 440. In a
further alternative, a reflective coating or textured surface is
applied to an exterior surface of the second portion 420 to reflect
light back into the cavity 405.
[0096] The traffic signal lantern 400 also includes a lens unit 410
adjacent to the second opaque portion 420. In this example, the
lens unit 410 includes a plurality of substantially spherical lens
elements, wherein each lens element is aligned with a corresponding
one of the plurality of apertures in the second portion 420. The
lens unit 410 can be coupled to the second opaque portion 420 or
alternatively the lens unit 410 and second opaque portion may be
integrally formed with one another.
[0097] As shown in FIG. 4, in this example the second portion 420
of the housing 415 and the lens unit 410 are angled slightly
downward, in the range of approximately 5 degrees to 20 degrees to
enable light emitted from the traffic signal lantern 400 to be seen
more easily by road users at street level.
[0098] The traffic signal lantern 400 further includes, in this
example, an optional baffle 460 disposed within the cavity 405. The
baffle 460 is positioned relative to the light source 450 such that
light emitted from the light source 450 is incident on at least one
surface within the housing 415 before passing through an aperture
of the second opaque portion 420. The baffle may be integrally
formed with the housing 415, such as through an injection moulding
process. Alternatively, the baffle 460 is disposed within the
cavity 405, through coupling to an internal surface of the housing
405, or some other means.
[0099] FIG. 4 shows a light trace 490 of a light photon emitted
from the light source 450. In the example shown, light emitted from
a second one of the three LEDs in the light source 450 is incident
on the baffle 460 and is reflected to be incident on the first
opaque portion 440 of the housing 415. The light 490 is reflected
to be incident on the second opaque portion 420, whereupon the
light 490 is reflected back towards the cavity 405. The light 490
is then incident on the baffle 460 before being reflected back
towards the second opaque surface 420. In this example, the light
490 passes through one of the plurality of apertures in the second
opaque portion 420 and passes through a corresponding lens element
in the lens unit 410 to be emitted to an exterior of the traffic
signal lantern 400.
[0100] As described above, various functions of the power control
system 110 may be implemented using digital computing techniques.
Such embodiments may utilise, for example, one or more computer
instructions executed by a microprocessor to perform a desired
function. Such computer instructions and microprocessor may form
part of an embedded device, as described above with reference to
FIGS. 3A and 3B and FIG. 4.
[0101] In one embodiment, the squaring module 145 is implemented
using a computer program in the form of a set of instructions
stored in a computer-readable memory for retrieval and execution on
a microprocessor. An example of suitable instructions, presented in
pseudo-code, for performing the functionality of the squaring
module 145 is presented in Table 1. If the input power supply is
non-sinusoidal, the instructions of Table 1 are executed
approximately every 200 microseconds. If the input power supply is
substantially sinusoidal, the instructions of Table 1 may be
executed less often than the non-sinusoidal case. In the sinusoidal
case, the Nyquist sampling rate is twice the mains frequency,
whereas in the non sinusoidal case a rate of 5000 samples per
second (yielding samples every 200 microseconds) is necessary to
properly sample the highest frequencies present without errors due
to aliasing.
TABLE-US-00001 TABLE 1 squarerInput = getInputSample( );
squarerOutout = squarerInput * squarerInput;
[0102] In one embodiment, the filter 155 is implemented using a
computer program in the form of a set of instructions stored in a
computer-readable memory for retrieval and execution on a
microprocessor. An example of suitable instructions, presented in
pseudo-code, for performing the functionality of the filter 155 is
presented in Table 2, wherein the functionality of the filter 155
is called "lowpassFilterFunction". The instructions of Table 2 are
executed typically whenever a new output is available from the
output of the squaring module 145.
TABLE-US-00002 TABLE 2 filterOutput =
lowpassFilterFunction(squarerOutput);
[0103] In one embodiment, the first function generator 160 is
implemented using a computer program in the form of a set of
instructions stored in a computer-readable memory for retrieval and
execution on a microprocessor. An example of suitable instructions,
presented in pseudo-code, for performing the functionality of the
first function generator 160 is presented in Table 3.
TABLE-US-00003 TABLE 3 functionGenerator160Output = 0 for
filterOutput < BreakPoint1 functionGenerator160Output = 50 for
BreakPoint 1 < filterOutput < BreakPoint2
functionGenerator160Output = 100 for filterOutput >
BreakPoint2
[0104] Computer program instructions for performing an alternative
transfer function in the first function generator 160 are shown in
Table 4, wherein a suitable interpolating function is selected for
filter output values between BreakPoint1 and BreakPoint2.
TABLE-US-00004 TABLE 4 functionGenerator160Output = 0 for
filterOutput < BreakPoint1 functionGenerator160Output = 100 for
filterOutput > BreakPoint2
[0105] In one embodiment, the second function generator 170 is
implemented using a computer program in the form of a set of
instructions stored in a computer-readable memory for retrieval and
execution on a microprocessor. An example of suitable instructions,
presented in pseudo-code, for performing the functionality of the
second function generator 170 is presented in Table 5, wherein a
function "pow" raises "filterOutput" to the power "Power". This is
a commonly available library function. A value of about -0.2 for
the constant "Power" could be chosen.
TABLE-US-00005 TABLE 5 functionGenerator170Output =
pow(filterOutput,Power)
[0106] In one embodiment, the multiplier 180 is implemented using a
computer program in the form of a set of instructions stored in a
computer-readable memory for retrieval and execution on a
microprocessor. An example of suitable instructions, presented in
pseudo-code, for performing the functionality of the multiplier 180
is presented in Table 6. The "getInputSample" function is the same
function as used in Table 1 in respect of the "squarer" function
described above. The result of the call made in the "squarer"
function and held in "squarerinput" could be used here in place of
the extra call to "getInputSample". The call is shown here
explicitly for clarity of exposition. The output from the
multiplier 180 controls the instantaneous current drawn by the
power supply 190.
TABLE-US-00006 TABLE 6 multiplierOutput = getInputSample( ) *
functionGenerator170Output;
INDUSTRIAL APPLICABILITY
[0107] The arrangements described are applicable to the electrical
power and lighting industries and particularly for the signalling
and traffic control industries.
[0108] The foregoing describes only some embodiments of the present
invention, and modifications and/or changes can be made thereto
without departing from the scope and spirit of the invention, the
embodiments being illustrative and not restrictive.
[0109] In the context of this specification, the word "comprising"
means "including principally but not necessarily solely" or
"having" or "including", and not "consisting only of". Variations
of the word "comprising", such as "comprise" and "comprises" have
correspondingly varied meanings.
* * * * *