Note: Descriptions are shown in the official language in which they were submitted.
B~CKGRO~ND 0~ T~IE INVENTION
Eield of the Invention
.. . _
This invention relates to lamp control circuits fo~
high intensity discharge lamps, such as mercury vapor lamps,
having two electrode termlnals and no heater. More specifi-
cally, the invention is directed toward programmable digital
lamp control systems.
DescriJption of the Prior Ar.t
Probably the simplest control circuit for a lighting
system consists of a switch placed in the power line to the
entire light system. A user turns on the switch to receive
full illumination and turns off the switch to extinguish all
lighting. It is o~ten desirable, however, to provide for
adjustable control of a lighting system to account Eor differ~
ent uses requirin~ di~ferent lighting levels. A school gymna-
sium, for exarnple, does not require as much lighting when
`; used for a banquet as during an athletic event. Furthermore,
in recent years, concern has developed over the energy con-
sumption of systems using electrical power. Therefore, it
has become increasingly desirable to satisfy lighting require-
ments while achi~ving a minimum amount of energy consumption.
One way in which to improve a lighting system is to
switch the power to each lamp in the system independently,
thereby providing a greater degree of control over the illumi-
nation levels which may be selected. Such a control system
may work quite well in applications involvlng a limited amount
of space, such as in a relatively small area which requires
~3-
L
.
only a small number of lamps. Individual switchiny, however,
is not practical when applied to larger commercial or indus-
trial installations. The extra wiring required can become
unduly expensive and, in addition, it woul~ be unrealistic
to expect the users of a large lighted area to take full
advantage of the potential of an individually s~itched lamp
system, since the time consuming manual switchiny which
would be required would soon become unduly burdensome.
Low voltage lighting control systems have been developed
which reduce the expense of installing a multiplicity of indi-
vidually switched lamp units and make such an alternative
more practical Eor larger applications. Low voltage control,
however, adds only a limlted amount of ~lexibility to a
lighting system. Each lighting unit must be either supplied
with full power or turned off. Thus a level of brightness
fallin~ between these extremes cannot be selected with such
systems.
In res~onse to the need for a ~reater range of control
over a lighting system, dimmer circuits have been developed.
Dimming circuits adapted for use with incandescent and fluo-
rescent liqhting systems are well known in the art. In
addition, a practical dimming circuit which may be used for
dim~ing high intensity gas discharge lamps has been invented.
Such a dimming system is disclosed in U.S. Patent No.
3,~16,7~4, entitled "~ligh Intensity Gas Discharge Lamp Dimmer
System", and, in improved form, in [).S. Patent No. 3,B94,265,
entitled "~igh Int~nsity Lamp Dimming Circuit", both assigned
to the same assignee as the present application. This system
allo~s for the selective reduction of current through a high
h~
intensity discharge lamp to provide dlmminy without damaye
to the lamp, by bypassing current around an accompanying bal-
last element and thereby achieving a reduction o~ the lamp
current for part of a half-cycle of the power cycle.
The use of dimming systems allows a lighting system to
be made much more adaptable to the particular lighting re-
~uirements to be fulfilledO Consequently, energy savings
can be realized through precisely adjusting the light power
to the minimum level required for acceptable illumination.
In addition, with a number of dimming units a lighting system
may be arranged to provide the optimum light intensity and
directional lighting pattern for each point within the lighted
area. Additional flexibility may be achieved with multiple
dimming controls at remote locations. Such a system, for
exampl~, which i5 designed for use with a high intensity gas
discharge lighting system, is disclosed in U. S. patent No.
4,144,478 granted March 13, 1979, entitled "Lamp System Take
Control Dimming Circuit", assigned to the same assignee as the
present application.
Even when using dimming controls, however, the extent
to which a lighting system can be adjusting to varying needs
is limited. As the size of the system increases, for example,
a practical limit is imposed on the number of dimming circuits
which can be utilized. As with individually switched lighting
units, it becomes impractical to effectively utilize individ-
ually dimmed lamps on a large scale. Furthermore, the re-
quirement for manually adjusting a lighting system may become
inconvenient in a large scale operation.
.~
In addition, other control parameters may be desirable
in a lighting system. ~ ~ore efficient system may be real-
ized, if dayligt~t i~ available to illuminate an area during
certain times of the day. A device which is responsive to
light, such as a photocell, could be incorporated into the
system to automatically extinguish some or all of the arti-
ficial light at times when the natural li~ht provides suffi-
cient illumination. Many other useful automatic inputs can
be envisioned. ~ 24 hour timer, for example, could auto-
matically and reliably reduce lighting levels at times whenregular lighting is normally not required.
The possibilities for more efficient and versatile con-
trol of electrical systems have expanded in recent years
with the availability of relatively inexpensive digital elec-
tronics. tlodern technology enables the production of micro-
processors which contain a large number of logic devices,
yet occupy a small amount of space. Such devices are also
becoming increasingly in~xpensive. A microprocessor can be
equipped witll a memory unit to perform a larye number of con-
trol tasks. Furthermore, such digital device~ may be readilyand conveniently reprogrammed, maki~ them highly adaptable
to chanying conditions~ One example of the application of
such a microprocessor to a liyhting control system may be
found in an article by McGowan and Feiker, entitled "A New
Approach To Lighting System Control", in the Journal of the
Illuminating Engin~ering Svciety, October, 1976, at page 3~.
It is therefore a eature o this invention to provide
a programmable dimmer control system for high intensity dis-
charge lamps.
z~
It is also a feature of this invention to provide a pro-
grammable dimmer control system which may be readily and eco-
nomically adapted to automatically contr~l any desired number
of lamps individually.
It is another feature of this invention to provide a
dimmer control system or a high intensity discharge light
ing system which may be easily reprogrammed to suit changing
needs in the lighted area.
It is another feature of this invention to provide a
programmabl~e dimmer control system which will accept inputs
from a variety of control sources.
It is yet another feature of this invention to provide
a programmable dimmer control system for high intensity dis-
charge lamps in which the gate source voltage for the dimmer
circuit is controlled by a digital logic component.
.
SIJI'IIIARY OF T~IE INVENTION
~ lamp control system for a high intensity gas discharge
lighting system includes a ballast means, with a reactor por-
tion, connected to a lamp. A gated~b~pass means is provided
for bypassing the reactor portion of the ballast. A detector
senses each zero voltage crossing point of the AC power and
synchronizes a digital processor, which provides a phase
delayed lamp control si~nal to the gated bypass meansO
In a preferred embodiment, the digital processor is a
microprocessor operating in conjunction with a read only
memory. The memory operates in conjunction with control
inputs to the microprocessor to enable the microproce.ssor to
z~s
compute appropriate phase delayed lamp control signals for
each lamp.
single digital processor may be utilized to control a
plurality o~ individual lamps through a gated bypass circuit
for each lamp.
BRIEF DESCRIPTION OF THE DRAWINGS
.. . . . . . . . . .. .... ..
In order to further describe the features, advantages,
and objects of the lnvention~ particular embodimen~s are
illustrated in the appended drawings, which form a part of
this- specification. It should be noted, however, that these
drawings illustrate only ty~ical embodiments of the invention
and thereEore should not be considered to iimit its scope, as
the inventive concept may be expressed in other equally effec-
tive embodiments.
.. .
In the drawings:
Figure 1 is a block diagram of a preferred embodiment of
a high intensity gas discharge lamp control system in accord-
ance with the present invention. ~
Figure 2 is a schematic diagram showing one embodiment
o~ a dimmer circuit for a high lntensity discharge lamp which
may be used with the present inven~ion.
Figure 3 is a wave form diagram illustrating the ampli-
tude and phase relationships be~ween certain voltages and
currents in the dimmer circuit shown in Figure 2.
. , .
--8--
DESCRIPTION C)F T~IE PREFERRED EME3ODI~1ENT
Referrillg to the drawings, and first to Figure 1, hi911
intensity discharge lamps 10 are connected to an AC power
line 12 through individual dimmer circuits 14. The dimmer
circuits 14 receive control signals from a microprocessor 16
through a digital driver 20. Microprocessor 16, which is
is sychronized to the pha~e of the AC power line by a zero
crossing detector 18, sends a synchronized control signal
to each dimmer circuit 14. The appropriate dimming signal
for each individual dimmer circuit is selected according
to a program provided by a preprogrammed read only memory
unit 22 in conjunction with any number of inputs, such as
inputs 24, 26, and 28.
The read only memory unit 22 provides the microprocessor
with a preselected program, enabling the microprocessor to
provide the apyroyriate light level for each lamp when a
given set of conditions, as indicated by one or more input
signals~ is received. The manual override input 24 typically
is a keyboard input allowing manual selection of individual
light levels for each lamp, or selec~lon of a preprogrammed
lighting pattern such as, for example, a work day lighting
pattern for an office, or a night time pattern at reduced
levels for a cleanup crew. Other inputs, such as inputs 26
and 28, may be used to provide automatic control. ~he signals
from such inputs may be utilized to adjust the lic3hting level
according to a particular time of the day or week, or ~o acl~
just the lighting level according to natural light ~vailable,
or may be inputs ~rom any number o~ other control sources.
$~
Now refe~ring to Figure 2, a schematic o~ a xero crossing
detection circuit 18 which may be u~ilized with the present
invention is illustrated, connected through microprocessor
16 to a dimming circuit 14 used with the present invention.
Those skilled in the art will recognize that a single dimming
circuit for one hi~h intensi~y discharge lamp is shown, while
one such dimming circuit i~ provided for each lamp in a
lighting system, as illustrated in Figure 1. TransEormer
io steps down the power line voltage, which is connected
across the-primary winding of transformer 30. ~he stepped
down voltage from the secondary of t-ransformer 30 is full
wave rectified by bridge rectiEier 32. This rectified voltage
is then applied to monostable multivibra~or 34, which employs
a Schmitt trig~er input.
One such multivibrator which may be utilized in this
invention is the Texas Instruments No. 74121. The value~ -
of the timing resistor 36 and the timing capacitor 38 are
appropriately selected to adjust the output of the multi-
vibrator 14 to the appropriate pulse width. The output
from monostable multivibrator 34 is applied as an input,
throuyh line 40, to the microprocessor. rrhe snicroprocessor,
by using this reerence timing pulse from the power line,
provides a phase delayed control signal which adjusts the
lamp current for the desired level o~ brightness.
Now referring to the dimming circuit 14 in Firgure 2,
a high intensity discharge lamp 10 is connected ~n series
with two inductive ballast elements 42 and 4~, the entire
series being connected across power lines 46 and 4~. ~ gated
bypass means is provided eor balla~ element 44 in the form
-10
of triac 50. The gate source voltage for triac 50 is 5Up-
plied to the gate terminal 52 of the triac by the secondary
of transformer 54 whith shunt resistor 56 being connected
across the secondary leads of transformer 54. A capacitor
58 and a resistor 60 are connected in series between the
first and second main terminals of the triac 50 and act as
a snub~er device, to prevent the triac 50 from exhibiting
false turn on due to commutatin~ dv/dt. The gate source
voltage turn on si~nal is received at the primary of trans- ;
former 54 from the microprocessor 16, throu~h resistor S2.
The operation of this dimming circuitry may be more fully
understood by reference to Figure 3, which illustrates the
phase relationships of the dimming circuitry. When triac 50
is conducting, a complete bypass around element 42 is achieved
with a maximum amount o~ current, desiqnated "Full Lamp
Currentn, ~lowing through lamp 10. Conversely, when triac
50 is not conducting, a minimum amount of current flows
through lamp 10, as indicated ~y the "Dim Lamp Current"
curve shown in Figure 3~ By allowing triac 50 to conduct
or part of the power cycler the currellt through lamp 10,
and hence the illumination ~herefro~ may be varied between
the dim lamp current and full lamp current values. Such
an intermediate current value i5 also indicated in Figure 3.
It is apparent, therefore, that merely controlling the period
of conduction of the triac 50 will also control the illumi-
nation level provided by lamp 10.
Triac 50 should not be rendered conductive until the
current throu~h and ~he voltage across element 42 are both
of the same polarity. If triac 50 were rendered conductive
when the voltage across element 42 ~nd the current there-
through were not of the same polariky, a phenomenon known
as "hal~ cycle conduction" would occur. In such a situation,
the lamp would appear to flash from dim to full bright
each half cycle, and would produce an irritating strobe
effect to the eye that would also be harmful to the lamp.
Considering the polarity cycles indicated in Figure 3,
the current through element 42 does not go positive until
point 6~. At this time, the reactor voltage is already
positive. At point 66, the reactor voltage goes negative,
although the current through the inductive element 42 is
still positive. The gate range 68 of time over which ~he
gate voltage may be applied is hence determined to be that
time lying between points 64 and 66.
The operation of the dimming circuitry described and
illustrated herein is similar to that disclosed in U. S.
Patent No. 3 r 894,265, entitled "High Intensity Lamp Dimming
Circuit", assigned to the same assignee as the present appli-
cation. For a more complete description of the operation
of such dimming circuitry, the above patent should be
consulted.
Referring now to the operation of the microprocessor
16, each time the microprocessor receives a reference timing
pulse from the zero crossing detector circuitry, an interrupt
routine is accomplished. In conjunction with data obtained
from the various inputs to the microprocessor, the read
only memory supplies a program se~uence which enables khe
microprocessor to compute an appropriate di~lming signal.
-12-
.~
The microprocessor then transmits a gate source voltage slgnal
to triac 50, which is thereby sufficientl~ delayed in phase
to provide the appropriate current level to the high intensity
discharge lamp 10. In this manner, the microproces50r con-
trols the brightness level at which the lamp is operating.
The microprocessor used in thi~ invention may be any
suitable s~andard model available. For example, one embodi-
ment of this invention has been constructed using the Motorola
MEK6800D2 evaluation k~t, including the MC6800 microproce~so~
unit. ~ sample program which has been used in this embodiment
of the inven~ion is listed în Table ~. This program set~
the data lines to func~ion as outpu~ lines, readies the
microprocessor to wait for an interrupt, and initializes the
microprocessor registers.
TABLE 1
LDA A ., I~
FF
STA A EXT Causes the data line on the B
side to function a~ outputs
~0
20 06
LDA A IMM Enables the interrupt by a
low to high transition on
the interrupt control line
07
STA A EXT
07
LDS IMM Sets the stack pointer
00
30. FF
LDX IMM Clears the index register
00
QO
01
CLI Clears the interrupt m~rk
NOP
NOP Wait~ for the interrupt
BRA
FC
The program in Table I is used in conjunction with an
interrupt service routine, which is set out in Table II.
The interrupt routine delays the gate signal by a predeter~
mined incremellt of time with respect to the zero crossing
of the line voltage, controls the gate signal pulse width,
and readies the microprocessor to await another interrupt,
TABLE I I
CLR A
STA A DIR Clears index register
FC
STA A DI~
FD
LDA B EXT Clears the interrupt flag
oE the PIA control register
06
LDA B IMM
EF
AND B DI~
F9
00
STA B EXT Clears the interrupt mask
of the CCR
F9
STA A DIR
FE
LDA A IMM
32
STA ~ DIR
FF
~TI
32 INX
CPX DIR Compares the index register
to memory location bo
bo
BNE REL
Fb
: LDA A IMM
FF
STA A ~x~r Set~ the output lin~s Otl
the B side
06
INC ~XT
00
B2
-14-
~$~
LU~ A IMM
Q5 Determines the gate signal
pulse wid~h
Sus A DIR
b2
~NE
F7
CLR A
STA A DIR
STA A ~XT Clears the output lines
on the B side
06
NOP
NOP Wai ts for an interrupt
BRA
FC
A microprocessor is an e~specially advantageous addition
to a lighting control system~ A single microprocessor is
capable of controlling a large number of lamps individually,
and thus a single microprocessor system, ~s here disclosed,
may be used to control the entire lighting system for a
large area,.t?r even to control an entire building's lighting
systems. Furthermore, once such a system is installed, any
alterations necessitated by changing lighting requirements
can be incorporated very simply. To modify the control se-
quence, a read only memory is programmed to meet the new
requirements, and the newly proyramln`è~ read only memory
simply replaces the memory unit previously installed in the
system~ In this fashion, any changes, however extensive,
can be readily incorporated into the lighting system. Thus,
for example, if a building is remodeled, such a lighting sys-
tem would not thereby be outdated. Once installed, the system
remains easily adaptable to meét changint3 lit3hting needs,
while conserving a ma~imum amount of energy anc3 thereby
effectint3 savings in operatiny costs.
-15-
While particular embodiments of this invention have been
shown and discussed, it will be understood that the inverltion
is not limited thereto, since many modifications may be made
and will become apparent to tho~e skilled in the art~
For example, although one zero cros5ing detecting cir-
cuit has been illustrated, any number of other circuits which
are capable of establishing a reference timing pulse from the
AC power line can ~e used as well. For example, a phase-
locked-loop can be locked to the line frequency and used to
provide timing pulses.
It should also be noted that many other inputs may be
provided to the microprocessor or obtaining the desired con-
trol of lighting in a given situation. In some areas, for
example, electric utility users are subject to a demand pen-
alty, which imposes a hiyher rate for electricity when the
user's consumption of electricity exceeds a certain rate.
In such a situation, the microproces50r could be programmec]
to monitor electrical consumption and automatically reduce
lighting levels should tha~ consumption approach the penalty
rate.
-16-
