U.S. patent number 3,816,794 [Application Number 05/353,793] was granted by the patent office on 1974-06-11 for high intensity, gas discharge lamp dimmer system.
This patent grant is currently assigned to Esquire, Inc.. Invention is credited to Carl R. Snyder.
United States Patent |
3,816,794 |
Snyder |
June 11, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
HIGH INTENSITY, GAS DISCHARGE LAMP DIMMER SYSTEM
Abstract
A dimmer circuit for a high intensity discharge lamp system that
controllably reduces the current through such lamps with consequent
reduction in illumination thereof without causing cessation in the
lamp current at any time. The circuit is controllable for changing
the rms value of the lamp current without changing the slope of the
lamp current as it goes through zero from one polarity to the
other. A triac bypasses one of two ballast elements, connected in
series, for varying the angles of conduction of the triac to
control the rms value of the lamp current. The triac is fired from
a gate source voltage in phase with line voltage, the amplitude of
the gate source voltage being controlled by a zener diode, or other
gate-signal control, device to properly time the turning on of the
triac in relation to the lamp current. The zener diode, or other
gate-signal control, device also prevents the triac from remaining
conuctve past a time when there might be opposite polarity
ballast-element voltage and lamp current.
Inventors: |
Snyder; Carl R. (Alief,
TX) |
Assignee: |
Esquire, Inc. (New York,
NY)
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Family
ID: |
26931965 |
Appl.
No.: |
05/353,793 |
Filed: |
April 23, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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238800 |
Mar 28, 1972 |
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Current U.S.
Class: |
315/194; 315/254;
315/272; 315/297; 315/195; 315/258; 315/283; 315/310 |
Current CPC
Class: |
H05B
41/3924 (20130101); G05F 1/445 (20130101) |
Current International
Class: |
G05F
1/10 (20060101); H05B 41/392 (20060101); H05B
41/39 (20060101); G05F 1/445 (20060101); H05b
041/38 () |
Field of
Search: |
;315/194,195,254,258,272,276,283,297,310,DIG.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: DeMeo; Palmer C.
Parent Case Text
This application is a continuation of application Ser. No. 238,800,
filed Mar. 28, 1972, and now abandoned.
Claims
What is claimed is:
1. In combination with a high intensity gas discharge lamp, a
dimmer circuit for controlling the brightness thereof,
comprising
ballast means connected to the lamp and connectable to an ac power
distribution line,
said ballast means including a reactor portion,
gated bypass means for providing at least partial bypass of current
around said reactor portion of said ballast means, and
controllable gate source voltage means operably connected to said
gated bypass means for controllably rendering said gated bypass
means conductive, and thereby bypassing said reactor portion of
said ballast, through a time range when the current through said
reactor portion and the voltage thereacross are of the same
polarity.
2. A dimmer as set forth in claim 1, wherein said ballast means
includes a first ballast element in series with said lamp and
wherein said reactor portion is a second ballast element in series
with said lamp.
3. A dimmer as set forth in claim 1, wherein said ballast means
includes a first ballast element in series with said lamp and said
gated bypass means and wherein said reactor portion is a second
ballast element connected in parallel with the series combination
of said gated bypass means and said first ballast element.
4. A dimmer as set forth in claim 1, wherein said gated bypass
means is a triac.
5. A dimmer as set forth in claim 1, wherein said gate source
voltage means is derived from a voltage in phase with the voltage
supplied by said ac power distribution line, and amplitude
regulated so that it cannot render said gated by-pass means
conductive when the voltage across said reactor portion is no
longer in polarity phase with the current therethrough.
6. A dimmer as set forth in claim 5 wherein said amplitude
regulation is provided by a pair of cathode-to-cathode connected
zener diodes for shifting the amplitude of the voltage in phase
with the power distribution voltage so that it reverses polarity no
later than the voltage across said reactor reverses in
polarity.
7. A dimmer as set forth in claim 1, wherein the voltage from said
gate source voltage means is derived from a voltage having a phase
leading the voltage supplied by said ac power distribution line
such that it reverses polarity no later than the voltage across
said reactor reverses polarity, thereby preventing the rendering of
said gated bypass means conductive when the voltage across said
reactor portion is no longer in polarity phase with the current
therethrough.
8. A dimmer as set forth in claim 7, wherein the ac power
distribution line is part of a three phase power system, and the
voltage from said gate source voltage means is derived from a
voltage from a voltage of a phase line of the power system leading
the voltage across said ballast means and lamp.
9. A dimmer as set forth in claim 1, and including at least one
additional ballast means and lamp connectable to the ac power
distribution line, said additional ballast means including a
reactor portion, and additional gated bypass means for providing
bypass current around said reactor portion of said additional
ballast means, said controllable gate source voltage means operably
connected to said additional gated bypass means for controllably
rendering it conductive, and thereby bypassing said reactor portion
of said additional ballast, through a time range when the current
through said reactor portion of said additional ballast and the
voltage thereacross are of the same polarity.
10. A dimmer as described in claim 1, wherein said controllable
gate voltage means includes
switch means operable when a predetermined voltage threshold value
thereof is exceeded; and
variable source voltage means connected to said switch means for
producing an amplitude controllable voltage substantially in phase
with the line voltage, the time the amplitude of the controllable
voltage reaching the threshold value of said switch means
determining the gating on of said bypass means.
11. A dimmer as described in claim 1, wherein said controllable
gate voltage means includes
switch means operable when an applied voltage reduces below a
predetermined value, the occurrence of said value being set to
occur before the voltage across the reactor portion changes
polarity with respect to the line current.
12. A dimmer as described in claim 1, wherein said controllable
gate voltage means includes
first switch means operable when a predetermined voltage threshold
value thereof is exceeded;
variable source voltage means connected to said switch means for
producing an amplitude controllable voltage substantially in phase
with the line voltage, the time the amplitude of the controllable
voltage reaching the threshold value of said switch means
determining the gating on of said bypass means; and
second switch means operably connected to said variable source
voltage means and closeably operable when the amplitude of the
controllable voltage reduces below a predetermined value, the
occurrence of said value occurring before the voltage across the
reactor portion changes polarity with respect to the line
current.
13. A dimmer as described in claim 1, wherein said controllable
gate voltage means includes
a transformer connected across the ac power distribution line;
a full wave bridge rectifier connected to the secondary of said
transformer; and
a variable resistance connected across the dc terminals of said
rectifier.
14. In combination with a plurality of high intensity gas discharge
lamps, a dimmer circuit for controlling the brightnesses thereof,
comprising
a plurality of separate ballast means connected to
each of the lamps and connectable to an ac power distribution
line,
each of said ballast means including a reactor portion,
separate gated bypass means for respectively providing bypass
current around said reactor portion of each of said plurality of
ballast means,
commonly controllable gate source voltage means operably connected
to each of said gated bypass means for controllably rendering said
gated bypass means conductive, and thereby simultaneously bypassing
said reactor portion of each of said ballasts, through a time range
when the current through said reactor portions and the voltages
thereacross are respectively of the same polarity.
15. A dimmer circuit as set forth in claim 14, wherein each of said
gate source voltage means is derived from a voltage in phase with
the voltage supplied by said ac power distribution line, and
amplitude regulated so that it cannot render said operably related
gated bypass means conductive when the voltage across said reactor
portion operably related thereto is no longer in polarity phase
with the current therethrough.
16. A dimmer as set forth in claim 15, wherein the ac power
distribution line is part of a multiphase power system, and wherein
each of said gate source voltage means is derived from a voltage in
phase with the voltage supplied by a separate phase line of the ac
power distribution system.
17. A dimmer circuit as set forth in claim 15, wherein each of said
gate source voltage means includes a gated bidirectional means
furnished with voltage in phase with the ac power distribution
line, and variable voltage control means operably connected to the
gate of said gated bidirectional means for rendering said gated
bidirectional means conductive.
18. A dimmer circuit as set forth in claim 17, wherein each of said
variable voltage control means includes a bridge driven in phase
with the ac power distribution and having dc terminals for external
connection, a variable load connected between a first and a second
of said bridges at said terminals, said remaining bridges being
connected in series at their terminals so that all of said bridges
are in series and with said variable load, the setting of said
variable load determining the output voltage for each of said
bridges for determining the time within said time range when the
output from its operably connected variable voltage control means
reaches a predetermined level for rendering its operably related
gated bidirectional means conductive.
19. A dimmer for controlling the brightness of at least one high
intensity, gas discharging lamp, comprising
first and second inductive means connected in series with said
lamp, said series combination being connectable to an ac power
distribution line;
first gated bilaterally-conductive semiconductor means connected
across said second inductive means, the timing of gate voltage
applied thereto determining the amount of current therethrough;
and
controllable gate source voltage means, including
transformer means for producing a stepped-down, controllable
voltage in phase with said line voltage;
a semiconductor, bilateral switch connected for application of said
controllable voltage, said switch closing when the amplitude of
said applied controllable voltage exceeds a predetermined
amplitude;
second grated bilaterally-conductive semiconductor means gated on
by the closing of said bilateral switch to permit passage of
current from said variable voltage control means; and
bidirectional voltage regulating means connected in series with
said second gated bilaterally-conductive semiconductor means for
maintaining a predetermined voltage thereacross when the voltage
threshold level is exceeded, the output from said voltage breakdown
means being applied as the gate voltage to said first gated
bilaterally-conductive semiconductor means.
20. A dimmer for controlling the brightness of at least one high
intensity gas discharge lamp, comprising
first and second inductive means connected in parallel to each
other and in series with said lamp, said combination being
connectable to an ac power distribution line;
first gated bilaterally-conductive semiconductor means connected in
series with said second inductive means, the timing of gate voltage
applied thereto determining the amount of current therethrough;
and
controllable gate source voltage means, including
variable voltage control means for producing a stepped-down,
controllable voltage in phase with said line voltage,
a semiconductor, bilateral switch connected for application of said
controllable voltage, said switch closing when the amplitude of
said applied controllable voltage exceeds a predetermined
amplitude,
second gated bilaterally-conductive semiconductor means gated on by
the closing of said bilateral switch to permit passage of current
from said variable voltage control means, and
bidirectional voltage regulating means connected in series with
said second gated bilaterally-conductive semiconductor means for
maintaining a predetermined voltage thereacross when the voltage
threshold level is exceeded, the output from said voltage breakdown
means being applied as the gate voltage to said first gated
bilaterally-conductive semiconductor means.
21. A dimmer for controlling the brightness of at least one high
intensity gas discharge lamp, comprising
autotransformer means connected across the lamp;
a reactor connected between the primary and secondary of said
autotransformer means,
said primary and reactor being connectable to an ac power
distribution line;
a first gated bilaterally-conductive semiconductor means connected
to at least partially bypass said reactor, the timing of gate
voltage applied thereto determining the amount of current
therethrough; and
controllable gate source voltage means, including
variable voltage control means for producing a stepped-down,
controllable voltage in phase with said line voltage,
a semiconductor, bilateral switch connected for application of said
controllable voltage, said switch closing when the amplitude of
said applied controllable voltage exceeds a predetermined
amplitude,
second gated bilaterally-conductive semiconductor means gated on by
the closing of said bilateral switch to permit passage of current
from said variable voltage control means, and
bidirectional voltage regulating means connected in series with
said second gated bilaterally-conductive semiconductor means for
maintaining a predetermined voltage thereacross when the voltage
threshold level is exceeded, the output from said voltage breakdown
means being applied as the gate voltage to said first gated
bilaterally-conductive semiconductor means.
22. In combination with a high intensity gas discharge lamp, a
dimmer circuit for controlling the brightness thereof,
comprising:
ballast means connected to the lamp and connectable to an ac power
distribution line,
said ballast means including a reactor portion,
gated bypass means for providing at least partial bypass of current
around said reactor portion of said ballast means, and
controllable gate source voltage means operably connected to said
gated bypass means for controllably rendering said gated bypass
means conductive, and thereby bypassing said reactor portion of
said ballast.
23. In combination with a high intensity gas discharge lamp, a
dimmer circuit for controlling the brightness thereof,
comprising:
ballast means connected to the lamp and connectable to an ac power
distribution line,
said ballast means including first and second reactor portions,
gated bypass means for providing at least partial bypass of current
around one of said first and second reactor portions of said
ballast means, and
controllable gate source voltage means operably connected to said
gated bypass means for controllably rendering said gated bypass
means conductive, and thereby bypassing said reactor portion of
said ballast, through a time range when the current through said
reactor portion and the voltage thereacross are of substantially
the same polarity.
Description
FIELD OF THE INVENTION
This invention relates to lamp dimming circuits and more
specifically to such dimming circuits that are uniquely applicable
to high intensity discharge lamps, such as mercury vapor lamps
having two electrode terminals and no heater.
DESCRIPTION OF THE PRIOR ART
Mercury vapor and other metallic-additive high intensity discharge
(H.I.D.) lamps have found wide-spread acceptance in lighting large
areas, such as warehouses, gymnasiums, and the like, primarily
because of their relatively high efficiency and low maintenance
when compared to incandescent lighting systems. There has been
general approval of such system for large area illumination in
spite of the fact that heretofore, there has been no satisfactory
method of reducing the illumination during periods when full
illumination has not been desired. When it is desired to reduce
illumination in an area normally lit by a high intensity discharge
lamp system, it has been necessary either to completely turn off
some of the lamps in the system or to switch to an auxiliary
incandescent or fluorescent lamp system.
Switching off some lamps and not others gives unsatisfactory
full-range control and increases the complexities of the system by
requiring additional wiring, switching equipment, etc. Having to
provide an auxiliary system likewise greatly increases the
complexities of the overall lighting system. In addition to
additional wiring and switches, additional fixtures, lamps and even
power handling equipment is required when an auxiliary system is
employed.
Heretofore, it has not been believed possible to incorporate a
dimming control system directly into a high intensity discharge
lamp network. First, it has widely been supposed that when power
consumption is reduced in a high intensity discharge lamp,
electrode sputtering would result, which would cause damage to the
environment within the lamp. Such damage would greatly reduce the
life of the lamps and also cause undesirable flickering. Second,
the existing dimming circuits for incandescent and fluorescent
lamps would extinguish a high intensity discharge lamp. This is
because such circuits actually turn off the lamps with which they
operate for short periods of time during each operating cycle.
Although this mode of operation is acceptable for incandescent and
fluorescent lamp operation, it would not be acceptable for
operation with high intensity discharge lamps. Such a lamp, once
turned off, requires a relatively long cooling period after
extinguishment before it can be restarted.
It has been discovered, however, that by employing a dimmer circuit
that does not cause off time during half cycles in lamp current,
but which is controllable for changing its rms value without
changing the time or the slope with which it goes through zero when
changing its polarity, it has been found that a practical high
intensity discharge lamp system may be dimmed. The reduction of
current through a high intensity discharge lamp can be effective in
providing dimming without damage to the lamp by bypassing current
around an accompanying ballast element and hence achieving the
reduction of lamp current for short operating periods, provided
such operation does not operate to cause current flow and a voltage
drop of opposite polarity across this accompanying ballast
element.
It is therefore a feature of this invention to provide dimming
apparatus incorporated directly as part of a metallic-additive high
intensity discharge lamp system for controllably reducing the
illumination from such lamps.
It is another feature of this invention to provide dimming
apparatus for a metallic-additive high intensity discharge lamp
system that does not shorten the life of the lamps in such system
compared to operation under full-power conditions.
SUMMARY OF THE INVENTION
A preferred embodiment of the present invention comprises, in
combination with a single high intensity discharge lamp, circuitry
operating with two ballast elements connected in series with the
lamp, the series combination being connected across a single phase
ac distribution line and power common. One of the ballast elements
is bypassed by a triac or other device. The gate terminal of this
triac is operated by a phase controllable clipped voltage that
operates the triac within predetermined time boundaries. That is,
the triac may be turned on only during periods when the reactor
voltage (voltage across the triac and the ballast element) and the
current through the lamp (and hence the ballast element and the
triac if it is conducting) are of the same polarity. Thus, a bypass
for current through the lamp is provided which continues after the
reactor voltage has changed polarity with respect to such lamp
current.
The timing of the gate firing voltage to the triac is provided by a
circuit including a second triac a bi-directional switch in the
gate circuit of this second triac, and bidirectional zener diodes
connected in series with the power terminals of the second triac.
The timing of the bidirectional switch operation is determined by a
variable resistance in series with the control voltage, in phase
with the line voltage. If the threshold value of the bidirectional
switch is reached very fast by a low resistance setting of the
resistance, then the switch, second triac and zener diodes will
turn on to provide a gate voltage to the first triac very close to
the time the lamp current crosses its zero value from one polarity
to the other. On the other hand, a high resistance setting of the
variable resistance for the gate source voltage delays the
occurrence of the switch threshold event and the subsequent
operations until a later time.
Turnoff of the gate to the first triac is provided by the excursion
of the gate signal voltage sine wave to a value below the zener
diode values. This occurs before the reactor voltage changes
polarity with respect to the lamp current. A zener diode pair in
combination with a fixable gate source voltage is especially
advantageous as a source for the gate voltage to the inductively
loaded first triac since during their respective periods of
conduction, a fixed cutoff of gate voltage can be achieved such
that no gate signal can be applied which is out of phase with lamp
current.
The sequencing of this bypass means around one of the ballast
elements maintains a non-injurious phase relationship between
current and voltage for lamp operation.
The control for the gate source voltage may be isolated from the
high voltage distribution line as a safety feature via transformer
connections and the variable control may be a simple
potentiometer.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above-recited features, advantages
and objects of the invention, as well as others which will become
apparent, are attained and can be understood in detail, more
particular description of the invention briefly summarized above
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings, which drawings form a part of
this specification. It is to be noted, however, that the appended
drawings illustrate only typical embodiments of the invention and
are therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
In the drawings:
FIG. 1 is a schematic diagram of a preferred embodiment of dimming
apparatus in accordance with the present invention.
FIG. 2 is a waveform diagram showing the amplitude and phase
relationships existing in the lamp voltage and the range of bright
and dim currents of the circuit shown in FIG. 1.
FIG. 2a is a waveform diagram illustrating relative currents to
achieve full and dim conditions.
FIG. 2b is a waveform diagram illustrating summing of currents to
achieve an intermediate current value between full and dim.
FIG. 3 is a schematic illustration of an alternative circuit for
producing gate source voltage.
FIG. 4 is a waveform diagram showing the amplitude and phase
relationships existing in various important voltages and currents
of the circuit shown in FIG. 1.
FIG. 5 is a lumens versus time diagram of a typical lamp operation,
showing the effects of operation in conjunction with the circuit of
FIG. 1.
FIG. 6 is a wattage versus time diagram of a typical lamp
operation, showing the effects of operation in conjunction with the
circuit of FIG. 1.
FIG. 7 is a schematic diagram of a preferred embodiment of the
invention connected in a three-phase power distribution system,
with single element control.
FIG. 8 is a partial schematic diagram showing the connection of
multiple lamp fixtures in a single control system in accordance
with the present invention.
FIG. 9 is a partial schematic diagram showing the employment of
parallel ballast inductors connected in series with a high
intensity discharge lamp.
FIG. 10 is a partial schematic diagram of a high reactance
autotransformer ballast, including a series - connected dimmer
reactor therewith and its bypass triac.
DESCRIPTION OF PREFERRED EMBODIMENTS
Now referring to the drawings and first to FIG. 1, high intensity
discharge lamp 10 is connected in series with two inductive ballast
elements 12 and 14, the entire combination being connected between
line 16 and common 18. Gated bypass means in the form of triac 20
is connected across element 14, main terminal one 22 of the triac
being connected to the line and main terminal two 24 being
connected to a junction point between the two elements. Gate
terminal 26 is connected to resistor 28 and is connected to fuse
29, which is connected with gate fuse 30 and in multiple with the
gate connection of other lamp and ballast circuits. A power factor
correction capacitor 32 is connected from line to common across the
entire combination just described.
When triac 20 is conducting to form a complete bypass around
element 14, a maximum amount of current (designated "full lamp
current" in FIGS. 2 and 4) flows through lamp 10. On the other
hand, when triac 20 is not conducting, then the minimum amount of
current flows through lamp 10, as indicated by "dim lamp current"
curve in FIGS. 2 and 4. By allowing triac 20 to conduct for part of
the cycle as shown by the dash lines in FIG. 2, then the current
through lamp 10, and, hence the illumination therefrom, may be
varied between the dim lamp current and full lamp current values. A
short period of conduction by triac 20 creates a curve 101, a
little longer conduction period like curve 103 and still longer
period like curve 105. It is apparent, therefore, that merely
controlling the period of triac 20 conduction will achieve
controllable illumination of the lamp 10.
Control of the conduction of triac 20 is accomplished by the
controllable gate voltage means connected to gate fuse 30. To
understand the operation of this circuit, some additional phase
relationships have to be appreciated, which can best be shown by
referring to FIG. 4. The voltage across element 14 ("reactor
voltage") is leading the lamp current by approximately 85.degree.
and is also leading the "line voltage" by approximately
30.degree..
It is readily apparent that triac 20 should not be rendered
conductive until the current through and the voltage across element
14 are both of the same polarity, either both positive or both
negative. Considering the positive polarity cycles, the current
through element 14 does not go positive until point 107. At this
time, the reactor voltage is already positive. At point 109, the
reactor voltage goes negative, although the current through
indicator 14 is still positive. The range 111 of time over which a
gate voltage may be applied is hence determined as being the time
between points 107 and 109.
It is again well known that the gate pulse to a triac controlling
an inductive load is desirably a continuously applied gate voltage,
rather than an instantaneous spiked pulse. Again referring to FIG.
1, bidirectional voltage regulating means in the form of
cathode-to-cathode zener diodes 33 and 34 are connected to gate
fuse 30. Connected in series with zener diodes 33 and 34 are main
terminals one and two of triac 36, the entire combination being
connected through components discussed hereinafter to line 16 via a
secondary 38 of power transformer 40. Capacitor 44 is provided for
transient suppression. It is readily apparent that the gate voltage
has for its source from secondary 38 a voltage which is in phase
with line voltage 16. This voltage is labelled "gate source
voltage" on FIG. 4.
Connected to the gate terminal of triac 36 is a semiconductor,
bilateral switch 42, which has very low forward voltage drop on the
order of one volt when a predetermined threshold is exceeded in
either polarity. Bilateral switch 42 is a part of a conventional
double time constant control circuit including capacitors 45 and 46
and resistor 48. This control circuit is of the type manufactured
and sold by RCA under manufacturer's designation AN 3697. Its input
is derived from the secondary of a transformer 50. Transformer 50
is supplied controlled voltage via secondary 54 of power
transformer 40 and its related components. Hence, the voltage
supplied to the control circuit is in phase with the line
voltage.
In operation, when the threshold of switch 42 is exceeded by the
application of the control voltage from secondary 54 and its
related components, a gate is supplied to triac 36 to cause
conduction thereof. Triac 36 conducts when the gate source voltage
exceeds the zener diode voltage of zener diodes 33 and 34. Such a
voltage provides an ample gate drive for triggering gate 26 of
triac 20.
Referring now to FIG. 2a, there is shown a waveform illustrating
summing of current taken at points I.sub.1 (through reactor 14) and
I.sub.2 (through triac 20) in FIG. 1. If triac 20 is not gated on,
No. I.sub.2 current flows and the only current flow through the
lamp (I.sub.T) is I.sub.1. This is reflected as the "dim state". On
the other hand, if triac 20 is gated on during the entire time,
then the entire current is bypassed around reactor 14 and through
triac 20. Hence, I.sub.1 becomes essentially zero and I.sub.T
equals I.sub.2, as shown by the full on state curve.
If traic 20 is gated on to an angle .theta. following the
occurrence when current through the lamp becomes positive, a triac
current I.sub.2 will be generated which is added to reactor current
I.sub.1, as shown in FIGS. 2 and 2b. At the same time, current
I.sub.1 that had been rising assumes essentially a steady state
I.sub.1a, until the time that triac 20 is no longer conducting.
Hence, current I.sub.T relative to time is equal to I.sub.1 before
the triac is fired, then equal to I.sub.2 plus I.sub.1a while the
triac is conductive, and then is equal to I.sub.1 again after triac
20 commutates.
As shown in FIG. 4, it is necessary that the gate voltage is
prevented from continuing past the gate cutoff point. Although the
gate voltage may be readily controlled by zener clipping as
indicated above and as illustrated in FIG. 4, it is deemed within
the scope of the present invention to provide other appropriate
circuit means for controlling the gate voltage to prevent voltage
past the gate cutoff point from energizing the triac. One such
means may conveniently take the form of a "Y" connected power
source circuit, as illustrated in FIG. 3. It may be observed that
lamp 10 and ballast elements 12 and 14 are connected in series
between two of the lines of the "Y", namely, L.sub.1 and L.sub.2.
As with the circuit shown in FIG. 1, element 14 is bypassed by
triac 20 having a gate resistor 28 and a fuse 29. Fuse 29 is
connected to the gate connection lead, which may be connected to
parallel lamp and ballast connections as with the other
embodiments. This connection is also connected to a network 80 in
leg L.sub.1 of the "Y". Network 80 may be identical to the circuit
shown in FIG. 1 from transformer 40 through fuse 30 that is
connected to the gate connection of the circuit, except there are
no zener diodes 33 and 34 in network 80. For convenience, capacitor
44 is shown separately connected, although it is really a part of
network 80. The secondary of the transformer in network 80 in leg
L.sub.1 of the "Y" provides a voltage which leads the voltage from
L.sub.1 to L.sub.2 by 30.degree.. By employing this voltage as a
gate source voltage for gating on triac 20, clipping of the voltage
becomes unnecessary. Other appropriate circuits may be provided
within the scope of this invention to produce a gate source voltage
that appropriately leads the line voltage, which may be some angle
other than 30.degree.. By selecting the time and amplitude of the
gate source voltage it is possible to eliminate clipping.
Once conduction of triac 20 is started, the gate source voltage
must return to zero before the reactor voltage reverses polarity.
This is accomplished in the circuit shown in FIG. 1 by the zener
diodes cutting off when the gate source voltage applied thereto
falls below a predetermined value, as shown in FIG. 4. Again a
voltage leading the line voltage by approximately 30.degree. may be
used for the gate source voltage thereby eliminating the zener
diodes 33 and 34.
The setting of the turn on time of triacs 36 and 20 is accomplished
by the setting of resistor 52, a variable potentiometer connected
between secondary 54 of transformer 40 and the primary of
transformer 50. The time of turn on is determined when the
amplitude of the voltage applied to switch 42 reaches its turn on,
or breakdown, value.
The turn off point of the zener diodes does not vary. It is
apparent, however, that the shutting off of the zener diodes and
hence the gate voltage to triac 20 does not instantaneously render
triac 20 nonconductive. The inductance of elements 12 and 14 causes
current to continue through triac 20 until the current commutates.
The current through lamp 10, after such commutation, is only
current through reactor 14 as illustrated in FIGS. 2, 2a, 2b and
4.
There are several operational characteristics of metallic-additive
high intensity discharge lamps that prevent heated cathode
fluorescent lamp dimmer circuits from being employed therewith,
although some instant start fluorescent lamp dimmer circuits may
have some applicability to such lamps. For example, with the rapid
start fluorescent lamps employing heaters, it is not necessary to
consider possible extinguishment of the lamp. Even with the
so-called instant start fluorescent lamps not employing heaters,
low pressure operation is such that they still do not have the
stability problems of the high intensity discharge lamps. If the
lamp is extinguished momentarily because of current reversal, the
fluorescent lamps relights whereas the high intensity discharge
lamp must cool to reduce pressure before it may relight. Hence, the
critical timing problem between lamp current and reactor voltage,
while still permitting the current amplitude to vary, is unique
with the high intensity discharge lamp application.
It has been shown in tests that lamp electrode sputtering
occasioned by low current, and hence low arc tube pressure, will
not occur when the dimmer circuitry of the present invention it
utilized, and hence there will be no deleterious effects to the
lamps.
Actual performance characteristics using the circuit hereinabove
described have been measured, resulting in the curves shown in
FIGS. 5 and 6. The bottom curve shown in FIG. 6 shows the gradual
increase in lumens and wattage when the lamp is turned on in the
dim state. The lumens reach a steady state value of about 2 percent
and the wattage reaches a steady state value of about 10
percent.
With a high intensity dischage lamp operating at full rated value,
turning the lamp to its dimmest operation results in a reduction in
lumens to about 20 percent (reduction in watts to less than 30
percent). As the lamp cools further, the voltage across the lamp
gradually decreases with an accompanying decrease in lumens and
wattage. Twenty minutes after being placed on full dim, the lumen
value decreases to about two percent of initial lumen value and the
wattage reduces to about 10 percent of full wattage.
Turning the lamp to full power after stabilization at full dim
shows the lamp instantaneously jumps to above 30 percent of lumens
(20 percent of wattage) and within four minutes was at full value
of lumens and wattage. For comparison, a cold lamp does not
instantaneously rise to 30 percent of lumens, but as shown in FIG.
5 does so only after about two-three minutes.
FIG. 7 shows a connection of the control circuit in a three-phase
power distribution system. Lines L.sub.1, L.sub.2 and L.sub.3
designate respective lines of the three-phase system, each line
being connected to a separate power transformer 210, 212 and 214.
The remainder of each respective control circuit is similar to that
shown in FIG. 1 for a single phase system with the exception of the
control network for changing the amplitude of the control voltages
firing individual diacs 42a, 42b and 42c.
For example, in the first phase network, a secondary of transformer
210 is connected to an ac terminal of full wave bridge rectifier
216 comprising diodes 218, 220, 222 and 224. Bridge 216, and
bridges 228 and 230, is commercially available as a single
component, but for clarity of connection and operation, the four
diodes comprising the bridge is illustrated. The other ac terminal
of bridge rectifier 216 is connected to isolation transformer 226.
In like manner, a full wave bridge rectifier 228 is connected in
the second phase network and a full wave rectifier 230 is connected
in the third phase network.
The dc terminals of bridges 216, 228 and 230 are connected in
additive series, the series combination being connected in series
with a limiting resistor 232 and a variable resistor 234. It is
apparent that changing the value of resistor 234 changes the
voltages across each transformer 226 and the corresponding
transformers 236 and 238 in the second and third phase networks.
Hence, by a single variable resistance control, dimming is effected
in each of the three phases. It may also be noted that the control
potentiometer may be located remotely from the other components in
the control network. Of course, if desired, each of the phases may
be separately controlled in the manner described above for the
circuit shown in FIG. 1.
Finally, it may be noted that each of the phases shown in FIG. 7
may be connected to a series of fixtures in the maner shown in FIG.
8. Each lamp 310, 312 and 314 has associated therewith its own
series connected ballast elements, a gated triac bypassing one of
the ballast elements, and a power factor correcting capacitor.
Power factor capacitors have the same function in the dimmer
circuit application as they do in connection with conventional
gaseous-discharge lanp ballasts (it is not uncommon for power
factor capacitors to be built internally with the ballast
elements). For example, the power factor equals approximately 90
percent when the lamps are full on. As the power to the lamps is
decreased, the inductive volt/ampere relationship is modified while
the capactive volt/ampere relationship remains the same. This
causes the power factor to go from approximately 90 percent lag to
approximately 50 percent lead although under no condition will the
line current exceed the normal operating line current with the
lamps full on. The same control simultaneously provides gate
control to each of the bypass triacs 20 thereby dim each lamp in
the multiple connection.
As an alternative to the use of series related reactors or ballasts
as illustrated in FIGS. 1 and 8, it may be convenient to connect
the ballast reactor elements in parallel for the purpose of
modifying the inductive devices of the circuit or to limit the
required current carrying capacity of the triac. For example, as
illustrated in FIG. 9, reactors or ballasts 320 and 321 are shown
to be connected in parallel across the line and common conductors
and are disposed in series with a gaseous-discharge lamp 322. A
power factor capacitor 323 bridges the ballast-lamp
combination.
Ballast 321 is connected in series with a triac 324 having a gate
terminal 325 connected to the gate conductor. A current limiting
resistor 326 is disposed in the gate terminal lead for the purpose
of limiting application of current to the gate terminal of the
triac.
If the multiple connection arrangement as illustrated in FIGS. 1
and 8, which may be referred to for convenience as the "series"
connection, are used, reactor or ballast element 12 would carry the
full lamp current and would be a standard ballast for a given lamp
and line voltage. Triac 20 would carry full lamp current when the
dimmer was full on. Triac 20 would have voltage blocking
requirements determined by the ratio of the impedance of reactors
12 and 14.
As indicated, reactor or ballast element 12 must be capable of
carrying the entire lamp current. Because the series-related
ballast element 14 is bypassed upon triggering of a triac 20,
ballast element 12 may be expected to be of heavier construction
than that of ballast element 14, which, at least for much of the
time does not carry full lamp current. For example, for operation
in dimmer circuitry for a conventional high intensity
gaseous-discharge lamp, identified at 10, it may be necessary for
the greater current carrying ballast element 12 to be of 90-ohm
value (1440 volt amps) while the impedance value of the ballast
element 14 may be on the order of 245 ohms (550 volt amps). The
90-ohm ballast would obviously be of much more expensive nature
than the 245-ohm ballast.
If the multiple connection arrangement as illustrated in FIG. 9,
which may be referred to as the "parallel" connection, is used,
reactor 320 would carry dim current and reactor 321 would carry the
remaining current for full operation. Hence, neither would have to
be as large as standard ballasts. Triac 324 would only carry the
current through reactor 321, but would be required to block full
line voltage.
In ballast design, the more critical design parameter is normally
the current-carrying capacity of the elements. Hence, it may be
seen that the ballast arrangement in the dimmer system may be
altered to provide a more economical arrangement without
sacrificing efficiency.
Finally, yet another ballast arrangement is illustrated in FIG. 10.
In this arrangement, high intensity discharge lamp 410 is connected
across high reactance autotransformer ballast 412 and a
series-connected dimmer reactor 414 is connected between the two
segments, primary 413 and secondary reactance 411, of the
autotransformer. The junction between this dimmer reactor 414 and
primary 413 of the autotransformer is connected to the line. A
triac 420 bypasses the dimmer reactor, the gate connection thereof
being connected to the gate voltage source as with the previous
embodiments. A power factor correcting capacitor is connected
across the primary winding.
In operation with triac 420 rendered non-conductive, line voltage
is applied to secondary 411 of the autotransformer via its primary
413 and via reactor 414. When triac 420 is rendered conductive for
short periods of time as previously discussed, current in the
secondary of the autotransformer is increased as reactor 414 is
bypassed, thereby increasing the current through lamp 410, as with
the other embodiments. When the gate source voltage is removed from
triac 420, the impedance of reactor 414 and secondary reactance 411
sustains conduction of triac 420, again in the manner illustrated
for the other embodiments in FIGS. 2 and 4.
While particular embodiments of the invention have been shown and
discussed, it will be understood that the invention is not limited
thereto, since many modifications may be made and will become
apparent to those skilled in the art.
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