Note: Descriptions are shown in the official language in which they were submitted.
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AN ARC LAMP LIGHTING UNIT
WITH LOW AND HI~H LIGHT LEVELS
sACKGROUND OF THE INVENTION
1. Field of the Invention:
_
The present invention relates to a lighting unit
which has low and high ligh-t levels and is energized
from a conventional ac source. The lighting unit uses
an arc lamp as its principal source of light.
The arc lamp is supplemented by a standby filamentary
lamp to provide light during starting of the arc lamp and
to provide low light levels.
2. Descrip~ion of the Prior Art:
The present invention deals with a lighting unit in
which the principal source of light is a high pressure
discharge lamp having up to six times the efficiency of
an incandescent lamp. High pressure metal vapor lamps
have been available for some time in high power units.
Recently, as disclosed in U.S. Patent 4,161,672 issued
July 17, 1979 to Cap and Lake, entitled "High Pressure
Metal Vapor Discharge Lamps of Improved Efficiency" and
assigned to the present assignee, smaller low wattage
metal halide lamps with eEficiencies approaching those
of the larger size have been invented. Such lamps are
an energy efficient replacement for the incandescent lamp.
The power supply of the present lighting unit employs
a high frequency power supply in which a ferrite trans-
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former controlled for non-saturated operation, a
transistor switch and a trigger oscillator are the
principal components. High and low settings of the
lighting unit are achieved by having the low light level
provided by an incandescent element and the high light
level provided by an arc lamp. It is of course desirable
that the lighting unit be usuable in a conventional socket
as well as a three-way socket.
SUMl!IARY OF THE INVENTION
It is an object of the present invention to provide
an improved lighting unit employing an arc lamp and
having a low and a high light level setting.
It is a further object of the invention to provide
an improved lighting unit in which an arc lamp provides
high illumination and an incandescent lamp provides low
illumination.
It is still another object of the present invention
to provide an improved lighting unit using an arc lamp
suitable for use in a three-way socket and having suc-
cessively low, high and low brightness settings, oralternatively low, high and high brightness levels.
These and other objects of the invention are
achieved in a lighting unit having three terminals for
selective connection to an ac supply, and including a
rectifier bridge having a pair of ac input terminals and
a pair of dc output terminals, with a first filter
capac~tor being connected across the dc output terminals.
The lighting unit further includes a main arc lamp
connected in a series path between a node and the common
bridge output terminal or ground, and a resistive filament
connected in a series path between the positive bridge
output terminal and the node. In the low light level
setting, the filament provides low level illumination.
In the high light level setting, the filament provides
standby illumination during starting of the arc lamp
and also provides ballasting action during operation of
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the arc lamp.
The lighting unit further includes an electrical
transformer having a primary winding connected in a
series path between the positive bridge output terminal
and the node and a second winding connected in a series
path between the node and the lamp anode; a first diode
connected in the series path between the first node and
the lamp anode in a polarity to conduct main lamp current
through the filament and in shunt with the second winding
for rectifying transformed potentials; a monostable,
normally nonconductive, solid state switch comprising a
first transistor connected in a series path between the
first node and ground, intermittent operation of the
switch developing a pulsating current in the filament
for standby illumination, an alternating potential in
the primary winding, and a transformed alternating
potential in the second winding, rectified by the first
diode and coupled to the anode of the main lamp for
starting; a rectifier device such as an SCR or a transistor
or a diode connecting the first node to the lighting unit
third terminal in a polarity to allow half-wave con-
duction through the rectifier bridge and the filament for
filamentary illumination in the low setting, and means
to maintain the solid state switch in a nonconductive
state in the low setting.
In a preferred form, a trigger oscillator is provided
responsive to the electrical state of the main lamp for
causing intermittent switch operation for starti~g the
main lamp, comprising a second transistor in an oscil-
latory configuration, a resistive voltage divider seriallyconnected between the node and ground, and a lamp
current sensing resistance connected between the lamp
cathode and ground. The base of the second transistor
is connected to a lower tap on the voltage divider for
sensing the voltage across the arc lamp and the emitter
of the second transistor is connected to the arc lamp
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current sensing resistance.
When the rectifier device is a diode, the preferred
means for maintaining the solid state switch in a
nonconductive state during low light level settings
functions by maintaining the trigger oscillator in a
non-oscillatory condition. Included are several diodes,
resistors, and a second capacitor. A second diode has
its cathode coupled to the third lighting unit terminal
and its anode connected to the positive terminal of a
second capacitor, the negative terminal being grounded.
A third diode has its cathode connected to the anode of
the second diode, and its cathode coupled to an upper
tap on the voltage divider. These components prevent the
trigger oscillator from operating during the low setting~
A second resistance is provided coupled between the
first node and the second capacitor for charging the
second capacitor to a value which reversely biases the
second diode and decouples the second capacitor from the
voltage divider during the high light level setting. This
permits immediate response to line transients during normal
lamp operation, undelayed by the second capacitor.
A third resistance is provided shunting the second
capacitor, selected to sustain a reverse bias on the third
diode during normal operation and to reduce the voltage
stresses on the second capacitor in the high setting.
A serially connected pair of diodes is provided between
the dc output terminals of the bridge, with the diode in-
terconnection being connected to the lighting unit third
terminal. This provides protection from transients on
the line, when only the first and third lighting unit
terminals are connected to the ac supply, and also
protection from starting current surges when the lighting
unit is first turned on.
The lighting unit so far described may be connected
to a three-way socket with the first terminal of the light-
ing unit going to the screw base, the` second lighti~g unit
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terminal going to the eyelet of the soc~et, and the
third lighting unit terminal going to the ring contact
in the socket. When so connected, the lighting unit will
provide successively low, high and low light level settings.
S When the aforesaid rectifier device is an SCR, the
preferred means for maintaining the solid state switch
in a non-conductive state during the low light level
setting functions by preventing sufficient voltage to
develop on the filter capacitor to operate the trigger
oscillator. With this use of an SCR, the lighting unit
will provide successively low, high, and high light level
settings.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel and distinctive features of the invention
are set forth in the claims appended to the present
application. The invention itself, however, together
with further objects and advantages thereof may best be
understood by reference to the following description and
accompanying drawings in which:
Figure 1 is an illustration of a novel lighting unit
having a low and a high illumination setting, suitable for
connection to a standard or a three-way lamp socket and
using an arc lamp source during the high setting and a
filamentary light source during the low setting;
Figure 2A is an electrical circuit diagram of the
lighting unit incorporating a compact power supply unit
and including the connections of the lighting unit into
a three-way socket;
Figure 2B is a table of switch and lamp conditions
when the novel lighting unit employed in a three-way
socket and exhibits a low, high, low light level sequence;
Figure 3 is a ferrite transformer forming an essential
element of the power supply unit;
Figure 4A is an electrical circuit diagram of an
alternative embodiment of the invention; and
Figure 4B is a table of switch and lamp conditions
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for the circuit of Figure 4A.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring now to Figure l, a novel lighting unit for
operation from a conventional low frequency (50-60 Hz)
alternating current power source is shown. The lighting
unit comprises a lamp assembly which produces light and
a power supply unit which supplies electrical power to
the lamp assembly. The lighting unit has two levels of
illumination, high and low, provided by a "three-way"
switch in the lamp socket. The lamp assembly includes
a glass enclosure 9 which contains a high efficiency arc
lamp ll and a resistive filament 12 for both ballasting
and light production. The power supply unit includes a
rigid case 10 attached to the glass enclosure and a screw-
in "three-way" plug l~. The plug 14 is a conventional
"three-way" plug normally used with a light having three
levels of illumination. The plug has three points for
connection including a screw base 6, a ring 7 and an
eyelet 8. The plug provides both electrical connection
and mechanical attachment of the lighting unit to a
conventional three-way lamp socket.
The power supply unit supplies the energization for
both filament and arc lamp. During the high setting,
the power supply unit develops the required energization
for the main arc lamp during starting and operating
conditions and provides immunity to certain line
transients. l~lso during the high setting, the power
supply unit provides power for supplemental filamentary
light production but only when needed during starting.
During the low setting, the power unit supplies power for
light production by the filament on a continuous basis
and supplies no power to the main arc lamp.
The filament and arc lamps are individually asso-
eiated with the low and high light levels respectively
except during starting in the high setting when both are
involved in light produetion. The low light level is
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provided by the ~ilamentary light source, and the high
light level is provided by the arc lamp. In the low
setting, the arc lamp is off and light is produced by
the filament alone. In the high light level setting,
the lighting unit may be switched on, restarted, or
turned off with the same immediate production of light
as an incandescent element. During the periods that
it may take for the arc lamp to reach full brightness
after a cold start or the longer periods required for a
hot restart, supplemental incandescent illumination is
provided by the filamentary light source.
The disposition of the elements of the lamp assembly
are best seen in Figure l. The arc lamp ll, and the 60
watt filament 12 are all installed inside the single large
glass envelope 9. The elements 11 and 12 are supported
on leads sealed into the base of the lamp assembly. The
gas filling the envelope 9 is an inert gas suitable for a
conventional incandescent lamp. The arc lamp 11 is
shown with the positive electrode or anode down (near
to the base) and the negative electrode or cathode up
(remote from the base). The two electrodes are in turn
sealed into the ends of a small quartz vessel whose outer
contour is cylindrical except for a small central region
of larger cross section, of less than 1/2" in diamter.
~5 The interior of the arc lamp, which is not specifically
illustrated, contains a spherical or elliptical central
chamber filled with an ionizable mixture: argon, an
ionizable starting gas, mercury, which is vaporized when
hot, and a vaporizable metal salt such as sodium and
scandium iodides. When operating, an arc is formed between
the elctrodes which creates illumination throughout the
chamber. Small, low power lamps of the type just
described are referred to as metal halide or metal vapor
lamps. A suitable lamp is more fully described in the
earlier cited U.S. Patent 4,161,672.
During normal final run operation the power supplied
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to the arc lamp is dc having some low frequency (50-60
Hz) ripple. In s~arting or restarting, the power supplied
to the arc lamp and the filament has substantial high
frequency content and means are provided for preventing
prolonged starting, such as might occur when arc lamp
failure precludes ignition.
The arc lamp exhibits several distinct states in
conventional use and each active state requires distinct
energization. From a practical viewpoint, the arc lamp
has three essentially active states denominated Phases
I- III and an inactive state.
In Phase I, "ignition" occurs. The duration of
ignition should be no longer than a second or two and is
often much shorter. It is the time required for a suit-
ably high voltage to cause "electrical breakdown" of thegas contained in the arc lamp to initiate a falling
maximum lamp voltage. This latter condition is also
referred to as the establishment of a "glow discharge".
Phase II - the glow to arc transition - extends
from one-tenth of a second to perhaps two seconds and
is characterized by a more sustained ionization level
and a lower maximum voltage. As Phase II begins, the
discharge is typically unstable, swinging between a
maximum and a minimum value, with the voltage of the
discharge falling continuously toward a lower maximum with
a recurring minimum near 15 volts. As the average level
of gas conduction increases, the maximum lamp voltage
falls, the consumed power increases, and the temperatures
inside the lamp also increase. As the maximum arc voltage
falls through values near 200-400 volts, a more substantial
energy (typically 2-4 watts) is required by a metal vapor
lamp.
Phase III begins with the establishment of the "arc"
which occurs when a portion of the cathode has reached
thermionic emission temperature. At the marked trans-
ition from Phase II to Phase III, the voltage of the
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discharge loses its unstable quality and holds to an
initial value of about 15 volts. In Phase III, a
sustained low lamp impedance is exhibited, and current
limiting is required to prevent excessive heating. At
the beginning of Phase III, the lamp dissipation is set
to be between 10 and 15 watts and significant light
production starts.
The warm-up period, which is the initial portion
of Phase III, normally lasts from 30 - 45 seconds.
During the warm-up period, the lamp reaches full operating
temperature and the contained gases reach their high,
final operating pressures. The voltage across the lamp
increases to a value of typically 87 volts with an
accompanying reduction in lamp conductance. When the
final run condition occurs, the lamp absorbs the maximum
power (typically 32 watts) and the maximum light output
is produced.
The pre-ignition period is a variable period having
a nominal minimum value of zero at standard ambient
conditions and a maximum value between 45 seconds and 4
minutes if there has been a failure of the arc and a hot
restart is required. If the lamp is de-energized in the
course of normal operation, the lamp will be at an
elevated temperature and at a high gas pressure for a
short while. To restrike the arc when the lamp is hot,
the potential required may be in excess of an order of
magnitude more than for a cold start (e.g., 10-30 KV).
The thermal time constants of the lamp are such that the
time required for cooling from a hot operating condition
to the point where a conventional (1-2KV) voltage will
restrike an arc may be from 45 seconds to 4 minutes.
Supplemental incandescent illumination is particularly
important during the longer warm-up and pre-ignition
periods, but in the interests of steady illumination,
supplemental incandenscent illumination is provided
through the shorter periods (ignition and the glow to arc
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transition) as well.
Suitable operating power for the arc lamp and the
standby light producing filament is provided by the power
supply illustrated with the lamp socket assembly in
Figure 2A.
The lighting unit whose electrical circuit diagram
is illustrated in Figure 2A, has as its principal
components the arc lamp 11, the filamentary lamp 12,
a dc power supply (14, 15, 16) for converting the 120
volt 60 Hz ac to dc, and an operating network (23-52) for
converting electrical energy supplied by the dc power
supply into the forms required for operation of the lamp
assembly~ The lamp socket assembly, whose wiring is
illustrated in Figure 2A, includes a three-way switch 13
(switch components 18-22), a lamp socket 17 and suitable
means for connection to a 120 volt ac supply.
The lamp socket assembly is conventional. The black
lead from the ac supply is connected to the stationary
contact 18 of the three-way switch to the left of the
rotor member 20 (as seen in Figure 2A). The white lead
from the ac supply is connected to the screw base of
the socket 17 where it makes contact with the screw base
6 in the lighting unit plug 14. The stationary contact
positioned on the right side of the rotor member is
connected by a red lead to the socket contact which
makes contact with the ring 7 of the lighting unit
plug. The stationary contact 21, positioned beneath
the rotor motor member is connected to the socket contact,
which makes con~act with the eyelet 8 of the lighting
unit plug. The rotor member 20 is seen to be a generally
rectangular member, approximately square in cross-section,
to three sides of which a continuous conductor 22 is
applied. Dependent on rotation, the rotor member makes
selective contact with the stationary contacts 18, 19 and
21. In accordance with the table illustrated in Figure
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2B, the switch provides a four position sequence. In
the first position, the uncontacted surface of the rotor
member abuts the stationary contact 18 to the black lead
of the ac supply and the lighting unit is off. Assuming
counter-clockwise rotation to the second position
(the illustrated position) the rotor member 22 connects
the stationary contacts 18 and 19 together, and the
black ac supply lead is connected to the ring 7 of the
lighting unit plug. In the third position, the rotor 22
contacts the stationary contacts 18 and 21 together, and
the black ac supply lead is connected to the eyelet 8 of
the plug. In the fourth position, the rotor member 22
connects all three stationary contacts together, and the
black ac supply lead is connected to the ring 7 and the
eyelet 8 of the plug. From this it may be seen that the
lower input terminal of the diode bridge is at all times
coupled to the white ac supply lead, while the upper
input terminal of the diode bridge and third input ter-
minal of the lighting unit (ring 7) are separately or
jointly connected to the black ac supply lead in
accordance with the table illustrated in Figure 2B.
The dc power supply circuit of the lighting unit is
conventional comprising a bridge rectifier 15 and a
filter capacitor 16. Energy is supplied from a 120 volt
60 hertz ac source via the plug 14 to the ac input
terminals of a full wave rectifier bridge 16 in positions
3 and 4 as described above.
The positive output terminal of the bridge becomes
the positive output terminal of the dc supply and the
; negative output terminal of the bridge becomes the
common "ground" or reference output terminal of the dc
supply. The filter capacitor 16 is connected across the
output terminals of the bridge to reduce ac ripple.
The output of the dc power supply during final run
operation of the arc lamp 11 at the high setting is 145
volts at about 1/2 amperes current, producing an output
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power of approximately 50 watts of which 32 watts is
expended in the lamp. In the high setting, the power
required of the dc power supply by the lighting unit
during a hot restart is approximately 60 watts and the
maximum required during warm-up of the arc lamp is
approximately 75 watts. ~n the low settings, power is
supplied to the filament only, using the bridge 15 in a
half wave rectification mode. With half wave rectification,
the conventional 60 watt filament produces a dissipation
of about 38 watts.
The operating network, which derives its power from
the dc supply, and in turn supplies energy to the lamp
assembly, comprises the elements 23-25 connected together
as follows. The filamentary light source 12, diode 23,
arc lamp 11 and lamp current sensing resistance 24 are
serially connected in the order recited between the
positive terminal and the common terminal of the dc supply.
The diode 23, which is poled for easy current flow from
the dc source to the arc lamp, has its anode coupled to
the node 26 and its cathode coupled to one terminal of the
arc lamp 11. The arc lamp, which has a required polariza-
tion, has its anode coupled to the cathode of the diode
23 and its cathode coupled to one terminal of the current
sensing resistance 24.
Continuing with a description of the operating
network, a triggered monostable solid state switch is
provided, constituted of a power transistor 27, a step-
up transformer 28, and components 29, 30. The power
transistor has base, emitter and collector electrodes.
The step-up transformer has a ferrite core for high
frequency operation (> 20 Khz), a main primary winding
31, a main second winding 32, a primary control winding
33 and a secondary control winding 34, all associated
with the core. The control windings provide a transistor
conduction control whose sense is responsive to the
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magnetic state of the ferrite core and produce monostable
action, avoiding full core saturation. The main primary
winding 31 has its undotted terminal coupled through the
capacitor 35 to the positive dc supply terminal and its
dotted terminal connected to the node 26. The main
second winding of transformer 28 has its undotted terminal
connected through the capacitor 36 to the anode of the
arc lamp 11. The emitter of the power transistor is
coupled to the unmarked terminal of the primary control
winding 33. The marked terminal of the primary control
winding 33 is connected to the cathode o~ the arc lamp
11. The base of the power transistor is coupled to the
cathode of a clamping diode 29, whose anode is coupled
through resistance 30 to the common dc terminal. The
secondary control winding 34 has its unmarked terminal
connected to the emitter. The base of transistor 27 is
the point for application of a trigger pulse for initia-
ting each conduction cycle.
The triggering oscillator which recurrently turns
on the solid state switch is a second portion of the
operating network. The trigger oscillator is turned on
and off and also shifted in frequency in response to
electrical conditions attributable to the electrical
state of the arc lamp. The trigger oscillator is also
responsive to the temperature of the switching transistor,
thus preventing prolonged triggering in the event of arc
lamp failure. The trigger oscillator transistor 37 has
its emitter coupled to the emitter of transistor 27, its
base coupled through the capacitor 38 to the base of
transistor 27, and its collector serially connected
through the resistance 39 and positive temperature
coefficient resistance 40 to the node 26. A voltage
sensing voltage divider (41, 42, 43) is provided
consisting of resistances 41, 42 serially connected
between node 26 and the base of transistor 37 and resistance
43 connected between the base of transistor 37 and the
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common source terminal. During warm-up and final run
operation, both dc states of the lighting unit (in the
high setting), the diode 23 is forward biased, and the
divider output voltage, at the base of transistor 37,
is a direct measure of the lamp voltage. During the high
frequency states of the lighting unit (in the high light
level setting, the diode 23 is reversely biased when
power is delivered to the lamp, so that the voltage on
the voltage divider reflects the loading effect of the
arc lamp upon the transformer circuit and is an indirect
measure of the lamp voltage. The connection of the
emitter of transistor 37 to the non-referenced terminal
of the resistor 24 in series with the arc lamp 11, makes
the trigger oscil~lator responsive to lamp current in the
form of the voltage proportional to the lamp current
developed in resistance 24. The trigger oscillator is
connected to respond in the manner noted above to the
different in sensed voltages.
The positive temperature coefficient resistor 40
(thermistor), the subject of Canadian Application
3G3,l84 filed Oc~o~er~4, ~9~ by Peil and McFadyen,
entitled "An Arc Lamp Lighting Unit With Means to Prevent
Prolonged Application of Starting Potentials" and
assigned to the present assignee, locks out the trigger
oscillator if starting is unduly prolonged, thermally
latching the transistor 37 in a low gain, moderate current
saturation mode. The thermistor 40 is in thermal contact
with the power transistor 27 and experiences a resistance
increase of several orders of magnitude with the abnormal
heat rise arising from unduly prolonged starting. The
increase in collector resistance produced by the thermistor
reduces the gain of the transistor 37, stopping the
generation of trigger pulses and forcing the transistor
into saturation. The saturation current level is sufficient
for self-heating to maintain the thermistor in its high
resistance state and thermally latch out the trigger
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35-EL-1507
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oscillator.
The dimming circuit, which supplies power to the
filament 12 during dimmed operation and which prevents
high fre~uency operation of the operating network during
dimmed operation, is the last portion of the operating
network. In Figure 2A, it comprises the components 45
through 52 not previously characterized, and connects
into the operating network at the node 26, the dc common
terminal, the ring contact 7 of the plug 14 and the
connection between voltage divider resistances 41 and
42 of the trigger oscillator.
The dimming network is completed by the elements 46
through 52, which, among other functions, prevent high
frequency operation of the operating network during
both low settings by preventing operation of the trigger
oscillator. The remaining elements of the dimming circuit
are specifically the diodes 46, 47, 48 and 52, the
capacitor 49 and the resistances 50 and 51. The cathode
of the diode 46 is connected to the ring contact 7 of
the plug 14 and also to the cathode of the diode 45.
The anode of the diode 46 is coupled to the cathode of
the diode 47 whose anode is connected to the intercon-
nection between voltage di~ider resistances 41 and 42
of the trigger oscillator. A resistance 50 is provided
between the node 26 and the interconnection between diodes
46 and 47. The capacitor 49 is connected between the
interconnection between diodes 46 and 47 and the dc
common terminal. The resistance 51 shunts the capacitor
49. The diodes 52 and 4B are serially connected across
the terminals of the capacitor 16. The cathode of diode
52 is connected to the positive capacitor terminal.
The anode of diode 59 is connected to both the ring contact
7 of the plug 14 and the cathode of diode 48. The anode
of diode 48 is connected to the negative terminal of
capacitor 16.
In both low settings, hal~-wave power is supplied to
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35-EL 1507
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the filament 12 along a current path including a branch
of the bridge 15 and a diode 45. More particularly,
with the switch 13 in the first low setting, a current
path is provided serially from the white lead (which is
un~cwitched and connected on one side of the ac supply)
to the screw base of the socket 17, the screw base 6 of
the plug 14,to the lower input terminal of the bridge 15.
The current path continues through ~he diode in the lower
right position of the bridge 15 from the anode to the
cathode to the unreferenced or positive dc output
terminal of the bridge, and through the filament 12 to the
node 26. The diode 45, which has its anode coupled to the
node 26 and its cathode coupled to the ring contact 7 of
the plug permits half-wave conduction in the sense just
described. The current path continues from the cathode
of diode 45 via the plug and socket ring contacts, the red
lead, the stationary contact 19, the rotary contact 22,
and the stationary contact 18. Finally, the contact 18
leads to the black lead which is connected to the other
side of the ac supply completing the current path.
In the second low setting, an additional contact
is made through switch 13 from the black lead to the
upper input terminal of the bxidge while a switched
contact of the black lead to the acthode of diode 45 and
an unswitched contact from the white ac supply lead to
the lower input terminal of the bridge continue as before.
As in the first low setting, the filament receives power
by half wave conduction through diode 45.
In both low settings, the capacitor 16 is supplied
with current on a full wave rectification basis. In
the first low setting, diodes 48, 52, 55 and 56 comprise
a bridge which charges capacitor 16 to the peak ac input
potential. In the high position, diodes 53, 54, 55 and
56 perform the bridge rectification function. In the
second low setting/ all six diodes are used with diode 52
paralleling 54 and diode 48 paralleling 53, since the
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35-EL-1507
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eyelet terminal 8 is connected to the ring terminal 7.
The dimming networX prevents trigger oscillator
operation in the first low setting in the following
manner. The wave~orm appearing at the node 26 is a
succession of negative going half waves, shifted
upward so that the negative tips of this waveform are
at approximately ground potential and the cut-off tops
of the waveform have a positive voltage of approximately
160 volts. As the ring 7 goes negative and the screw
base 6 goes positive, the active bridge diode and diode
45 conduct. Since they are of low impedance in relation
to the impedance of the filament, the principal voltage
drop occurs across the filament and the voltage at the
node connected terminal of the filament approaches zero.
At the same time, the negative swing of the ring 7 causes
the diodes 46 and 47 to conduct, drawing the upper tap
on the base connected voltage divider 41, 42, 43 toward
ground. This reduces the charge on the capacitor 49 to
near ground potential. At the same time the diode 47,
which connects the capacitor to the upper tap of the
voltage divider 41, 42, 43, clamps the potential at the
upper tap to a near zero potential insuring cut-off of
the oscillator transistor. During the second half cycle,
when the voltage on the ring becomes positive with
respect to that on the screw base, the diode 45 is back-
biased and the node 26 reaches its maximum positive value
(+160 volts). During this half cycle the diode 46 leading
to the capacitor 49 is also back-biased, precluding
charging of the capacitor by that path. On the other hand,
the presence of the positive potential on the node 26 and
the resistive paths presented by resistor 50 and resistor
41 (which acts through diode 47) permit charging, and a
resulting gradual increase in the voltage across the
capacitor 49. The charging time constant is set suf-
ficiently long to insure continued cut-off of the
oscillator transistor 37 throughout the half cycle. With
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35-EL-1507
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the indicated values, the voltage on the capacitor
increases to 16 volts, while the voltage on the upper
tap increases to the same value plus a diode drop. The
voltage at the lower tap connected to the base electrode
is the ~oltage at the upper tap divided by a ratio of 1
to 30 established by the resistances 43 and 42, re-
spectively. Thus, the voltage remains less than
approximately a half volt for the entire cycle and
insufficient to forward bias the transistor 37. When the
next negative swing occurs, the diodes 46, 47 again
become conductive discharging the capacitor 49 to near
zero and repeating the cycle just described. In the
second low setting, the process is essentially as
described above. With the indicated values, cut-off is
maintained and the trigger oscillator remains inactive,
and as a consequence, the switching transistor 27 remains
in the normal nonconductive state.
The suppression of trigger oscillations is accomplished
without adverse effect upon operation of the lughting unit
in the high setting. In other words, the oscillation
suppression circuit has no adverse effect upon starting
or restarting or upon the arc maintenance function
providing immunity of the arc to power line transients.
Non-interference is achieved without the need for costly
mechanical or electrical switching devices and requires
no more than the simple circuit elements herein described.
The prevention of interference is achieved primarily by
the diode 47 which is maintained reversely biased and
thus decouples the capacitor 49 from the base voltage
divider during all significant modes of operation in the
high setting. When the power is first turned on in the
high setting, the capacitor 49 is at an initially low
voltage and will initially prevent the trigger oscillator
from coming into operation. The capacitor, however, charges
quickly, typically in 50 milliseconds, to a value allow-
ing the trigger oscillator to commence oscillation. In
~ 5~ 35-EL-1507
-- 19 --
the remainder of the starting process, when trigger
pulses are being recurrently generated and the transistor
switch 27 is switching recurrently, the node 26 alternates
between a high positive potential and a near zero potential.
The eapacitor 49 will charge through resistance 50, and at
times through resistance 41 to an average value dependent
on the duty cycle but less than the peak value appearing
at the node 2~. The diode 47 thus isolates the capacitor
49 from the node during the time the switching transistor
is on and a portion of the time that the transistor switch
is off and at a voltage not yet exceeding that stored on
the capacitor 49. This isolation and the large size of the
resistances 50 and 41 in the charging oaths reduee the
eurrent flow into the eapaeitor 49 so that there is no
signifieant reduetion in power for starting the arc lamp.
The eireuit also has no signifieant effect upon the
operating frequency of the arc lamp since the repetition
frequeney is determined primarily by the low (lK)
resistanee 43 and the eapaeitor 38. Assuming that the
are lamp has reached a normal final run voltage producing
approximately 90 volts at the node 26, the capacitor will
eharge to a value set by the ratio between resistances
50, 51, i.e. one-third that value or 30 volts, permitting
the use of a relatively inexpensive 50 volt electrolytic
eapaeitor.
The arc maintenance feature is unaffected by trigger
suppression eircuitry The voltage on eapaeitor 49 sets
the voltage on the eathode of diode 47. At the same time,
the anode of the diode 47 is eonneeted to a similar tap
on the voltage divider eireuit 41, 42. At this tap the
devision ratio is one-fifth the voltage at the node 26
and assuming that the node is at 90 voltsi the diode is
reversely biased at approximately 12 volts throughout the
run mode. Thus, should the voltage change on
the voltage divider or the eurrent in the are
lamp, the input bias on the trigger oscillator
s~
35--EL--1507
-- 20 --
transistor 37 remains unaffected by the presence of the
capacitor 49 or the other components used to suppress
trigger oscillations. In short, the arc maintenance
feature is unimpaired.
The pair of diodes 48 and 5Z are provided to protect
the lighting unit from both high voltage transients and
starting surges primarily in the first low position.
Transient protection in the high and second low position
results from the presence of the bridge and the capacitor
16. The diodes 52 and 53 shunt the filter capacitor 16
and their interconnection point is led to the ring 7, as
earlier described. The protection is primarily for the
times that the switch is in the second position, but due
v to contact problems may also be present in the ~ourth
position if the eyelet contact is poor.
The principle of the protection is to discharge any
line surges harmlessly through a low impedance diode into
the 50 microfarad capacitor 16. The diode 52 protects
against positive going surges on the ring coupling the
surge into the capacitor 16 via its positive terminal.
The diode 48 protects in a similar way from negative
going line transients, by coupling the surge into the
capacitor 16 via its negative terminal. Inexpensive diodes
have quite large current capacities and with a large
capacitor to absorbe the charge, any significant current
or voltage transients prevented from being applied to
other elements of the circuit.
Protection against starting surges is provided by
the diode 48 which is shown connected between the ring
and the common dc supply terminal. If one were to remove
the line transient protection feature from the present
embodiment for cost reasons,,diode 48 should still exist
in the position shown in Figure 2A or at the node 26 to
preveni node 26 from going negative during the start-up
surge. (The second embodiment to be described with
reference to Figure 4A similarly lacks measures ~or line
;~ 5 ~
- 21 - 35-EL-1507
transient protection.) An adverse consequence of -the
node 26 going negative is the application of a reverse
voltage on the small 2.2 microfarad capacitor 49 and
excessive current flow in the output junction of the
transistor 27. The condition causing the node to go
negative occurs when the lighting unit is first turned
on, normally in the first low setting. The critical
period is the first instant after turn-on, as the
capacitor 16 begins to charge to a positive value.
The surge current is determined by the ac line impedance,
the series junction elements and the 2 ohm resistance
24 in series across the ac line. ~ maximum surge of 50
amperes might be expected but a value of 10 amperes is
more typical in view of the other series elements.
Assuming a 10 ampere surge, the voltage drop across the
2 ohm resistance would be 20 volts negative with respect
to circuit ground (in the absence of diode 48). This
voltage minus the collector base forward drop of
transistor 27 would appear at node 26. Since diodes
45 to 46 are also conducting, this voltage would also
appear across capacitor 49. Thus, the presence of diode
48 (in either position) prevents the node 26 from going
negative and in turn the normally positive electrode
of the capacitor 49 from going negative. By its
presence, the diode 48 eliminates the need for an ac
tolerant capacitor and permits a relatively low voltage,
electrolytic capacitor as earlier described.
With respect to the transistor 27, the diode 48
(in either position) protects it from the same heavy surge
current that occurs when the capacitor 16 is first being
charged. Commencing with the reference terminal or ground,
the path for current through the transistor may be regarded
as continuing through resistance 24, windings 33, 34, base
and collector respectively of transistor 27, the node 26,
diode 45, in and out of the plug and socket connection to
ring 7 and base 6 (where the 120 volt ac generator is
~3~5~
35-EL-1507
- 22 -
inserted) the fuse, the lower right diode in the bridge
15, the positive terminal of capacitor 16, whose other
terminal is grounded, -to complete the circuit. The
diode 38, either connected between ground and the ring 7
(with diode 45 conducting) or between the node 26 and
ground, is poled in the same direction as the output
junction of transistor 27 and connected in parallel with
the portion of the circuit just described which includes
the 2 ohm resistance 24, windings 33 and 34, base and
collector respectively of transistor 27. Initially, when
the node 26 goes negative with the initial surge of current
into the capacitor 16, most of the current as between
transistor 27 and diode 48 will be drawn by the transistor
since its junction area is massive in relation to that of
the diode 48 and since at lower currents, the effect of
the voltage drop in the 2 ohm resistor 24 is negligible
in diverting the surge current into the diode 48. As
the current surge increases, the voltage of the drop
occasioned by the resistor 24 added to that of the trans-
istor output junction will exceed the junction drop ofthe smaller diode 48. As this occurs, a major portion of
any surge current will be diverted into the diode 48 and
diverted away from the output junction of the transistor
27, saving the latter from high current stressing. A
relatively low cost diode can withstand surges in the
tens of amperes without harmful effect and thus it effect-
ively protects the transistor, which is must less
tolerant of such surges.
In going to the second low setting from the high
setting it is necessary to turn off the arc tube. This
is accomplished by diode 45 (when the ring terminal 7
goes negative) stealing the current from the arc tube
for a long enough period to extinguish it and by diode 47
which steals base current from the oscillator transistor
37, thus disabling the transient catch feature which
would otherwise try to keep the arc tube ionized.
~IL~t~3~95~
35-EL-1507
- 23 -
Figure 4A is similar to Figure 2A except for the
dimming circuit. In Figure 4A the dimming circuit
comprises components 60 through 63, which are connected
into the circuit at node 26, transistor 27, and the ring
contact 7 and eyelet contact 8. The silicon controlled
rectifier (SCR) 60 has its anode connected to node 26,
cathode connected to the base contact 7, and gate
connected to the junction of a resistor 61 and capacitor
62 which are connected in series between the ring 7 and
eyelet 8, as shown. Also a diode 63 is provided having
its anode connected to the node 26. The cathode of
diode 63 is connected to the collector of transistor 27
and the upper end of PTC resistor 40.
The circuit of Figure 4~ functions in the same
manner as Figure 2A except for the dimming circuit.
The dimming circuit of Figure 4A functions as follows:
With the switch 13 in its second position (low light
level), half-wave power is supplied through the filament
12 via the SCR 60 which is gated to the "on" condition
during alternate half cycles by current flow through the
capacitor 62. The diode 63 prevents the filter capacitor
16 from charging to a high enough voltage to operate
the trigger oscillator 37 during this low light level.
In the third switch position (high) the ring 7
is not connected to power input, and thus the SCR is
"out" of the circuit and the arc lamp operates as
described above. In the fourth switch 13 position
(high) ring 7 and button contact 8 are connected
together and connect the resistor 61 and capacitor 62 in
parallel and bias the SCR to the "off" condition.
Referring to the operating network depicted in
Figures 2A and 4A, in pre-ignition, ignition and glow-
to-arc transition (in the high setting), the transformer
28, the transistor switch 27 and the ~rigger oscillator
(37, etc.) of the operating network assume an active role
in generating a high frequency output. The change in
i6
35-EL-1507
- 24 -
electrical output to dc occuring between the glow to arc
transistion and warm-up is in response to conditions in
the main lamp. More gradual changes in electrical
output of the operating ne-twork occur between pre-
ignition and ignition and between ignition and the glowto arc transistion, and these changes are also in
response to conditions in the main lamp.
In pre-ignition, ignition and the glow to arc
transition, the operating network produces short duration,
high voltage pulses for ignition of the arc lamp, the
voltage falling to a lower value in response to lamp
loading in the glow to arc transition. During preignition,
the unidirectional high voltage pulses have substantial
ringing, and they ocaur at a rate of 50 KHz. In the glow
to arc transition, the ringing is reduced and the frequency
shifts to 35 KHz. The downward shift in frequency produces
a shorter transistor conduction duty cycle, which increases
the energy supplied to the lamp in the glow to arc tran-
sition. The operating network also supplies current to
the filamentary resistance 12 in the form of a series of
unidirectional pulses at the 50-35 KHz rate.
The operating network produces the high frequency
electrical energization described above as a result of
high frequency switching of the monostable transistor
switch. Intermittent switching of the transistor switch
produces an alternating component in the main primary
einding 31 of the step-up transofrmer, a stepped up
alternating component in the transformer output and a
pulsating current in the filamentary resistance 12 which
is primarily unidirectional.
Alternating current flow in the main primary winding
takes place in the following manner. Assuming that the
transistor 27 has been turned on by a suitable trigger
signal coupled to its input junction, a displacement
current oath is completed between the positive and
common terminals of the dc supply.
s~
35-EL-1507
-- 25
me switching transistor presents a low impedance
when conducting, and the capacitor 35, the primary
feedback winding 33 and the resistance 24 are also low
impedances. As the current in the circuit increases, the
primary feedback winding, which is inductively coupled
to the secondary feedback winding 34, produces regenerative
feedback in the input circuit of the transistor and turns
it on more strongly. The current build-up continues,
however, until a prescribed flux level is reached in
the core of the power transformer. ~t that point, the
feedback is inverted to become degenerative, turning off
the transistor 27 before full core saturation is reached.
The discontinuance of conduction through transistor 27
opens the prior path for current flow through the primary
lS winding and allows a portion of the energy stored in
the circuit to dissipate in the form of a reverse current
through the filamentary resistance 12.
The transformer 28 which exhibits the feedback
reversal characteristic turning off the transistor
before full core saturation is reached is illustrated in
Figure 3, with the drawing illustrating the double E core
or 8 core structure with a control aperture at the base
of the center leg formed by the bars of the "E". The
main power windings 31 and 32 are shown wound around
the center branch corresponding to the bars of the E's
while the primary and secondary control windings 33 and
34 are wound through the aperture. The sense of the
feedback is dependent upon the flux level in the core
surrounding the aperture. The feedback coupling to the
secondary control winding 34 is regenerative at low flux
levels and degnerative at high flux levels.
The transformed version of the high frequency alter-
nating voltage appearing across the transformer primary
winding during pre-ignition~ ignition, and the glow to arc
transition appears at the terminal of the winding 32
remote from winding 3I. The output is coupled from the
~3~6 35-EL-1507
- 26 -
winding 32 by means of the capacitor 36 to the anode of
the arc lamp 11. The output takes the form of unidirectional
pulses by virtue of the presence of the diode 23 whose
anode is coupled to node 26 and the undotted terminal o
the second winding and whose cathode is coupled to the
anode of the arc lamp. The diode 23 is poled to permit
application of a stepped-up secondary voltage to the
arc lamp developed during the reverse current flow in the
transformer primary circuit and to suppress application
f the secondary voltage developed during forward current
flow when the switching transistor is conducting. The
transformer 20 is a step-up transformer with a transformer
ratio of 640/140 and with the indicated polarity of diode
23 delivers energy to the arc lamp during off periods of
the transistor switch. With the indicated parameters, and
assuming substantial ringing, the available pre-ignition
potential is 1600 volts peak to peak. Preignition is
nominally of zero duration when the lamp is cold and from
45 seconds to 4 minutes when the lamp is hot.
The current for standby illumination during preignition,
ignition, and the glow to arc transition is produced by high
frequency switching of the transistor switch. At the
instant that the transistor switch becomes conductive, a
direct current path is completed between the positive and
common terminals of the dc supply. The dc path includes
the standby light producing filamentary resistance 12,
the transistor 27 (collector and emitter electrodes,
respectively), the primary -feedback winding 23 and the
current sensing resistance 24. The transistor 27
presents a low impedance when conducting, and the primary
feedback winding 23 and the resistance 33 are also low
impedances.
In addition to the intermittent current supplied to
the filamentary resistance in the dc path just described,
the return portion of the alternating current flowing in
the primary winding 31 of the transformer also flows
~;3~35~
35-EL-1507
- 27 -
through the filamentary resistance as discussed earlier.
During pre-ignition, with the secondary winding of the
transformer 28 being substantially open-circuited, the
heating effect of the reverse current in the primary
circuit is negligible. During the glow to arc transition,
when the lamp draws the more substantial energy, the
alternating current adds significantly to the total
dissipation in the filament, in which pulsating dc
energization is reduced.
In the high setting, the operating network is
responsive to the electrical state of the arc lamp to
produce the outputs previously characteri7ed during
pre-ignition, ignition and the GAT period. The means by
which this responsiveness is accomplished includes the
triggering oscillator (transistor 37, etc.) lamp current
sensing resistor 24 and the voltage sensing resistors 41,
~2 and 43.
The trigger oscillator causes active operation of the
transistor switch 19 during pre-ignition, ignition and
the GAT period and controls the transistor duty cycle to
supply additional energy to the arc lamp during the GAT
period. Since the transistor switch is monostable, each
trigger pulse supplied from the trigger oscillator
initiates a conduction sequence. Should one not want
the arc lamp to operate at all, as when the lighting
unit is in a low setting and only filamentary illumination
is desired, then in accordance with the invention, high
frequency operation is prevented by preventing oscillations
of the trigger oscillator. The dimming feature, as earlier
stated, preserves the flexibility of the power supply
to react to rapid changes in lamp voltage and current
or line transients.
In the high setting, the trigger oscillator is
activated at the time the operating network is first
energized, and remains energized through the prei~nition,
there is no lamp current, while during ignition and the
~3~5~
35-EL-1507
- 28 -
glow to arc transition, the lamp current increases to
one-fifth of an ampere peak in short pulses. The
voltage developed in the transformer primary winding
at node 26 is high (> 300V) during pre-ignition, falls
appreciably under the loading affect of the lamp during
ignition, and the glow to arc transition, and consists
of a series of pulses initially with substantial ringing.
The foregoing current and voltage conditions reflect-
ing the lamp condition during pre-ignition, ignition and
glow to arc transition are sensed in the operating network
and combined differentially at the input junction of the
oscillator transistor, and used to activate the trigger
oscillator. Any lamp current flowing in the lamp current
sensing resistance, to which the emitter electrode of the
~unction transistor 37 is coupledvia the low impedance
a voltage in a sense tending to back-bias the input
junction. (The lamp current~is zero at the start and
remains small during these lamp conditions.) The voltage
at the node 26 is applied across the voltage divider (41,
~2, 43), the lower tap of which is coupled to the base
electrode of the transistor 37. The voltage appearing at
the node 26 is positive and a *raction (1/181) of that
voltage is applied to the base electrode. Here, the
voltage is in a sense tending to forward bias the input
~unction. During pre-ignition, the voltage at node 26
is a maximum and sufficient, assuming time has been
allowed for the capacitor 38 to charge up, to forward bias
the transistor 37 and initiate oscillation.
The trigger oscillator operates as a relaxation
oscillator, capacitor 30 being recurrently charged through
the passive elements of the operating network and re-
currently discharged by the transistors 27~ 37. The
charging period of capacitor 38 is determined primarily
by the value of capacitor 38, the value of resistor 43,
and the differential voltage applied to charge the
capacitor 33, The turn-off action of the transformer 28
;3i;~5~
35-EL 1507
- 29 -
leave a residual inverse voltage on the capacitor at
the end of switch conduction limited by the serially
connected diode 29 and resistance 30.
As an examination of the circuit will show, when
sufficiently high potentials are present at the node 26
and assuming a low lamp current, the oscillator will start
to conduct when the capacitor 38 reaches the value
required to forward bias the input junction of the
transistor 37 (+0.6 volts) as indicated above. The
voltage on the capabitor is determined by the difference
between the voltage at the lower voltage divider tap
and the voltage due to lamp current in resistor 24.
Once the transistor 37 conducts, current flows in
the primary feedback winding 33 and the strongly re-
lS generative feedback action involving secondary feedbac~
winding 34 and capacitor 38 produces a short during trigger
pulse for turning on transistor switch 27.
Assuming that the arc lamp current has begun to
flow and the voltage across the lamp has begun to increase,
the differential voltage used to charge capacitor 38 falls
on the average, increasing the period required to turn on
the transistor 37 and initiate the next trigger pulse.
This provides more time for the energy stored in the
input circuit of the operating network to be relaesed
to the lamp. Earlier in the starting cycle, the lamp
cathode current may be truncated by the next conduction
interval, and less stored energy is delivered to the arc
lamp. The circuit has been designed so that the non-
conduction period is maximum when the lamp voltage is in
the glow region (approximately 200-400 volts), to maximize
the output power at about 9 watts for metal vapor lamps.
In the high setting, once the arc lamp has reached
thermionic operation corresponding to warm-up, the
high frequency output produced by transistor switching
is designed to stop and the dc state commences. The
trigger oscillator, which triggers the monostable
3i~S~
35-EL-1507
- 30 -
transistor switch into active operation, remains
reversely biased due to a new setof current condition in
the operating network and becomes inactive. The
rectified high frequency voltage at node 26, previously
applied across the voltage divider 41, 42, 43 is
replaced by a sustained dc voltage with some ripple,
representing the lamp voltage. The dc voltage continues
in a sense favouring conduction, but is lower by 1 or 2
orders of magnitude. The diode 23, now forward biased,
connects the voltage divider across the lamp, and the
voltage divider now senses l/181th of the new lamp
voltage, initially 15 volts. Simultaneously, a maximum
initial lamp current of 6/lOths of an ampere occurs in
resistor 24, developing a conduction inhibiting voltage
of approximately 1.2 volts. The differential voltage
produces a reverse bias on the input junction of the
transistor switch.
As warm-up continues into final run condition, the
lamp voltage rises and the lamp current falls. The
lamp condition sensors are set to keep the trigger
oscillator inactive through warm-up and final run. In
final run, the lamp reaches a current of 0.3 amperes and
a voltage of 87 volts. Should the lamp voltage rise 10
volts above the normal values (e.g. 97 volts) and the
current fall to 0.050 ampere, then the trigger oscillator
will be reactivated as a safeguard against transistor
dropout.
