Spare lamp control circuit for a light projection system

United States Patent [191
[11]
4,034,259
Schoch
[45]
July 5, 1977
means, generally a resistor, in series connection with
the switch and the lamps, senses the current through
[541 SPARE LAMP CONTROL CIRCUIT FOR A
LIGHT PROJECTION SYSTEM
[75] lnventor: David K. Schoch, Downers Grove,
[73] Assignee:
the main lamp thereby dropping a small portion of the
voltage source. A pair of opposite polarity voltage ref
111.
erences are established by rectifying the voltage
Audio Visual Innovators
dropped across the current sensing resistor and by
rectifying the voltage across the input lines of the volt
age source. A tracking voltage reference, proportion
ally tracks voltage variations on one of the input lines
Corporation, Darien, 111.
Apr. 14, 1976
[22] Filed:
[21] Appl. No.: 676,747
[52]
to distinguish between operation of the system at re
duced voltages and failure of the main lamp, and is
US. Cl. .............................. .. 315/93; 240/37.l;
provided by summing and dividing the voltages of the
opposite polarity voltage references. A voltage com
307/39; 315/88; 315/90
[51]
[581
Int. Cl.2 ....................................... .. H05B 37/04
Field of Search ............................. .. 3l5/88-9l,
parator monitors the voltage reference, and has an
output adapted to control the switch. Failure of the
main lamp causes the voltage across the current sensing
315/93; 240/37.1; 307/39, 131; 352/198
resistor to collapse, thereby causing the tracking volt
References Cited
UNITED STATES PATENTS
[561
2,197,700
3,809,917
4/1940
MacGregor ................... .. 315/93 X
5/1974
Vore .................................. .. 307/39
age reference to differ signi?cantly from the potential
on one of the input lines, further causing the voltage
comparator to change its output and the switch to
Attorney, Agent, or Firm—McWilliams & Mann
change position such that the spare lamp is energized.
The output of the voltage comparator generally con
trols an electromechanical device for changing posi
[57]
ABSTRACT
tions of the switch. A second switch, in series with the
circuit between the input lines, is controlled by the
A control circuit for a light projection'system for ener
gizing a spare lamp when the circuit detects failure of a
electromechanical device. The second switch assumes
an open state after the ?rst switch energizes the spare
Primary Examiner-Eugene La Roche
main lamp. A pair of input lines apply an alternating
lamp, thereby interrupting energization of the electro
current voltage source to the circuit, to the main lamp
and to a spare lamp which is substantially in parallel
connection with the main lamp. A switch is in series
connection with the main and spare lamp for selec
mechanical device and the circuit.
tively energizing one of the lamps. Current sensing
9 Claims, 3 Drawing Figures
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87
US. Patent
July 5, 1977
Sheet 2 of 2
4,034,259
may
4,034,259
1
2
.
of the input lines despite variations in the potential of
the voltage source. A voltage comparator monitors the
voltage differences between one of the input lines and
SPARE LAMP CONTROL CIRCUIT FOR A LIGHT
PROJECTION SYSTEM
BACKGROUND or THE INVENTION
the tracking voltage reference.
5
This invention relates in general to a control circuit
for a light projection system, and more particularly to a
control circuit wherein a voltage comparator compares
the potential on one of a pair of input lines to a voltage
Failure of the main lamp interrupts current through
the current sensing resistor, causing the ?rst voltage
reference to collapse. As this occurs, the tracking volt
age reference also assumes a different potential from
that of the input line which it is tracking, causing the
reference generated by the circuit such that the circuit 0 voltage comparator tochange in output. The output of
the voltage comparator is adapted to control an elec
is capable of detecting failure of a main lamp and auto
tromechanical device for changing the position of the
matically energizing a spare lamp and is further capable
of distinguishing between failure of the main lamp and
switch, thereby energizing the spare lamp for continued
light projection. Because the voltage references are
operation of the projection system at reduced input
established by recti?cation of the alternating current
voltages.
input voltage, or a portion thereof, the voltage referen
Various types electrically, mechanically and ther
ces will change proportionally with any variation in the
mally activated devices are known in the prior art for
potential of the alternating current voltage source.
energizing a spare lamp in a light projection system
Therefore the tracking voltage reference also changes
upon failure of the main lamp. Many of the mechani
cally and thermally activated devices are unsuitable for 20 proportionally, which enables the tracking voltage ref
commercially used light projection systems because of
erence to follow variations in the alternating current
voltage source.
the length of time taken between failure of the main
Such a tracking phenomena is important in enabling
lamp and energization of the spare lamp. Especially in
the circuit to distinguish between failure of the main
commercial usage of light projection systems, such as
presentations before large or important audiences in 25 lamp and operation of the projection system at reduced
input voltage level. Many commercial applications of
cluding sales or marketing conferences, training ses
sions, conventions and the like, rapid sensing of the
light projectors include operating sequences wherein
failure of the main lamp and energization of the spare
lamp are required to avoid annoyance and inconve
.the projectors are alternatively switched on and off, or
nience to everyone involved.
30
Prior art controls, including circuits, also suffer from
the inability to distinguish between failure of the main
lamp and operation of the main lamp at reduced volt
ages. In those control systems which employ circuitry,
the circuitry is generally operated from direct current
voltage sources, requiring expensive and inef?cient
where their superimposed images are dissolved by op
erating of the projectors through a range of input volt
ages such that the projector lamp operates at a range of
voltages other than its nominal voltage.
A second switch is located in series with the circuit
between the pair of input lines and is normally closed
35
means to isolate the alternating current voltage source
generally associated with projection systems from di
while the main lamp is functioning. This second switch
is also controlled by the electromechanical device.
After the main lamp fails, the circuit energizes the
electromechanical device to begin operation of the
rect current voltage source required for the circuitry.
spare lamp, at which time the electromechanical device
also opens the second switch. Opening of the second
mal sensors are typical of these isolation techniques.
switch disables the control circuit; the operation of
which is no longer required after the spare lamp has
SUMMARY OF THE INVENTION
been energized upon failure of the main lamp.
The control circuit of the present invention operates
Various other objects, features and advantages of the
directly from the alternating-current voltage source 45 invention will become apparent from the following
generally provided in and to a light projection system.
detailed disclosure when taken in conjunction with the
Motors, transformers, photoelectric devices and ther
40
A pair of input lines apply the alternating-current volt
age source to the circuit. A main lamp and a spare
lamp, substantially in parallel connection with the main
lamp, are in series connection with a switch for'selec 50
tively energizing either the main lamp or the spare lamp
across the input lines. Current sensing means, generally
a resistor of low resistive value, is also in series connec
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a plan view, partially in section, of the inter
ior of a portion of a light projection system illustrating
the lamp and optical arrangement of the invention;
tion with the lamps for sensing the current through the
FIG. 2 is a block diagram of the control circuit of the
main lamp and for dropping a small portion of the 55 invention, functionally illustrating the operation
voltage source thereacross.
A ?rst recti?cation means associated with the cur
rent sensing resistor estabishes a ?rst voltage reference
FIG. 3 is a schematic diagram of the control circuit
for sensing the failure of the main lamp and automati
by recti?cation of the portion of the line votage
dropped across the current sensing resistor. A second
system.
reci?cation means provides a second voltage reference
by rectifying the voltage appearing across the input
thereof; and
cally switching to the spare lamp of the projection
'
' DESCRIPTION OF THE PREFERRED
EMBODIMENTS
ence with respect to one of the input lines is opposite to
Turning to FIG. 1, there is shown a portion of the
that of the ?rst voltage reference. Voltage summing 65 interior of a light projection system in plan view. FIG.
and dividing means are connected between the oppo-v
1 is partly in section and illustrates a light projection
site polarity voltage references to provide a tracking
system, generally designated 10, which is particularly
voltage reference which will track the potential on one
useful in a slide projector.
lines such that the polarity of the second voltage refer
3
4,034,259
4
Many other components, beside those illustrated in
FIG. 1, are employed in a typical light projection sys
main lamp 18 is preferably located within a housing 27
?xedly attached to the rear of the projector 10. It is
tem used in a slide projector. Such components include
a motor for ventilating heat from the interior of the
projector and actuating means for a slide changing
mechanism. However these additional components are
not necessary for an appreciation and understanding of
the invention herein.
understood that the front of the projector 10 is com
monly the side of the projector 10 nearest to the focus
ing lens 15. Also located within the housing 27 is sens
ing means for detecting the failure of the main lamp 18.
The sensing means consist of a number of electrical
circuit elements 28 mounted on a circuit board 29, with
the circuit board 29 ?xedly secured within the housing
The projector, generally designated 10, of FIG. 1 has
a frame 11 suitable for securing various internal com
0 27.
ponents thereto. A heat absorbing glass 12 is usually
located on the lamp side of a slide 13. A condensing
lens 14 is interposed between the slide 13 and the heat
absorbing glass 12 and condenses illumination from a
light source. A focusing lens 15 is located on the oppo
5
The lamps 18, 19 are a high brilliancy type which
generally have a relatively short life-span. These lamps
l8, 19 have self-contained re?ectors for providing light
with a highly directional light pattern.
To facilitate light transmission from the main lamp
18 along the optical axis 16, a window area 30 is pro
vided in the frame 11 about the axis 16. Another win
dow area 31 is provided in the web 17 to allow light
the illuminated slide upon a screen (not shown) or the
transmission from the spare lamp 19. Between the main
like. A common optical axis 16 is shared by the focus
20 lamp 18 and the frame 11 may be interposed a shock
ing lens 15 and the condensing lens 14.
absorbing material 32. The material 32 is generally a
A web 17 generally meanders through the interior of
site side of the slide 13 and is usually movable through
a limited distance for focusing the image presented by
the projector thereby subdividing the interior of ‘the
gasket capable of withstanding high temperatures at
which the main lamp 18 will operate. Shock absorbing
projector 10 into various compartments. These various
material 33, similar to that of the material 32, may be
compartments are usually designed for best light trans
mission, heat ventilation and the like. Such consider 25 interposed between the spare lamp and the web 17.
Both of the lamps 18, 19 are secured against the shock
ations are beyond the scope of this invention. However
absorbing material 32, 33 by resilient means 34. Exam
the web 17 is‘ useful for mounting various components
ples of the resilient means 34 include elongated coil
required by the invention.
springs or wires which exhibit spring tension.
According to one aspect of the invention, there is
An electromechanical device 35, with a plunger 36
provide a main lamp 18 ?xedly mounted with respect
movable with respect to the device 35, is fixed in rela~
to the frame 11 on the optical axis 16 of the lenses 14,
tion to the frame 11 and is preferably affixed to the web
15. Also ?xedly mounted with respect to the frame 11,
17. The plunger 36 operates releasable securing means,
at a position off of the optical axis 16, is a spare lamp
generally designated 38, for the mirror holder 21, per
19. As shown in FIG. 1, the spare lamp 19 is at oblique
angle with respect to the optical axis 16. Both of the 35 mitting the mirror 20 to assume its second position 47
when resiliently biased thereto. The electromechanical
lamps 18, 19 preferably have highly directional light
device 35 and the plunger 36 comprise the actuation
patterns for optimum light transmitting ef?ciency. A
means for the releasable securing means 38. The re
re?ecting mirror 20 is positionable between two posi
leasable securing means 38 typically comprises a lever
tions as illustrated in FIG. 1. In the ?rst position, shown
in dark lines and generally designated 26, the mirror 40 39 with one end 40 thereof secured to an end 41 of the
plunger 36. Another end 42 of the lever 39 is hook
does not obstruct light transmission between the main
shaped to engage another vertical edge 43 of the mirror
lamp and the projection lenses l4, 15. In the second
support 21 in the ?rst position 26 thereof. Intermediate
position, shown in the lighter lines in FIG. 1 and gener
the ends 40, 42 of the lever 39 is a point 44 of the lever.
ally designated 47, the mirror is in position to re?ect
light from the spare lamp 19 along the optical axis 16 of 45 The point 44 is attached to the web 17 in a fulcrum or
pivotable fashion. One means of achieving the fulcrum
the projection lenses 14, 15. A mirror holder 21 sup
or pivotable relation between the lever 39 and the web
ports the mirror 20 and pivots the mirror 20 between its
?rst and second positions 26, 47, respectively. The
17 is to have the lever 39 pass through an aperture in a
mirror holder 21 has tabs 22 at the top and bottom
edges thereof bent or rolled through 180 degrees to
de?ne a channel in which the mirror 20 is secured. One
web 17, with the lever 39 having the series of bends 45
vertical edge 23 of the mirror support 21 is pivotally
near the point 44 such that the lever 39 cannot move
about its length with respect to the web 17 but can only
pivot with respect to the web 17 at the point 44. When
secured with respect to the frame 11. One means of
the electromechanical device 35 is energized, causing
accomplishing the pivoting relationship is to have the
the plunger 36 to move into the device 35, the lever 39
horizontal edge 23 bent to de?ne a cylindrical aperture 55 will assume the dotted position 46 thereof, thereby
releasing the mirror support 21 and the mirror to as
therealong. A post 24 ?xedly attached with respect to
sume the second position 47 thereof.
the frame pivotally secures the end 23 of the mirror
A mirror stop means 48 is ?xedly attached in rela—
support 21 to the frame 11. The post 24 is located away
tionship to the frame 11 and is located to limit move
from the optical axis 16 such that light from the main
lamp 18 is not obstructed. Resilient biasing means 25, 60 ment of the mirror support 21 to the second position 47
resiliently biases the mirror 20 from the ?rst position . thereof. The mirror stop means 48 has a base plate 49
attached to the frame 11 with a shock absorbing por
thereof to the second position thereof. The biasing
tion‘50 projecting upwardly from the base plate 49.
means 25 is typically a coil ‘spring wrapped about the
The shock absorbing portion 50 stops the mirror sup
post 24, with one end of the means 25 cooperating with
the frame 11 to urge the mirror 20 and the mirror 65 port 21 upon reaching the second position thereof in an
essentially vibration-free manner. The base plate 49 of
- support 21 toward the second position 47 thereof.
the stop means 48 may employ slotsSl therein to per
To enable both of the lamps 18, 19 to be located the
mit adjustment of the mirror stop means 48 to permit
same optical distance from the condensing lens 14, the
5
4,034,259
?ne adjustment of the re?ected light from the spare
lamp 19 along the optical axis 16.
A switch 53 is ?xedly mounted to the web 17 at a
location near the ?rst position of the mirror 20. A pin
54 projects from the switch 53 for sensing whether the
mirror 20 is in the ?rst position 26 thereof, with the
mirror 20 urging the pin 54 into the switch 53. The
switch 53 is electrically connected to the circuit board
29, the main lamp 18 and the spare lamp 19 by a plural
6
losses, improper adjustment of the re?ecting device
and the like. However after failure of the main lamp,
such losses can be tolerated with respect to spare lamp
10 until nonuse of the projection system allows suffi
cient time for replacement of the main lamp 18. When
the projector 10 is partially disassembled for replace
ment of the burned-out main lamp 18, the mirror 20 is
manually reset into the ?rst position 26 by pushing it
from the second position 47 back into the ?rst position
ity of leads 55 in a manner which will be hereinafter 0 26. The hook-shaped end 42 of the securing means 38
engages the vertical edge 43 of the mirror support 21 to
explained.
retain the mirror 20 in the ?rst position 26. As will be
It will be appreciated that the electromechanical
hereinafter explained, the electromechanical device 35
device 35 controls the state of switch 53 because of the
moves the securing means 38 to the releasing positions
mechanical interconnection from the plunger 36, to the
46 for only a brief interval after failure of the main
releasable securing means 38, to the mirror support 21,
lamp 18'. Thus, the securing means 38 is able to again
to the mirror 20, and ?nally to the pin 54 of the switch
retain the mirror in the ?rst position 26 whenever it is
53. When the main lamp 18 fails and the current sens
convenient to replace the main lamp 18 and manually
ing means energizes the electromechanical device 35
reset the mirror 20. It is important that the re?ecting
causing the mirror securing means 38 to assume the
mirror 20 and the associated mirror support 21 are
second position 46 thereof, the pin 54 of the switch 53
located in a position off of theaxis 16 such that light
will be released as the mirror 20 begins to move toward
from the main lamp 18 is not obstructed in any manner
its second position 47, thereby switching the state of
during operation of the main lamp 18. Also the mirror
the switch 53 as the mirror 20 begins to leave the ?rst
20 must pivot from its ?rst position 26 to its second
position 26 thereof. Thus the spare lamp 19 is immedi
ately energized and the spare lamp 19 begins to in 25 position 47 at a point remote from the axis 16 such that
light transmission from the main lamp 18 is not inter
crease in illumination intensity toward full brilliancy as
fered with. The mirror support 21 is preferably fabri
the mirror 20 assumes the second position 47 thereof.
Because the transition of the mirror 20 from its ?rst
position 26 to its second position 47 requires only a
fraction of a second and the spare lamp 19 is increasing
in illumination intensity during this period, light projec
tion along the optical axis 16 is substantially uninter—
rupted by failure of the main lamp 18. The main lamp
18 does not stop providing light exactly at the instant in
cated from material with low mass properties, such as
aluminum. Mirror 20 is preferably as thin as possible to
keep the mass thereof at a minimum. Preferably, the
combined mass of the mirror 20 and the support 21 is
less than 3 ounces. The low masses of the mirror 20 and
the mirror support 21 further aid in keeping vibration
caused by transition of the mirror 20 and the support
which failure thereof occurs, but continues providing 35 21 from the ?rst position 26 to the second position 47
at a minimum. Because the projector 10 is typically
light in decreasing intensity as the ?lament thereof
cools toward lower temperatures. Thus, light overlap
located some distance from the screen upon which the
between the burned-out main lamp 18 and the newly
energized spare lamp 19 further aid in continuity of
enlarged image of the slide 13 is projected, any small
movement of the projector 10 about the optical axis 16
translates into a sizeable displacement of the enlarged
image on the screen. Such displacement is particularly
projected light.
Various other electrical interconnections are made in
undesirable in presentations before large audiences
FIG. 1. A pair of leads 56 connect the electromechani
where the images of a plurality of projectors are super
cal device 35 through the circuit board 29. Electrical
imposed on the screen and where a portion of the pro
connection between the spare lamp 19 and the circuit
board 29 is accomplished by means of a socket 57 45 jected image is off of the screen.
Slide projectors which are suitable for practicing the
connecting to a pair of leads 58 of the spare lamp 19,
invention taught herein are commercially available
with a pair of wires 52 interconnecting the socket 57
from the Eastman Kodak Company of Rochester, N.Y.
with the circuit board 29. Similarly, a socket 59 con
and are identi?ed by that Company as Ektagraphic
nects to the leads 60 of the main lamp 18, with a pair of
wires 61 electrically connecting the socket 59 to the 50 Models B-2 and E-2.
A control circuit, generally designated 80, for detect
circuit board 29. A plurality of other leads 62 electri
ing the failure of the main lamp 18, is illustrated in FIG.
cally connect the lamps 18, 19, circuit board 29, switch
3. To better facilitate understanding of the operation of
53 and electromechanical device to the alternating
the circuit 80, a block diagram of the circuit is illus
current voltage source, power switch 83 and a current
trated in FIG. 2.
.
sensing resistor 96. The need for leads 62 and their
With reference to FIG. 2 there are provided a pair of
signi?cance will become apparent when FIGS. 2 and 3
input lines, including a line 81 and a line 82, for apply
are considered hereinafter.
ing an alternating-current voltage source to the circuit
The above description of the lamp system has been
80. A manually-operated power switch 83 is operable
on a piecemeal basis. It is now appropriate to consider
between on and off positions to control application of
the overall function and advantages of the lamp system.
the voltage source to the circuit 80. The switch 83 is
Both the main lamp 18 and the spare lamp 19 are pref
erably located at approximately equal optical distances
usually provided with most projectors by the manufac
from the condensing lens 14. A typical optical distance
turers thereof. In addition, most projectors suitable for
commercial purposes include a pair of jacks 84, 85 in
would be about 9 centimeters. The main lamp 18 is
located directly in line with the optical axis 16 for maxi 65 electrically parallel connection with the switch 83. The
jacks 84, 85 provide capability to control the main
mum light transmission. It is known to those skilled in
lamp 18 or the spare lamp 19 from a remote source.
the art that use of any re?ecting device results in about
Remote source controls could include dimming devices
15 to 20% of light loss due to light scattering, re?ecting
7
.
4,034,259
to control the illumination intensity of the main lamp
8
18 or the spare lamp 19, such as when dissolving from
references 100, 104 on the leads 108, 110 to provide a
tracking voltage reference at an output lead 111 of the
the image provided from one projector to the image
provided by another projector. In more sophisticated
applications the jacks 84, 85 enable control of a plural
ity of projectors by programmable computers for auto
voltage summing and dividing means 109. As long as
both the ?rst voltage reference 100 and the second
voltage reference 104 are operative, the tracking volt
age reference appearing on the lead 111 will be approx
mated and creative presentations.
imately equal in potential to the potential appearing on
the input lead 81. A voltage comparator 112 compares
the potential of the tracking voltage reference on the
The main lamp 18 and the spare lamp 19 are wired in
substantially parallel connection. A lead 86 from the
main lamp 18 and a lead 87 from the spare lamp 19 are
connected to the input line 82. A lead 88 from the main
lamp 18 and a lead 89 from the spare lamp 19 are
connected to contacts 90, 91, respectively, of the
switch 53. As previously discussed, the switch 53 is
usually held closed relative to the contact 90 when the
mirror 20 is in the ?rst position 26 thereof, as illus
trated by the dark lines in FIG. 1. The switch 53 will
lead 111 to the potential on the input line 81. A lead
113 references the voltage comparator 112 to the line
81.
As is known in the lamb art, failure of a lamp is char
acterized by an open ?lament thereof. Thus, failure of
the main lamp 18 will provide an open circuit to the
current sensing means 95 resulting in no main lamp
current therethrough. Cessation of current through the
current sensing means 95 causes that portion of the
open from contact 90 and close with respect to contact
91 as the mirror 20 is released from its ?rst position 26.
voltage source dropped thereacross to vanish, resulting
Another terminal 93 (FIG. 2) of the switch 53 is 20 in no alternating-current voltage for the recti?cation
connected by a lead 94 to the current sensing means 95
means 97 to rectify. Thus, the ?rst voltage reference
for the main lamp-.18. The current sensing means 95 is
100 collapses. The second voltage reference 104 is
in series between one of the input lines 81 and the lead
then able to directly in?uence the tracking voltage
94. Typically the current sensing means comprises a
appearing at the lead 111, causing said tracking voltage
resistor 96 (FIG. 3) of low ohmic value. The current 25 reference to change in potential with respect to the line
sensing resistor 96 is found in many projectors, not
81. The change in potential between the lead 111 and
employing the invention herein, to limit the inrush
the line 81 cause the voltage comparator 112 to change
current to the main lamp 18 when the voltage source is
in output on a lead 115 thereby causing an electronic
?rst applied thereto by closing the power switch 83.
switch means 116 to also change its conduction state.
The resistor 96 also functions to drop a small portion of 30 Change in conduction state of the electronic switch
the input voltage source thereacross, as compared to
the voltage dropped by the main lamp 18 or the spare
lamp 19, thereby operating the lamp 18 or the spare
lamp 19, at a slightly reduced voltage from that of its
nominal voltage rating. Operation of such lamps at a
slightly reduced voltage level is known to prolong their
operative life span.
With the‘ basic wiring of a projector employing a
spare lamp 19 in mind, fundamental operation of the
circuit 80 may be understood by considering the block
diagram of FIG. 2. According to another aspect of the
means 116 on a lead 117 causes an electromechanical
means 118 to change in energization state. The electro
mechanical means 118 is mechanically coupled, as
indicated at 120, to the switch 53 and to a second
switch 53a. The second switch 53a is physically a part
of the switch 53 and the operation and signi?cance
thereof are hereinafter described. Change in energiza
tion» of the electromechanical means 118 causes the
switch 53 to change from the position illustrated in
FIG. 2 to electrically connect the terminal 93 with the
contact 91 thereby energizing the spare lamp 19. The
invention, recti?cation means 97 is connected by a lead
98 to the lead 95 for rectifying the small portion'of the
alternating-current voltage source dropped across the
electromechanical means 1 18 is referenced to the input
line 82 by a lead 119.
The turn-on delay 105 is interposed between the
current sensing means 95. A lead 99 from the recti?ca 45 second voltage reference 104 and the voltage summing
tion means 97 establishes a voltage reference 100 be
and dividing means 109 to allow potential from the ?rst
tween the lead 99 and the input line 81.‘ A second
voltage reference 100 on the lead 108 to rise faster
recti?cation means 101 recti?es the voltage appearing
across the input lines 81, 82 to establish a second volt
than the potential fromv the second voltage reference
age reference 104 which is opposite in polarity with
respect to the input line 81 to the voltage reference
50 circuit 80. The difference in potential rise times on the
100. The second recti?cation means 101 is connected
the lead 111 near the potential on the input line 81 to
by lead 102 through a second switch 53a to the input
line 82, and by lead 103 to the second voltage refer
avoid having the voltage comparator 112 inadvertently
104 on the lead 110 when power is ?rst spplied to the
leads 108, 110 keeps the tracking voltage reference on
detect the difference between the tracking voltage
ence 104. Because the recti?cation means 97, 101 55 reference on the lead 112 and the potential on the
rectify alternating-current voltages, the ?rst voltage
reference 100 and the second voltage reference 104
are both direct-current potentials. Furthermore, these
potentials are both referenced to the input line 81 and
?oat with respect thereto despite any alternating-cur
rent voltage variation in the line 81.
' The second voltage reference 104 is presented to a
input line 81 as indicative of the failure of the main
lamp 18 when the voltage source is ?rst applied to the
circuit 80 by closing the power switch 83. It will be
' readily appreciated by those skilled in the art that the
60
need for any turn-on delay 105, and whether such delay
105 is required with respect to the second voltage ref
erence 104 or the ?rst voltage reference 100, depends
upon the characteristics of the voltage comparator 112
and the respective rise times of the ?rst voltage refer
turn-on delay 105 through a lead 106. Both the ?rst
voltage reference 100 and an output of the turn-on
delay 105 are presented to a voltage summing and 65 ence 100 and the second voltage reference 104. Be
dividing means 109 by a lead 108 and a lead 110, re
cause the control circuit 80 is operated directly from an
spectively. The voltage summing and dividing means
109 sum and proportion the potentials of the voltage
alternating-current voltage source and it is generally
not known whether input line 81 will be positive or
4,034,259
9
.
10
the resistor 131 and the capacitor 132 are selected to
negative with respect to input line 82 at the instant in
provide a relatively large resistive-capacitive time-con
stant with respect to the operating frequency of the
which power is ?rst applied to the circuit 80, it is possi
ble that some delay will have to be associated with one
of the voltage references 100, 104 to avoid a turn-on
voltage source. Thus, when the voltage source is ?rst
has caused the switch 53 to close against the contact 91
applied to the circuit 80 by closing the power switch 83
the potential at the junction at 132 with respect to the
line 81 will rise considerably slower than the potential
thereby energizing the spare lamp 19, current through
at the junction 129.
the current sensing means 95 will cause the circuit 80
to again assume a monitoring mode wherein the elec
A resistor 135 is connected between the junction 125
and another junction 136. Another resistor 137 is con
nected between the junction 136 and the junction 132.
hazard in the voltage comparator 112.
After the main lamp 18 has failed and the circuit 80
v
tromechanical means 118 assumes the prior energiza
The resistors 135, 137 serve to sum and proportion the
tion state. From an energy consumption standpoint, it
first voltage reference appearing at terminal 125 and
is preferably to have the electromechanical means 118
the delayed second voltage reference appearing at the
de-energized while the circuit 80 is in a monitoring
mode and to have the electromechanical means 118 - 5 terminal 132 to thereby provide a tracking voltage
reference at the junction 136, and at the lead 111 con
energized for the brief instant after which the main
nected to the junction 136.
lamp 18 has failed but the switch 53 has not yet
A transistor 139 has a base terminal thereof con
changed position from the contact 90 to the contact 91.
nected by the lead 111 to the junction 136 and an
However since circuit 80 has completed its function
when it has caused the switch 53 to change positions 20 emitter terminal thereof connected through the lead
113 to the input line 81. Transistor 139 is of the PNP
such that the spare lamp 19 is energized, further energy
consumption considerations make it preferable to in
terrupt the functioning of the circuit 80. For this pur
pose, the switch 53 preferably has another pair of
type. The tracking voltage reference established by the
voltage summing and dividing resistors 135, 137 on the
the circuit 80 between the input lines 81,82. These
separate contacts 121, 122 comprise the second switch
53a. The switch 53a is normally closed against the
mately equal to the potential appearing at the line 81.
However, it is preferable to select the values of the
voltage summing and dividing resistors 135, 137 such
lead 111 will keep the transistor 139 in a non-conduc
contacts 121, 122 with the contact 121 in series with 25 tive state if the tracking voltage reference is approxi
that the tracking voltage reference on the lead 111 is a
the main lamp 18 fails and the circuit 80 causes the 30 couple volts positive with respect to potential appear
ing on the line 81 to avoid the transistor 139 from being
switch 53 to change position in response to the electro
rendered conductive because of electrical noise in the
mechanical means 118 as previously described, the
circuit 80.
switch 53a opens against the contact 122 thereby inter
When the main lamp 18 fails and current ceases to
rupting and rendering inoperative the control circuit
contact 121 to allow operation of the circuit 80. When -
80. Thus, further energy consumption in, and biasing
of, the circuit 80 are avoided.
Turning now to FIG. 3, the current sensing resistor
96 drops several volts of alternating-current voltage
thereacross during operation of the main lamp 18. A
35
?ow in the current sensing resistor 96, no voltage drop
will appear across the current sensing resistor 96 and
the diode 124 will no longer peak-charge the capacitor
126. Thus, the ?rst voltage reference appearing at the
junction 125 will begin to drop below the potential of
line 81 as the capacitor 126 discharges through the
resistors 135, 137, 131. As this discharge of capacitor
rectifying diode 124 has an anode terminal connected 40
through the lead 98 and the lead 94 to one terminal of
136 continues, a point in time will be reached at which
the current sensing resistor 96. The cathode terminal of
the emitter~base junction of the transistor 139 becomes
the diode 124 is connected through the lead 99 to the
foward biased. At this time, the transistor 139 is ren
terminal 125. A capacitor 126 is connected between
the junction 125 and the line 81 on the other side of the 45 dered conductive. Thus, the emitter-base junction of
the transistor 139 behaves as a voltage comparator in
resistor 96. The diode 124 half-wave recti?es the alter
nating-current voltage appearing across the resistor 96
during that portion of the cycle in which the lead 94 is
positive with respect to the line 81, in a peak-charging
comparing the tracking voltage reference on the line
111 to the potential on the input line 81.
A collector terminal of the transistor 139 is con
manner. A ?rst voltage reference is thereby established 50 nected by lead 117 to an electromechanical device 35,
with said device having a movable plunger 36 mechani
across the capacitor 126.
cally adapted to change the position of switch 53 and
A second rectifying diode 128 has a cathode terminal
the switch 53a. Another terminal of the device 35 is
referenced to the input line 82 by lead 102 through the
connected by a lead to a resistor 141. The other termi
switch 53a. The anode terminal of the diode 128 is
connected by lead 103 to a junction 129. A capacitor 55 nal of the resistor 141 is connected to an anode termi
nal of a diode 142, with a cathode terminal thereof
130 is connected between the input line 81 and the
connected to the lead 102 at a junction 143. Another
junction 129. The diode 128 half-wave recti?es the
diode 144 is connected between the leads 117, 119, in
voltage source between the input lines 81, 82 to estab
parallel with the electromechanical device 35. The
lish a second voltage reference across the capacitor
130, in a peak-charging manner. It will be appreciated 60 diode 144 is poled such that a cathode terminal thereof
is connected to the collector terminal of the transistor
that because of the manner in which the diodes 124,
139 and to the lead 117, with the anode terminal
128 are poled, the second voltage reference across the
thereof connected to the lead 119 and the resistor 141.
capacitor 126, and both capacitors 126, 130 are refer
The diode 142 is poled such that an anode terminal
enced to the input line 81.
'
Also connected to the junction 129 is a resistor 131 65 thereof is connected to the resistor 141 and the cath
ode terminal thereof is connected to the junction 143.
with the other terminal thereof connected to another
The diode 142 serves to prevent conduction of the
junction 132. A capacitor 133 is connected between
transistor 139 during those portions fo the alternating
the junction 132 and the input line 81. The values of
4,034,259
11
current cycle in which the line 82 'is positive with re
spect to the line Sland also serves to prevent reverse
voltage breakdown of the transistor 139 during said
12
in fading and dissolving modes of operation. It is there
fore extremely important that any means of detecting
failure of the main lamp 18 be capable of distinguishing
between operation of the circuit 80 at reduced voltage
portions of the alternating-current cycle. Besides func
tioning as a voltage comparator, the transistor 139
behaves as an electronic switch in applying the voltage
source levels and between failure of the main lamp 18.
The control circuit 80 is capable of performing this
source across the lines 81, 82 to the electromechanical
function. As the voltage source appearing across the
input lines 81, 82 is decreased, less current passes
through the main lamp l8 and through the current
sensing resistor 96 such that the portion of the voltage
device 35, the resistor 141 and the diode 142. It will be
readily appreciated by those skilled in the art however
that the transistor 139 could behave as a voltage com
parator alone with the collector terminal thereof driv
ing a separate semiconductor (not shown) or switch
means (not shown), with the separate semiconductor
or switch means controlling energization of the electro
mechanical device 35.
When transistor 139 is rendered conductive, the
source dropped across the current sensing resistor 96
also decreases. This further causes a corresponding
decrease in the level of the ?rst voltage reference ap
pearing across the capacitor 126 because the diode 124
has a lower level of alternating-current voltage to half
wave rectify. Similarily, the second voltage reference
electromechanical device 35 is energized causing the
appearing across the capacitor 130 decreases in poten
plunger 36 to move and the switch 53 to change posi
tial in direct correspondence to the decrease in the
tion from the contact 90 to the contact 91. _During
energization of the device 35, the resistor 141 limits the 20 voltage source appearing across the lines 81, 82. Be
cause the tracking voltage reference appearing at lead
maximum current which can pass through the windings
111 is obtained by ‘summing and dividing the ?rst and
of the device 35 to a suitable level. The diode 144 is
second voltage references, any descrease in the ?rst
normally non-functioning or is reverse biased. When
and second voltage references proportionally affects
the transistor 139 again returns to its non-conductive
state, the diode 144 provides an inductive current path 25 the potential of the tracking voltage reference. Thus,
proper selection of the resistors at the lead 11-1 to track
for the device 35 as the device 35 de-energiz'es. The
diode 144 limits the negative voltage across the device
35 to a forward-biased diode drop and thereby avoids
source .across the input lines 81,82. As further previ
having the device 35 place a large negative inductive
ously discussed, failure of the main lamp 18 causes
any voltage variation in the potential of the ‘voltage
, voltage spike on the collector terminal of the transistor 30 collapse of the ?rst voltage reference appearing across
the capacitor 126 because the capacitor 126 discharges
through the resistors 135, 137, 131 when a portion of
139.
When the transistor 139 energized the electrome
chanical device 35, switch 53a was caused to move
the voltage source dropped across the current sensing
from contact 121 to contact 122 to open the switch
resistor 96 is interrupted by failure of the main lamp
53a, thereby de-energizing the electromechanical de
18. Thus the circuit 80 is capable of distinguishing
vice 35. The device 35 is energized only for the‘ brief
between operation of the main lamp 18 at reduced
voltage source levels and between failure of the main
interval necessary to change position in switches 53,
53a. Opening'of the switch 53a also interrupts ,normal
biasing of the circuit 80 and further avoids placement
lamp 18.
type which cannot withstand large negative voltages
equivalents thereof.
It will be understood that various changes and modi
of a large negative voltage on the capacitor 126. The 40 ?cations may be made without departing from the spirit
capacitor 126 is preferably of an electrolytic, polarized
of the invention as de?ned in the following claims, and
thereacross. Normal biasing current for the circuit 80 is
I claim:
in the range of a couple millamperes.
1. A control circuit for a light projection system for
All of the electrical circuit elements within the
45 operation from an alternating-current voltage source,
dashed line 29a in FIG. 3 are suitable for mounting
said circuit comprising:
upon the circuit board 29 in FIG. 1.
a
a pair of input lines for applying said alternating
Typical component values and ratings for the various
circuit elements in FIG. 3, with the circuit 80 operating
from a 120 volt source, are as follows;
Diode l24
IN4002
Diode I28
Diode I42
Diode I44
IN4006
IN4006
IN4006
Capacitor I26
Capacitor I30
Capacitor I33
25 micro-farads, I5 volts
1 micro-farad, 200 volts
5 micro-farads, I50 volts
Resistor 96
,
current voltage source to said circuit;
a main lamp;
50
switch means in series connection with said main
lamp and said spare lamp for selectively energizing
said main lamp or said spare lamp across said pair
55
lamp and for dropping a portion of the voltage
wound
47 kilo-ohms
22 kilo-ohms
Resistor I35
3.9 kilo-ohms
Transistor I39
Electromechanical device 35
Solenoid, 24 volts drop
source thereacross;
60
2N54l6
means rectifying said portion of the voltage source
duty, 8l ohms
Type ELI-l
dropped across said current sensing means;
voltage comparator means for comparing the voltage
65
As previously discussed, light projection systems
used in commercial applications are frequently oper
ated at less than nominal vo1tages,especially when used
-
recti?cation means;
a voltage reference established ‘by said recti?cation
out, intermittent
Lamps l8, I‘)
of input lines;
current sensing means in series connection with said
switch means for sensing current through said main
5 ohms, 30 watts, wire
Resistor I31
Resistor I37
a spare lamp substantially in vparallel connection with
said main lamp;
difference between a pair of inputs, one of said
inputs referenced to one of said input lines, another
of said inputs for monitoring said voltage refer
ence, said voltage comparator means having an
13
4,034,259
14
output responsive to said pair of inputs and
of the voltage source dropped across said current
adapted to control said switch means, whereby
failure of said main lamp causes said portion of the
voltage source dropped across said current sensing
means to be removed therefrom, causing said volt
age reference to collapse and said voltage compar
sensing means to be removed therefrom, causing
said ?rst voltage reference to collapse and said
voltage comparator means to change said output,
said switch means responding to the changed out
put of said voltage comparator means to energize
ator means to change said output, said switch
means responding to the changed output to said
4. The control circuit as in claim 3 wherein said cur
said spare lamp.
rent sensing means comprises a resistor, said ?rst volt
age reference is established across a capacitor with one
terminal of said capacitor connected to one terminal of
said resistor, and said ?rst recti?cation means com
prises a diode connected between another terminal of
voltage comparator means to energize said spare
lamp.
.
>
2. A control circuit as in claim 1 wherein said voltage
comparator means controls the state of said switch
means by energizing an electromechanical device upon
said resistor and another terminal of the capacitor, said
ence to collapse, said electromechanical device having 5 diode half-wave rectifying the portion of the voltage
source dropped across said resistor.
mechanical interconnection to said switch means to
5. The circuit as in claim 3 further comprising delay
cause said switch means to change state and energize
means interposed between said second voltage refer
said spare lamp upon energization of said electrome
ence and said voltage summing and dividing means to
chanical device.
3. A control circuit for a light projecting system for 20 cause said tracking voltage reference to follow said ?rst
voltage reference when said voltage source is ?rst ap
operation from an alternating current voltage source,
plied to said circuit.
said circuit comprising:
6. The circuit as in claim 5 wherein said delay means
a pair of input lines for applying said alternating
comprises a resistor in series between said second volt
current voltage source to said circuit;
25 age reference and said voltage summing and dividing
a main lamp;
means; and a capacitor between said voltage summing
a spare lamp substantially in parallel connection with
and dividing means and one of said input lines.
said main lamp;
the failure of said main lamp causing'said voltage refer
7. The circuit as in claim 6 wherein said voltage com
parator means comprises a transistor with an emitter
said main lamp or said spare lamp across said pair 30 connected to one of said input lines, a base connected
to said tracking voltage reference; and collector con
of input lines;
.
nected to an electromechanical device, said electrome
current sensing means in series connection with said
switch means in series connection with said main
lamp and said spare lamp for selectively energizing
chanical device controlling said switch means.
8. The circuit as in claim 7 further comprising second
35 switch means responsive to the position of the switch
source thereacross;
means for selectively energizing said main lamp or said
?rst recti?cation means;
spare lamp; said second switch means being connected
a ?rst voltage reference established by said recti?ca
switch means for sensing current through said main
lamp and for dropping a portion of the voltage
in series between another of said pair of input lines, and
tion means rectifying said portion of the voltage
said second recti?cation means and said electrome~
source dropped across said current sensing means;
40 chanical device; said second switch means being in a
second recti?cation means;
closed state during operation of said main lamp, said
a second voltage reference connected in series with
said second recti?cation means across said pair of
input lines, said second recti?cation means poled
such that said second voltage reference is opposite
in polarity to said ?rst voltage reference;
voltage summing and dividing means connected be
second switch means assuming an open state shortly
after said switch means energizes said spare lamp to
interrupt energization of said electromechanical device
45 and said second recti?cation means.
tween said ?rst voltage reference and said second
9. The control circuit as in claim 5 wherein said light
projecting system is of the type which includes a light
voltage reference whereby said voltage summing
reflection means pivotable between a ?rst position and
and dividing means provides a tracking voltage
a second position for allowing direct light transmission
reference which will track the voltage on one of 50 from said main lamp to a projecting lens when said
said input lines when said voltage source is varied
re?ecting means is in said ?rst position, and for re?ect
in potential;
voltage comparator means for comparing the voltage
ing light from said spare lamp to said projecting lens
after failure of said main lamp when said re?ecting
difference between a pair of inputs, one of said
means is in said second position, said switch means
‘
inputs referenced to one of said input lines, another 55 furthermore sensing whether said re?ecting means is in
said ?rst position, said switch means energizing said
of said inputs for monitoring said tracking voltage
spare lamp as said re?ecting means leaves said ?rst
reference, said voltage comparator means having
position such that said spare lamp increases in illumina
an output responsive to said pair of inputs and
tion intensity as said re?ecting means pivots to said
_ adapted to control said switch means, whereby said
second position whereby said light projection system is
voltage comparator means distinguishes between
substantially uninterrupted by failure of said main
operation of said circuit at varied potentials of said
lamp.
voltage source and between failure of said main
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lamp, failure of said main lamp causing said portion
65
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