Lamp system take control dimming circuit

A circuit for providing remote control at a plurality of locations for a lighting system, such control functions including on/off, dimming intensity and rate of dimming. Visual indication of take control is also provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to control circuits for lighting systems and more 
particularly to control circuits permitting remote take control of dimming 
operations, rate of dimming and the like in high intensity discharge lamp 
systems. 
2. Description of the Prior Art 
It is only a fairly recent development that high intensity lighting systems 
have been equipped with the capacity to dim. The advent of this 
development is represented by the dimming circuit shown in U.S. Pat. No. 
3,816,794. More recently, a more sophisticated system has been developed, 
as disclosed in U.S. Pat. No. 3,894,265. 
Lighting systems with which such a dimming circuit are employed are often 
quite large, involving tens and sometimes even hundreds of individual 
lights deployed over large areas. It is a distinct advantage to be able to 
control the system from more than one location, such as at two doorway 
locations at the opposite ends of a large building. In fact, it is very 
desirable to have the ability to provide full control at numerous 
locations. 
Through experience, it has developed that it is not only desirable to 
change the amount of light intensity of a lighting system, but also to 
change the rate of intensity change from bright to dim or from dim to 
bright. 
Therefore, it is a feature of the present invention to provide improved 
apparatus for permitting the full take over of dimming controls for a high 
intensity lighting system at a plurality of locations. 
It is another feature of the present invention to provide an improved 
apparatus for permitting full takeover of intensity and rate of dimming 
for a high intensity discharge system at a plurality of locations. 
It is still another feature of the present invention to provide an improved 
apparatus for permitting full takeover of on/off and of dimming functions 
for a high intensity discharge system at a plurality of locations, a 
visual indication also being provided to indicated that a given "take 
control" station is operating the system. 
SUMMARY OF THE INVENTION 
A preferred embodiment of the invention comprises equipping each take 
control station with a gated semiconductor device connected to a constant 
current generator. A variable electronic resistor connected to the device 
establishes the intensity control to a common dimming network, the gate 
control to the device determining the operation of the device. 
A rate control having a time constant network is connected through a 
semiconductor to the electronic resistor. The setting of a resistor in 
this time constant network determines the rate of intensity change each 
time the variable electronic resistor is changed to change the intensity. 
An L. E. D. device is used at each take control station to show when that 
station is operating. Switching means is included at the take control 
stations and in a common interface network to ensure that all other 
stations except the one in charge are disconnected. This interface network 
also includes an electronic capacitance multiplier as part of the time 
constant network and various voltage compensating devices to ensure 
reliable operations.

BRIEF DESCRIPTION OF THE DRAWINGS 
So that the manner in which the above-recited features, advantages and 
objects of the invention, as well as others which will become apparent are 
attained and can be understood in detail, more particular description of 
the invention briefly summarized above may be had by reference to the 
embodiments thereof which are illustrated in the appended drawings, which 
drawings form a part of this specification. It is noted, however, that the 
appended drawings illustrate only typical embodiments of the invention and 
are therefore not to be considered limiting of its scope, for the 
invention may admit to other equally effective embodiments. 
In the drawings: 
FIG. 1 is a simplified schematic of the principal components of a take 
control station in the present invention. 
FIG. 2 is a simplified schematic in somewhat expanded form of the schematic 
illustrated in FIG. 1, also showing interconnection with the interface 
network of the present invention. 
FIG. 3 is a schematic diagram of a suitable dimming circuit for a lighting 
system, with which the take control circuit of the present invention can 
be operated. 
FIG. 4 is a schematic diagram of a single station take control station in 
accordance with a preferred embodiment of the present invention. 
FIG. 5 is a schematic diagram of an on/off switching network for a take 
control station of the present invention. 
FIG. 6 is a schematic diagram of a four-station take control station 
network in accordance with a preferred embodiment of the present 
invention. 
FIG. 7 is a schematic diagram of an interface network of a preferred 
embodiment of the take control circuit of the present invention. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now referring to the drawings and first to FIG. 1, a simplified schematic 
of a single take control station is illustrated. Such a station operates 
in conjunction with an interface network and with a lighting system 
operated by a master control station, both of which are described 
hereinafter. However, several features of a take control station may be 
observed by reference to the simplified schematic. 
First, the take control station operates in conjunction with a constant 
current generator 110 located in the interface network connected to 
terminal 1, a large capacitance located in the interface network connected 
to terminal 2 and a common terminal 4. The current generator supplies a 
nominal 10 milliampere current to the circuit. The take control station 
includes, in series with the current generator, a transistor switch 
embodied as SCR 112, a variable voltage device, illustrated as a variable 
resistor 114, and a visual indicator, illustrated as light emitting diode 
(L. E. D.) 116. Also included is variable resistor 118 connected between 
terminal 2 and the anode of the SCR. Variable resistor 114 provides means 
for varying the dc level of the voltage on terminals 4 and 2, and hence 
operates as an intensity control, and resistor 118 provides means for 
controlling the current flow from terminal 1 to terminal 2, and hence 
operates as a rate control. 
Current source 110 in FIG. 1, in combination with elements 112, 114 and 
116, forms a variable voltage source with variable output impedance 
charging or discharging capacitor 126 in FIG. 2, the desired voltage level 
being at a rate determined by the setting of resistor 118. 
Referring to FIG. 2, a slightly expanded version of the circuit shown in 
FIG. 1 is illustrated, similar components being identically marked, for 
convenience. 
Connected from the gate to the anode of SCR 112 is switch 120. Momentary 
closing of the switch applies a gate trigger to the SCR, which puts it 
into conduction and allows the station illustrated to "take control" of 
the operation of the system. Conduction of the SCR provides bias capacitor 
122 with current. After a short period of time, npn transistor 124, 
connected to the cathode of SCR 112 and to capacitor 122, is biased into 
condition, thereby providing a circuit through the emitter-collector of 
transistor 124. Completion of this connection supplies current to L. E. D. 
116 to light this L. E. D. as an indication that this take control station 
is now in control of system operation. The setting of variable resistor 
114 determines the absolute voltage level applied to terminal 2, and hence 
is the intensity control. A high position setting puts a large value of 
resistance in the circuit, i.e., the level setting is proportional to the 
value of the resistance. A low position inserts a lessor resistor value 
into the circuit and is the lowest variable setting. A latching connection 
setting at its low end is equivalent to a zero value resistor in the 
circuit, and, hence, represents the lowest setting. 
Capacitor 126 in the interface network connected to terminal 2 may be 
thought of as a memory capacitor. The voltage level on this capacitor had 
been previously set by the station in charge of the system before the 
present station has been switched to take control. If the value of the 
voltage as determined by the setting of resistor 114 is the same as 
previously established on capacitor 126, then there is no change. If, 
however, there is a voltage level change, the resistance of resistor 118 
represents a time constant value with capacitor 126 and determines if the 
voltage value thereon reaches its new value quickly or slowly. Hence, the 
setting of resistor 118 determines the rate of change of this voltage 
level. 
Operation of transistor 124 under assumed voltage conditions reveals more 
fully the operation of the voltage changes on capacitor 126. When 
transistor 124 conducts, the collector may either be positive or negative 
with respect to the emitter value. If the collector happens to be 
positive, then transistor 124 saturates and it functions as a normal 
transistor. On the other hand, if the collector happens to be negative, 
then the transistor acts like a diode through its base-collector junction, 
permitting the voltage level on capacitor 126 to readjust to the new 
setting at a rate cooperatively determined by the setting of resistor 118. 
Now referring to FIG. 3, high intensity discharge lamp 10 is connected in 
series with two inductive ballast elements 12 and 14, the entire 
combination being connected between lines 16 and 18. Gated bypass means in 
the form of triac 20 is connected across element 14, first main terminal 
22 of the triac being connected to line 16 and second main terminal 24 
being connected to a junction between the two inductive ballast elements. 
Gate terminal 26 is connected to shunt resistor 28, which is also 
connected to line 16. Resistor 30 and capacitor 32, connected in series 
with each other and in parallel with element 14, are provided as a snubber 
device to provide triac 20 immunity from commutating dv/dt false turn on. 
Two pairs of diodes 34 and 36 and 38 and 40 connected to gate 26 provide 
the gate source voltage to triac 20 from transformer 42. These diodes are 
connected so that two diodes 34 and 36 face forward and two diodes 38 and 
40 face backwards, with the junction point between each pair being 
connected together. Diodes 34, 36, 38 and 40 provide a slight forward 
voltage drop to block out the residual magnetizing force from transformer 
42 and to thereby prevent false firing of triac 20. Everything between and 
including transformer 42 and its accompanying series resistor 52, and 
inductor 14 may be considered to be in triac module 15. 
When triac 20 is conducting to form a complete bypass around element 14, a 
maximum amount of current flows through lamp 10. On the other hand, when 
triac 20 is not conducting, then the minimum amount of current flows 
through lamp 10. By allowing triac 20 to conduct for part of the cycle, 
then the current through lamp 10, and hence the illumination therefrom, 
may be varied between the dim lamp current and full lamp current values. 
Merely controlling the period of conduction of triac 20 will achieve 
controllable illumination of lamp 10. 
Control of the conduction of triac 20 is accomplished by the controllable 
gate voltage means connected to transformer 42. To understand the 
operation of the control circuit, some additional phase relationships have 
to be appreciated. The voltage across element 14 (reactor voltage) is 
leading lamp current by approximately 85.degree. and also is leading the 
line voltage by approximately 30.degree.. 
Triac 20 should not be rendered conductive until the current through and 
the voltage across element 14 are both of the same polarity, either both 
positive or both negative. If triac 20 where rendered conductive when the 
voltage across element 14 and the current therethrough were not of the 
same polarity, a phenomenon known as "half cycle conduction" would occur. 
The lamp would appear to flash from dim to fully bright each half cycle 
and would produce an irritating strobing effect to the eye that would also 
be harmful to the lamp. 
Power is applied to transformer 42 via the secondary 44 of power 
transformer 46, whose primary is connected across lines 16 and 18. One 
terminal of secondary 44 is connected to fuse or circuit breaker 48. Load 
resistors 50 and 52 connected to the two sides of the primary of 
transformer 42 are connected to ground. The power connection from the 
secondary 44 of transformer 46 to the primary of transformer 42 is through 
a bidirectional voltage regulating means in the form of cathode-to-cathode 
Zener diodes 54 and 56 and triac 58. It is well-known that alternatively 
Zener diodes 54 and 56 may be connected anode-to-anode and operate in the 
same manner. 
It may be seen that cathode-to-cathode Zener diodes 54 and 56 are connected 
in series with the main terminals of triac 58, the entire combination 
being connected as previously mentioned in series with secondary 44 of 
transformer 46. It is readily apparent that the gate voltage has for its 
source from secondary 44 a voltage which is in phase with the voltage 
across lines 16 and 18. 
Connected to the gate terminal of triac 58 is the cathode of programmable 
unijunction transistor (PUT) 60. The gate connection to PUT 60 is 
connected to a rectified dc voltage via variable resistor 62. The timing 
of the conduction of PUT 60 is determined by the voltage differential 
between the voltage applied via resistor 62 and the voltage applied to the 
anode of PUT 60. Both the voltage applied to the anode and to the gate of 
PUT 60 are important to its conduction. The anode voltage must be slightly 
larger than the gate voltage to cause conduction. That is, conduction is 
dependent on the arithmetic difference between the voltage applied to the 
anode and gate. Therefore, the setting of resistor 62 "programs" what 
anode voltage is required to produce conduction. The dc voltage applied to 
resistor 62 is developed by bridge rectifier 64 connected to secondary 66 
of transformer 46. A Zener diode 68 and current limiting resistor 70 
ensure that the voltage applied to resistor 62 never exceeds a 
predetermined value. 
The output from bridge rectifier 64 is also connected through diode 72, 
fuse 73 and variable resistor 74 to a time constant control network 
connected to the anode of PUT 60. This time constant network includes 
capacitors 76 and 78 and resistor 80. A diode 82 is included in series 
with the voltage from resistor 74. 
A diode 84 in the anode circuit of PUT 60 and capacitor 86 in the gate 
circuit of PUT 60 ensure positive reset of PUT 60 following conduction. It 
should be noted that the operating adjustment for PUT 60 is determined by 
variable resistor 62. The ultimate control for determining the amount of 
brightness of lamp 10 is determined by the setting of resistor 74. As PUT 
60 ages, the setting of resistor 62 can be changed, as well as permitting 
an easy setting for initial conditions. 
In operation, programmable unijunction transistor 60 is turned on by the 
voltage difference between the voltage on the anode of PUT 60 (voltage on 
capacitor 78) and the voltage on the movable contact of resistor 62. On 
each cycle of ac voltage applied to the bridge, there is a rise to a dc 
level at the output of this bridge for application to the gate of PUT 60 
through resistor 62. In a more sluggish fashion, a voltage determined by 
the setting of resistor 74 will be applied to the anode of PUT 60. When 
the difference in these two voltages is reduced at the gate and anode of 
PUT 60 to the point of causing conduction, a gate voltage is supplied to 
triac 58. Triac 58 conducts when the secondary voltage of 44 applied 
thereto exceeds the Zener diode voltage of diodes 54 and 56. When diodes 
54 and 56 conduct, there is a complete circuit in secondary winding 44 of 
transformer 46. 
Yet another method of achieving the desired timing of PUT 60 to achieve 
firing, even without Zener diodes 54 and 56, may be accomplished by 
selecting the components of resistor 74, resistor 75, which is connected 
between resistor 74 and ground, resistor 80, capacitor 78, the voltage 
determined by Zener diode 68, and the setting of the voltage on the gate 
of PUT 60 by the setting of the movable arm on resistor 62. The setting is 
determined by placing variable resistance 74 at its lowest or dim setting. 
If triac 20 is not gated on, no I.sub.2 current flows through triac 20 and 
the only current flow through the lamp (I.sub.T) is the current I.sub.1 
through reactor 14. This is reflected as the "dim state". On the other 
hand, if triac 20 is gated on during the entire time, then the entire 
current is bypassed around reactor 14 and through triac 20. Hence, I.sub.1 
becomes essentially zero and I.sub.T equals I.sub.2. This is the "full on 
state" condition. 
It is necessary that the gate voltage is prevented from continuing past the 
gate cutoff point. Although the gate voltage may be readily controlled by 
Zener clipping, other appropriate circuit means may be used for 
controlling the gate voltage to prevent voltage past the gate cutoff point 
from energizing the triac. 
Further, it is assumed that the ballasting is such that the line voltage, 
and hence the reactor voltage, leads the lamp current. Should there be a 
lagging situation so that the phase relationships are the other way, 
gating means may be provided so that the gate range would still only be 
while the reactor voltage and lamp current are of the same polarity. 
Once conduction of triac 20 is started, the gate source voltage must return 
to zero before the reactor voltage reverses polarity. This is accomplished 
by the Zener diodes cutting off when the gate source voltage applied 
thereto falls below a predetermined value. 
The turn off point of the Zener diodes does not vary. It is apparent, 
however, that the shutting off of the Zener diodes and hence the gate 
source voltage to triac 20 does not instantaneously render triac 20 
nonconductive. The inductance of elements 12 and 14 causes current to 
continue through triac 20 until the reactor current crosses zero and the 
triac commutates. The current through lamp 10, after such commutation, is 
only current through reactor 14. 
Two switches are provided, either of which may be used to replace the 
variable control of the circuit to a full bright or full dim operation, if 
desired. Switch 90 is connected between diode 82 and resistor 74. This 
switch is a three-position switch. When it is placed to its center 
connection, connection is made to the variable contact of resistor 74 and 
operation is as previously described for variable control operation. When 
placed to the HIGH position, contact is made to the top of resistor 74 and 
the greatest amount of voltage is applied. The LOW position of the switch 
disconnects voltage from diode 82. 
In operation, the highest setting of resistor 74 causes the anode voltage 
applied to PUT 60 to reach the level of firing the PUT in the shortest 
period of time. This assures gate voltage to triac 20 and hence full lamp 
current to lamp 10, as explained above. Absence of voltage, or low voltage 
operation, achieves the opposite effect. 
Alternatively, switch 92 may be used to achieve high (full brightness) or 
low (dim) operation. In the LOW position of switch 92, there is a 
disconnect of transformer 46 from transformer 42. This means that no gate 
voltage is provided triac 20 and hence dim current is always supplied to 
lamp 10. In the HIGH position of switch 92, a center-tap connection is 
made from secondary 44 of transformer 46 to transformer 42. This supplies 
all the gate voltage that is necessary to keep the triac conducting the 
maximum amount of time and therefore supplies full lamp current to lamp 
10. Only part of transformer secondary 44 is used since switch 92 provides 
operation without having to supply power also to the variable control 
circuit. 
Reset operation of PUT 60 involves capacitor 86, capacitor 78, which is 
somewhat smaller than capacitor 86, diode 84 and triac 58. As already 
mentioned, when the exponential voltage rise on the anode of PUT 60 
reaches a value that is a predetermined difference to the voltage applied 
to the gate of PUT 60, PUT 60 conducts. Assuming that the anode voltage 
never reaches the critical level with respect to the steady state dc level 
on the gate for conduction, PUT 60 will conduct nevertheless because the 
voltage on the gate of PUT 60 reduces until the critical predetermined 
voltage difference between gate and anode exists. In other words, there is 
a force firing of PUT 60. The firing of PUT 60 is caused by capacitor 86 
discharging through the path comprising resistor 70, the resistor in the 
center of bridge 64, capacitor 78 and the anode-to-gate path of PUT 60. 
When PUT 60 turns on, capacitor 78 discharges through the PUT and triggers 
triac 58. If the secondary voltage of 44 exceeds the Zener threshold 
voltage of Zener diodes 54 and 56, then the gate source voltage from this 
control circuit is produced, as previously described. In any event, 
because capacitor 86 is bigger than capacitor 78, eventually diode 84 
conducts to cause a slight reverse build-up on capacitor 78. Since triac 
58 commutates, the cathode of PUT 60 becomes zero, and hence there is an 
anode-to-cathode reverse bias which turns off the PUT. Moreover, when the 
line again begins to build-up, the gate voltage of PUT 60 rises to further 
ensure that gate current stops until the rising voltage on the anode again 
establishes conduction conditions. 
Variable resistor 81 is connected in series between diode 82 and resistor 
80 to provide an additional resistive element to the RC time constant 
determining voltage build-up on capacitors 76 and 78. This series resistor 
allows a manual setting of the rate of build-up or drop off in the light 
setting with a change of setting of the wiper on resistor 74. Terminals 4, 
5 and 6 provide connection points for the interface network to the 
lighting system just described. Terminal 6 merely provides power to a 
latching relay 83 when there is power supplied to the interface network 
for closing contacts to the power lines and, hence, providing power to the 
system. Terminal 5 provides a connection to the system for varying the 
critical voltage level that controls the dimming operation just described. 
This is where the results are applied of the interface network, that 
received a signal from the take control station in command of the system. 
Terminal 4 is the common connection, which may also be ground, as shown. 
Now referring to FIG. 4, an actual single take control station schematic 
diagram is shown, similar parts being identically numbered in accordance 
with the scheme set forth in the simplified diagrams shown in FIGS. 1 and 
2. To turn on SCR 112 from the constant current source connected to 
terminal 1, it is necessary to close switch 120, which, for convenience, 
is merely a push button. Prior to the closing of the switch there was some 
voltage on the anode, but no voltage on the cathode. The closing of the 
switch provides a charging path for capacitor 128 through the switch, 
through limiting resistor 130, to the gate of the SCR. Resistor 132 
connected in parallel with capacitor 128 discharges capacitor 128 after 
push button 120 is released, thereby interrupting the gate current to SCR 
112. Resistor 134 limits the gate voltage build-up due to SCR gate leakage 
current. 
When the voltage level builds up on the base of transistor 124, it 
conducts, as previously discussed. Resistor 136 is a leakage bypass 
resistor. The remainder of the components connected between L. E. D. 116 
and transistor 124 are range limiting components for the basic variable 
resistor 114. If resistor 114 is not in its lowest position, which also is 
its switch latching position, then the variable portion determines the 
voltage level on the emitter, as limited by resistor 138 connected 
thereacross, resistor 140 connected in series with the parallel 
combination of 114 and 138, and resistor 142 connected via transistor 144 
across resistors 114, 138 and 140. Latching of resistor 114 in the low 
position turns on transistor 144 to provide a discontinuity step to a low 
voltage below the variable range that exists when the transistor is not 
conducting. The purpose of this is explained hereinafter. 
Now referring to FIG. 5, a take control power on/off station switch and 
indicator is shown. Terminal 3 is connected in the interface network to 
the contacts of a latching relay. Connected to one set of contacts is a 
diode connected in the same polarity arrangement as diode 146 of the FIG. 
5 circuit and connected to another set of contacts is a diode connected in 
the same polarity as diode 148. The latching relay in the interface 
network, after push button 154 has been momentarily depressed into the 
"on" position, latches to this "on" position, thereby initially providing 
power to the lighting system. In the presence of a power interruption and 
restoration, this interface network latching relay switch does not drop 
out, but remains in. Positive half cycles of the restored voltage are 
passed through the latching relay contacts and the similarly aligned diode 
in the interface network and through diode 148, limiting resistor 150 to 
L. E. D. 152, to show the presence of restored power. 
In summary, therefore, if the light does not come on, then to provide power 
to the system it is necessary to close spring-loaded switch 154 to the 
"on" position, which, through the operation of the latching relay circuit 
in the interface network, causes the latching relay contacts to switch 
over to the "on" position. Finally, if the light is on at the take control 
system and it is desired to turn the system off, then momentary switching 
of switch 154 to the "off" position provides this disconnection. Operation 
of the latching relay in the interface network is discussed more fully in 
conjunction with the discussion of the interface network. 
Now referring to FIG. 6, a four-station take control system is shown. With 
such an arrangement, an operator at any one of the stations can take 
complete control of the entire system and control the intensity of the 
lights and the rate of change of intensity. As discussed with respect to 
the single station arrangement, like numbers are used to identify the 
component parts of each station, the numbers being supplemented with "a", 
"b", "c", and "d" for the respective four stations. Where the parts are 
similar to the component parts of the single station take control circuit 
shown in FIG. 4, the numbers match with these numbers, as well. 
The only differences between the individual take control networks in the 
four-station system and the single station network shown in FIG. 4 are 
with respect to simplified arrangements for the variable intensity 
resistor arrangements. Unlike the single station take control circuit 
shown in FIG. 4, there is no transistor 144. Further, at the "b", "c" and 
"d" stations, variable intensity control resistors 114b, 114c and 114d are 
not connected in parallel with another resistor. Finally, at station "a", 
the L. E. D. has an additional in-series resistor 156 connected thereto. 
When there are multiple stations, not only is it necessary for the 
respective push buttons 120a, 120b, 120c or 120d to operate to take 
control for the station operated, the other stations must be affirmatively 
disconnected. Assuming switch 120a is momentarily shut, not only is the 
required gate signal applied to SCR 112a, but also the anodes of SCR's 
112b, 112c, and 112d connected to line 1 are all pulled slightly negative 
with respect to their cathodes, causing cut-off to occur of whichever SCR 
was conducting prior to the closing of switch 120a. As soon as that SCR 
112 stops conducting, the associated transistor 124 will no longer receive 
base drive, so that its base and emitter voltages will drop to zero volts. 
The collector will not conduct any current any longer (except leakage), 
and the take control station is not only effectively disconnected from 
line 1, but also from line 2. 
Now referring to FIG. 7, a schematic of the interface network is shown. The 
various componets perform a number of different functions. 
Terminal 1 is connected to the collector of a pnp transistor 210, whose 
emitter is connected through emitter resistor 212 and diode 214 to ac 
transformer 216. The base of transistor 210 is connected through diode 218 
and resistor 220 to diode 214 and through resistor 222 to the common lead. 
These components comprise the constant current generator 110 previously 
discussed in conjunction with FIGS. 1 and 2. 
Terminal 2 is connected to an electronic capacitance multiplier, which acts 
as the simplified capacitor illustrated as capacitor 126 in FIG. 2. A 
memory capacitor 224 is connected to terminal 2 through resistors 226 and 
228 and connects to the input of an operational amplifier 230, together 
with the components of a high frequency filter comprising resistor 232 and 
capacitor 234. Resistor 228 is a stop resistor ensuring the low limit to 
which the external rate resistor in the take control circuit can be set. 
Operational amplifier 230 operates in the analog linear mode and supplies 
its output through resistors 236 and 237 to output transistor 238. The 
collector of transistor 238 is connected to output terminal 5 through 
diode 240 and is connected back through a voltage dividing network 
comprising resistor 242, isolation diode 244, and resistor 243 to 
noninverting buffer operational amplifier 246. The ouput of this 
operational amplifier through resistor 248 completes the basic connection 
for the electronic capacitance multiplier. Resistor 248 is typically about 
a 1000-ohm resistor and resistor 226 is typically about a 1-megohm 
resistor, thereby achieving a multiplication ratio of about 1000. It 
should be noted that resistor 254 to operational amplifier 230 is the same 
value as resistor 226. Hence, amplifier 246 acts like a voltage follower 
or buffer amplifier with a net gain of 1. 
There is a connection to the reference terminal of operational amplifier 
230 through resistor 252. The voltage on this resistor may vary to have an 
overriding effect on the level of voltage on capacitor 224. 
Operational amplifier 256 has a sensing input connected through resistor 
258 to terminal 1. The reference level is determined by voltage divider 
action from the line to terminal 6 by resistors 259, 260 and 262. When the 
sensed level from terminal 1 goes below the reference level at the 
positive input, then the output level from operational amplifier 256 goes 
up, causing conduction of diode 264 and an adjustment of the reference 
level to operational amplifier 230. In case all remote stations are off, 
no input signal is received at terminal 2, so that the voltage at that 
point drops to a low value. However, the voltage across capacitor 224 is 
kept at a level determined by the voltage at the junction of resistor 259 
and 260, minus a voltage drop of diode 266. This level corresponds to a 
dim light setting, so that when a remote station is energized, capacitor 
224 will already have an initial "dim" charge, rather than having to be 
charged up from zero. 
Operational amplifier 268, connected for operation as dc comparator, is 
useful in providing a possible override connection to operational 
amplifier 230 when the take control station SCR's are all disconnected. 
When this occurs the junction between resistors 270 and 272 connected as 
an input may be exceeded by the voltage on terminal 1 through resistor 
258. Note that the voltage of the reference connection is set by Zener 
diodes 274 and 276 through resistor 277 and through capacitor 278. When 
the terminal 1 level exceeds the reference level at resistors 270 and 272, 
diode 280 connected to the output of comparator 268 conducts to override 
the sensing level of terminal 2 applied to resistor 226. Diodes 281, 282, 
283 and 284 are connected in pairs for transient reduction. 
In operation, it may be seen that the reference level to operational 
amplifier 256 floats with the level on the line to terminal 6, whereas the 
reference level to comparator 268 is set by the Zener diodes. The sensing 
connection to each, however, is at the same point. 
Now referring to the lower part of the diagram, the on/off system having a 
memory is shown. If contacts 310 of latching relay 312 are in the "OFF" 
position, then a signal is required to cause the latching relay to switch 
from the "OFF" position to the "ON" position. The "OFF" position signifies 
that no power is supplied to the lighting load, and that none of the take 
control stations are in control. The master control shown in FIG. 3 is 
always energized, awaiting an instruction to energize the lighting load. 
Placing the take control station on/off switch 154 shown in FIG. 5 in the 
"ON" position while interface latching relay contacts 310 are in the "OFF" 
position completes a path through diode 314, through resistor 315, through 
transistor 316, to resistors 317 and 319, thus biasing transistor 326. 
Transistors 316 and 326 form a modified multistable multivibrator whose 
time constant is determined mainly by resistor 318 and capacitor 320. 
Transistor 316 acts in a grounded base mode. Once transistor 316 is 
conducting, its emitting circuit flows through diode 328. Resistor 322 and 
capacitor 324 are a spike filtering system. Transistor 326, illustrated as 
a Darlington pair, is operated full on by regenerative action to cause the 
latching action to act in a positive manner, thus placing switching 
contacts 310 to the "ON" position. A second set of contacts, via a relay 
in the master control box (not shown), will energize a lighting load 
contactor in the ac power lines. 
When contacts are already in the "ON" position and power is reestablished 
after an outage, it is not necessary to place switch 154 in the "ON" 
position. If desired, deenergizing the lighting load can be achieved by 
placing switch 154 temporarily in the "OFF" position. When switch 154 is 
placed in the "OFF" position, the cathode of diode 148 is then placed to 
the common voltage level during positive half cycles of applied voltage. A 
path exists for the positive half cycles from transformer 216, through 
resistors 328 and 330 and diode 332, through contacts 310 via line 3 to 
diode 148 and to ground. The voltage across resistor 328 is divided by 
resistors 322 and 334, to develop the bias voltage to make transistor 316 
conductive, now in a grounded emitter mode. The same regenerative process, 
takes place a previously discussed forcing latching relay 312 to change 
the position of its contacts. 
It should be further observed that when none of the take control stations 
are operating and hence contacts 310 are to "OFF", then transistor switch 
338 is pulled down to zero each half cycle. With none of the take control 
stations operating, the voltage at connection terminal 1 will be high, 
because current source transistor 210 conducts fully. This makes the 
output of comparator 268 high, pulling the junction of resistor 248 and 
resistor 226 up, so that the voltage on capacitor 224 quickly goes to a 
high level. This causes amplifier 230 to deliver a low output voltage, 
causing transistor 238 to conduct fully and causing the output voltage at 
connection terminal 5 also to become high. Thus, the connected dimmer 
master control box (FIG. 3) drives a lighting load up to a full power 
level when no take control station is in the circuit. 
Without comparator 268, overriding signals at connection terminal 2, the 
output voltage at terminal 5, as well as the resulting light level, would 
not be well determined. When the system power is off, only the lighting 
power is off. However, the interface circuit as well as the master 
controller are continuously energized. It would be useless to have any 
take control station operating with an LED 116 on when the main lights are 
not energized. To prevent any take control station from being energized 
under such conditions, transistor 338 is incorporated. It is made to 
conduct fully every negative half cycle, by means of resistor 337, thereby 
pulling it collector voltage and thus the voltage at connection terminal 1 
repetitively to zero volts, thus forcefully commutating any SCR 112 that 
might have been triggered previously and to thereby keep all LED's off. 
The output voltage on terminal 5 is either in the range from 12 to 32 
volts, in an exemplary system, or zero, when a take control station is in 
control and the intensity resistor control is placed to its catching 
position. The input level on terminal 2 to the interface network, to 
accomplish the desirable output range, is in the appropriate range of 8 to 
22 volts or 5 volts. 
While particular embodiments of this invention have been shown and 
discussed, it will be understood that the invention is not limited 
thereto, since many modifications may be made and will become apparent to 
those skilled in the art. For example, the electronic resistor employed as 
the heart of the intensity control may be a signal generator, if desired.