EP0020493B1

EP0020493B1 - Fluorescent lamp lighting system

Info

Publication number: EP0020493B1
Application number: EP19790901332
Authority: EP
Inventors: Don F. Widmayer
Original assignee: Controlled Environment Systems Inc
Current assignee: Controlled Environment Systems Inc
Priority date: 1978-09-26
Filing date: 1980-04-22
Publication date: 1986-03-12
Also published as: JPS5598500A; DE2967585D1; MX149353A; CA1128605A; FR2443183B2; EP0020493A4; WO1980000776A1; EP0020493A1; FR2443183A2

Abstract

An energy conserving lighting system wherein a plurality of fluorescent lamps (L1', L2') are powered by a poorly regulated voltage supply which provides a decreasing supply voltage with increasing arc current so as to generally match the volt-ampere characteristics of the lamps. A transistor ballast and control circuit connected in the arc current path controls the arc current, and hence the light output, in accordance with the total ambient light, i.e., the light produced by the lamps together with whatever further light, is produced by other sources such as daylight. In another embodiment, a transistor ballast is utilized in combination with an inductive ballast (1001). The transistor ballast provides current control over a wide dynamic range up to a design current maximum at which maximum the transistor (60''') is saturated and the inductive ballast takes over the current limiting function. An operational amplifier (116) is preferably connected in the base biasing circuit of the control transistor of the transistor ballast. In an embodiment wherein two sets of lamps with separate inductive ballasts (100', 142) are provided, the arc currents for the two ballasts are scaled or matched to provide the desired light output.

Description

Technical Field

The present invention relates to fluorescent lamp lighting systems for illumination purposes and the like.

Background Art

IN GB-B 2,007,880 (Don Frederick WIDMAYER), published after the priority date of the present application, there is described an energy conserving lighting system in which a plurality of fluorescent lamps are powered by a poorly regulated voltage supply which provides a decreasing supply voltage with increasing arc current so as to generally match the. volt-ampere characteristics of the lamps. A transistor ballast and control circuit connected in the arc current path controls the arc current and hence the light output in accordance with the total ambient light, i.e. the light produced by the lamps together with whatever further light is produced by other sources such as daylight. In another embodiment, a transistor ballast is utilised in combination with an inductive ballast. The transistor ballast provides current control over a wide dynamic range up to a design current maximum at which maximum the transistor is saturated and the inductive. ballast takes over the current limiting function.
While the above types of system are advantageous in their application to single ballast fixtures or units containing one or more lamps, difficulties can arise in attempting to operate a plurality of such units in parallel from a common light regulating system.
It is an object of the present invention to provide a fluorescent lamp lighting system capable of controlling two or more lamp units each comprising one or more lamps and a ballast therefor from a single light regulating system.
This object is solved by the lamp lighting system as set forth in the appendant claim.
Other features and advantages of the invention will be set forth in, or apparent from, the detailed description of the preferred embodiments found hereinbelow.

Figure 1 is a schematic circuit diagram of a fluorescent lamp lighting system of the kind with which the present invention is concerned in which a single lighting unit is controlled by a control unit in dependence upon the light output from the lighting unit;
Figure 2 is a schematic circuit diagram of a modified form of the system illustrated in Figure 1 in which two lighting units are controlled by a single regulating system; and
Figure 3 is a schematic circuit diagram of a further modified form of the system illustrated in Figure 2.

Referring to Figure 1, an embodiment is illustrated wherein a basic arc control circuit such as is disclosed in the above mentioned GB-B-2007880 (Don Frederick WIDMAYER) is altered so as to use an operational amplifier and a transformer power supply.
Whilst this modified basic arc control circuit is not an example of the present invention, the detailed description of its construction and operation which now follows is essential to a full appreciation of the invention as exemplified in the embodiments shown in Figures 2 and 3.
Considering the power supply portion of Figure 1, a transformer 102 steps down the line voltage (which may be 116 VAC, 277 VAC or other available line voltages) to a 10 VAC voltage appearing on the isolated secondary winding thereof. A diode 104 acts as a half-wave rectifier so as to permit the positive half-cycle of the secondary voltage to charge a capacitor 108 connected across the secondary to a level approximately 14 VDC above the voltage of the common bus, referred to hereinafter as the signal common. This voltage level will hereinafter be referred to as the plus or positive supply. A further diode 106 permits the negative half cycle of the 10 VAC secondary voltage to charge a capacitor 110 to a level approximately 14 VDC below signal common, which level will hereinafter be referred to as the minus supply. A resistor 82'" is connected in series combination with a zener diode 78"', with zener diode 78'" being connected to the signal common bus and resistor 82'" to the plus supply, as shown, in order to provide a regulated voltage above the signal common voltage above for signal generation purposes.
The use of a plus and minus power supply is desirable, although a single sided supply can be employed, when an operational amplifier is used.
The employment of such an operational amplifier whether used in a virtual ground summing mode or a differential input configuration has numerous advantages including the exceedingly high gain attributes of most operational amplifiers. Figure 1 shows operational amplifier 116 connected in a differential input configuration. The setting of a potentiometer 64'" provides a reference signal at the plus input of operational amplifier 116. A light controlled variable resistance photocell 74"', which is connected to a resistor 112 and a resistor 114 as shown, is connected to the minus input. Before proceeding it should be noted that the function of potentiometer 64'" can also be replaced by a remote program signal, signal generator or the like in an application requiring remote adjustment of the reference signal.
When photocell 74"' and resistor 112 are connected in a circuit between signal common and the plug regulated bus, they act as a voltage divider wherein the amplitude of the voltage at their junction node 113 will vary from almost zero volts (with photocell 74''' in darkness) to almost that of the plus regulated bus (in bright light). As noted above, junction node 113 is connected to the minus input of operational amplifier 116 through resistor 114. Resistor 114 is part of an RC time constant network that further includes a capacitor 118. This network helps to prevent abrupt changes in the output of the system where this is desirable. Alternatively, for a faster response system, the RC network might be modified to different component values or be removed with the minus input of operational amplifier 116 can be connected directly to the junction of photocell 74''' and resistor 112.
The output of operational amplifier 116 is connected to a further diode 120. The latter is also connected to a diode 122 whose anode is also connected to the junction of a pair of voltage divider resistors 124 and 126.
The values of resistors 124 and 126 are selected such that the junction voltage, i.e., the voltage on the anode of diode 122, provides a minimum "on" signal through diode 122 to a transistor 60"'. Hence, transistor 60''' is "on" at some minimum level related to the voltage division of resistor 124 and 126 whenever the system has AC line power.
Transistor 60''' drives a control transistor 26''' via a resistor 128 which acts as a current source to minimize component thermal drifts and the like. Transistor 26"' is connected through a diode bridge formed by diodes 92', 94', 96' and 98' to an inductive ballast 100' for a pair of lamps L₁' and L₂'. Ballast 100' and the connections to lamps L₁' and L₂' are conventional. Transistor 26"' normally operates in the active region, thereby limiting the current in the ballast primary only when the lamps are ignited. However, transistor 26"' is effectively saturated "on" during the "lamps off" portion of the AC cycle so full magnetising and lamp filament current is provided at least up to lamp ignition. To reiterate, it is important to understand that, except for the minor losses in the bridge across and saturated transistor 26"', the full line voltage is applied to the ballast 100' until the lamps ignite. Hence, the ballast 100' is provided with magnetizing current and the lamps have their rated cathode current when applicable. The bridge diodes 92', 94', 96' and 98' rectify the AC of the ballast 100' and transistor 26"', being located in the DC leg, permits DC control techniques to be employed. When the lamps L₁ and L₂ ignite the load applied to the secondary (not shown in Figure 1) of the inductive ballast 100' is reflected to the primary (not shown in Figure 1) and an increase in primary current is demanded by the lamps. The base drive set by the light loop, determines the amount of collector current that is allowed to flow through transistor 26'''. Therefore, when the current demand of the lamps is not satisfied by transistor 26"', the voltage across the primary of the ballast 100' falls. At the same instant in time, this drop in ballast primary voltage is applied to the collector-emitter circuit of transistor 26'''. This voltage, when added to the ballast primary voltage, equals the line voltage until the lamps are extinguished further on in the half cycle. At this latter time, the voltage from the collector to emitter of transistor 26''' is reduced to a minimum and transistor 26''' therefore reverts to a saturated condition. The signal information for the closed loop is thus generated at a 120 Hz rate for a 60 Hz system and a 100 Hz rate for a 50 Hz system, and in approximately 6 millisecond bursts from the lamps for a 60 Hz system and in 8 milliseconds bursts for a 50 Hz system. These bursts of light are averaged by the time constant circuit associated with operational amplifier 116.
Briefly considering the operation of the embodiment of Figure 1, when the system is energized with either 116 VAC or other line voltages, current flows through the primary of ballast 100' and two of the diodes 92', 94', 96' and 98', depending on the polarity of half cycle of the AC input. Further transistor 26"' is conducting, transistor 26"' being "saturated on" by the reference signal derived from potentiometer 64"', providing that this reference is sufficient to drive the output of operational amplifier 116 to a voltage level sufficient to back bias diode 122. Alternatively, if the output voltage of operational amplifier 116 is insufficient to back bias diode 122, the minimum signal provided by diode 122 will back bias diode 120, with diode 122 providing a minimum signal from voltage divider resistors 124 and 126 to transistor 60"'. The signal from diode 120 or diode 122 turns on transistor 60'" through resistors 128 and transistor 26'" is saturated "on" as long as the lamps have not ignited. It is noted that a transistor is saturated "on" when that transistor has sufficient minority carriers in the base region so as not to limit any current which would flow through the collector diode. Expressed another way, the collector current of the transistor is now unlimited and will remains so to the extent of the availability of minority base region carriers.
For this saturated condition of transistor 26"', the primary ballast transformer 100' essentially receives the full line voltage and the saturated transistor 26"' conducts the magnetizing current of ballast 100' (together with the load current of the lamp heaters if rapid start lamps are used). After the cathodes in lamps L₁ and L₂ are heated, and the halfwave AC lamp voltage rises to a firing level, the lamps ignite. Current through lamps L₁ and L₂ then rises to a level dependent on base drive of transistor 26"', as explained hereinabove. Once this current level is reached, the transistor 26"' comes out of saturation and the current flow is not limited. At this time, the circuit voltages adjust due to the fact that the change in circuit current ceases. In particular as the AC half- wave ballast primary voltage falls, the difference between the line voltage and this ballast primary voltage appears across transistor 26"'. This adjustment in voltage continues such that the sum of ballast primary voltage and transistor voltage equals the line voltage, i.e. the instantaneous supply voltage, until the lamps extinguish. This occurs each time the AC half-wave declines to non-sustaining arc level. At this time, the circuit current will begin to be less than the regulated value and the transistor 26"' then resaturates and the collector-emitter voltage reaches a saturation minimum. The ballast primary voltage is then once again equal to the line voltage minus the small saturation voltage of the saturated transistor-diode bridge combination.
The operation of the circuit of Figure 1 described above is repeated during a part of each half cycle of the line voltage depending on the duration of the current limiting period. The base drive or regulated collector current of transistor 26"' is set by the closed loop completed through lamps L₁ and L₂ and photocell 74"'. The loop response is slowed down by the RC network formed by resistor 114 and capacitor 118 such that fast changes in light level are averaged over a several second time period. However, as noted above, the loop can also have a fast response by providing adjustments to, or the elimination of, the RC network.
The value of current limiting provided in response to a related light level is set by setting the tap or wiper of potentiometer 64''' to produce the desired output voltage. Feedback is provided by sensing the light output from the lamps L₁ and L₂ and/or some other light components via a light collecting lens CL attached to a bundle of fiber optics FO to transmit a measure of the ambient light level at a given location to photocell 74'" generally located with the control circuitry within a lamp fixture without using electrical conductors. This ensures that the selected lamp current will be limited to a level related to the reference signal level. In operation, the feedback light produces a voltage at the junction of photocell 74'" and resistor 112. Assuming that light is falling on photocell 74"', this voltage increases until it is virtually equal to the potentiometer voltage at the positive input of operational amplifier 116. The almost zero difference voltage referred to constitutes the signal which produces the regulated current through lamps L₁ and L₂. The light output of the lamps L, and L₂ may be increased or decreased by changing the reference level signal provided by potentiometer 64'" within the bounds of the lower limit set by the voltage at the junction of resistors 124 and 126 and the upper level set by the inherent current limiting of the ballast 100'. Whenever the current limit of ballast 100' is reached, transistor 26"' is again saturated "on".
It is noted that in the embodiment described above the minimum level signal is established by adjustment of the reference or command signal potentiometer (element 64"') so as to establish a minimum reference signal level at the transistor summing point. To summarize, the control transistor is saturated "on" for the period of time during each AC half cycle that the lamps are not ignited. Therefore, firing of the lamps is not inhibited and once the lamps fire, the control transistor then operates in a new unsaturated linear range up to the point that the ballast limits the current. Further, with the use of a sufficient input reference signal, the ballast will provide limiting and the control transistor is again saturated with lamps "on". This sequence repeats itself each half cycle.
Before considering the embodiment of Figure 2, certain background considerations should be examined. In most instances in the commercial lighting field each pair of lamps in a fixture has an AC inductive ballast; in fact, many fixtures contain four lamps with two ballasts in the ballast compartment of the fixture. While an individual system could be used for each ballast, substantial savings might be realized if two or more ballasts could be operated from a single control system. However, in actual practice two ballasts cannot be operated in parallel from a single system because the lamp pairs, in effect, act in a manner somewhat analogous to zener diodes. Specifically, one pair inevitably ignites and thereafter, while the other pair may subsequently ignite, this pair will operate in a low uncontrolled current region so that only the pair that first reaches the arc discharge region is controlled. This behaviour of paralleled ballasts is due to the arc-discharge phenomena and is a substantial obstacle to realizing the economies referred to above.
One simple but unique solution to this problem is illustrated in Figure 2. Generally speaking, apart from the circuitry used in providing the solution in question, Figure 2 corresponds to Figure 1 with addition of a second pair of lamps L₃ and L₄ and an associated ballast, and the same reference numerals are used for common components. In accordance with this solution referred to, another four diode bridge formed by diodes 134, 136, 138 and 140, a control transistor 141, and a pair of emitter resistors 130 and 132, are connected as shown in Figure 2. It is noted that one of these emitter resistors, viz., emitter resistor 130, is added in the emitter leg of transistor 26''' and the base lead of transistor 141 is connected to the junction between resistor 128 and transistor 26"'. If it is assumed, for example, that when the lamps L₁ and L₂ connected to the ballast 100' ignite, the system (and the associated lamp pair) proceed to a current limited mode set by the collector-emitter current of transistor 26'" it will be seen that the collector-emitter current will generate a voltage across resistor 130 tending to reduce the base drive for transistor 26''' relative to transistor 141. This will happen unless there is a similar current flow in ballast transistor 141 whereby a matching voltage would be developed across emitter resistor 132. Therefore, the collector-emitter currents of transistor 26"' and 141 would tend towards matching due to the "emitter degeneration" caused by the emitter resistors 130 and 132. It will also be appreciated that the value of resistor 128 must be reduced so as to provide the extra current to drive the additional transistor for the second ballast.
This concept, with appropriate modification, could also be extended to include additional ballasts in other fixtures. The fixture with the sensing and reference signal circuitry will hereinafter be referred to as the "master unit" and the second ballast and/or other fixtures with other ballast(s), together with their full wave bridges and control transistors with emitter resistors, will hereinafter be referred to as "follower units". The power supply, as well as transistor 60'" of the master unit, must be suitably rated to provide sufficient signal levels to accommodate the needs of a plurality of control transistors. Electro-optical devices can also be employed to eliminate wiring used in conductive coupling between master and follower units.
Referring to Figure 3, another embodiment of the master-follower concept is illustrated. Figure 3 is similar to Figure 2 and like elements have been given the same reference numerals. The advantage of the embodiment of Figure 3 over that of Figure 2 is that the currents flowing in the primaries of the one or more follower ballasts are more precisely matched or sealed. In addition to the components added in Figure 2, a further transistor 60₁ and further operational amplifier 116₁ are also incorporated in the follower circuit. The reference signal supplied to the plus input of operational amplifier 116₁ is derived from the voltage generated across emitter resistor 130 and the feedback or minus base input to operational amplifier 116₁ is derived from the voltage generated across emitter resistor 132. With a rated forward yoltage gain of 50,000, operational amplifier 116₁ provides maximum output for less than a millivolt of differential signal input. Because of this, the embodiment of Figure 3 provides precise current matching or scaling of a plurality of ballast currents. The transistor currents can be scaled by providing an appropriate ratio between the values of the respective emitter resistors.
As discussed above, follower units could be provided for many ballasts with interconnecting signal wiring from the master unit or optical coupling devices. Alternatively, by using the AC line as a carrier, signals can be coded and transmitted and thereafter received and decoded at selected fixtures. The current-matching capability of the circuit of Figure 3 is so precise that the full- wave bridge formed by diodes 134, 136, 138 and 140 and the second ballast 142 could be eliminated and the collector of transistor 141 connected directly to the collector of transistor 26' ' ' as indicated in chain-dashed lines so as to increase the current capacity of the master unit. This would be particularly useful with the higher current ballasts employed with higher current arc discharge lamps or as a simple method for connecting a plurality of output stage transistors in parallel to provide a unique high current source capable of handling up to a hundred or more amperes.
Returning again to commercial lighting systems, another problem related to energy savings is what might be termed the light turn-on/ turn off problem. This occurs for example, when someone forgets to turn off the lights when leaving an area and/or when maintenance personnel turn lights on after hours for longer than necessary. Some buildings are not equipped with light turn-on and turn-off programs and many software programs and/or sensors are available for doing the same thing. However, the cost of the magnetic conductors, housings, power handling wiring and other power switching problems inhibit the provision of automatic programming for light systems. However, with a system in accordance with the present invention in place, a computer signal delivered to any master or single unit could shut off the lights controlled thereby by the addition of simple circuitry which would serve to pull the base of transistor 60'" in Figure 3 negative to the point of providing shut off. In a simple example illustrated in Figure 3, a photo-transistor or other optical device, denoted 144, is connected to the base of transistor 60"' and to a resistor 146 connected to the minus 15 volt power supply bus. With this arrangement, the software program referred to above would, at the appropriate time, energize a light emitting diode (not shown) to switch the photo-transistor 144 "on", thereby pulling the base of transistor 60"', negative to the point of cut off. This would of course turn off transistor 26"' and terminate flow of the ballast magnetizing currents and hence cut off power to the lamps.
Although the present invention is particularly applicable to illuminating light, the invention would also be useful in many photographic and other technical or scientific applications where light control is of a definite advantage. As stated, a simple yet highly efficient energy conserving system is provided in accordance with the invention which controls-the level of light from a fluorescent lamp(s) and which has applications for controlling the quantity and other characteristics of the outputs of gaseous arc discharge lamps in general, as well as special purpose load devices, over a wide dynamic operating range. The actual savings which can be realized would amount to millions of barrels of oil where the principles of the invention were utilized on a sufficiently widespread basis.
It will be appreciated that although an inductive ballast is shown in the specific embodiments illustrated, other ballasts can be employed and that the term "reactive ballast" as used in this application refers to inductive or capacitive ballasts.

Claims

A fluorescent lamp lighting system comprising a master lamp unit and at least one slave lamp unit, each lamp unit containing at least one fluorescent lamp (L1, L2; L3, L4) and a reactive ballast (100', 142) through which energy is supplied from an AC supply to each of the at least one lamps and a control circuit connected to the ballasts for controlling the light output of the at least one lamp, each control circuit comprising
rectifying means (92 to 98, 134 to 140),
control transistor means connected to said rectifying means for controlling the arc current through each of the at least one lamps by limiting and controlling the arc current supplied to each of the at least one lamps during at least a part of the portion of a half-wave of the A.C. supply during which each of the at least one lamps is ignited and for providing substantially no current limiting during that portion of a half-wave of the A.C. supply when said at least one lamps are extinguished, at least said control transistor means in the master lamp unit including a control transistor (26"') having a base biasing circuit (60"', 128) and an operational amplifier (116) connected in the base biasing circuit of said control transistor,
said system further comprising a single light regulating system for controlling the output of said at least one follower lamp unit (L3, L4, 142) in accordance with the output from the said master lamp unit (L1, L2, 100') said system comprising optical-electrical transducer means (74"') connected to the control transistor means in the master lamp unit and coupled to the control transistor means in the following lamp unit and light collecting and coupling means (CL) for collecting the light output from the at least one lamp in the master lamp unit and for coupling the said output of said at least one lamp in the master lamp unit to said optical-electrical transducer means so as to control the arc currents through the master lamp unit and the follower lamp unit by means of their respective control transistor means in accordance with the light input received thereby.