Patent Application
20100134035
Dimmable ballast systems provide varying levels of light output through a variety of means. For multi-lamp fixtures, conventional dimming ballast techniques include discrete dimming (so-called “step-dimming”) and continuous dimming. One example of discrete dimming is a multiple-lamp discrete ballast in which one or more lamps are shut off to provide a lower light output. This is sometimes implemented using external controls to turn off individual ballasts or fixtures until the selected light level is achieved. Discrete dimming approaches, however, only provide a finite number of predefined lighting levels and transitions between these discrete levels are often perceptible by users. Some continuous dimming designs operate multiple lamps in series with the power applied to the lamps being reduced for dimming. Series-connected dimming ballasts, however, suffer from inability to produce light when one or more lamps fail. Other proposed approaches include varying a DC bus amplitude via pulse width modulation (PWM) control to power a voltage or current fed inverter for driving one or more lamps, but this dimming control technique adds cost and may not provide the desired amount of dimming for certain applications. Also, continuous dimming techniques can cause early cathode failure by dimming a lamp if no separate cathode heating power is provided to keep the cathode operating within its normal temperature range. However, separate cathode heating contributes to inefficiency at dimming levels below a critical arc power level since the cathode heating power supply loss is in addition to the fact that the lamp light output is not linearly proportional to the lamp power (i.e. it may take 75% lamp power to provide 50% lamp lumens.) Thus, conventional continuous dimming techniques can lead to premature lamp degradation or failure through undesirable lamp cooling and/or extinguishment unless additional cost is incurred for cathode heating to prevent premature lamp degradation caused by the dimming operation. Continuous dimming ballasts, moreover, suffer from reduced power efficiency. Thus, there is a need for improved fluorescent lamp dimming apparatus and techniques for efficiently providing varying lighting levels to match a desired lighting level while maintaining high efficiency and without lamp stress or damage or increased cost, thereby allowing a user to selectively achieve energy savings by dimming lighting installations.
Multi-lamp dimming ballasts and control methods are disclosed by which one or more of the above-mentioned deficiencies can be mitigated or overcome in driving fluorescent lamps.
Dimming ballast embodiments are presented for operating multiple lamps, which include a DC power source receiving AC input power and providing DC electrical power, as well as a DC-AC converter that provides an AC output to drive the lamps and a controller operative to control power applied to the lamps. The controller implements dimming operation according to a dimming level setpoint by selectively dimming at most one of the lamps while controlling all the remaining lamps to be substantially at 0% or 100% power. The ballast may further provide a cathode heating circuit to selectively heat one or more cathodes of the lamp being dimmed according to the setpoint dimming level.
In one embodiment, the controller selectively dims only a predetermined lamp while controlling all the remaining lamps to be substantially full on or off, so as to economize on cathode heating apparatus and dimming circuitry. In other embodiments, the controller selects one of the lamps for dimming operation and selectively dims only the selected lamp while controlling all the remaining lamps to be substantially on or off, where the selection can be by an algorithm such as random selection or round-robin selection in various embodiments. Certain embodiments of the ballast may provide a separate inverter for controlling the dimmed lamp, and may include a dedicated inverter to power each lamp. Further embodiments provide dimming at multiple predetermined levels according to the dimming level setpoint, where the controller selectively dims the selected lamp slowly in concert with selectively turning one or more of the other lamps on or off in order to smoothly transition between predetermined levels.
Methods are disclosed for powering fluorescent lamps, including receiving a dimming level setpoint value or signal indicating a desired dimming level for the dimming ballast, and selectively dimming at most one of the lamps while controlling all the remaining lamps to be substantially at 0% or 100% power at least partially according to the dimming level setpoint. Embodiments of the method may further include receiving the dimming level setpoint value or signal indicating a desired one of a plurality of predetermined discrete levels for the dimming ballast, as well as dimming at most one of the lamps slowly in concert with selectively turning one or more of the other lamps on or off so as to smoothly transition between predetermined levels.
One or more exemplary embodiments are set forth in the following detailed description and the drawings, in which:
Referring now to the drawings, where like reference numerals are used to refer to like elements throughout, and wherein the various features are not necessarily drawn to scale,
The ballast 102 includes a controller 150 operatively coupled with the DC-AC converter 140 to control power applied to the lamps 108, and may also provide control signals to a dimming circuit 142 of the DC-AC converter 140, as well as to a cathode heating circuit 170 for selective heating of one or more lamp cathodes. The controller 150 can be any suitable types of hardware, software, or combinations thereof, and includes a dimming control component 152 and a heat control component 154. Controller 150 receives a dimming level setpoint 160, such as a signal or value and operates to selectively dim at most one of the lamps 108 while controlling all the remaining lamps 108 to be substantially at 0% or 100% power based at least in part on the dimming level setpoint 160. The on/off control of the other lamps 108 need not be strictly 100% and 0% of rated power, respectively, wherein the on state can be within 2-3% of rated and the off state can be up to 2-3% of rated power to constitute substantially 100% and substantially 0% as used herein.
By only dimming a single lamp at any given time, cathode heating only needs to be applied to the dimmed lamp, thereby reducing the amount of energy expended on non-lighting functions in the ballast 102. Moreover, only one of the lamps 108 is in a lower efficiency dimmed mode of operation, thereby increasing the overall efficiency of the ballast 102 compared with conventional continuous dimming approaches. In this regard, linear fluorescent lamps 108 are most energy efficient when operating near their rated power, and as the power into the lamp is reduced (e.g., during dimming), the lumens drop off faster than watts, such that the user is provided with greatly reduced light levels for only slightly reduced power consumption. The disclosed ballast 102 thus facilitates reduction in user lighting energy consumption without significant ballast cost impact. Furthermore, the ballast 102 provides continuous dimming capabilities, and thus allows finer adjustment resolution than discrete step-dimming systems.
The heat control component 154 of the controller 150 in this embodiment also provides a control signal or value to the cathode heating circuit 170 to selectively heat one or more cathodes of the dimming lamp 108a during all or a portion of the dimming operation to extend the life of the lamp 108a. The controller 150 may provide any suitable control signaling or messaging to the cathode heating circuit 170 to implement a heating function, which may but need not correlate with the 0-100% signal used to actuate the dimming circuit 142, where the dimming control and heat control components 152 and 154 may implement different control algorithms based on the received dimming level setpoint 160. The setpoint 160, in this regard, may be an analog signal, such as a 0-10 v DC electrical signal set by a user whose voltage level represents the desired overall ballast light output amount, or may be a digital value communicated to the controller 150, or may be any other suitable signal or value that indicating the desired light level. The controller 150 may be implemented as a processor-based system having a microprocessor, microcontroller, or other programmable or configurable processing or logic components, and the controller 150 and the components 152, 154 thereof can be implemented in software, firmware, or combinations of various hardware, software, firmware, etc., in a single control device 150 or in distributed fashion with one or more functions being implemented separately from others.
In operation, the controller 150 receives the setpoint 160 and determines the on or off status of inverters 146b-146d based on the setpoint 160 to be at or below the desired light output value, and determines the amount of dimming for the inverter 146a to set the overall output of the ballast 102 to meet the setpoint amount. In this regard, for a given non-zero setpoint 160, the controller 150 will provide the dimming control signals via component 152 so that all, some, or none of the inverters 146b-146d are on, and will control the dimming circuitry 142 so that the first inverter 146a powers the corresponding predetermined lamp 108a at 0-100% of its rated output. For example a dimming setpoint 160 having a value in the range of 75 to 100% light output, the controller 150 will dim the lamp 108a as needed to achieve that average light level while holding the other inverters 146b-146d on. For a desired setpoint of 75% light level, the inverter 146a is off (0%) with the other inverters 146b-146d on. For a setpoint between 50 and 75%, one of the three lamps 108b-108d is turned off, and the lamp 108a is dimmed to a level so that the average light level from the entire fixture is equal to the setpoint value. For the fully dim (0%) to 25% range of the setpoint 160, the controller 150 turns the inverters 146b-146d off and operates the dimming circuit 142 to drive the lamp 108a between its full-bright and dimmest level.
In this manner, the ballast 102 can achieve continuous dimming at any value of the setpoint 160 by selectively dimming only the lamp 108a while individually controlling all the remaining lamps 108b-108d to be substantially at 0% or 100% power. Other embodiments are possible in which two or more of the lamps 108b-108d are driven by a shared inverter with on/off control. For example, a single inverter 146 could drive lamps 108c and 108d with on/off capability controlled by the dimming component 152, with another on/off controlled inverter 146 driving the lamp 108b and the dimming-capable inverter 146a driving the predetermined lamp 108a with selective cathode heating being provided for the lamp 108a via the heat control component 154 and the heating circuitry 170. In other possible implementations, the cathode heating circuit 170 can be operable to selectively heat one or more cathodes of more than one of the lamps 108. Moreover, the controller 150 in the embodiment of
The method 200 begins in
If not (NO at 220), a determination is made at 224 as to whether the dimming level equals 50%. If so (YES at 224), two lamps are turned on and two lamps are turned off at 226 (
Other embodiments of the method 200 are possible in which cathode heating is selectively provided to one or more cathodes of the lamp 108 being dimmed. In certain embodiments, moreover, receiving the dimming level setpoint value or signal at 202 may include receiving the dimming level setpoint value or signal 160 indicating a desired one of a plurality of predetermined discrete levels for the dimming ballast 102. In this embodiment, the selective dimming at 250 may include selectively dimming at most one of the lamps 108 slowly in concert with selectively turning one or more of the other lamps 108 on or off so as to smoothly transition between predetermined levels.
The exemplary ballasts 102 and method 200 facilitates maintenance of high fixture efficiency while not causing abrupt light level changes associated with conventional continuous and discrete dimming techniques. Various embodiments, moreover, provide for selective application of power to heat the cathodes of the dimmed lamps 108 in order to allow the dimmed lamp to operate to its rated life. The embodiments of
The above examples are merely illustrative of several possible embodiments of various aspects of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, software, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. Although a particular feature of the disclosure may have been illustrated and/or described with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, references to singular components or items are intended, unless otherwise specified, to encompass two or more such components or items. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. The invention has been described with reference to the preferred embodiments. However, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.
