Abstract:
The present invention is a power supply for a fluorescent light, particularly a sub-miniature fluorescent light (SFL) which provides compensation for temperature and age effects of the fluorescent light. One or more SFLs are powered by a variable output anode controller and a variable output cathode controller, wherein the illumination output of the SFLs is selectively adjustable based upon the voltage output of one or both of the anode and cathode controllers. In a first example of implementation of the invention, an illumination feedback circuit is provided to the anode/cathode controller, wherein the voltage output is adjusted to compensate for diminished illumination, caused for example by cold operating conditions or age of the sensed SFLs. In a second form of the present invention, a temperature feedback circuit is provided to the anode/cathode controller to provide the aforesaid voltage adjustment to compensate for diminished illumination. In another aspect of the present invention, the SFLs are placed into a ready-state for being presently illuminated based upon sensing of a wake-up signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to fluorescent lighting systems, and more particularly to a fluorescent lighting system adapted for quickly achieving full illumination in cold environments. 
     2. Description of the Prior Art 
     In many lighting applications, fluorescent lighting is needed to achieve the proper background illumination. Fluorescent lighting traditionally has provided high illumination at low cost and low power consumption. In contrast with an incandescent light which produces light by heating of a filament, a fluorescent light produces light by exciting atoms of a gas. 
     An example of a common tube-shaped fluorescent light is depicted at FIG. 1. A fluorescent bulb  10  includes a tubular glass shell  12  which is internally coated with a phosphor  14 , such as for example calcium tungstate. Within the glass shell, the air is pumped out and replaced with an inert gas, usually argon. Added to the noble gas is a small amount of mercury. Two mutually spaced apart electrodes  16 ,  18  are located at either end of the shell. In operation, power is applied to the circuit (120 VAC), and a starter switch  20  is momentarily closed. About a second later, the starter switch opens, whereupon a choke or ballast  22  provides a voltage pulse which causes the gas within the shell to become excited and thereby emit light as electrons strike the gas molecules. The emitted light is mostly in the invisible ultraviolet portion of the spectrum. However, when this emitted light strikes the phosphor  14 , the phosphor fluoresces, providing copious amounts of visible light. 
     A fluorescent light requires a unique power supply that heats the electrode only temporarily to achieve electron excitation of the mercury vapor. The ballast balances the inrush current in combination with a high voltage required for gas excitation. These power supplies require careful attention to design, and add an additional cost above that which would be required to power an incandescent light bulb. In addition, fluorescent lighting is notoriously slow to illuminate at cold temperatures, for example less than about zero degrees C. Still another limitation for the application of fluorescent lighting is the relatively long bulbs that are required. These bulbs have to be packaged with maximum mechanical damping to survive even modest vibrations. 
     One advance of conventional tube-type fluorescent lighting systems provides quick starting. According to one form of improvement, known as “preheat”, the cathode electrodes are preheated when first turned on. When the starter switch opens, the current arcs through the tube, keeping the cathode electrodes hot. According to another form of improvement, known as “instant-start”, there is no starter switch and the cathode electrodes are short circuited. A high voltage (for example 500 volts) is applied at the start of the fluorescent light. The high voltage induces illumination, and the ballast returns the voltage to operating levels. According to yet another form of improvement, known as “rapid-start”, there is no starter switch, but the cathode electrodes are not short circuited. Special windings in the ballast provide preheat of the cathode windings, and the fluorescent light is started by a high voltage as in the instant-start modality. 
     A new type of fluorescent lighting system on the market is “sub-miniature fluorescent light” (SFL), an example of which is available from Stanley Electric Co., Ltd. of Tokyo, Japan, and is currently being sold as model T4.7SSL. The Stanley SFL  50 , shown at FIGS. 2A and 2B is a low power, low voltage type, having a convexly configured glass shell  52  coated interiorly by a phosphor  56 , and filled by an inert gas with a little mercury  54 . Electrically, situated within the shell are a cathode  58  having a resistive cathode element  60 , an anode  62  spaced from the cathode, and three terminal leads: a ground  64  terminal lead, an anode terminal lead  66 , and a cathode terminal lead  68 . The Stanley SFL  10  is packaged in a size analogous to small automotive incandescent lights of the type used for automotive interior lights. This small packaging allows for a small bias voltage Va at the anode, typically 24 volts. The cathode element is approximately 26 ohms to the ground terminal lead, requiring a cathode voltage Vc of only 5 volts to provide enough excitation power to warm the ionized gas inside the shell. When the gas warms it is able to conduct anode current to ground through the ionized gas, and light is emitted as electrons strike the mercury atoms. The emitted light is mostly in the invisible ultraviolet UV portion of the spectrum. However, when this emitted light strikes the phosphor  56 , the phosphor fluoresces, providing copious amounts of visible light V. 
     While an SFL is technically improved over conventional fluorescent lights, it still has some drawbacks. For example, if the ambient temperature is cold the cathode warming of the gas is insufficient to conduct the required anode current. This results in a fluorescent light that does not illuminate well at cold temperatures and/or a fluorescent light that takes minutes to warm enough to produce the required illumination. Still another limitation is that the expected life of an SFL is relatively short, for example around 5000 hours. This illumination life is based on an expected decrease of illumination with use, wherein life is considered to have ended when an aged SFL has an illumination output that is one half of that when it was new. 
     Accordingly, while an SFL overcomes the fluorescent light problems of fragility and power supply complexity, it remains a problem in the art to overcome the disadvantages associated with poor cold starting and short life expectancy. 
     SUMMARY OF THE INVENTION 
     The present invention is a power supply for a fluorescent light, particularly a sub-miniature fluorescent light (SFL) which provides compensation for temperature and age effects of the fluorescent light. 
     One or more SFLs are powered by a variable output anode controller and a variable output cathode controller, wherein the illumination output of the SFLs is selectively adjustable based upon the voltage output of one or both of the anode and cathode controllers. 
     In a first example of implementation of the invention, an illumination feedback circuit is provided to the anode/cathode controller, wherein the voltage output is adjusted to compensate for diminished illumination, caused for example by cold operating conditions or age of the sensed SFLs. For example, the illumination feedback is provided by a light sensor adjacent one or more of the SFLs which detects the illumination being output by at least one of the SFLs. 
     In a second form of the present invention, a temperature feedback circuit is provided to the anode/cathode controller to provide the aforesaid voltage adjustment to compensate for diminished illumination. For example, a thermistor adjacent the SFLs provides a temperature signal which is used by a control program to provide adjustment of the anode and/or cathode controller output based upon a predetermined temperature to illumination output relationship. 
     In another aspect of the present invention, the SFLs are placed into a ready-state for being presently illuminated based upon sensing of a wake-up signal. For example, when a user performs an act, as for example the opening of a car door, a wake-up routine is initiated which adjusts the anode and/or cathode controllers so as to ready the SFLs for illumination in a predetermined present length of time. An example for carrying-out this feature of the invention is to use any of the aforesaid feedback modalities in combination with a predetermined wait-state illumination output from at least one of the SFLs. 
     Accordingly, it is an object of the present invention to adjust illumination output of fluorescent lighting compensatorily for effects of temperature and age. 
     It is a further object of the present invention to provide a power supply for a fluorescent lights which includes an illumination feedback circuit which serves as an indicator for power supply output adjustment so that illumination of the fluorescent lights is compensated for any of cold temperature and aging. 
     It is another object of the present invention to provide a wake-up feature in association with a fluorescent light power supply having illumination compensation capability. 
     These, and additional objects, advantages, features and benefits of the present invention will become apparent from the following specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a prior art tube-type fluorescent lighting system. 
     FIG. 2A is a schematic view of a prior art sub-miniature fluorescent light. 
     FIG. 2B is a schematic view of a prior art circuit for a sub-miniature fluorescent light. 
     FIG. 3 is a schematic view of a plurality of sub-miniature fluorescent lights, a variable output power supply therefor and a feedback circuit according to the present invention. 
     FIG. 3A is a variation of FIG. 3, wherein two sensors are provided in the feedback circuit. 
     FIG. 4 is a flow chart for compensating sub-miniature fluorescent light illumination, based upon an illumination feedback circuit. 
     FIG. 5 is a flow chart for compensating sub-miniature fluorescent light illumination, based upon a temperature feedback circuit. 
     FIG. 6 is a flow chart for providing a wake-up, wait-state illumination for a sub-miniature fluorescent light, based upon an illumination feedback circuit. 
     FIG. 7 is a flow chart for providing a wake-up, wait-state illumination for a sub-miniature fluorescent light, based upon a temperature feedback circuit. 
     FIG. 8 is a schematic diagram of a power source circuit for a variable output fluorescent light power supply according to the present invention. 
     FIG. 9 is a schematic diagram of a cathode controller circuit for the variable output fluorescent light power supply according to the present invention. 
     FIG. 10 is a schematic diagram of a feedback control and gain circuit for the cathode controller circuit of FIG.  9 . 
     FIG. 11 is a schematic diagram of an anode controller circuit for the variable output fluorescent light power supply according to the present invention. 
     FIG. 12 is a schematic diagram of a gain and filtering circuit for the anode controller circuit of FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the Drawing, FIG. 3 depicts a plurality of sub-miniature fluorescent lights (SFLs)  100  connected in parallel, and including an indicator SFL  100 ′. The indicator SFL is enclosed in a housing  102 , which is preferably light-tight. A sensor  104  is located within the housing  102 . The sensor  104  senses a predetermined condition of the indicator SFL  100 ′, which condition is a presupposed contemporaneous condition of the other SFLs  100 . 
     The sensor  104 , may for example be a light intensity sensor or a temperature sensor. In the case of a light intensity sensor, as for example in the form of a conventional photovoltaic cell, the illumination of the indicator SFL  100 ′ is converted into a sensor signal, the value of which is related to the light intensity L. The sensor signal may be used to sense, for example, a diminished light intensity output of the sensor SFL due to its age or due to a cold operating environment. In the case of a temperature sensor, as for example in the form of a conventional thermocouple or thermistor, the environmental temperature of the indicator SFL  100 ′ is converted into a sensor signal, the value of which is related to the light intensity in that a known relationship exists between the temperature and the light intensity emitted from the SFLs. 
     Each of the SFLs  100 ,  100 ′ are powered by a variable power supply  106  including two component controllers: a variable output cathode controller  108  and a variable output anode controller  110 . A cathode output lead  112  of the cathode controller  108  is connected to the respective cathode terminal lead  114  of each of the SFLs  100 ,  100 ′ and an anode output lead  116  from the anode controller  110  is connected to the respective anode terminal lead  118  of each of the SFLs. In this regard, the cathode and anode output leads provide, respectively, the operating voltage for the cathode  120  and anode  122  of each of the SFLs  100 ,  100 ′. A power source  124  provides a positive lead  128  to the cathode and anode controllers  108 ,  110 , and a negative lead  126  provides a ground for each of the cathode and anode controllers, the SFLs  100 ,  100 ′, and the sensor  104 . 
     The sensor signal from the sensor  104  is routed by a sensor feedback lead  128  to each of the cathode and anode controllers  108 ,  110 , although the sensor feedback lead could be connected to just one of the cathode or anode controllers. The voltage level of the sensor signal provides an indicator of operating condition of the SFLs  100 ,  100 ′, wherein a predetermined adjustment of the voltage at either or both of the cathode output lead  112  and the anode output lead  116  is provided to compensate for the sensed condition, and thereby drive the SFLs such as to provide a desired optimum illumination output. 
     For example, the illumination output L may be diminished due to either a cold operating temperature of the SFLs or due to age of the SFLs. In any case, the sensor signal voltage will be less than an optimum voltage, due to the diminished light intensity striking the photovoltaic cell. The low sensor voltage is sensed by the circuitry of the cathode and/or anode controllers  108 ,  110 , and a compensatory increase in power voltage at either or both of the cathode and anode output leads  112 ,  116  is provided which drives the SFLs harder (that is, by increasing release of electrons at the cathode and/or increasing speed of the electrons from the cathode toward the anode), thereby causing an increase in the illumination output. The power voltage may be set to a predetermined value or may be progressively incremented until the sensor signal voltage reaches optimum, or another predetermined value. 
     For another example, the illumination output L may be diminished due to a cold operating temperature of the SFLs. In any case, the sensor signal voltage will be less than an optimum voltage, due to the low voltage output of the thermistor or thermocouple. The low sensor voltage is sensed by the circuitry of the cathode and/or anode controllers  108 ,  110 , and a compensatory increase in power voltage at either or both of the cathode and anode output leads  112 ,  116  is provided which drives the SFLs harder, thereby causing an increase in the illumination output, which serves to warm the SFLs. The power voltage may be increased to a predetermined value or may be progressively incremented until the sensor signal voltage reaches optimum, or another predetermined value. 
     For yet another example, the power supply  106  may provide a wait-state level of illumination output in response to a wake-up signal being received from a wake-up indicator  130 , as for example a car door open switch  132  connected to the power source  124 . When a voltage appears at a wake-up lead  134 , either or both of the cathode and anode controllers provide an appropriate voltage the respective cathode and anode outputs  112 ,  116  to place the SFLs  100 ,  100 ′ in condition that enables the SFLs to achieve an operative level of illumination output very rapidly upon the requisite voltage being subsequently applied at the cathode and anode outputs. 
     While FIG. 3 depicts an example of the present invention wherein depicted is a plurality of SFLs  100 ,  100 ′, those having ordinary skill in the relevant art will appreciate that the present invention is readily adaptable to any number of SFLs and any number of sensors, with or without the housing  102 . For example, FIG. 3A depicts an indicator SFL  100 ′ and housing  102 , wherein SENSOR 1   104 ′ is a temperature sensor having a feedback sensor lead  128 ′ to the power supply  106 , and SENSOR 2   104 ″ is a temperature sensor having a feedback sensor lead  128 ″ to the power supply. 
     Variations in housing environment, such as for example an opening of a trunk or a change from daylight operation to nighttime operation can be sensed and the power supply may then provide, based upon sensor feedback, cathode and/or anode power voltages which compensate the illumination output of the one or more SFLs to a level appropriate to the sensed condition. Further, it is to be understood that the power voltage compensation performed by the variable power supply  106  may be executed electronically by an appropriately designed electrical circuit or via an appropriately ROM programmed electronic control module (ECM)  134 . 
     Turning attention now to the exemplar examples of FIGS. 4 through 7, a pre-programmed ECM will be assumed, although the indicated steps may be equally well executed electronically by an electrical circuit. 
     Referring firstly to FIG. 4, depicted is a flow chart of steps performed by the variable power supply  106  to provide a compensated SFL illumination output in response to sensor feedback associated with a light intensity type sensor. The program initializes the power supply at execution block  200  to provide a preset power voltage at the cathode and anode outputs to the one or more SFLs. The program then inquires at decision block  202  whether the illumination output of one or more sensed SFLs is less than a preset illumination. If it is, then at execution blocks  204  and  206 , the program applies an incremented power voltage at each of the cathode and anode outputs and then returns to decision block  202 . When the illumination output achieves the preset value at decision block  202 , the program then resets the power voltage of the cathode and anode outputs to respectively preset values at execution blocks  208  and  210 . The program then inquires at decision block  212  whether the illumination output of the one or more sensed SFLs is less than the preset illumination. For example, the illumination could be less than the preset value because of age of the SFLs. If not, the program then increments the power voltage to the anode output at execution block  214  and returns to decision block  212 . At decision block  212 , when the illumination output is equal to the preset illumination, then at execution block  216  the program holds the last value of power voltage to the anode output. 
     Referring next to FIG. 5 depicted is a flow chart of steps performed by the variable power supply  106  to provide compensated SFL illumination output in response to sensor feedback associated with a light intensity type sensor and a temperature type sensor (see FIG.  3 A). The program initializes the power supply at execution block  300  to provide a preset power voltage at the cathode and anode outputs to the one or more SFLs. The program then inquires at decision block  302  whether the temperature adjacent one or more SFL is less than a preset temperature, for example whether the temperature is less than zero degrees centigrade. If it is, then, at execution blocks  304  and  306 , the program applies a predetermined higher power voltage at each of the cathode and anode outputs and then returns to decision block  302  and waits. When the temperature achieves the preset value at decision block  302 , the program then resets the power voltage of the cathode and anode outputs to respectively preset values at execution blocks  208  and  210 , and the program repeats the program steps thereafter depicted at FIG. 4 to provide for age compensation. 
     Referring next to FIG. 6, depicted is a flow chart of steps performed by the variable power supply  106  to provide a wake-up level of power to the one or more SFLs in conjunction with a feedback circuit associated with a light intensity type sensor. At execution block  400  the system is initialized, wherein the power supply  106  is placed into a wait-for-wake-up-signal mode. At execution block  402  a wake-up signal is provided to the ECM, such as by the wake-up indicator  130 . The program then inquires at decision block  404  whether the power supply has been turned on. If not, the program then proceeds to execution block  406  whereat the program applies a predetermined high power voltage to each cathode. At decision block  408  the program inquires whether the system is on. If not, the program waits for a preset amount of time at decision block  410 , whereupon if the time has elapsed without the system turning on, then the program returns at execution block  412 . If the system turns on during the preset time, then the program advances to decision block  202 , and the execution steps indicated thereafter at FIG. 4 are repeated. 
     Referring next to FIG. 7, depicted is a flow chart of steps performed by the variable power supply  106  to provide a wake-up level of power to the one or more SFLs in conjunction with a feedback circuit associated with a light intensity type sensor and a temperature sensor. At execution block  500  the system is initialized, wherein the power supply  106  is placed into a wait-for-wake-up-signal mode. At execution block  502  a wake-up signal is provided to the ECM, such as by the wake-up indicator  130 . The program then inquires at decision block  504  whether the power supply has been turned on. If not, the program then proceeds to execution block  506  whereat the program applies a predetermined high power voltage to each cathode. At decision block  508  the program inquires whether the system is on. If not, the program waits for a preset amount of time at decision block  510 , whereupon if the time has elapsed without the system turning on, then the program returns at execution block  512 . If the system turns on during the preset time, then the program advances to decision block  302  and the execution steps indicated thereafter at FIG. 5 are repeated. It is to be understood that steps  400  through  410  of FIG. 6 may be substituted for steps  500  through  510  of FIG.  7 . 
     Turning attention now to FIGS. 8 through 11, FIG. 8 depicts a diagram of a preferred example of a power source circuit  124 ; FIGS. 9 and 10 depict a preferred example of a cathode controller  108 , including a feedback control and gain therefor, as well as a sensor  104 ; and FIGS. 10 and 11 depict a preferred example of an anode controller  110 , including a gain and filtering therefor. A component listing for FIGS. 8 through 11 is as follows: V cc  is a positive 5 volts; diode D 2  is a SM8A27; diodes D 3  and D 6  are a MA3091CT; diodes D 4 , D 5  and D 7  are a MA152ACT; chokes L 1  and L 2  are a PM153-471k; N channel MOSFET Q 1  is a IRFZ044; and the electronic controller chip of FIGS. 9 and 11 is a PWM controller CS 4124. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.