Abstract:
An ignitor disabling apparatus is provided to reliably and automatically disable a universal sodium ignitor with hot re-strike capability, or a 120 Hz pulse capability. The ignitor is configured to disable the ignitor portion of a HID lamp if the lamp fails to start. Timing operation of the disabling circuit is achieved using a power supply that ramps to a steady state to provide triggering of a timer circuit. A normally closed, solid state gating device is used for disabling the ignitor to minimize sparks. The disabling apparatus can be retrofit into an existing universal sodium ignitor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present invention claims benefit under 35 U.S.C. section 119(e) of a provisional U.S. Patent Application of Isaac L. Flory, and Christopher A. Hudson, entitled “Method and Apparatus for Disabling a Sodiumn Ignitor Upon Failure of Discharge Lamp,” Serial No. 60/246,594, filed Nov. 8, 2000, the entire contents of said provisional application being incorporated herein by reference.  
         [0002]    Related subject matter is disclosed in U.S. patent application Ser. No. 09/280,581, filed Mar. 30, 1999, the entire contents of said application being expressly incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0003]    The invention relates generally to a disable circuit that stops the ignitor function of a high intensity discharge (HID) lamp ignition circuit. More particularly, the invention relates to an apparatus and method to control the timing and triggering of the disable function of the igniter circuit.  
         BACKGROUND OF THE INVENTION  
         [0004]    High intensity discharge (HID) lamps such as metal halide (MH) and high pressure sodium (LIPS) lamps have increasingly gained acceptance over incandescent and fluorescent lamps for commercial and industrial applications. HID lamps are more efficient and more cost effective than incandescent and fluorescent lamps for illuminating large open spaces such as construction sites, stadiums, parking lots, warehouses, and so on, as well as for illumination along roadways. An HID lamp comprises at least an arc-tube containing two electrodes, chemical compounds and a fill gas. The fill gas can comprise one or more gases. To initiate operation of the lamp, the fill gas is ionized to facilitate the conduction of electricity between the electrodes.  
           [0005]    HID lamps can be difficult to start. An HID lamp such as a conventional HPS lamp uses a 2500 to 4000 volt pulse at least once per half-cycle and at selected times during the cycle in order to start, as set forth in a number of standards such as ANSI C78.1350 on HPS lamps, for example. An ignitor is used to provide the necessary pulses to start the conventional HID lamp. If the lamp is extinguished after lamp operation has elevated lamp temperature, the lamp cannot be restarted until after the lamp cools down and the fill gas can be ionized again. For many types of HID lamps, this lamp cooling period can be between approximately 40 seconds and 2.5 minutes, which can be considered unacceptable in situations where, for example, emergency lighting is desired.  
           [0006]    A number of circuits have been developed to start or hot restrike HID lamps. These ignitors generally include resistors, pulse transformers and other components, in addition to a conventional ballast. These devices can reduce system efficiencies and substantially increase system cost.  
           [0007]    An exemplary ignitor  100  is depicted in FIG. 1. Terminals  102  and  104  of a lighting unit are connected to an AC power source  106 , as well as to a ballast  108  and a lamp  110 . The ballast  108  comprises a tap  112  and two winding portions  114  and  116 . The ignitor  100  has terminals which are connected to terminals  102 ,  112  and  110 . A charging circuit for hot restarting a high pressure xenon HPS lamp or other HID lamp having similar hot restart requirements is provided which comprises a semiconductor switch  118  such as a silicon-controlled rectifier (SCR) or the like is connected so that one end of its switchable conductive path is connected to the end of the first portion  116  of the ballast. The other end of the conductive path of the SCR  118  is connected to the tap  112  via a storage capacitor  120 . A number of sidacs  122  or other breakdown devices are connected between the gate and the anode of the SCR  118 . A current-limiting resistor  126  is provided in series with the sidacs  122  and  124 . If the voltage on the capacitor  120  increases to a level which reaches or exceeds the threshold voltage of the breakdown devices  122  and  124 , the sidacs  122  and  124  become conductive, placing the SCR  118  in a conductive state. Accordingly, the capacitor  120  discharges through the portion  18  of the ballast. Because the winding portions  114  and  116  of the ballast are electromagnetically coupled, the portion  116  of the ballast operates as the primary of a transformer in that a voltage is induced in the winding portion  114 . The high voltage generated in the winding portion  114  of the ballast  108  is imposed on the lamp  110 . The relationship of the winding portions  114  and  116  is selected to create a voltage using the SCR  118  and the sidacs  122  and  124  which is sufficiently high to ionize the material within the arc tube of the lamp  110 .  
           [0008]    With further reference to FIG. 1, a charging circuit  144  for the capacitor  120  is connected between the tap  112  and the terminal  102  at the other side of the AC power source  106 . This charging circuit preferably comprises two diodes  128  and  130 , a pumping capacitor  132  and two radio frequency chokes  134  and  136  connected in series between the tap  112  and the terminal  102 . Two diodes  138  and  140  are connected between the capacitors  120  and  132  and are poled in the opposite direction from the diodes  128  and  130 .  
           [0009]    The charging circuit  144  depicted in FIG. 1 provides for the controlled, step-charging of the storage capacitor  120 . During one half cycle of the AC power source  106 , a current flows through the chokes  134  and  136 , the capacitor  132  and the diodes  128  and  130  to charge the capacitor  132 . The capacitor  132  is selected to be relatively smaller than the capacitor  120  (e.g., 0.047 microfarads (μF) versus 5 μF). On the next half cycle of the AC power source  106 , the capacitor  120  is charged and the voltage across the capacitor  132  increases the incoming half wave from the AC power source  106  so as to provide energy on the order of 2.7 microjoules to the storage capacitor  120 . Since the capacitor  120  requires more energy due to its relative size, the capacitor  120  can be provided with energy from both the incoming AC signal and the capacitor  132  in one cycle. On the next half cycle, the capacitor is charged again and delivers energy to the capacitor  120  again on the subsequent half cycle. Thus, the charge on the capacitor  120  is increased with each alternate half cycle using a pumping action.  
           [0010]    When the capacitor  120  reaches the breakdown voltage of the sidacs  122  and  124 , the sidacs become conductive and therefore render the SCR  118  conductive. The capacitor  120  therefore discharges through the portion  116  of the ballast  108  to generate a high voltage in the portion  114  of the ballast. The large magnitude of the capacitor  120  discharges significantly more energy into the magnetic field of the ballast  108  as compared with a conventional HID lamp ignitor and therefore excites the ballast  108  to a relatively high degree. The highly excited ballast  108 , with its corresponding collapsing magnetic field, pushes the lamp into a discharge state and therefore a low impedance state so that the discharge state can be maintained by the normal AC power source  106 . The discharging capacitor  120  produces current flow which is in the same direction as the continued current flow produced by the collapsing field, and which is provided through the lamp as the SCR  118  is turned off by the instantaneous back voltage bias placed on the capacitor  120  by the same collapsing field energy. The resistor  152  can be connected in series with the SCR  118  to cause the peak of the high voltage pulse to be lower and the base (i.e., width) of the pulse to be longer. The resistor  152  limits the high voltage and therefore reduces dielectric stress to allow the use of lower cost magnetic components.  
           [0011]    The ignitor  100  depicted in FIG. 1 further comprises an HPS lamp starting circuit comprising a capacitor  146  connected in series with a resistor  148  and a sidac  150  or similar breakdown device. The resistor  148  is connected to the junction between the inductors  134  and  136  and the capacitor  132 . The ignitor  100  comprises a current-limiting resistor  152  in series with the parallel combination of the SCR  118  and the sidacs  122  and  124 .  
           [0012]    The above-mentioned HID lamps should be provided with a disabling circuit such that, if the lamp fails to start, the disabling circuit would discontinue the hot or cold strike used to initiate the HID lamp. This feature is useful in prolonging the life expectancy of the ignitor, helps protect the ballast system, and provides the ability to apply HID ignitors to harsh and hazardous environments.  
           [0013]    Accordingly, a need exists for a reliable means of disabling the ignitor portion of a HID lamp, and an accurate method to time when the disablement of the ignitor occurs. Further, a need exists for a power supply for proper operation of semiconductor devices used in the disabling circuitry, and a solid state contact in the lamp circuit that will not release sparks when actuated by the disabling circuit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The various aspects, advantages and novel features of the present invention will be more readily comprehended from the following detailed description when read in conjunction with the appended drawings, in which:  
         [0015]    [0015]FIG. 1 is a schematic diagram of an exemplary existing ignitor;  
         [0016]    [0016]FIG. 2 is a schematic diagram of a circuit having a HID lamp restrike function integrated with a disabling function in accordance with an embodiment of the present invention;  
         [0017]    [0017]FIG. 3 is a schematic diagram of an universal sodium ignitor constructed in accordance with an embodiment of the present invention  
         [0018]    [0018]FIG. 4 is a schematic diagram of a timer with an external trigger constructed in accordance with an embodiment of the present invention;  
         [0019]    [0019]FIG. 5 is a schematic diagram of an analog trigger mechanism constructed in accordance with an embodiment of the present invention  
         [0020]    [0020]FIG. 6 is a schematic diagram of a power supply with an advantageous ramp up operation constructed in accordance with an embodiment of the present invention; and  
         [0021]    [0021]FIG. 7 is a schematic diagram of an isolated solid state switch mechanism constructed in accordance with an embodiment of the present invention. 
     
    
     SUMMARY OF THE INVENTION  
       [0022]    One aspect of the present invention is to provide a reliable means to disable ignitor operation for operation in harsh and hazardous environments.  
         [0023]    Yet another aspect of the present invention is to provide accurate method to time when the disable operation occurs.  
         [0024]    Still another aspect of the present invention is to provide a novel method to trigger the start of the time interval.  
         [0025]    Another aspect of the present invention is to provide a power supply for proper operation of semiconductor devices.  
         [0026]    Another aspect of the present invention is to provide a solid state, normally closed contact that will give no sparks when actuated.  
         [0027]    Another aspect of the present invention is to provide the ability to retrofit an existing HID sodium lamp with disable circuitry.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    [0028]FIG. 2 depicts a disabling circuit  200  provided in accordance with an embodiment of the present invention. Disabling circuit  200  is provided to operate a normally closed triac  392  (FIG. 7) in order to disable the igniter  300  of FIG. 3 of a HID lamp upon failure to start the lamp. By way of an example and as described below, the node  202  in the disabling circuit  200  can be provided in the ignitor  300 , as shown in FIG. 3. This disabling feature is useful in prolonging life expectancy of the ignitor, helping to protect the ballast system, and providing the ability to apply HID igniters to harsh and hazardous environments by encapsulating the disabling circuit  200  and igniter  300  of FIG. 3 in a can, for example, or any other appropriate encapsulating product.  
         [0029]    With continued reference to FIG. 2, the disabling circuit  200  comprises a monostable timer  340  (FIG. 4), a triggering circuit  350  (FIG. 5), a power supply  360  (FIG. 6), and an isolated solid state switch  380  (FIG. 7). Accordingly, when power is applied to the ignitor  300  of FIG. 3, both legs (e.g., the hot restrike function  302 , and the standard pulse ignitor  304 ) of the ignitor begin operation. This allows the power supply  360  to ramp up to a threshold voltage, thus initiating the triggering function of the trigger circuit  350  which, in turn, begins the timer  340 . Upon expiration of a pre-selected period of time (e.g., 180 seconds or any other appropriate period of time), the timer  340  activates the solid state switch  380  which, in turn, activates the triac  392 , thereby removing power from the ignitor  300  and disabling the ignitor  300 .  
         [0030]    The ignitor  300  of FIG. 3 produces two types of pulses, as mentioned above, a hot re-strike pulse generated by circuitry  302  and a standard pulse ignitor generated by circuitry  304 . The major difference between a standard ignitor  304  and a hot restrike ignitor  302  is that a restart ignitor produces a pulse which is higher in voltage and contains significantly more energy than a pulse generated by a standard ignitor (e.g. on the order of 700 volts). The hot re-strike ignitor is indicated generally at  302  and is a DC ignitor that charges and discharges in one direction only. The rectifiers  305  produce a DC level that increases with each successive half-cycle of the ballast (not shown) secondary voltage. Capacitor  306  is employed in a pumping arrangement to increase the voltage on capacitor  308  to preferably twice the peak open circuit ballast voltage. When the voltage on capacitor  308  reaches a sufficient level to break-over the semiconductors  310 , transistor  312  is gated on. The charge in capacitor  308  carries through the tap  314  of the ballast (not shown), thus creating a voltage transformation loop. This high current provided through the tap produces a large voltage on the secondary of the ballast across the sodium lamp. The secondary voltage of is sufficient amplitude such that under certain conditions, the sodium lamp hot re-starts essentially instantly.  
         [0031]    With continued reference to FIG. 3, the regular ignitor  304  is an AC ignitor. It charges and discharges through the series combination of capacitors  316  and  317 , and resistor  318  in an alternating fashion. The voltage produced across capacitor  317  is sufficient to break-over semiconductor  320 . A current pulse is provided at least once per half-cycle in both directions through the tap  314  of the ballast (not shown). In addition, this current pulse preferably provides a high voltage pulse across the sodium lamp in the direction of the ballast (not shown) secondary voltage every half-cycle.  
         [0032]    The series combination of resistor  322  and rectifiers  324  and  326  provide a means of storing DC energy in the ballast capacitor (not shown) to facilitate the hot re-start ignitor  302  of the lamp (not shown). Both ignitor legs  302  and  304  feed through the RF chokes  328 . If the current through these chokes is terminated, then the pumping action of the ignitor  302  and pulsing action of  304  ceases to function, thus enabling the triac to open at point  202  in FIG. 3. Placing the triac  392  at node  202  in FIG. 3, thus enabling the triac  392  to de-activate, therefore producing the current disruption.  
         [0033]    The triac  392  located with in the disable circuit  200  can be opened to cause the ignitor  200  to cease operating. The location of the disable circuit within the ignitor circuit is preferably at point  202  of FIG. 3. This particular insertion point  202  is advantageous because it provides for the protection of the low voltage semiconductors in the disable circuit  200  by placing the circuit inside the RF chokes  328  and away from the two above-referenced ignitor pulses that vary from  3 . 5  KV to over  7  KV. The disable circuit  200  is self-contained within the same parameters and connections to which the ignitor  200  is subject. The disable circuit preferably maintains its connections internal to the ignitor  200  itself. Thus, the entire package can be configured to have only three external connections, that is, LAMP, TAP, and COM.  
         [0034]    Another aspect of the invention is the selection of the appropriate length to allow the ignitor to function before it disables. Since the majority of all sodium lamps will re-ignite after approximately 90seconds, the interval disable time period is selected to be at least twice this period (i.e., a 180-second disable interval). Accordingly, the timer includes a timing cycle of approximately  180  seconds, for example. In addition, there are primarily two modes of operation of the timer  340 : astable and monostable. An embodiment of the present invention employs the monostable mode which is a method by which a  555  timer is preferably provided. An RC time constant is employed to place the timer output at high for a given duration, set by the RC time constant, and then return the output to low.  
         [0035]    However, the timer&#39;s timing cycle does not begin until an external trigger, such as the triggering circuit in FIG. 5, starts the operation. The trigger voltage generated by the triggering circuit preferably starts at a level greater than that of Vthresh (FIG. 4), and then decreases below this level before rising above it once again. When the trigger voltage rises above the level of Vthresh, the timing cycle begins. The duration of the cycle is given by the following equation:  
         τ   .     =     R   ·   C   ·     ln        (     Vcc     Vcc   -   Vth       )                 τ   :=     1.1   ·   R   ·   C                           
 
         [0036]    wherein capacitor  342 =47 microfarads, t=180 seconds and resistor  344 =3.4 megohms (approx,) Resistor  344  is preferably 3.9 megohms which is the closest standard value. It is desirable to start the time duration immediately upon the application of power to the ignitor system. Accordingly, a trigger/conttol mechanism is needed to provide the means to start the timer operation. As described above, the three conditions employed to appropriately begin the operation of a timer  340  via an external trigger pulse  346  are:  
         [0037]    1. Vtrig≧Vthresh during time 1  
         [0038]    2. Vtrig≦Vthresh during time 2  
         [0039]    3. Vtrig≧Vthresh during time 3  
         [0040]    To achieve state  1  above, a pull-up resistor  358  is applied to the trigger pin  346  of the timer  340 . Thus, the voltage at the trigger pin  346  is on the order of Vcc. To achieve state  2  above, a transistor  348  of the trigger circuit  350  of FIG. 5 is also connected to the trigger pin  346 . When gated, even for a short duration, the transistor  348  pulls pin  346  to ground. To achieve state  3  above, the transistor  348  is turned off. The pull-up resistor  358  allows the trigger pin  346  to rise to Vcc again.  
         [0041]    The control of the transistor  348  gate signal is an important aspect of an embodiment of the present invention. Transistor  348  is controlled via the DC charge of capacitor  352  via resistors  354  and  356 . Resistor  356  provides a means for the gate to go to ground when no current flows through resistor  354  (i.e. a pull down resistor). Whittle Vcc charges to a steady DC level, so does capacitor  352 . Current flows through the resistor  354  and the capacitor  352  series combination, thereby tuning on the transistor  348 . The trigger pin  346  is therefore pulled to ground. When capacitor  352  has approximately reached the level of Vcc, it allows no more current to pass. This effectively turns off the transistor  348 . As mentioned above, transistor  348  turns off and the etie&#39;s trigger pin  346  rises to Vcc, thereby starting the timer&#39;s 340 tg cycle. An embodiment of the present invention employs a high pass filter via capacitor  352  and resistor  354  and a power supply as described in detail below (e.g., one that ramps up to its steady state), to directly supply the gate current needed in order to properly turn on and off the transistor  348 . When the power supply  360  ramps up, the high pass filter gates the transistor  348 . When the power supply maintains a steady state, the high pass filter provides no current to the gate of the transistor  348 . The gate is therefore pulled to ground via the resistor  356  and the transistor  348  is turned off.  
         [0042]    The power supply  360  of FIG. 6 is important to the application of the timer  340  described above. The power supply  360  has two characteristics that achieve proper operation of the timing circuit  340 . First, it has a steady state, regulated voltage that has at least the minimum required DC for proper operation of the timer (e.g., on the order of 4.2 volts). Second, the power supply ramp up to the steady state is of sufficient frequency that the high pass filter passes current to the transistor  348 , thus activating the trigger and timing cycle. A rectifying bridge  362  is preferably provided to gain DC current to the power supply regulating circuit  360 . A two-stage circuit is employed to ensure a high degree of regulation and the proper current draw through capacitor  364  which drops the open circuit voltage (OCV) of the ballast (not shown) from 400V peak to about 10V peak when measured at the diode bridge  362 . Resistor  366  is preferably provided across the output of the bridge  362  to ensure that enough current is drawn to produce the open circuit voltage and to discharge any residual charge left on capacitors  368  and  374 . There is no bandwidth limitation to the charge of capacitor  368 . Thus, whatever voltage peak is produced across resistor  366 , the capacitor  368  achieves this level in one cycle. In other words, the charge current to capacitor  368  is not regulated or limited by a resistor. The zener diode  370  has been placed across the output of the bridge  362  to provide over-voltage protection and pre-regulation of the second power stage. The low pass filter combination of resistor  372  and capacitor  374  gives the required ramp up on the voltage output of the power supply  360 . The charge frequency of capacitor  374  is fast enough to overcome the bandwidth limitation of the transistor control. The charge frequency is:  
         f=1/(2π*(R8*C6))=800 kHz.  
         [0043]    Zener diode  376  has been placed across the output of the power supply  360  to regulate the steady state condition at no more than 6.2VDC. This protects the timer circuit  340  from failure.  
         [0044]    The timer  340 , the trigger circuit  350 , and the power supply  360  work in conjunction with each other to operate the solid state switch mechanism  380  illustrated in FIG. 7. The switch mechanism  380  is employed to operate the triac  392  at point  202  of ignitor  300 . The switching mechanism substantially comprises a two stage opto-isolater  390 , and a triac  392 . The gate of the triac  392  is controlled by the output of the opto-isolator  390 . There are two opto-isolaters contained in one package, connected in a cascaded fashion; therefore, the state of the first device determines the state of the second.  
         [0045]    The opto-isolater  390  has DC inputs on line  345  and solid state contacts that are normally closed. The typical state for the disable circuit  200  is to allow the ignitor to operate normally. However, upon expiration of the timer  340 , the control of the first of the opto-isolaters  390   a  is high, and the triac  392  is on. When the control goes low on line  345 , opto-isolater  390   a  has a shorted output, thus activating the input of  390   b . By activating  390   b,  the output of  390  b opens, thus allowing no current through the triac  392 , and therefore disabling the ignitor  300 . The triac  392  remains off until the input  44   390   a  goes high and once again activates the triac  392 .  
         [0046]    The reliability of the disable feature is extremely consistent. Accordingly, the entire system is not sensitive to component variation, since the power supply  360  is regulated and the timer  340  is accurate. The largest concern is the tolerance of the components on the timer  340  portion. Timers can vary from lot to lot and the disable time interval may vary from ignitor to ignitor on the order of 5%, (i.e., typically about a 30-second difference between the fastest disable and the slowest disable). However, the design constraint of the timer  340  being twice the maximum re-strike (e.g.,  180  seconds) time provides an ample buffer to overcome the tolerance issues of any timer circuit.  
         [0047]    Additionally, it should be noted that the disable circuit  200 , as shown in FIG. 2, can be retrofitted onto any existing universal sodium ignitor circuit, as shown in FIG. 3, when the disable feature is placed at point  202  of the ignitor  300 . This allows further flexibility for the disable circuit in accordance with an embodiment of the present invention.  
         [0048]    Although only several exemplary embodiments of the present invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims.