Abstract:
A starting aid for a luminaires includes a trigger circuit for supplying a trigger voltage pulse to a lamp in response to the presence of a line voltage signal supplied by a photodetector, a feedback circuit for detecting the lamp voltage and means, responsive to the line voltage signal and the feedback circuit, for comparing the voltage on the lamp to a nominal voltage level for disabling the trigger circuit and terminating the trigger voltage pulse in the presence of a lamp cycling or lamp out condition.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/128,635, filed Apr. 9, 1999. 
    
    
     FIELD OF INVENTION 
     This invention relates to luminaries such as street lamps, and more particularly to a starting aid device for a luminaire which automatically turns the luminaire on and off, can sense a faulty condition and can communicate that condition locally or to a remote location. 
     BACKGROUND OF INVENTION 
     Servicing a luminaire such as a single street light can cost $100 or more on busy roads, and in busy areas. Moreover, since there are 60,000,000 street lights in the United States alone, the cost of servicing high pressure sodium (HPS) street lights cycling towards the end of their useful life is severe. The phenomena of cycling of HPS lamps as they age from use is the result of the electrode material being plated off the electrodes and then being deposited on the inside of the arc tube. This makes the tube darken and traps more heat inside the arc tube. As a result, an increased voltage is required to keep the lamp ignited or ionized. When the voltage limit of the ballast is reached, the lamp extinguishes by ceasing to ionize. The lamp must then cool down for several minutes before an attempt at re-ignition can be made. The result is “cycling”, in which the worn out lamp keeps trying to stay lighted. The voltage limit is reached again, the lamp extinguishes, and then after an approximately one-two minute cool down period, the arc tube re-ignites and the light output increases again and until the voltage limit is reached whereupon the lamp extinguishes yet again. This repetitive on and off process is called cycling. 
     Cycling can waste electricity, cause radio frequency interference (RFI) which adversely affects communication circuits, radios, and televisions in the area, and may adversely effect and prematurely wear out the ballast, starter, and photocontroller. 
     For example, if an HPS lamp undergoes cycling for a few nights before it is finally serviced and replaced, the ballast or starter can also be damaged or degraded. However, when the HPS lamp is replaced, such damage or degradation might not be detected. Consequently, additional service calls must then be made to service these problems. The ballast and starter components are more expensive than the lamp or the photocontroller. 
     The cycling problem is well documented, but so far the only solutions offered are to replace the HPS lamps and luminaires with less efficient mercury lamps and luminaires or to reconfigure the photocontroller with a special fiber optic sensor which senses light from the lamp and sends a signal to a microprocessor to indicate whether the lamp is on or off. After three on/off cycles, the microprocessor turns the lamp off and turns on a red strobe light which can be seen from the street. Unfortunately, this prior art solution requires modifications to the existing light fixture (e.g. a hole must be drilled in the fixture housing) and the use of an expensive fiber optic sensor. 
     Another problem with all luminaries including HPS or other types of lamps is the cost involved in correcting the cycling problem and other faults such as a lamp out condition. For example, a resident reports a lamp out or a cycling condition. However, by the time the repair personnel arrives several hours later, the lamp may have cycled back on. Considering the fact that the lamp pole may be 25-35 ft. high, repair personnel can waste a considerable amount of time checking each lamp in the area. Also, repair and maintenance personnel may not be able to service a given residential area until daylight hours when all of the street lights are off by design. 
     BRIEF SUMMARY OF THE INVENTION 
     It is therefore an object of this invention to provide a starting aid circuit for a lamp which can detect a faulty condition. 
     It is a further object of this invention to provide such a starting aid circuit which is microprocessor-based. 
     It is a further object of this invention to provide such a starting aid circuit which prevents hot restriking of a cycling or a dead lamp. 
     It is a further object of this invention to provide such a starting aid circuit which communicates that a fault in the lamp has occurred. 
     It is a further object of this invention to provide such a starting aid circuit which can communicate such a condition to a worker on the ground. 
     It is a further object of this invention to provide such a starting aid circuit which can communicate a faulty condition to a remote location. 
     It is a further object of this invention to provide such a starting aid circuit which automatically turns on and off in response to daytime and nighttime lighting conditions. 
     It is a further object of this invention to provide such a starting aid circuit which also turns the lamp off. 
     It is a further object of this invention to provide such a starting aid circuit which can detect whether the lamp is on or off. 
     It is a further object of this invention to provide such a starting aid circuit which can detect cycling of the lamp. 
     It is a further object of this invention to provide such a starting aid circuit which reduces maintenance of the lamp. 
     It is a further object of this invention to provide such a starting aid circuit which prolongs the life of the lamp. 
     It is a further object of this invention to provide such a starting aid circuit which is cost efficient to produce. 
     The invention results from the realization that a truly effective luminaire starting aid device can be obtained by providing a trigger circuit including a feedback loop that supplies a trigger voltage to the lamp and monitors the voltage of the lamp to determine if it has indeed started. If the lamp does not start, a microprocessor that controls the trigger circuit instructs the trigger circuit to repeat attempts to start the lamp a predetermined number of times, after which, if the lamp does not start, a faulty condition of the lamp is communicated either locally at the site of the luminaire or to a remote location. 
     This invention features a starting aid for a luminaire including a device for detecting a load drawn by or voltage across a lamp, a microprocessor, responsive to the means for detecting, for controlling start-up of the lamp, a power supply for operating the microprocessor and a trigger circuit, responsive to the microprocessor, for turning on the lamp. 
     In a preferred embodiment of the invention, the starting aid circuit may further be programmed to detect a condition of the lamp in response to the load drawn or voltage across the lamp. The starting aid circuit may further include means, responsive to the microprocessor, for indicating the occurrence of the condition detected. The starting aid circuit may further include a photo controller for automatically turning the lamp on during periods of darkness and off during periods of daylight and means, responsive to the microprocessor, for shunting the lamp to turn off the lamp. The means for detecting may include a voltage divider. The trigger circuit may include a SIDAC circuit for turning on the lamp and a relay circuit, responsive to the microprocessor, for enabling the SIDAC circuit. the trigger circuit may further include an opto-coupler, responsive to the microprocessor, for enabling the SIDAC circuit. The power supply may include a full wave rectifier and/or a half wave rectifier. The trigger circuit may further include a TRIAC circuit, responsive to the microprocessor, for enabling the SIDAC circuit. The starting aid circuit may further include means, responsive to the microprocessor, for shunting the lamp to turn off the lamp. The means for shunting may include a relay circuit, responsive to the microprocessor, for shorting the lamp. The means for shunting may include a TRIAC circuit or another silicon device such as a SCR circuit, responsive to the microprocessor, for shorting the lamp. The means for indicating may include a visual alarm, an audible alarm and/or a transmitter for transmitting the detected condition to a location. The condition may be a lamp dead condition and/or a cycling condition. 
     This invention also features a diagnostic starting aid for a luminaire including means for detecting a load drawn by or voltage across the lamp, a microprocessor, responsive to the means for detecting and the photocontroller, for controlling start-up of the lamp, the microprocessor programmed to detect a condition of the luminaire in response to the load drawn, a power supply for operating the microprocessor, a trigger circuit, responsive to the microprocessor, for turning on the lamp and means, response to the microprocessor, for indicating the occurrence of the condition detected. 
     This invention also features an automatic aid for a lamp including a photocontroller for automatically turning the lamp on during periods of darkness and off during periods of daylight, means for detecting a load drawn by or voltage across the lamp, a microprocessor, responsive to the means for detecting and to the photocontroller, for controlling start-up of the lamp, a power supply for operating the microprocessor and a trigger circuit, responsive to the microprocessor, for turning on the lamp. 
     In the preferred embodiment, the automatic starting aid may further include means, responsive to the microprocessor, for shunting the lamp to turn off the lamp. The microprocessor may be programmed to detect a condition of the lamp in response to the load drawn, further including means, responsive to the microprocessor, for indicating the occurrence of the condition detected. 
     This invention also features a starting aid including a trigger circuit for supplying a trigger voltage pulse to a lamp in response to the presence of a line voltage signal supplied by a photodetector, a feedback circuit for detecting the lamp voltage and means, responsive to the line voltage signal and the feedback circuit, for comparing the voltage on the lamp to a nominal voltage level for disabling the trigger circuit and terminating the trigger voltage pulse in the presence of a lamp cycling or lamp out condition. 
     In the preferred embodiment, the means for comparing may include a processor programmed to determine when the lamp voltage switches between a nominal voltage level and a non-nominal voltage level N times indicative of a lamp cycling condition. N may be 5. The means for comparing may include a processor programmed to determine when the voltage on the lamp falls to reach a nominal voltage level after M trigger voltage pulses. M may be 2. The starting aid may further include means, responsive to the line voltage signal, for supplying to the trigger circuit a series of trigger pulses at predetermined portions of the line voltage signal. The means for supplying may include a microprocessor programmed to determine a zero crossing point of the line voltage signal and to output the series of pulses when the line voltage signal reaches 90° and 270°. The trigger circuit may include a transformer which is activated by the series of trigger pulses and in response produces a lamp starting voltage to the lamp. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
     FIG. 1 is a three dimensional view of the starting aid for a lamp according to the present invention; 
     FIG. 2 is a block diagram of the starting aid circuit according to the present invention; 
     FIG. 3 is a schematic diagram of a first embodiment the starting aid according to the present invention; 
     FIG. 4 is a schematic diagram, similar to FIG. 3, further including a photo controller for automatically turning the lamp on and off and a lamp off circuit for shunting the lamp to turn it off; 
     FIG. 5 is a schematic design of a third embodiment of the invention, in which the trigger circuit includes a SIDAC circuit for turning on the lamp and a relay circuit for enabling the SIDAC; 
     FIG. 6 is a schematic diagram of a third embodiment of the invention, in which the relay circuit is replaced by a photocoupler for enabling the SIDAC; 
     FIG. 7 is a schematic diagram of a fifth embodiment of the invention; 
     FIG. 8 is a schematic diagram of a sixth embodiment of the invention 
     FIG. 9 is a schematic diagram of a seventh embodiment of the invention; 
     FIG. 10 is a flow chart generally showing the operation of the starting aid circuit according to the present invention; 
     FIG. 11 is a flow chart depicting the routine for detecting a lamp out condition in accordance with the present invention; and 
     FIG. 12 is a flow chart depicting the routine for detecting a cycling condition of the lamp in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Luminaire starting aid  10 , FIG. 1, includes thermoplastic, impact resistant, ultra violet stabilized polypropylene cover  12  and clear window  14  made from UV stabilized, UV absorbing acrylic for the light sensor, not shown, which resides on a circuit board within cover  12 . Luminaire starting aid  10  is typically configured to fit an existing luminaire receptacle. Prongs  16  plug into a luminaire assembly and retaining clips  18  hold device  10  in place: the device according to the present invention is mounted underneath the luminaire such that alarm LED  20  can be viewed by a worker from the ground to determine if a fault exists without having to be raised up to the lamp assembly. 
     Luminaire starting circuit  22 , shown in block form in FIG. 2, generally includes power supply  24 , microprocessor  26 , load detection circuit  28 , trigger circuit  30  and communication device  32 , which may include both on site and offsite portion  33   a  and  33   b,  respectively. Starting circuit  22  may optionally include a photocontroller  34 , a lamp off circuit  36 , a condition sensing circuit  38  including lampout device  39   a  and cycling detector  39   b  and diagnostic circuitry  40 . 
     The basic operation of starting aid circuit  50 , FIG. 3, is such that power supply  56 , which includes inductor L 1 , diode bridge BR 2 , resistor R 3 , capacitor C 2  and Zener diode Z 1 , delivers the necessary voltage needed for each of the sub circuits. Bridge BR 2  (which could also be four individual diodes), R 3 , Z 1  and C 2  make up a 5 volt power supply. Inductor L 1  is used to increase the impedance at high frequency of starting aid circuit  50 . Bridge BR 2  rectifies the AC voltage coming from the tap of ballast  52 . However, it should be noted that the voltage to drive starting aid circuit  50  could also come from the lamp side of ballast  52 . Resistor R 3  is a current limiting resistor. The value of resistor R 3  is such that it will limit the current so that microprocessor circuit  58 , alarm LED  64 , and trigger circuit  60  will receive sufficient current in order to operate normally. Zener diode Z 1  regulates the voltage to microprocessor circuit  58  and trigger circuit  60 . Capacitor C 2  is used to filter any AC ripple which may be present on the 5-volt line and further provides peak pulse current to trigger circuit  60  and alarm LED circuit  64 . Initially microprocessor  66  of microprocessor circuit  58  will wait a predetermined period of time, for example one second, before carrying out any instructions. This allows capacitor C 1  of voltage divider  62  to charge up. Thereafter, the main loop of the program is started. 
     Voltage divider  62  is provided in order to detect a load drawn by lamp  54 . Resistors R 1  and R 2  make up a 100:1 voltage divider. The rectified voltage is thus delivered to microprocessor  66  as a sample voltage, proportional to the voltage across lamp  54 . Microprocessor  66  uses this voltage to determine the status of lamp  54 . Capacitor C 1  further filters the sample voltage being used by microprocessor  66 . Zener diode Z 2  ensures that the sample voltage does not damage the input circuit of microprocessor  66 . A voltage reading is taken at node V 1 . When lamp  54  is off, the voltage detected at node V 1  should be proportional to the line voltage, or the highest voltage the circuit will see. This voltage is then multiplied by 0.75 to determine the trip voltage. By choosing 75% of the highest voltage, the present circuit provides a universal starting aid that can be used in conjunction with 55 volt or 100 volt lamps without modification. 
     Microprocessor circuit  58  includes resistor R 4 , capacitor C 3  and microprocessor  66  which may be for example, a 12C671 or a 12C672 available from Microchip of Arizona. Resistor R 4  is a current limiting resistor which provides microprocessor  66  with a clock pulse derived from the line frequency. Capacitor C 3  is a bypass capacitor for microprocessor  66 . The 12C671 (or 12C672) microprocessor has analog to digital (A/D) capabilities. This allows the analog voltage sampling of the lamp voltage to be converted to a digital value so that microprocessor  66  can determine the status of the lamp, as described below. 
     In operation, microprocessor  66  sends out a pulse train to trigger circuit  60 . Trigger circuit  60  includes resistor R 5 , transistor Q 1 , transformer T 1 , diodes D 1  and D 8  and capacitors C 4  and C 30 . Resistor R 5  is a current limiting resistor which is used to develop the base current to turn on transistor Q 1 . Transistor Q 1  is driven on and off by microprocessor  66  in response to pulses sent by microprocessor  66 . These pulses are coupled to lamp  54  by transformer T 1 . The primary winding of transformer T 1  is connected between a regulated five (5) volts from power supply  56  and Q 1 . When transistor Q 1  is pulsed on, the five (5) volts is stepped up to approximately 3500 volts. The pulse is typically 1.5μsec in duration and should be sufficient to start lamp  54 . Capacitor C 4  limits the leakage current that will flow through the secondary windings of transformer T 1 . Microprocessor  66  waits a predetermined period of time, for example two (2) seconds. A second voltage reading is taken at node V 1 . If the second voltage read at node V 1  is lower than the trip voltage which, as discussed above, is taken as 75% of the line voltage, the lamp has started. However, if the second voltage reading at node V 1  is not lower than the trip voltage, microprocessor  66  sends another pulse train to trigger circuit  60 . In the preferred embodiment, this process is repeated four more times for a total of five times. If the voltage never drops below the trip voltage it is assumed that the lamp  54  is dead and the indicator circuit  64  is activated to notify a line worker that the lamp  54  is not working. Alarm circuit  64  includes resistor R 6  and light emitting diode D 2 . Resistor R 6  is current limiting resistor for LED D 2 . LED D 2  will light in response to instructions from microprocessor  66  to indicate to a line worker that lamp  54  is dead. If, on the other hand, after lamp  54  starts it is then cycled off, microprocessor  66  will wait a predetermined period of time, for example two minutes, and then try to start the lamp  54  again. This is done to prevent hot restriking of lamp  54 . If lamp  54  does start again and again cycles, microprocessor  66  monitors the number of times the cycling occurs and limits restarting of the lamp  54  to a maximum number, for example five (5) times, in a single night. If the lamp  54  cycles the predetermined number of times, the lamp  54  will be considered faulty and LED D 2  of alarm circuit  64  will be activated. 
     The operation of the starting aid circuit  50  will now be described with reference to the flow charts of FIGS. 10-12. After the circuit is initialized, block  400 , the system enters he main loop, block  402 . If the microprocessor  66  determines that the alarm is on, block  404 , the alarm LED is activated, block  406 , and the system returns to the main loop  402 . If the microprocessor  66  determines that the system is not in an alarm state, the system determines whether the lamp  54  is on, block  408 . If it is not, the system enters the lamp out routine, block  412 , which is shown in greater detail in FIG.  12 . 
     As shown in FIG. 12, at block  420 , a count N is set to 5 during initialization. A pulse is sent to the lamp in order to try and start the lamp, block  410  and then the voltage at node V 1  is read, block  422 . If the voltage at node  410  is not less than the trigger voltage, block  424 , indicating the lamp has not been started, the count N is decremented by one, block  426 . If the count N is not equal to 0, block  428 , another pulse is sent to the lamp in order to attempt to start the lamp, block  410 . Again, the voltage at node V 1  is read, block  422  to determine if the lamp has been started. If, at block  428 , the count N is equal to 0, indicating that the lamp has been attempted to be started five times, the alarm is set, block  430  and the system returns to the main loop, block  431 . If, at block  424 , the voltage at node V 1  is less than the trigger voltage, a “lamp on” flag is set, block  432  and the count N is reset to 5, block  434 . The system then checks if the lamp is cycling, block  436 . Referring back to FIG. 10, since, at block  408 , it is determined that the lamp is on, the cycling routine is run, block  414 , as shown in FIG.  11 . 
     In the cycling routine, FIG. 11, first the count N is set to 5 during initialization, block  440 , and the voltage at node V 1  is read, block  442 . If the voltage at node V 1  is less than the trigger voltage, block  444 , the system determines that the lamp is indeed on and returns to block  442  to monitor the voltage at node V 1 . If in block  444 , it is determined that the voltage at node V 1  is not less than the trigger voltage, the system determines whether a predetermined period of time in minutes has passed, block  446 . If it has not, the system returns to block  442  and continues to monitor the voltage at node V 1 . If the predetermined time period has passed, all flags are cleared, block  448 , the count N is decremented by 1, block  450 , and it is determined whether the count N is equal to 0, block  452 . If it is not, the system returns to block  442  and continues monitoring the voltage at node V 1 . If, at block  452 , the count N is equal to 0, the alarm is set, block  454 , and the system returns to the main loop, block  456 . 
     Another embodiment of the invention is shown at  100  in FIG.  4 . Starting aid circuit  100  includes a photo control circuit  102  for turning lamp  54  on during nighttime hours and off during daytime hours. Photo control circuit  102  includes resistors R 17 , R 18 , and R 19  and transistor Q 2 . Resistors R 17 , R 18  and R 19  are used as calibration resistors. These resistors may be snapped out of the circuit  100  to lower the calibration point to ensure that the microprocessor  66  turns the lamp  54  on at the correct light level. Transistor Q 2  is a light sensing device, for example a phototransistor, that conducts proportionally to the light level it detects. This produces a voltage which is input to A/D pin  70  of microprocessor  66 . This voltage reading is converted to a digital number and microprocessor  66  determines if lamp  54  is to be turned on, turned off, or maintained in its current state. If the lamp is to be turned on, pulses are sent to trigger circuit  60  as described above. If, however, lamp  54  is to be turned off, pulses are delivered to lamp off circuit  104 . Lamp off circuit  104  includes transformer T 2 , resistor R 10 , and TRIAC X 2 . Lamp off circuit  104  turns lamp  54  off by placing a short across, or shunting the lamp. Transformer T 2  is an isolation transformer and is needed since microprocessor  66  is not referenced to neutral as the lamp  54  is. Resistor R 10  is a biasing resistor for TRIAC X 2 . A resistor or some other current limiting device may also be placed in line with TRIAC X 2 . 
     Another embodiment of the invention is shown at  150  in FIG.  5 . Staring aid circuit  150 , includes relay trigger circuit  152  which includes relay K 1  to enable SIDAC trigger circuit  154 . The primary difference between trigger circuit  154  and trigger circuit  60  is that, rather than a pulse train being sent by microprocessor  66 , a single pulse of a duration of 2 seconds is used to energize relay K 1 . Resistor R 5 , transistor Q 1 , diode D 1  and relay K 1  are used to enable SIDAC circuit  154  which includes SIDAC  156 , inductor L 10 , capacitor C 24  and resistor R 16 . Resistor R 5  is a current limiting resistor which develops the base current for transistor Q 1  which energizes relay K 1 . Diode D 10  operates as a back swing clipping diode intended to eliminate voltage spikes developed by relay K 1  when the relay is de-energized. 
     When relay K 1  is energized, SIDAC circuit  154  is enabled and lamp  54  will start. When relay K 1  is de-energized, the lamp will not be triggered. This circuit  154  represents a traditional starting aid trigger circuit. The SIDAC  156  has high resistance until a specified voltage is reached, in which case it has low resistance. Indicator L 1  is used to dampen the voltage spike that will be developed by C 4 , the ballast and the SIDAC. R 6  is a current limit resistor. 
     When relay K 1  is energized, SIDAC  156  will switch from a high resistance to low resistance. Capacitor C 24  discharges through ballast  52  and a voltage spike is seen by lamp  54 . This occurs every one-half cycle. When the voltage seen by SIDAC  156  drops below a specified voltage, SIDAC  156  returns to a high resistance state. When relay  156  is de-energized, there is no current path back to the SIDAC  156  and thus trigger circuit  154  is disabled. 
     Another embodiment of the invention is shown at  200  in FIG.  6 . Starting aid circuit  200 , includes power supply  56  with the addition of resistor R 7  which limits current and further helps prevent any transient voltage or current spikes from entering the rest of the circuit. Also included is opto-coupler circuit  204 , which includes resistors R 25  and R 28 , transistor Q 2 , and opto-coupler circuit  206 , which provide a switch to turn on the circuit  202 . Resistor R 25  is a current limiting resistor that provides base current to transistor Q 20 . Transistor Q 20  enables opto-coupler  206 . Transistor Q 20  is driven in response to microprocessor  66  to light LED  208  within opto-coupler  206 . Resistor R 28  limits the current to LED  208 . The light produced by LED  208  causes opto-coupler  206  to conduct. When opto-coupler U 2  is conducting, SIDAC circuit  202  is enabled, lighting lamp  54 . 
     Another embodiment of the invention is shown at  250  in FIG.  7 . Starting aid circuit  250  is identical to starting aid circuit  200 , FIG. 6, except for the opto-coupler circuit  254 , which includes a diode D 5  and phototransistor Q 30  for enabling SIDAC circuit  202 . 
     Another embodiment of the invention is shown at  300  in FIG.  8 . Starting aid circuit  300 , includes power supply  302  which is a half wave power supply. Power supply  302 , as compared to power supply  56 , FIG. 7, provides half wave rectification. Resistor R 7  and capacitor C 5  serve to limit current while diode D 3  serves as a blocking diode. Zener diode Z 1 , resistor R 3  and capacitor C 2  operate in the same manner as in power supply  56 , FIG.  7 . However, capacitor C 2  has much larger capacitance in order to provide the same filtering. 
     Trigger circuit  306 , includes resistors R 15  and R 13 , capacitor C 6 , and TRIAC X 1 . Resistors R 15  and R 13  and capacitor C 6  are pulse conditioning components. When TRIAC X 1  receives a pulse at its gate, it will to enable SIDAC circuit  202 . The advantage of starting aid circuit  300  is that because halfwave rectification is be used, opto-couplers or isolation transformers are no longer needed. 
     Lamp off circuit  304  includes relay  308 , resistors R 5  and R 12 , and transistor Q 3 . Resistor R 5  and transistor Q 3  drive relay  308  on and off in response to microprocessor  66 , and relay  308  turns lamp  54  on and off. When relay  308  is energized, a short circuit is placed across lamp  54 , extinguishing the lamp. This circuit also includes photo control circuit  30 , similar to photocontrol circuit  102 , FIG.  4 . Cycling detection may also be included to determine if the lamp is cycling or off due to lighting conditions. 
     Another embodiment of the invention is shown at  350  in FIG.  9 . Starting aid circuit  350  includes lamp off circuit  352  comprised of resistors R 12 , and  14 , capacitor C 7  and TRIAC X 2 . Because power supply  302  provides half wave rectification, no isolation transformer is required as shown in circuit  300  of FIG.  8 . 
     Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. The words “including”, “comprising”, “having”, and “with” as used herein are to be interpreted broadly and comprehensively and are not limited to any physical interconnection. Moreover, any embodiments disclosed in the subject application are not to be taken as the only possible embodiments. Other embodiments will occur to those skilled in the art and are within the following claims: