Abstract:
A starter circuit is provided for starting an HID lamp. The circuit de-couples the high voltage starting pulse from the input lines (ballast output lines) so that the starter can function properly regardless of the distance between the ballast and the lamp.

Description:
FIELD OF THE INVENTION 
     The invention relates to a starting device for a discharge lamp, and in particular to a starting device for a high-pressure discharge lamp adapted to be located remotely from the ballast. 
     BACKGROUND OF THE INVENTION 
     High-Intensity Discharge (HID) lamps produce light by driving current through a gas filled arc-tube. A light emitting discharge arc is produced between two electrodes exposed within the arc-tube. A starting device is required to initiate the arc between the two electrodes. Typically, the starting device must produce a pulse of several kilovolts across the two electrodes in order to initiate the arc and start the lamp. 
     Many conventional HID lamps require a ballast and starting circuit to generate a starting pulse and to supply the operating lamp with the necessary operating current. Conventional starting circuits charge a capacitor to a certain value until an automatic switch closes allowing the capacitor to discharge through the primary winding of a transformer. The primary winding is inductively coupled to a secondary winding, and the combination of the rapidly discharging capacitor through the primary winding, along with the winding ratio of the secondary winding to the primary winding, generates a pulse of sufficient voltage and duration across the electrodes of the HID lamp to initiate operation. Unfortunately, conventional ballasts and starting circuits have to be located relatively close to the HID lamp because parasitic impedances in the conductors connecting the HID lamp to the starting circuit tend to attenuate the starting pulse. Because of this effect of parasitic impedances, many ballast manufacturers place a maximum “lamp-to-ballast” distance on every ballast-starter combination that is offered. These distances typically range from 2 to 75 feet, depending on the ballast and the ignitor circuit being used. 
     It would be advantageous to provide a starting circuit which is capable of starting and operating an HID lamp such that the lamp could be located at an unrestricted distance from the ballast. 
     SUMMARY OF THE INVENTION 
     The above-described disadvantages are overcome and other advantages are realized by providing a starting circuit in accordance with the present invention. According to the first embodiment of the invention, an ignitor circuit for a discharge lamp is provided which comprises a voltage input terminal, an ignitor output terminal, and a first capacitor having first and second capacitor terminals. The first capacitor terminal is connected to the voltage input terminal. The ignitor circuit further has a transformer having a primary winding inductively coupled to a secondary winding. An automatic switch is connected in series with the primary winding. The switch and primary winding are connected across the first capacitor, and the secondary winding is connected between the starting circuit voltage input terminal and the output or “lamp” terminal. A resistor is connected between the second capacitor terminal and the common terminal, and the second capacitor is connected across the resistor. The second capacitor is selected to have a value such that it represents a low impedance path for the high-frequency pulse generated by the transformer. Therefore, the pulse is de-coupled from the input lines and is presented across the electrodes of the discharge lamp. 
     In another embodiment of the present invention, an ignitor circuit for a discharge lamp is provided that comprises input terminals, an ignitor output terminal and a first capacitor having first and second capacitor terminals. The first capacitor terminal is connected to one of the input terminals. The ignitor circuit also has a transformer having a primary winding inductively coupled to a secondary winding. Furthermore, an automatic switch is connected in series with the primary winding, such that the switch and primary winding are connected across the first capacitor. The secondary winding is connected to the voltage input terminal and the ignitor output terminal. A resistor is connected between the second capacitor terminal and a common terminal, and a second capacitor is connected between the first input terminal and the second input terminal. In this embodiment the second capacitor presents a low impedance path for the high-voltage pulse generated by the transformer such that the pulse is applied across the terminals of the HID lamp. 
     In the third embodiment of the invention, an ignitor circuit for a discharge lamp is provided that comprises a voltage input terminal, an ignitor output terminal, and a transformer having a primary winding inductively coupled to a secondary winding. A resonant circuit is connected between the voltage input terminal and a common terminal, wherein the resonance circuit comprises the primary winding connected in series with an automatic switch and a first capacitor. The first capacitor is connected to the voltage input terminal. A second capacitor is connected in series to the secondary winding, such that the second capacitor and secondary winding are connected across the ignitor terminal and the common terminal. Finally, and inductor device is connected between the voltage input terminal and the ignitor terminal. In this manner, the high-frequency pulse generated in the secondary winding of the transformer is present across the terminals of the discharge lamp through the low impedance path of the secondary capacitor. Furthermore, the pulse is de-coupled from the input terminals by the inductor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantages and novel features of the invention will be more readily appreciated from the following detailed description and in conjunction with the accompanying drawings in which: 
     FIG. 1 is a circuit diagram of a first embodiment of the invention; 
     FIG. 2 is a circuit diagram of a first embodiment of the invention, including an optional tertiary winding; 
     FIG. 3 is a circuit diagram of a second embodiment of the invention; 
     FIG. 4 is a circuit diagram of a second embodiment of the invention, including an optional tertiary winding; and 
     FIG. 5 is a circuit diagram of a third embodiment of the invention. 
    
    
     Throughout the drawing figures, the same reference numerals will be understood to refer to the same parts or components. 
     DETAILED DESCRIPTION OF THE INVENTION 
     An ignition circuit  100  according to the present invention is illustrated in FIG.  1 . The circuit  100  includes a voltage input terminal  102  and a common terminal  104 . These input terminals are preferably connected to the outputs of a ballast, which can be located at any distance from the starting circuit due to the de-coupling nature of the circuit design. The circuit  100  also includes an HID lamp  106 . The circuit also includes a transformer  108  comprising a primary winding  110  and a secondary winding  112 . The primary winding of the transformer  108  is connected in series with an automatic switch  114 . The automatic switch preferably has a break-over voltage of 240V. However, a wide range of possible break-over voltages are contemplated to be within the scope of the invention. A first capacitor  116  is connected across the primary winding  110  and the automatic switch  114 . The capacitor preferably has a value of 0.33 uF. A first terminal of the first capacitor  116  is connected to the voltage input terminal  102 . The secondary winding  112  of the transformer  108  is also connected to the voltage input terminal  102 . The other terminal of the secondary winding  112  is connected to one terminal of the HID lamp  106 . A resistor  118 , preferably 5 k ohms, is connected between the first capacitor and the common terminal  104 . Finally, a second capacitor  120  is connected across the resistor  118 . The second capacitor  120  preferably has a value of 0.01 uF. It is to be understood that the values suggested for the capacitors are merely exemplary, and a wide range of possible values is contemplated to be within the scope of the invention. 
     In operation, the output of a ballast is applied to the voltage input terminal  102 . Current through resistor  118  charges capacitor  116  until the voltage across automatic switch  114  reaches a break-over voltage. Once automatic switch  114  begins to conduct, current flows through a primary winding  110 , inducing a voltage across primary winding  110 . Due to transformer action, a corresponding voltage is induced across secondary winding  112 . The high-frequency pulse across the secondary winding  112  is applied to the HID lamp  106 . The voltage of the high-frequency pulse is determined by the winding ratio between the primary winding  110  and the secondary winding  112 . The winding ratio is preferably 8 to 1 so that a pulse of sufficient voltage (preferably 3400V) is applied across HID lamp  106  to cause an arc between the exposed terminals in the lamp. The values of the first capacitor  116  and the second capacitor  120  are selected such that they present a low impedance path for the high-frequency pulse induced in secondary winding  112 . Therefore, the high-frequency, high-voltage pulse is applied across the lamp terminals. Due to the low impedance path through the capacitors  116 ,  120 , the pulse is de-coupled from the voltage input terminals  102  and  104 . 
     FIG. 2 illustrates an embodiment of the present invention similar to FIG. 1 with the addition of an optional tertiary winding to the transformer. Transformer  208  includes primary winding  210  and secondary winding  212  connected in a manner similar to the transformer  108  depicted in FIG. 1. A tertiary winding  222  is added to the circuit  200  and connected between the common terminal  104  and the second terminal of the HID lamp  106 . In this embodiment of the circuit, the winding ratio between the primary winding  210  and the secondary winding  212  is preferably 4 to 1. The winding ratio between the primary winding  210  and the tertiary winding  222  is also preferably 4 to 1. In this embodiment, when automatic switch  114  begins to conduct and the voltage across capacitor  116  is applied to primary winding  210 , corresponding voltages are induced in both secondary winding  212  and tertiary winding  222 . The voltages that are induced in secondary winding  212  and tertiary winding  222  are applied to the terminals of HID lamp  106 . The values of capacitors  116  and  120  are selected such that they present a low impedance path to the high-frequency pulse generated in secondary winding  212  and tertiary winding  222 . Thus, the high-frequency pulse is de-coupled from inputs  102  and  104 . 
     FIG. 3 illustrates a second embodiment of the present invention. The starter circuit  300  includes a voltage input terminal  102  and a common terminal  104 . These input terminals are preferably connected to the outputs of a ballast, which can be located at any distance from the starting circuit due to the de-coupling nature of the circuit design. The circuit provides a high-voltage pulse to HID lamp  106 . In order to begin an arc between the electrodes within the lamp enclosure, a transformer  308  is provided to generate the high-voltage pulse from stored energy via capacitor  116  received from the ballast or other voltage source. A primary winding  310  of the transformer  308  is connected in series with an automatic switch  114 . A capacitor  116  is connected across the automatic switch  114  and the primary winding  310 , and also has one of its terminals connected to the voltage input terminal  102 . A resistor  118  is connected between the second terminal of the capacitor and the common terminal  104 . Current through resistor  118  and capacitor  116  charges capacitor  116  until the voltage across it reaches the break-over voltage of automatic switch  114 . When the voltage of capacitor  116  reaches the break over voltage, automatic switch  114  begins to conduct and capacitor  116  discharges rapidly through primary winding  310 . Secondary winding  312  is inductively coupled to primary winding  310  such that a voltage is induced in secondary winding  312  which corresponds to the winding ratio between primary winding  310  and secondary winding  312 . Capacitor  320  is connected between voltage input terminal  102  and common terminal  104 . The value of capacitor  320  is selected such that it provides a low-impedance path for the high-frequency pulse induced in secondary winding  312  (preferably 0.01 uF). The high-voltage pulse is therefore applied across the terminals of HID lamp  106 , and de-coupled from input terminals  102  and  104 . 
     An ignitor circuit in accordance with the second embodiment of the invention is illustrated in FIG.  4  and also comprises an optional tertiary winding  422 . In the ignitor circuit depicted at  400 , a three-winding transformer  408  delivers a high-voltage, high-frequency pulse to HID lamp  106 . Capacitor  116  is charged until the voltage across the capacitor reaches the break-over voltage of automatic switch  114 . When automatic switch  114  begins to conduct, the charge accumulated in capacitor  116  begins discharging through primary winding  410 . A voltage appears across winding  410 , and because primary winding  410  is inductively coupled to secondary winding  412  and tertiary winding  422 , corresponding voltages are induced in the secondary and tertiary windings, respectively. The voltages induced in secondary winding  412  and tertiary winding  422  are related to the voltage induced in primary winding  410  by the winding ratio between the primary winding and the secondary winding and between the primary winding and the tertiary winding. Capacitor  320  is connected between voltage input terminal  102  and common terminal  104 . The value of capacitor  320  is selected so that the high-voltage, high-frequency pulse generated in windings  412  and  422  has a low impedance path between the terminals of HID lamp  106 . 
     A third embodiment of the present invention is depicted in FIG.  5 . Starter circuit  500  includes a voltage input terminal  502  and common terminal  504 . The circuit  500  supplies a starting pulse to HID lamp  506 . Transformer  508  includes primary winding  510  and secondary winding  512 . Primary winding  510  forms part of a resonant circuit with capacitor  516 , which is activated by automatic switch  514 . As the voltage input terminal  502  increases, the voltage across automatic switch  514  also increases until the break-over voltage is reached, at which time automatic switch  514  begins conducting. When the automatic switch  514  begins conducting, current is forced through primary winding  510  inducing a voltage across winding  510 . The values of capacitor  516  and the inductance of winding  510  and the electrical resistance of automatic switch  514  and primary winding  510  are selected so that a high frequency pulse is generated across winding  510  when the automatic switch  514  begins conducting. 
     Secondary winding  512  is inductively coupled to primary winding  510 , so that a high-voltage pulse corresponding to the winding ratio between secondary winding in  512  and primary winding  510  is generated across secondary winding  512 . Capacitor  518  is connected between HID lamp  506  and secondary winding  512 . The value of capacitor  518  is selected such that the capacitor presents a low impedance path to the high frequency pulse induced in secondary winding  512 . This high-frequency, high-voltage pulse is applied directly across HID lamp  506  causing an arc and starting the lamp. The high-voltage, high-frequency pulse is de-coupled from voltage input  502  by inductor  520  which is connected between the HID lamp and voltage input terminal  502 .