Abstract:
An arc lamp system comprises a power supply coupled to a xenon arc lamp through an interface constructed on a heavy printed circuit board. Such plugs directly into an igniter printed circuit board. In turn, a xenon arc lamp module with heatsinks plugs directly onto banana plugs bolted on the interface printed circuit board. Copper traces buried on inner layers of the interface printed circuit board are very wide and heavy, and kept as short as possible.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates generally to arc lamp based systems, and specifically to the low electromagnetic radiation and low power loss interfacing of power supply systems with xenon arc lamps.  
           [0003]    2. Description of the Prior Art  
           [0004]    Short arc lamps provide intense point sources of light that allow light collection in reflectors for applications in medical endoscopes, instrumentation and video projection. Also, short arc lamps are used in industrial endoscopes, for example in the inspection of jet engine interiors. More recent applications have been in color television receiver projection systems.  
           [0005]    A typical short arc lamp comprises an anode and a sharp-tipped cathode positioned along the longitudinal axis of a cylindrical, sealed concave chamber that contains xenon gas pressurized to several atmospheres. U.S. Pat. No. 5,721,465, issued Feb. 24, 1998, to Roy D. Roberts, describes such a typical short-arc lamp. A typical xenon arc lamp, such as the CERMAX marketed by EGG/ILC Technology (Sunnyvale, CA) has a two-legged strut system that holds the cathode electrode concentric to the lamp&#39;s axis and in opposition to the anode.  
           [0006]    Voltages as high as thirty kilovolts are needed to “ignite” or start a xenon arc lamp. Once current starts to flow, the voltage can be reduced and the current regulated to safe limits. The arc lamps usually start on a first attempt by the igniter, but if that fails several more pulses of high voltage can be issued.  
           [0007]    The pulsed nature of the voltages, the high voltages involved, and the current delivered to the arc lamp can all combine to generate strong electromagnetic interference (EMI). Significant impedances can also exist in the wiring that connects the power supply to the arc lamp, and these can dissipate substantial power. In some cases, poor coupling can prevent igniting the lamp on the first strike of the igniter.  
         SUMMARY OF THE PRESENT INVENTION  
         [0008]    It is therefore an object of the present invention to provide an efficient interface between a power supply and a xenon arc lamp.  
           [0009]    Briefly, an arc lamp system embodiment of the present invention comprises a power supply coupled to a xenon arc lamp through an interface constructed on a heavy printed circuit board. Such plugs directly into an igniter printed circuit board. In turn, a xenon arc lamp module with heatsinks plugs directly onto banana plugs bolted on the interface printed circuit board. Copper traces buried on inner layers of the interface printed circuit board are very wide and heavy, and kept as short as possible.  
           [0010]    An advantage of the present invention is that a xenon arc lamp system is provided with an interface that improves EMI and lamp operation.  
           [0011]    These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the drawing figures.  
       
    
    
     IN THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a side view of an arc lamp system embodiment of the present invention;  
         [0013]    [0013]FIG. 2 is a functional block diagram of an arc lamp power supply embodiment of the present invention;  
         [0014]    [0014]FIG. 3 is a schematic diagram of a full bridge resonant converter (FBRC) power supply embodiment of the present invention;  
         [0015]    [0015]FIG. 4 is a diagram representing an igniter that was built and tested; and  
         [0016]    [0016]FIGS. 5A and 5B are respectively top and bottom views of an igniter that was built and tested in one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    [0017]FIG. 1 represents an arc lamp system embodiment of the present invention, and is referred to herein by the general reference numeral  100 . The system  100  comprises a power supply  102  that feeds DC electrical power to an exciter  104 . A pair of machine screws  106  and  108  are used to mechanically secure the printed circuit board (PCB) of the exciter  104  and electrically connect it to the power supply  102 . A pair of output connections (±) are represented by a male spade connector  110  and a female spade connector  112 . These provide igniter and normal operating power to an interface PCB  114 . A pair of buried inner circuit traces, e.g., represented by a copper foil  115 , independently connect the respective spade connectors on the input side (left in FIG. 1) through to the output side (right in FIG. 1). A pair of (±) output connections is represented by a banana plug  116 . These plug into a pair of female banana connectors  118  on a removable lamp module  120 . A pair of cathode and anode aluminum heatsinks  122  provide an electrical connection to and cooling of an arc lamp  123 . All this is housed in a plastic or epoxy molding  124  that helps channel a cooling forced-air flow, and provides high-voltage insulation from chassis ground. The lamp module is typically four inches cubed, and weighs twenty-eight ounces.  
         [0018]    The interface PCB  114  is subject to a lot of mechanical stress caused by plugging and unplugging the lamp module  120 , so heavier PCB material is used. For example, 0.125″ thick epoxy laminate type G10-FR4. The exciter PCB  104  is subject to less mechanical abuse, and can be a much lighter-duty 0.0625″ G10-FR4 material.  
         [0019]    [0019]FIG. 2 represents a power supply embodiment of the present invention for a high-intensity short arc lamp, and is referred to herein by the general reference numeral  200 . Utility power is input (AC-in) through a line-side safety interlock  202 . A switch mode controller  204  receives the AC-input and control signals from a system shut-down monitor  206 . A lamp-current adjustment  208  is provided. A full-bridge resonant mode converter  210  drives a switch-mode transformer  212 . An output diode  214  converts the AC power from the switch-mode transformer  212  into direct current. A CERMAX 30KV igniter  216  provides a starting pulse needed by an arc lamp through an interface board  217 .  
         [0020]    In typical embodiments of the present invention, the switch-mode transformer  212  is used to power a lamp-current feedback  218 , an auxiliary power supply  220 , a fan power supply  222 , and a boost power supply  224 . A remote enable  226  allows external lamp control A line-input auto-selector  228  automatically maintains its DC rectified output at a near constant voltage despite being connected to a variety of mains-voltages. It does this by changing between half-wave and full-wave operating modes.  
         [0021]    In alternative embodiments of the present invention, the power supply  200  automatically shuts down in a failsafe condition should the lamp fail to ignite after five seconds of turn on. In operation, the lamp is ignited by one trigger pulse. Too many trigger pulses being needed indicates a problem with the lamp. Once the lamp ignites, a heavy DC electrode current will flow. Too high a voltage across the lamp, or too high a current during operation can also signal trouble. The power supply  200  preferably shuts down automatically in a failsafe condition should the lamp develop a short circuit, or if the cooling fan loses its operating power. Alternatively, power supply embodiments of the present invention automatically shut down in a failsafe condition when the average lamp load current exceeds a safe level, e.g., 25.0 amps.  
         [0022]    [0022]FIG. 3 represents a full bridge resonant converter (FBRC) power supply embodiment of the present invention, and is referred to herein by the general reference numeral  300 . Such FBRC power supply is preferably used as a power supply for a high-intensity short arc lamp. The general specifications preferred for such power supply are listed in Table I.  
                           TABLE I                                       Topology   Full Bridge Resonant Mode               Converter           Switching Frequency   250 KHz ± 10%           Line Operating Voltage   90-132, 180-264 VAC           Max Input Current   6 A           Output Current Range   4-24 A           Trigger Voltage   25-35 KV           Boost Voltage   270-300 V DC           Fan Output Voltage   +12 V DC @ 1 A Max           Features:   Auto shut down &gt;24 A               Remote Enable               Lamp ON Indication               Lamp Replace Indication           Regulatory requirements:   UL2601-1, CSA222 No 6061               UL3101 No 1010-1 CB Certificate                      
 
         [0023]    Referring now to the schematic of FIG. 3, AC-mains utility power is input to the power supply  300  through a filter choke (L 1 )  302  and is rectified by a bridge rectifier (BR 1 )  304 . A DC operating voltage of +400V is obtained from bridge rectifier (BR 1 )  304  and across filter capacitors (C 6 ,C 7 )  306  and  308 . Bridge rectifier (BR 1 )  304  can be switched to operate as either a full-wave or half-wave bridge by a silicon controlled rectifier (SCR 1 )  310 . Which mode is used depends on the input line input voltage in conjunction with the auto select line input.  
         [0024]    The objective of switching between full-wave or half-wave bridge operation is to produce about the same DC operating voltage of about +400V across filter capacitors (C 6 ,C 7 )  306  and  308  for either 320VAC or 230VAC inputs. Silicon controlled rectifier (SCR 1 )  310  is controlled by a universal voltage monitor (UVM) integrated circuit (IC 1 )  312 , e.g., a Motorola type MC34161. IC 1  has two level-comparators that are each referenced to an internal “1V27” standard. Two resistors (R 1 ,R 2 )  314  and  316  are used to set a voltage threshold “+Ve” that causes the half-wave to full-wave changeover to occur at an AC-input of about 332VAC. A second threshold is used for the full-wave to half-wave changeover, and is determined by a resistor (R 5 )  318 . Therefore, SCR 1  forces DB 1 , C 6 , and C 7  to operate in a full-wave bridge mode at AC-input line voltages of 90-132VAC and to a half-wave mode at AC-input line voltages of 380-265VAC.  
         [0025]    A current-sense transformer (T 4 )  320  allows the output load to be sampled. A current control loop with a voltage proportional to the lamp current is obtained from the secondary winding of T 4 . Such voltage is rectified and output on a feedback terminal  321 . The arc lamp powered by the power supply  300  is connected across output load terminals  322  and  324 . Such arc lamp may be of the CERMAX type marketed by EGG/ILC Technology (Sunnyvale, Calif.).  
         [0026]    A “resonant-bridge” is formed by transformers (T 1 , T 2 )  326  and  328 . Inputs from the switch mode controller illustrated in FIG. 2 are received at a gate-drive-one input  330  and gate-drive-two input  332 .  
         [0027]    A resonant mode converter is constructed by controlling the resonant-bridge with two totem-pole pairs of MOSFET transistors (TR 1 ,TR 2 ,TR 3 ,TR 4 )  334 - 337 , e.g., type IRFP450 MOSFET devices. A resistor is connected between the source and gate of each MOSFET device to reduce parasitic turn-on. Transformers T 1  and T 2  control the resonant bridge and output anti-phase pulses. A resonant part of the circuit which operates at 250KHz ± ten percent comprises a switch-mode transformer (T 3 )  338 , the primary winding of transformer (T 4 )  320 , and a capacitor (C 10 )  340 .  
         [0028]    The switch-mode transformer (T 3 )  338  has four secondary windings: a main output winding  342  that produces 31VAC, a boost output winding  344  that produces 200VAC, an auxiliary supply winding  346  that produces 30VAC, and a fan supply winding  348  that produces 30VAC (all for a nominal 240VAC line input). The main winding  342  consists of nine turns, center-tapped, and is connected to a  300 A,  400 V bridge rectifier (BR 2 )  350 , e.g., a type MUR3040. BR 2  preferably has a peak rectified forward current of 30A @345° C., and is mounted on a ceramic heat-sink.  
         [0029]    The boost output winding  344  helps produce a 300VDC boost voltage that is used to initiate the arc lamp. The fan winding  348  delivers a maximum of 30VAC and is half-wave rectified and filtered for use by a fan connected to a pair of fan output terminals  351  and  352 .  
         [0030]    The 300V DC boost voltage is only required during ignition of the arc lamp. To ensure this voltage is afterwards isolated from the output, a positive temperature coefficient (PTC) thermistor (PT 1 )  354  is used, e.g. 3,000 ohms at 25° C. Once the arc lamp has struck, the boost voltage will become isolated because the resistance of thermistor (PT 1 )  354  will greatly increase as it passes current.  
         [0031]    An external light emitting diode (LED) to indicate the lamp needs replacing is connected to an open-collector NPN-transistor  356 . The “replace lamp” warning is given when the operating voltage across the lamp output terminals  322  and  324  exceed some threshold, e.g., 38VDC. As a CERMAX lamp ages its operating voltage will increase. This is always associated with a worn out lamp. The base of transistor  356  will become forward biased by a simple voltage divider connected across lamp output terminals  322  and  324 . If the lamp connected between output terminals  322  and  324  is on at all, a transistor  358  will switch on and drive another external LED indicator, this one for “lamp on”. A transistor  360  will prevent transistor  358  from switching on as long as the voltage across output terminals  322  and  324  is too high, indicating a lamp that is not connected or has not been ignited. Such LED indications can be placed remotely at convenient observation points in the user&#39;s application. Both of these LED drivers are primary side isolated.  
         [0032]    The igniting of CERMAX lamps requires a boost voltage of at least 250V DC be applied together with series-induced trigger-pulses of 25-30KV. A trigger circuit  362  supplies just these voltages. It comprises a DIAC  364 , a charge pump network  366 , a spark gap (SG 1 )  368 , and autoformer (T 5 )  370 . When a 300V DC boost voltage is applied across the DIAC  364 , a pulse is sent through the autoformer (T 5 )  370  and feeds into the charge-pump network  366 . When the pulse voltage reaches 6,000 volts, spark gap (SG 1 )  368  will break down and cause a 30,000 volt pulse two-hundred nanoseconds wide to be generated in an autoformer (T 6 )  372 . This will appear in series with the boost voltage at the output terminals  322  and  324  and initiate the CERMAX lamp.  
         [0033]    [0033]FIG. 4 represents an igniter  400  that was built and tested. Its PCB was mounted to a power supply with three screws, e.g., at plated-through holes  401 - 403 . Holes  401  and  402  provide (±) power input. A pair of male spade connectors  404  and  406  provide output power connections, e.g., to an interface board  500  in FIGS. 5A and 5B. These plug into a pair of female spade connectors  502  and  504 . Electrical power is conducted inside a thick laminate PCB material  506  by respective patterned conducting foils  508  and  510 . In one implementation that provided good results, foil  508  was about 0.875″ square and foil  510  was about 0.875″ by 2.5″. A number of mounting holes  511 - 515  provide for support fasteners. A pair of banana plugs  516  and  518  provide output power to a CERMAX lamp, and are typically set apart from one another by 1.5″.  
         [0034]    It is critical to the present invention to interconnect the CERMAX lamp and the igniter/power supply with an interface board like that shown in FIGS. 5A and 5B. Simple wire connections radiate too much EMI and dissipate too much power, e.g., by virtue of the poor and uncontrolled impedance matches that result.  
         [0035]    In general, arc-lamp power supply to arc-lamp interface embodiments of the present invention include a printed circuit board (PCB) for providing mechanical support of a modular arc lamp assembly, a pair of power input connectors on a first side of the PCB for connecting to an arc-lamp exciter, a pair of power output connectors on a second side of the PCB that are positioned for a sliding connection to the modular arc lamp assembly, and a pair of patterned copper foils disposed in the PCB and each providing a powerplane-type connection between corresponding ones of the pairs of input and output power connectors. The principle advantages of this is electromagnetic interference (EMI) is reduced and power transfer efficiency is improved. The pair of patterned copper foils are preferably about 0.75 inches wide, and lie within a common plane. As such, they are on-edge to one another. As shown in FIG. 1, the pair of patterned copper foils lie within a common plane and are normal to a printed circuit board base for the arc-lamp exciter. The preferred power input connectors comprises spade-type connectors to allow dissasembly of the exciter from the PCB. The preferred power output connectors comprises banana-type connectors to allow removal of the modular lamp assembly from the PCB. The PCB is preferably about 0.125″ thick and comprises G10-FR4 fiberglass-epoxy material. In an alternative embodiment of the present invention, the pair of patterned copper foils each comprise two separate parallel copper foils patterned in the same shapes on both sides of the PCB and are connected together at each end by the input and output power connectors.  
         [0036]    Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.