Abstract:
This invention relates to circuits for operation over a range of voltages, more particularly for a vehicle lamp circuit that provides lighting over a range of voltages. The invention provides a circuit that allows the operation of an LED array lamp over a range of voltage. This is achieved by making use of three-terminal adjustable regulators. One of the three-terminal regulators is configured as a voltage regulator. It regulates the voltage by a connection to a voltage divider. A second three-terminal regulator is connected to the voltage regulator. The second regulator is configured to be a current regulator with the current set by one resistor. This circuit can be further modified with additional adjustable three-terminal regulators to increase in functionality.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to circuits for operation over a range of voltages, more particularly for a vehicle lamp circuit that provides lighting over a range of voltages.  
         BACKGROUND OF THE INVENTION  
         [0002]    In recent years the automotive industry has recognized the need to increase the power generation in vehicles. Thus, the automotive industry has agreed to move from a 14-volt system to a 42-volt system. This increase in voltage will provide the higher power loads that will be incorporated into future vehicles. This increase in vehicle power load is due to the requirements for emission control, safety and new optional features for vehicles such as navigation systems, sensors, audio, video, cellular and other items driven by wire products.  
           [0003]    Some of the areas that will gain from the 42-volt technology include power steering, electrically operated brakes, water pumps, instant stop-start and electric air conditioning. However, the move to 42-volts also involves a major redesign in vehicular electrical systems from light bulbs to integrated systems. To initiate the move towards a 42-volt system, most automotive manufactures will probably start with a dual 14/42 volt system to allow the system to be used on vehicles that use either voltage system. Interestingly, even though vehicle voltage is increasing, the voltage for microprocessors, digital signal processors, light emitting diodes for vehicle lamps and other electronic components is decreasing to allow better integration with closer spacing at the chip level. Therefore, some components in the vehicle will need the higher voltage while other components will need lower voltages, potentially making voltage regulation more complex and an area of great development in the automotive industry.  
           [0004]    In addition, there are electric vehicles currently in use that use 48 volt operating system rather than the standard 14 volt system. Also, some busses have an operating power of 28 volts. Both of these vehicles can benefit from the invention presented below.  
           [0005]    The prior art has a number of examples of circuits to either regulate the voltage or the current in a system. For example, U.S. Pat. No. 5,942,883 to Preis et. al. is generally directed to a circuit for supplying current. This patent includes a power supply circuit with a switching regulator and further includes at least one additional circuit whose two outputs are guided together to a common or joint output. The circuit in the patent is able to establish two different output currents rather than establishing two output voltages. The patented circuit is particularly good for the energy supply of electrical loads having a variable internal resistance such as the type in gas-discharge lamps. This circuit is not designed to accept a range of voltages while simultaneously keeping constant the output current for the load, although it is rather well suited for allowing a wide range of output currents. It also incorporates a complex series of switches.  
           [0006]    U.S. Pat. No. 4,739,226 to Murata discloses a dimming circuit, which adjusts the light output of a lamp by controlling the current flow. The patent includes a switching means, a control signal generating circuit and a protective circuit. The disclosed patent controls the excess of current flow by turning off the switching means. The disclosed patent only provides for a reduction in light intensity and cannot bring about an increase in light intensity in a lamp. An increase in intensity is necessary for the function of a tail/stop lamp.  
           [0007]    There is a diverse number of patents in the prior art such as U.S. Pat. No. 5,663,875 or 6,175,200 B1 that teach circuits that provide power to a vehicle gas discharge lamp. These patents do not teach a process to accept a range of voltages or a higher voltage than required for the proper functioning of the lamp.  
           [0008]    U.S. Pat. No. 5,528,474 to Roney et. al. teaches an LED array vehicle lamp. This patent again lacks a circuit to allow the operation of the LED lamp over a wide range of voltages.  
           [0009]    Due to the future change of voltage systems in vehicles there is a need to design circuits that handle a higher range of voltage for elements that do not require a high voltage. An example of such an element is a light emitting diode (“LED”) lamp for use in a vehicle.  
           [0010]    It is therefore an object of the invention to provide a cost-effective circuit to operate a vehicle lamp over a range of voltages.  
           [0011]    Another object of the invention is the creation of a circuit to handle the new voltage 42-volt standard for vehicles but still handle low voltage elements such as LED lamps.  
           [0012]    A further object of the invention is to create a reasonably priced circuit that will allow the function of a vehicular lamp over a range of voltages.  
           [0013]    Still another object of the invention to provide a circuit that will allow the operation of an LED array lamp over a range of voltage.  
           [0014]    An additional object of the invention is to be able to power a stop/tail/clearance combination lamp over a voltage range.  
           [0015]    Another object of the invention is the design of a simple circuit that will not crowd a circuit board but still effectively function over a voltage range.  
         SUMMARY OF THE INVENTION  
         [0016]    The above objects are achieved according to the present invention by making use of three-terminal adjustable regulators. In the present invention, multiple three-terminal adjustable regulators are used. One of the three-terminal regulators is configured as a voltage regulator. It regulates the voltage by a connection to a voltage divider formed by at least two resistors. A second three-terminal regulator, which is configured to be a current regulator with the current set by one resistor in series, is connected in series to the voltage regulator. This circuit is appropriate for use with a marker lamp having an LED array as its light source.  
           [0017]    The circuit can be further modified by the addition of a third three-terminal adjustable regulator, a transistor switch, a shunt and a MOSFET. This circuit modification can be utilized in connection with a combined vehicle stop/tail lamp. The circuit becomes active if either the stop or tail voltage is present. The transistor switch is connected to the gate of a P-channel MOSFET. The MOSFET will allow current to pass through two resistors or shunt around one of the resistors, thereby increasing or decreasing the current going to the main LED array. This allows for the increase or decrease of light intensities required for a tail/stop lamp. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 shows a schematic of the circuit to operate a marker lamp over a range of voltages.  
         [0019]    [0019]FIG. 2 shows a schematic of the circuit with additional components to operate a clearance, stop/tail lamp.  
         [0020]    [0020]FIG. 3 shows a front view of a lamp with the incorporated circuit. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    Referring now to the drawings in detail, for the ease of the reader, like reference numerals designate identical or corresponding parts throughout the drawings. To better describe the circuits, examples for marker and clearance/tail/stop lamp combinations will be presented. However, it should be understood that these embodiments are not presented to represent a limitation on the invention. Other vehicle lamps and other electronic devices can benefit from a circuit that overcomes the limitation of higher voltage range by sharing the voltage drop between two three-terminal adjustable regulators connected in series.  
         [0022]    [0022]FIG. 1 shows a schematic of the circuit that allows lighting over a wide range of voltages. In the preferred embodiment, the operating voltage of the circuit is from 10 to 50 volts, however the circuit can operate on higher voltages provided the voltage drop from input to output of the individual linear regulators does not exceed 40 volts. The use of larger and/or more efficient heat sinks can manage the increased heat generated by higher voltages and larger voltage drops.  
         [0023]    [0023]FIG. 1 shows that the input voltage is applied to line  6  through a diode rectifier  7  to the IN terminal of an adjustable three-terminal regulator  8 . This regulator  8  is configured as a voltage regulator. The regulator  8  is connected to two resistors  9  and  10  that act as a voltage divider. In a preferred embodiment, the voltage regulator  8  is regulated at 18 volts with the resistors  9  and  10  acting as voltage dividers. It can be appreciated by those well-versed in the art that the voltage regulator can be set to a variety of values by selecting different values for the resistors that are acting as voltage dividers. Thus, the example used is to describe this invention in detail but is not meant to limit the invention to an 18 volt regulator. Regulators of the type such as an LM317T, manufactured by National Semiconductor can serve as the low cost voltage regulator described in the instant invention. It will be appreciated by those skilled in the art that other voltage regulators can be used in the present invention and that the suggestion of the National Semiconductor regulator serves only to satisfy the inventor&#39;s duty to disclose the best mode of this invention.  
         [0024]    The output from the voltage regulator  8  is applied to a second adjustable three-terminal regulator  12 , which is configured to be a current regulator. A resistor  13  in series with regulator  12  sets the output current of the current regulator  12 . It is well known in the art that an appropriate resistor can control current amperage in a circuit. In a preferred embodiment, the current regulator is set to 50 mA by the value of the resistor  13 . Thus, the example used is to describe this invention in detail but is not meant to limit the invention to a 50 mA regulator. In the embodiment shown in FIG. 1, the output of the current regulator  12  is applied to a light source  14 , such as is found in an LED array in vehicle marker lamps. Regulators of the type such as an LM317LZ, manufactured by National Semiconductor can serve as the low cost current regulator described in the instant invention. It will be appreciated by those skilled in the art that other regulators can be used in the present invention and that the suggestion of the National Semiconductor regulator serves only to satisfy the inventor&#39;s duty to disclose the best mode of this invention.  
         [0025]    It should be recognized that the subject invention is not limited to the embodiment disclosed in FIG. 1. Additional three-terminal regulators each combined with appropriate resistors as described may be added in series to the circuit to reduce voltage input in a step down process. The additional three-terminal regulators may be configured as either voltage regulators or current regulators.  
         [0026]    This dual regulator circuit arrangement allows for the functioning of light sources or other electrical devices over a wide range of input voltages. In one embodiment, lamps, such as vehicle marker lamps, can be made to operate over an approximate range of 10 to 50 volts. Such lamps comprise a housing, lens cover, a light source, and a circuit board provided with input and output lines connecting the lamp to the circuit that is the subject of this invention. In a preferred embodiment, the housing can be removably secured to the vehicle itself. The light source can be an incandescent bulb, a single light emitting diode (LED), an array of LEDs or a plurality of such arrays. In a preferred embodiment, potting material, such as an epoxy, may be used to hold the light source and circuit board in place and to seal the lamp assembly from water and environmental damage.  
         [0027]    At voltages below 20 volts, the voltage regulator  8  passes the input voltage through with losses. Provided there is enough voltage to drive the lamp  14  and the regulator  12 , the current through the lamp  14  will be limited to the amount dictated by the value of the resistor  13 . At higher voltages, the voltage regulator  8  limits the voltage applied to the current regulator  12  to the voltage determine by the resistors  9  and  10 . In some cases a heat sink (not shown) is required for the voltage regulator  8 . The heat sink can be made of any material capable of adequately dissipating the heat generated at the maximum operating voltage under the most severe operating conditions. In a preferred embodiment the heat sink is made of zinc. In a more preferred embodiment, the heat sink is made of aluminum. The heat sink can be located between the cover lens and the circuit board with the LED attached to it. In an alternative embodiment, the heat sink can be placed under the circuit board. If the heat sink is located on top of the circuit board, portions of the heat sink can be cut to define a hole(s) that allows the forward passage of light for a bright marker lamp.  
         [0028]    [0028]FIG. 2 shows a schematic of another preferred embodiment of the circuit with additional components. In this preferred embodiment, the disclosed circuit can be used to power a stop/tail/clearance lamp. The circuit is operatively similar to the circuit in FIG. 1 with the addition of circuitry that allows a controlled change in value of the resistance in an additional circuit. Current passes from voltage regulator  8  through current regulator  12  to supply a non-varying current to a device  23 . Such a device could be an LED found in the center array of a marker/stop/tail lamp in a vehicle where the marker function utilizes a constant current. In one embodiment, the current requirement for the center LED is approximately between 35 mA and 50 mA depending on the type of LED used. In a preferred embodiment, the center array has the function of a clearance lamp and is composed of a single LED. It is clear that advances in LED technology may allow lower current requirements that may modify the invention parameters while remaining within the scope and spirit of the present invention. In addition, other devices that operate most efficiently with a constant current can utilize the circuit of the subject invention. Similar to the circuit demonstrated in FIG. 1, in the circuit seen in FIG. 2, resistor  13  sets the current in the current regulator  12 . It is clear that changing the value of resistor  13  can change the set values of the current regulator  12 .  
         [0029]    In the circuit shown in FIG. 2, the tail lamp voltages are applied through a diode rectifier  7  and the stop lamp voltages through a diode rectifier  15 . The voltages are combined at the input of the adjustable three-terminal regulator  8 , so that the circuit becomes active if either a stoplight or a higher tail light voltage is present. Current passes from voltage regulator  8  to current regulator  18  to supply current to a stop/tail function  22 . An additional diode rectifier  16  applies voltage to a transistor switch  17  such as any general purpose NPN transistor manufactured by numerous manufacturers including National Semiconductor that has its collector connected to the gate of a P-channel MOSFET  19 . In the preferred embodiment, a MOSFET is used to remove or add a resistor to the circuit by sensing voltage levels. It should be understood that the use of a MOFSET is intended as an example only and is understood that other electric components could be used. In a more preferred embodiment, a logic level version of the MOSFET is used to assure turn off and on in a range of 4-10 volts. This turns on the MOSFET  19  which shunts a resistor  20  effectively removing it from the circuit. With resistor  20  removed from the current path, more current will travel to an electrical device. In a vehicle circuit, the increased amperage will cause a stop/tail lamp to shine more brightly when MOSFET  19  shunts current around resistor  20 . Removing the stop lamp voltage turns off the transistor switch  17  which allows the gate of the MOSFET  19  to go high thereby turning it off, resulting in the addition of the previously shunted resistor  20  to the circuit. MOSFETs identical to or similar to part no. IRF-7204 manufactured by International Rectifier can serve as the MOSFET described in the subject invention. However, it is apparent to one skilled in the art that other MOFSETs manufactured by other manufacturers. When both resistors  20  and  21  are utilized in series, the added resistance reduces the current to produce dimmer tail lamp light illumination. In one preferred embodiment, the main LED array for the tail/stop functions of the lamp is composed of six series strings of three terminal regulators in parallel. It should be understood that changes in the configuration of the array such as the use of a single LED to produce stop lamp intensities are within the scope and spirit of this invention.  
         [0030]    It should be recognized that the invention seen in FIG. 2 is not limited to that single embodiment. Additional three-terminal regulators each combined with appropriate resistors as described may be added in series to the circuit to reduce voltage input in a step down process. The additional three-terminal regulators may be configured as either voltage regulators or current regulators.  
         [0031]    [0031]FIG. 3 shows the circuit represented in FIG. 2 on a circuit board  24  for a vehicle lamp. It should be appreciate that the simplicity of the circuit allows for a slim design for the lamp. The cost of the circuit is kept low by using off the shelf components.  
         [0032]    Although, for convenience, the method and resultant apparatus of the present invention has been described hereinabove primarily with respect to its preferred embodiments, it will be apparent to those skilled in the art that many variations of this invention can be made without departing from the spirit of the invention as claimed.