Abstract:
A battery powered LED lamp including an array of high-performance LEDs disposed in a lightweight directionally oriented shade. Converting electronics are provided which may include a step-down DC voltage switching regulator for converting a higher voltage of the battery power source to a lower voltage required to drive the LEDs at greater than 90% efficiency. The converting electronics may also include an LED current monitoring circuit for preventing thermal runaway of the LEDs and for reliably operating the LEDs near their maximum rating so to provide the maximum amount of brightness from the LED array and maximum battery life.

Description:
RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application No. 60/717,308, entitled BATTERY POWERED LED LAMP, filed Sep. 15, 2005, and hereby fully incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to electronic lighting devices and more specifically to lighting devices using light emitting diodes (LEDs) as an illumination source. 
   BACKGROUND OF THE INVENTION 
   It is often desirable to use printed materials in low ambient light venues. For example, musicians sometimes need to read sheet music in performances at concerts, theatrical productions, clubs and other venues where house lighting may be low or non-existent. Further, it is sometimes desirable to read books and consult printed materials in locations where ambient lighting is insufficient for comfortable reading, as for example, at night in an automobile. Prior attempts at providing a lighting source for such venues have not been entirely successful. 
   In some prior devices, incandescent bulbs, powered by batteries or AC power have been used. Incandescent sources, while being relatively inexpensive, also have the drawback of relatively low energy utilization efficiency. This low efficiency results in low light level for amount of power consumed, as well as excessive heat production in the bulb. For battery powered devices, batteries are quickly depleted requiring frequent replacement for alkaline batteries, and frequent recharging for rechargeable type batteries. Moreover, AC power lamps have the drawback of requiring a nearby AC power source. An AC power source is often not readily available in locations where a lamp is desirably used, for example in automobiles. Also, a bulky power cord sometimes including a transformer is required. Further, incandescent bulbs have a relative short service life and require frequent replacement. 
   Other prior devices have used fluorescent bulbs. These devices have an advantage over incandescent devices in that they typically have better overall energy utilization and run cooler. A drawback, however, is the generally bulky and relatively heavy ballast required for fluorescent bulbs. Also, while having a much longer life than incandescent bulbs, fluorescent bulbs contain mercury and other harmful substances, requiring specialized disposal when the bulb is replaced. 
   In recent years, LED&#39;s have emerged as a viable, low power, relatively high brightness light source for portable lamps. Prior compact LED lamps, however, have generally suffered from a number of drawbacks. In these devices, inexpensive LEDs having a relatively low light output are used in an effort to save cost and provide acceptable battery life. In these devices, the light is usually of poor quality even with fully charged batteries, and has poor overall color and temperature characteristics. The quality of light from these devices degrades quickly as the batteries are discharged. 
   Just as significant is the poor overall energy consumption efficency of prior simple LED driving circuits. These circuits are usually no more than a power source connected directly to an LED with a current limiting resistance inserted in series. These simpler circuits dissipate electrical energy in the form of heat via the series resistance. The energy loss is proportional to the voltage drop across the series resistance. The voltage drop across the series resistance is essentially the difference in the power source voltage and the voltage required to drive the LED&#39;s. For a battery power source, the highest energy loss occurs upon utilizing fresh batteries as this is when the power source voltage is at its highest. For example, given a 6VDC power source, 11 ohm series resistance and 3.25VDC LED voltage, total power consumption of the circuit would be 1.5 Watts of which 0.6875 Watts is dissipated as heat across the series resistance and 0.8125 Watts of useful LED light power. This calculates to 54% efficiency. 
   As a result of the low efficiency of prior LED lamps, frequent battery replacement or recharging is required in battery powered devices to maintain an acceptable light level. AC powered LED lamp devices have been developed which alleviate the problems with battery usage, but these devices suffer from many of the same deficiencies as AC powered incandescent devices. 
   What is needed in the industry is a compact, battery powered lamp that alleviates the limitations of prior devices. 
   SUMMARY OF THE INVENTION 
   The present invention is a compact battery powered LED lamp that addresses the aforementioned needs of the industry. In an embodiment of the invention, an array of high-performance LEDs is disposed in a lightweight directionally oriented shade. The shade may be coupled with a clip or other attaching element for attaching the lamp to a music stand or other item such as a book. A flexible and selectively positionable gooseneck may be used for coupling the shade and attaching element. 
   According to an embodiment of the invention, converting electronics are provided which may include a step-down DC voltage switching regulator IC. This IC regulator converts the higher voltage of the battery power source to the lower voltage required to drive the LEDs at greater than 90% efficiency. 
   The converting electronics may also include an LED current monitoring circuit for preventing thermal runaway of the LEDs. This circuit reduces the voltage applied to the LEDs as the LED&#39;s temperature rises, thereby reaching a stable condition. The current monitoring circuit may include a low valued current sensing resistor in series with the LEDs, forming a feedback loop to the threshold voltage input pin of the switching regulator. 
   A benefit of the current monitor circuit incorporated in the converting electronics of embodiments of the invention is to reliably operate the LEDs near their maximum rating so to provide the maximum amount of brightness from the LED array. Simple provisions via a potentiometer arrangement within the current monitoring circuit provide a user adjustable LED light dimming capability without a reduction in overall efficiency. For a battery power source, reducing the light brightness yields longer operating times due to lower battery energy consumption. 
   An advantage of embodiments of the invention is that a relatively constant light output level is maintained throughout the life of the batteries. In some embodiments, from 9 to 45 hours of operation may be achieved before any dimming of the light output is encountered or the batteries are depleted. 
   In other embodiments of the invention, a battery charging circuit is incorporated in a housing and attachment clip assembly. A lithium-ion or other high performance battery may be also enclosed in the housing. The battery charging circuit may include digital logic enabling rapid and safe charging of the battery. 
   In other embodiments, the LED lamp may include a shade with a translucent or transparent lower edge flange to refract light emitted from the LEDs. The flange may appear luminescent, forming a neon-like ring around the lower edge of the shade when the LEDs are lit. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is a perspective view of an embodiment of an LED lamp according to an embodiment of the present invention; 
       FIG. 1   a  is an exploded view of a power pack assembly of an LED lamp according to an embodiment of the present invention; 
       FIG. 2  is a bottom plan view of the LED lamp depicted in  FIG. 1 ; 
       FIG. 3  is a rear elevation view of the LED lamp depicted in  FIG. 1 ; 
       FIG. 4  is a side elevation view of the LED lamp depicted in  FIG. 1 ; 
       FIG. 5  is an opposite side elevation view of the LED lamp depicted in  FIG. 1 ; 
       FIG. 6  is a top plan view of the LED lamp depicted in  FIG. 1 ; 
       FIG. 7  is a front elevation view of the LED lamp depicted in  FIG. 1 ; 
       FIG. 8  is a perspective view of an alternate embodiment of an LED lamp according to the present invention; 
       FIG. 9  is a perspective view of an alternate embodiment of an LED lamp according to the present invention; 
       FIG. 10  is a bottom plan view of the LED lamp depicted in  FIG. 8 ; 
       FIG. 11  is a schematic diagram of a circuit board assembly of an embodiment of an LED lamp according to the present invention; and 
       FIG. 12  is a schematic diagram of a circuit board assembly of an alternative embodiment of an LED lamp according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As depicted in  FIGS. 1-10 , an embodiment of the LED lamp  20  of the present invention generally includes power pack assembly  22 , gooseneck  24 , and shade assembly  26 . Power pack assembly  22  generally includes housing  28 , which may be formed in two halves  28   a ,  28   b , and circuit board assembly  30 , which may include battery  32 , and attachment element  34 . Housing  28  may be formed from lightweight polymer or other suitable material and is of sufficient size to house circuit board assembly  30  as well as other any electronics for lamp operation. 
   In an embodiment depicted schematically in  FIG. 11 , circuit board assembly  30  generally includes charging circuit  36  and regulator and light circuit  38 . Charging circuit  36  functions to recharge rechargeable battery  32  from a power source, which may be a regulated DC adapter coupled with a 110V or 240V AC house system, connected through input jack  40 . In an embodiment, charging circuit includes a Maxim/Dallas MAX1501ETE highly integrated, linear battery charger with thermal regulation, available from Maxim/Dallas Direct! at www.maxim-ic.com for integrated circuit U 1 . It will be appreciated, however, that any other suitable circuit for battery charging may be used while remaining within the scope of the present invention. Further, in an embodiment, rechargeable battery  32  is a single cell high performance lithium-ion (Li+) battery as is commonly available in the art. It will be appreciated, however, that rechargeable battery  32  may also be any other type of rechargeable battery as may be known in the art, including without limitation, nickel-metal hydride (NiMH) or nickel-cadmium (NiCd). 
   In the embodiment of  FIG. 11 , LED D 1  is green in color, and LED D 2  is red in color. Each of LEDs D 1  and D 2  are visible from outside housing  28  through apertures  42 ,  44 , respectively. LED D 1  is used to indicate a full charge condition of rechargeable battery  32  and LED D 2  is used to indicate that battery charging is in progress. 
   Regulator and light circuit  38  generally includes lighting LEDs  46 , denoted as D 3 -D 11  in schematic  FIG. 11 , regulator integrated circuit U 2  and on/off/intensity switch  48 . In an embodiment, LEDs  46  are model NSCW455AT white LEDs made by Nichia Corporation. LEDs  46  have been found to provide a light having a temperature and other qualities particularly suitable for illuminating music scores and books for reading. As depicted in the embodiments of  FIGS. 2 ,  10 ,  11 , and  12 , nine of LEDs  46  are used to provide an amount and quality of light suitable for music reading. It will of course be appreciated that other types and numbers of suitable LEDs could be used while remaining within the scope of the present invention. 
   LEDs.  46  may be surface mounted on printed circuit board  48 , which has traces  50  for electrically connecting LEDs  46  in parallel. Printed circuit board  48  is mounted within shade  26  as depicted in  FIGS. 2 and 10 , and traces  50  are in turn electrically connected with regulator and light circuit  38  via wires  52  extending through gooseneck  24 . 
   Regulator integrated circuit U 2  may be a National Semiconductor LP3982IMM micropower, ultra-low dropout CMOS regulator available from Digi-Key Corporation, 701 Brooks Avenue South, Thief River Falls, Minn., under the designation LP3982IMM-ADJCT. According to an embodiment of the invention, regulator integrated circuit U 2 , which also may be any suitable prepackaged regulator as may be known in the art, converts the higher voltage of battery  32  to a lower voltage for driving LEDs  46 . While the voltage from battery  32  can range from a low value of approximately 3.5 volts to a larger value of approximately 10 volts, regulator integrated circuit U 2  maintains a nominal drive voltage of 3.25 volts to LEDs  46 . 
   To alleviate potential “thermal runaway” and resultant destruction of LEDs  46 , regulator and light circuit  38  incorporates an LED current monitoring circuit which reduces the drive voltage applied to LEDs  46  as the temperature of LEDs  46  rises, thereby reaching a stable condition. The current monitoring circuit includes a low-valued, current-sensing resistor, designated Rtemp in  FIG. 11 , which is connected in series with LEDs  46  and which is also connected in a feedback loop to adjust input Adj of regulator integrated circuit U 2 . In operation, as the temperature of LEDs  46  increases, the feedback loop through Rtemp applies a biasing signal to the Adj input of regulator integrated circuit U 2 . Based on logic within regulator integrated circuit U 2 , the output voltage from regulator integrated circuit U 2  is decreased, thereby decreasing the drive voltage and resulting current through LEDs  46 . Another benefit of the current monitor circuit is to reliably operate LEDs  46  near their maximum current rating so to provide the maximum amount of light output from LEDs  46 . Rechargeable battery  32  exhibits a declining voltage as its energy is consumed by LEDs  46 . Without regulator integrated circuit U 2  and the feedback loop, the effect would be for the light intensity of LEDs  46  to decline as the battery voltage declines. With regulator integrated circuit U 2  and the feedback loop, however, the light intensity of LEDs  46  is maintained until rechargeable battery  32  is nearly entirely depleted. Hence, operation time of LED lamp  20  is extended between recharges, and rechargeable battery  32  is more fully depleted between recharges, enabling longer battery life due to avoidance of “memory” in the battery. 
   On/off/intensity switch  48  is connected in series between rechargeable battery  32  and LEDs  46  to enable LED lamp  20  to be turned on and off as well as set to a desired brightness level. In the depicted embodiment, switch  48  is a three position switch having an off position, a first on position and a second on position. In one or both of the on positions, a resistor (not depicted) is connected in series with switch  48  to limit the voltage applied to regulator integrated circuit U 2  and accordingly LEDs  46 , thereby enabling selection of different illumination levels for LED lamp  20 . It will be appreciated that a switch with any number of discrete positions, each connected with a resistor having a different resistance value, could be provided in order to provide any number of different illumination levels. Further, it will be appreciated that a continuously variable analog or digital potentiometer could be substituted for switch  48  to provide still more variability in light output. 
   Brackets  50   a  are coupled at each end of circuit board assembly  30 . Each bracket  50   a  is attachable to housing  28  with a fastener  52   a  to secure circuit board assembly  30  in place therein. 
   Gooseneck  24  is coupled at one end  54  to housing  28  and at an opposite end  56  to shade assembly  26 . Gooseneck  24  defines a central lumen (not depicted) through which wires  52  run from printed circuit board  48  in shade  26  to regulator and light circuit  38  within housing  28 . Gooseneck  24  is selectively shapable to enable selective positioning of shade  26  in nearly any orientation. Gooseneck  24  may be any suitable hollow, selectively shapable, lightweight gooseneck element as is commonly known in the art. 
   In an embodiment, attachment element  34  generally includes bayonet portion  58  and opposing portion  60  which are coupled at a pivot  62 . Spring  63  biases portions  58 ,  60 , together at ends  64 . Bayonet portion  58  is received in bayonet brackets  66  on housing  28 . In operation, a user may force ends  64  apart by pressing ends  67  toward each other against the bias of spring  63 . Attachment element  34  may then be clamped clothespin fashion on any object that will fit between ends  64  when forced apart. As an alternative to this bayonet arrangement, housing  28  may be equipped with shiftable legs  67   a  as depicted in  FIGS. 1 ,  2 - 7 , and  9 . Legs  67   a  are selectively positionable in a first position adjacent housing  28  as depicted in  FIGS. 1 ,  2 - 7 , and a second position as depicted in  FIG. 9  when desired to enable LED lamp  20  to stand on a flat surface  67   b.    
   Shade assembly  26  generally includes unitary housing  68 , which defines enclosure  70  for containing printed circuit board  48  with LEDs  46 . Housing  68  may be formed in a single integral piece from suitable lightweight polymer or other material. Preferably, housing  68  is of sufficient depth to receive substantially all of printed circuit board  48  therein. Lower edge flange  72  extends around periphery  73  of enclosure  70  below printed circuit board  48  to provide lateral containment of the light emitted from LEDs  46 . The distance lower edge flange  72  extends below printed circuit board  48  may be selected to provide the desired spread of light under shade assembly  26 . 
   In embodiments of the invention, as depicted in  FIGS. 1-7 , and  9 , shade assembly  26  including enclosure  70  and lower edge flange  72  are generally opaque to provide maximum control of the spread of light from LEDs  46 . In other embodiments, as depicted in  FIGS. 8 and 10 , lower edge flange  72  may be made from translucent or transparent plastic, either clear or with color. The translucent or transparent lower edge flange  72  refracts light emitted from LEDs  46  so as to appear luminescent, forming a neon-like ring around the lower edge of enclosure  70 . For example, lower edge flange  72  may be made from translucent cobalt blue plastic so as to form a luminescent cobalt blue ring around the lower edge of enclosure  70  when LEDs  46  are lit. The effect may particularly pronounced in low ambient light conditions, so as to give the effect of a luminescent halo suspended in the air. Moreover, in an embodiment, translucent or transparent lower edge flange  72  may tend to transmit a refracted view of each individual LED so as to give an appearance of multiple brighter light points within the generally luminescent flange. It will be appreciated that, in addition to the translucent or transparent lower edge flange described above, any other portion of shade assembly  26  may be made translucent or transparent as desired to lend any particular desired lighting effect. 
   In an alternative embodiment of the LED lamp  20  of the invention, battery  32  may be non-rechargeable such as one or more standard alkaline batteries.  FIG. 12  is a schematic depiction of a regulator and light circuit  78  for non-rechargeable batteries. Circuit  78  includes a step-down DC voltage switching regulator IC U 1 , which may be the National Semiconductor LP3982IMM unit used with regulator and light circuit  38 , or any other suitable prepackaged regulator as may be known in the art. Again, voltage switching regulator IC U 1  converts the higher voltage of the battery power source to the lower drive voltage required to drive LEDs  46 , denoted as D 3 -D 11 . While the voltage from battery  32  can range from a low value of approximately 3.5 volts to a larger value of approximately 10 volts, regulator integrated circuit U 2  maintains a nominal drive voltage of 3.25 volts to LEDs  46 . 
   Again, to alleviate potential “thermal runaway” and resultant destruction of LEDs  46 , regulator and light circuit  78  incorporates an LED current monitoring circuit which reduces the drive voltage applied to LEDs  46  as the temperature of LEDs  46  rises, thereby reaching a stable condition. The current monitoring circuit includes a low-valued, current-sensing resistor, designated Rtemp in  FIG. 12 , which is connected in series with LEDs  46  and which is also connected in a feedback loop to adjust input Vfb of voltage switching regulator IC U 1 . In operation, as the temperature of LEDs  46  increases, the feedback loop through Rtemp applies a biasing signal to the Vfb input of voltage switching regulator IC U 1 . Based on logic within voltage switching regulator IC U 1 , the output voltage from voltage switching regulator IC U 1  is decreased, thereby decreasing drive voltage and corresponding current through LEDs  46 . Another benefit of the current monitor circuit is to reliably operate LEDs  46  near their maximum current rating so to provide the maximum amount of light output from LEDs  46 . Non-rechargeable battery  32  exhibits a declining voltage as its energy is consumed by LEDs  46 . Without regulator integrated circuit U 2  and the feedback loop, the effect would be for the light intensity of LEDs  46  to decline as the battery voltage declines. With regulator integrated circuit U 2  and the feedback loop, however, the light intensity of LEDs  46  is maintained until non-rechargeable battery  32  is nearly entirely depleted. The regulator and light circuit  78  of the present invention may enable the extraction of over 90% of the useful energy in a standard alkaline battery  32  without causing significant dimming of LEDs  46 , enabling longer operation times on a set of batteries and lower overall battery cost. 
   The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without the departing from the spirit and scope of the invention.