Patent Publication Number: US-6987366-B2

Title: Step down circuit for an LED flashlight

Description:
FIELD OF THE INVENTION 
   The present invention relates to handheld lights such as flashlights, but more particularly to a miniature flashlight that includes a voltage reducing circuit for reducing power from the power source to the light source. 
   BACKGROUND OF THE INVENTION 
   Flashlights of various sizes and shapes are well known in the art. Many use two or more dry cell batteries arranged in a housing as a source of electrical energy. 
   Battery technology is such that as electrical power is withdrawn from the battery cell, the voltage available across a given current load will decrease. In the case of a flashlight, this decrease of available voltage across the load causes reduced light output, gradually dimming the light as the battery charge depletes. 
   To prolong battery life, light emitting diodes (LEDs) are becoming more common as light sources for handheld flashlights, especially miniature flashlights. There are other advantages to using LEDs as opposed to other light sources in handheld flashlights. For example, LED bulbs are more durable, longer lasting and energy efficient than incandescent light bulbs. In contrast to regular incandescent bulbs, LEDs do not have a filament. Incandescent bulbs rely on filaments for conducting current that results in light being emitted from the bulbs. These filaments are easily broken or burned out, which requires bulb replacement quite frequently. 
   Most importantly, LEDs are extremely efficient. They have a battery life that is 10 to 15 times that of regular incandescent lights and consume less than 10% of the energy of an incandescent lamp. As such, the need to replace the batteries in an LED flashlight as opposed to an incandescent bulb flashlight is much less. 
   The energy emitted by an LED is related to the electrical charge q of an electron and the voltage V required to light the LED by the expression: E=qV. By substituting known values for q and V into this equation, it is apparent that LEDs require very little energy to emit light, thus minimizing the need to replace batteries as frequently. Because the energy requirements for LEDs are so low, many developers of LED flashlights utilize very low voltage battery cells which are small in size but hold an adequate charge for driving an LED to emit light for many hours. Thus, the present invention seeks to minimize the need for battery replacement even more by providing a flashlight that utilizes a larger battery having a higher voltage to further minimize the need for replacement in LED flashlights. 
   SUMMARY OF THE INVENTION 
   The present invention provides a voltage reducing circuit for a handheld flashlight to obviate the need for frequent battery replacement. 
   The flashlight of the present invention includes a battery and a light emitting device having an on-voltage threshold that is less than the voltage or potential difference stored in the battery. 
   A voltage reducing circuit such as a DC/DC converter is provided in electrical communication with the battery and the light emitting device. The voltage reducing circuit is operative to reduce the voltage received from the battery to a voltage level equal to or slightly above the on-voltage of the light emitting device causing it to illuminate. In this fashion, power dissipation is minimal because the majority of the energy being expended in the circuit is due to the light emitting device itself with a negligible amount being utilized by the voltage reducing circuit. 
   A housing is provided to support the battery, the light emitting device and the voltage reducing circuit therein such that the light emitting device is capable of emitting light from the housing once its on-voltage has been received. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawings wherein like reference characters refer to like parts in which: 
       FIG. 1  illustrates a block diagram of a flashlight including the voltage reducing circuit as according to the present invention; 
       FIG. 2  illustrates an alternative embodiment of the flashlight as according to the invention further including a switching circuit; and 
       FIG. 3  illustrates a schematic view of a flashlight that exemplifies a voltage reducing circuit which may be used in constructing the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Due to the small amount of energy expended by LEDs during illumination, most LED flashlights utilize very low voltage battery cells that are small in size but hold an adequate charge for driving an LED to emit light for many hours before battery replacement is required. The present invention operates to minimize the need for battery replacement even more by providing a flashlight that utilizes a larger battery having a higher stored charge, relative to a smaller battery, in communication with energy regulating circuit to further minimize the need for battery replacement in LED flashlights. 
   Referring now to  FIG. 1 , a flashlight is shown generally at  10  that includes a voltage reducing circuit  16 . 
   The flashlight  10  as according to the invention includes a battery  12  for supplying energy to the light emitting device  14  of the flashlight  10 . The battery  12  is selected for use in the flashlight  10  such that its voltage level or potential difference is greater than the on-voltage threshold of the light emitting device  14 . For example, if the on-voltage threshold of the light emitting device  14  is 1.7 volts, then the battery voltage as according to the invention may be 5 or more volts. 
   It is appreciated that the charge of a battery  12  is directly proportional to its voltage level or potential difference. Thus, choosing a battery  12  that has a higher voltage level operates to reduce the need for battery replacement when used in the flashlight  10  as according to the invention. 
   Many types of batteries may be used in the present invention including alkaline, lithium ion, nickel cadmium, or other chemistry suitable for the intended purpose and having a voltage level greater than the on-voltage threshold of the light emitting device  14 . The battery  12  or batteries used may also be rechargeable and/or recyclable and packaged as button cell, canister shape or other conventional forms suitable for such purpose. 
   Preferably, the flashlight  10  of the present invention utilizes a light emitting device  14  that is a solid state device. Most preferably, the solid state device is a light emitting diode (LED) but other types of low power solid state devices that emit light may be used which illustratively includes lasers and laser diodes. It is appreciated that other types of light sources may be used including incandescent bulbs. LEDs are most desirable due to the relatively low cost and durability however these general characteristics are not intended to be limiting on the scope of the invention. 
   A voltage reducing circuit  16  is placed in communication with the battery  12  and the light emitting device  14  such that the voltage reducing circuit  16  electrically connects to the positive and negative poles of the battery  12  as well as the positive and negative terminals of the light emitting device  14 . The voltage reducing circuit  16  operates to reduce the voltage received from the battery  12  to a level equal to or above the on-voltage threshold of the light emitting device  14 . In this manner, the light emitting device is only supplied the voltage necessary to remain on in a steady state condition. 
   Preferably, the voltage reducing circuit  16  imposes a minimal drain on the battery power as compared to that of the light emitting device  14 .  FIG. 3  exemplifies a flashlight  10  as according to the present invention where the voltage reducing circuit  16  is a DC/DC converter illustratively from the Texas Instruments TPS6200xDGS series of high efficiency step-down low-power DC/DC converters. The power dissipated by such a circuit is primarily dependent on the power requirements of the light emitting device  14  as the power dissipated by the converter is directly proportional to the current demands of the load. It is appreciated that other transformerless voltage reducing circuits are operative herein and illustratively include a conventional voltage regulator circuit which may regulate the output voltage delivered to the light emitting device to just above the on-voltage threshold similar to the DC/DC converter. Alternatively, a Zener diode may be used as a regulating device to limit the output voltage across a light emitting device  14  to the on-voltage threshold such that power dissipation across the load will be minimal. Still other circuits having the capability of stepping down an input voltage without causing a substantial drain on the power source relative to the load may become apparent to those skilled in the art that without exceeding the scope of the invention. 
   Preferably, a switch element  17  is included in the flashlight  10  such that an operator may turn the flashlight  10  on and off as desired. 
   As illustrated in  FIG. 2 , an alternative embodiment further includes a switching circuit  20  that is operative to switch the light emitting device  14  on and off at a rate that causes the light to appear that it is on continuously. Illustratively, the speed at which the light emitting device  14  alternates between an activated/deactivated state is greater than or equal to 60 hertz such that the state changes are not discernable by the human eye. It is appreciated that the switching circuit  20  may also be operative to switch the light emitting device between states at a frequency below 60 hertz which may be desirable for certain situations. Additionally, adding a switching circuit  20  into the flashlight  10  also functions to preserve the power source as switching the power source causes less energy is being delivered to the load over any given period as opposed to a load receiving continuous DC. Pulse width modulation circuitry is commonly used for switching power to a load and may be used herein for such purpose. Alternatively, an astable multi-vibrator circuit may be employed to accomplish the desired switching thus reducing power dissipation at the load. 
   A housing  18  is provided for supporting each of the battery  12 , the light emitting device  14  and the voltage reducing circuit  16  therein such that the light emitting device  14  emits light from the housing  18  upon receiving a voltage that is greater than or equal to its on-voltage threshold. Preferably, the housing  18  is made of a lightweight hard plastic material formed in an injection molding process. Alternatively, it is appreciated that other materials are operative herein such as various other polymers and metals. 
   A preferred embodiment of the light as according to the invention is a lightweight handheld device. Ideally, it is sized such that it may be carried on a key ring or in a small carrying case which can be placed in a user&#39;s pocket or attached to an outer garment. 
   From the foregoing it can be seen that the present invention provides a simple and yet effective means of further obviating the need for replacing the battery used in a handheld flashlight that utilizes a solid state light source. Having described the invention, however, many modifications thereto will become apparent to those skilled in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims.