Patent Application
20080068832
The present application is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:
With reference to
The flashlight 100 also includes a light management system such as a generally parabolic reflector 112 and lens 114, a circuit board 116, and a light source 118 such as one or more light emitting diodes (LEDs) which, as illustrated, are carried by the second end cap 106. A user-operable switch 120 such as a pushbutton on/off switch allows a user to control the operation of the flashlight 100 as desired. As illustrated in
The batteries 110, switch 120 and circuit board 116 configured as an intrinsically safe electrical circuit suitable for use in hazardous locations and through which energy from the batteries 110 is used to selectively illuminate the light source 118.
Turning now to
As the batteries are ordinarily capable of supplying energy sufficient to render the flashlight 100 non-intrinsically safe, an energy limiter such as a fuse F1 and a current limiting resistor RL are disposed electrically in series between the batteries 110 and the input Vin of the converter circuit 202. The fuse F1 and current limiting resistor RL cooperate to limit the available energy so that any spark or thermal effect produced during normal operation or under fault conditions is incapable of causing ignition of a mixture of a flammable or combustible material in air in the mixture's most easily ignitable concentration. The energy limiter should be located as near as practicable to the battery receiving region 108, and the requisite electrical connections 124 should be suitably spaced and insulated so as prevent or otherwise reduce the likelihood of shorts, opens, or other faults.
The light source 118 is connected to the output Vout of the charge pump 202. In one implementation, the light source 118 is a 1 Watt (W) white LED. Such LEDs typically have a nominal forward voltage of approximately 3.6 VDC (with specification limits typically ranging from roughly 3 to 4 VDC) and an operating current of approximately 350 milliamperes (mA). Where the flashlight 100 is powered by two (2) series connected alkaline primary batteries each having a nominal open circuit output voltage of 1.5 VDC, the nominal open circuit input voltage to the charge pump is about 3 VDC. Two series connected Nickel Metal Hydride (NiMH) secondary batteries having a nominal open circuit output voltage of 1.2 VDC likewise provide a nominal voltage 2.4 VDC. Note that the converter circuit 202 is advantageously configured to have an input dynamic range which is suitable for use with either chemistry and which accommodates decreases in input voltage which occur as the batteries 100 are loaded and/or become discharged. In either case, the converter 202 ordinarily serves as a voltage step up or boost converter.
A feedback resistor RFB is connected in series with the light source 118. The resistor RFB provides a feedback signal VFB to the converter circuit 202, which implements a closed loop control circuit which varies the average output voltage Vout as needed to maintain the LED current ILED at a desired operating current. In this sense, the converter 202 can be considered to operate as a current source.
One advantage of such an arrangement is that it tends to ameliorate the effects of variations in the performance of the light source 118, as well as changes in battery output voltage, particularly as the batteries 110 discharge. Those of ordinary skill in the art will recognize that, while the illumination provided by the light source 118 is a function of LED current ILED, the converter need not function as an ideal current source.
The circuit also includes decoupling capacitors C1, C3 such as 0.01 μF ceramic capacitors and a filter capacitor C2 such as a 1.0 microfarad (μF) electrolytic capacitor.
A suitable charge pump for use in the converter circuit 202 is the BCT3511S DC/DC converter integrated circuit (IC) available from BlueChips Technology of Selangor Darul Ehsa, Malaysia (www.bluechipstech.com). In the case of an intrinsically safe circuit suitable for use in Class I, Division 1, Group A, B, C, and D locations pursuant to the UL913 standard, a suitable fuse F1 is a very fast acting, encapsulated 750 mA fuse such as a Series 263 fuse available from Littlefuse Company of Des Plaines, Ill. USA (www.littlefuse.com). A suitable resistor RL is a 0.25 Ohm (Ω)+/−5%, 1 Watt (W) resistor. Note also that the thermal characteristics of the various components should be selected so that the temperature rise under fault conditions is insufficient to cause ignition of flammable or combustible materials. Internal wiring and other connections should also be insulated and spaced appropriately. One source of guidance with respect to thermal issues, reactive component values, spacing, and the like is the known UL 913 standard.
Various alternatives are contemplated. The flashlight 100 may be designed as intrinsically safe for use in other classes, divisions or groups (e.g., classes II or III, Division 2, Groups B-G, or the like). The flashlight 100 may also be designed to conform to IEC, ATEX/CENELEC, or other classification standards, for example in Zones 0, 1, or 2.
While the above discussion has focused on a flashlight having two (2) D-size batteries and a light source which includes a single 1 W LED, other battery types and/or light sources 118 are contemplated. In one variation, the flashlight 100 is configured to accept two (2) AA size batteries and the light source 118 includes three (3) 72 mW LEDs. A suitable circuit implementation is shown in
The flashlight may also be designed to accept AAA-size, C-size, Type N, other generally cylindrical batteries, prismatic batteries, coin cells, or other batteries, either alone or in combination. Other chemistries are also contemplated, including but not limited to lithium ion (Li Ion), lithium iron disulfide (Li/FeS2), and nickel cadmium (NiCd), provided that the batteries are otherwise suitable for use in the desired hazardous location. The flashlight 100 may also be configured to accept only a single battery 110 or three (3) or more batteries 110.
Other numbers and wattages of LEDs may also be provided, as may colors other than white. Examples include cyan, green, amber, red-orange, and red. Two (2) or more of the LEDs may also be connected electrically in series.
While the above discussion has focused on a flashlight 100 having a generally cylindrical form factor, other form factors are also contemplated. For example, the flashlight may be configured as a lantern style flashlight or as a wearable light. In one variation, the flashlight 100 includes clip or carabineer for attaching the flashlight to a belt or other article of clothing. In still another variation, the flashlight 100 is configured as a headlamp, for example as part of headgear such as a safety hardhat or connected to a headband which is worn around the user's head. The flashlight 100 may also include one or more flat surfaces which facilitate placement of the flashlight on suitable surface. It may also include suitable clamps, brackets, cut and loop fasteners, magnets, or other fasteners for selectively attaching the flashlight 100 to an object in the external environment.
The flashlight 100 may also be configured to produce other than a light beam, for example to provide an area light. It may also include more than one independently controllable light source 118, batteries 110, and/or circuits 202. Thus, for example, one light source 118 may provide a light beam while another serves as an area light. The flashlight may also include a light source 118 which serves as a distress or signal light, for example by flashing and/or emitting a red or other suitably colored light. The intensity of the light provided by a light source 118 may be varied by varying the value of its feedback resistor RFB, for example via a potentiometer, switch, or other user operable brightness control. In one implementation, the intensity is substantially continuously variable. In another, the intensity is variable between three or more levels, for example between an off state and two (2) or more illuminated conditions. Where the light source 118 includes multiple LEDs, the illumination intensity may also be varies by selectively powering one or more of the LEDs.
Other converter 202 implementations are also contemplated. For example, the converter 202 may be implemented using other DC to DC converter ICs, discrete circuitry, or combinations thereof. Note also that the filter capacitor C2 may be omitted, particularly where the switching frequency of the converter circuit 202 is fast enough so that any resultant flicker in the LED output is not noticeable or otherwise acceptable.
Other converter topologies are also contemplated. Additional circuits are discussed in commonly owned U.S. patent application Ser. No. [unknown] to Spartano et al., and entitled Intrinsically Safe Battery Powered Power Supply, filed on even date herewith and which is expressly incorporated by reference in its entirety herein.
Note also that the switch 120 may also be located on the negative side of the batteries 110. The switch 120 may also be implemented as a slide, toggle, rocker, rotary, or other switch.
Operation of the flashlight 100 will now be described in relation to
The invention has been described with reference to the preferred embodiments. Of course, modifications and alterations will occur to others upon reading and understanding the preceding description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims and the equivalents thereof.
