Replacement illumination device for a miniature flashlight bulb

Disclosed is a method and apparatus for providing a solid state light emitter and driving circuitry integrated into a component module that will retrofit common incandescent light bulb applications. The disclosed embodiment is directed to the retrofitting of small flashlights using miniature bulbs, such as the Mini Maglite®. Because the emitter and driving circuitry cannot readily fit within the envelope of the bulb being replaced, the volume occupied by the module needs to be acquired from within the flashlight's interior, such as from part of the volume occupied by the reflector. In that case, the invention includes a replacement reflector supplied with the module. The invention provides that no original functionality of the flashlight is sacrificed. Consideration is also given to the conduction of heat from the light emitter and module.

FIELD OF INVENTION

This invention relates to a solid state replacement for a miniature bulb in a flashlight.

BACKGROUND

Non-provisional patent application Ser. No. 10/820,930, filed on Apr. 8, 2004, described an invention which can replace incandescent light bulbs with more efficient light emitters such as light-emitting diodes (LEDs). The Background section of that patent application provided the justification for doing so, and it is incorporated herein by reference.

However, the description of the embodiment of that invention of that prior patent application and its claims prescribed circuitry which fit within the 3-d spatial envelope defined by the incandescent bulb, which is replaced by an instance of that prior invention. Furthermore, although instances of that invention would include flashlight bulbs, it did not focus in particular on the problem imposed by flashlights with tiny incandescent bulbs. The above-referenced, previous patent application described circuitry using current off-the-shelf components and a printed circuit board to employ them. Although it may be technologically possible, it is not economically attractive to implement that invention in a form that will fit entirely inside the spatial envelope of certain tiny standard incandescent light bulbs. For example, a so-called “grain-of-wheat” bulb is aptly named and would present an implementation challenge to fit all the circuitry of the above invention, as well as a light-emitting, solid state, semiconductor chip in such a small volume at a reasonable cost for a consumer product. This would currently apply to any light bulb which is, for instance, less than about 5 millimeters in diameter.

Therefore, in light of the foregoing limitation, the first objective of this invention is to provide a replacement light source for very small incandescent bulbs which employs the principles and circuitry of the aforementioned prior patent application, but where the invention is not limited in size by the envelope of the bulb it is replacing. Implicit in this first objective is the more efficient use of the batteries than with an incandescent bulb: providing longer battery life for the same light intensity or providing brighter light for the same battery life or a compromise in-between. Also implicit in the first objective is presumed advantage that solid state light emitters have over incandescent filaments regarding their relative expected operational lifetimes.

A second objective is to do this is a way which minimizes the cost and the effort for a consumer to retrofit the replacement. A third objective is to provide a replacement light source which fits entirely within the envelope of a commercially available, consumer flashlight, and which ideally still uses the type and same number of batteries for which the flashlight was designed. A fourth objective is to preserve the attractive features possessed by the flashlight before the incandescent bulb was replaced. These features may include, for example, user-adjusted beam focus and the on-off switch function (which itself may be integrated with the beam focus feature).

The principal advantage of such an illumination device is that the advantages of solid state illumination can be more quickly offered to consumers for a variety of existing flashlight models, without requiring them to buy a new, custom-designed flashlight. It also allows the consumer to revert back to the incandescent bulb if necessary.

SUMMARY OF THE INVENTION

To accomplish the stated objectives, the present invention comprises essentially the same elements as U.S. patent application Ser. No. 10/820,930, the summary of which is incorporated herein by reference. These elements include a standard light bulb power connector, at least one light emitter, and a driving circuit embedded in a module. The power connector provides a conductive contact with a electrical power source (typically batteries) and normally also provides physical support too. The light emitter typically would be a light emitting diode (LED) or other such solid state device. The module typically is a miniature printed circuit board. The flashlight to be upgraded with the present invention and the batteries are not elements per se of the invention, but clearly they are necessary for its operation. For certain cases, the invention also comprises an additional element: namely a resized reflector to replace the original one.

Although the elements are the same as in patent application Ser. No. 10/820,930, some constraints on them differ. Most importantly, the light emitter and its drive circuitry need not fit entirely within the spatial envelope defined by the bulb surrounding the filament of the miniature incandescent light source. Nevertheless, the drive circuitry must fit within the flashlight in such a way that the battery compartment volume remains fixed—or at least it is changed so little that the same number and type of batteries can still be used in it. Furthermore, existing attractive features such as the on-off switch and user-adjusted beam focusing (if previously present) must not be degraded.

A specific instance of such a flashlight is the popular, consumer flashlight known as the Mini Maglite®, manufactured by Mag Instrument, Inc. For it, user-adjusted focusing and its integrated, twist-activated switch must be preserved by the present invention. Furthermore, for a model which uses N dry cells as batteries, the model should continue to use the same N cells after retrofitting the flashlight with the present invention. However, to accomplish the retrofit, space for the driver circuit module must be acquired somewhere. In this specific case, this is accomplished by providing an inexpensive replacement parabolic reflector, nearly like the original, but slightly shorter. This approach could be used for retrofitting other flashlights having tiny light bulbs. In other cases, it might be possible to “steal” some space from battery compartment-if for example a spring which holds the batteries in place provides enough extra leeway for the thickness of the driver circuit module.

The method of retrofitting the illumination source while retaining other existing flashlight features, such as user-adjusted beam focus, comprises steps ofproviding a power connection equivalent to the original incandescent light bulb,physically and electrically connecting a circuit module to the power connection,physically and electrically connecting the circuit to a light emitter (such as an LED),fitting the module and light emitter into the body of the flashlight,maintaining sufficient spatial volume for the original batteries, andregulating the input power efficiently to supply ideal power to the light emitter.
In some cases, the method comprises an additional step: replacing the existing reflector with a replacement reflector (generally slightly shorter).

Of course, a flashlight with N batteries (N greater than 1) could be retrofitted with a module which replaces one of the batteries, but this is less than desirable, because it significantly reduces the available energy—negating the advantage of the solid state light source over the incandescent bulb regarding extended battery life.

While the primary application of this invention is in flashlights, the principles clearly could be used in other illumination systems which employ tiny incandescent light bulbs. However, a very specific objective of this invention is to replace the incandescent light bulb in the Mini Maglite® and the like.

The numeric identifiers in the figures correspond to the elements as follows:2a transparent lens adapted to emit a majority of the light peripherally3at least one light-emitting semiconductor chip4a small (round) printed circuit board6hard protective material encasing the electronic components15and179a socket for the LED module comprising2and312the pin to be electrically connected to the positive side of the battery pack14the pin to be electrically connected to the negative side of the battery pack15an exemplary integrated circuit (IC) component17another integrated circuit (IC) component21replacement reflector (shorter than original), if necessary22lens replacing normal protective transparent window23exemplary focused light ray302, . . . ,333components of the driving circuit

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A perspective view of a preferred physical form for this invention is shown inFIG. 2. A cross-section ofFIG. 2appears asFIG. 1.

InFIG. 1, the standard light bulb power connector is shown as pins12and14, respectively conductively connected to the positive and negative power source of the flashlight (presumably batteries). The light emitter3typically would be an LED chip embedded in a transparent plastic lens2and a driving circuit embedded in a module. (Of course, potentially more than one light emitting chip could be used, perhaps to simulate white light with multiple chips each emitting a different wavelength.)

Also inFIG. 1, the transparent lens2of the light emitter preferably is so shaped that it refracts a majority of the emitted light laterally toward the reflector21. Reflector21would ideally have the shape of a portion of a paraboloid, with the light-emitting chip3on the centerline (axis of revolution) near the focal point of the paraboloid. Alternatively, reflector21could simply be a portion of a cone. The reflector21of the Mini Maglite® flashlight25and its housing27may be rotated with respect to the flashlight barrel29and is attached thereto by the helically threaded, mating portions31of the barrel and housing. As the reflector is rotated its focal point is moved along the centerline relative to the light-emitting chip3. As the focal point is moved relative to the chip3, the shape of the beam reflected off the reflector21is changed from a broad cone-like beam to a narrower beam. Light ray23is exemplary of all such rays composing the beam.FIG. 1also illustrates a battery compartment volume33within the barrel29and it generally indicates the overall envelope of the flashlight at35, as recited in previously in Paragraphs 005 and 008.

Because of the tiny size of the incandescent bulbs used in miniature flashlights, a inexpensive, conventionally-implemented driving circuit for a solid state replacement source of light would not fit within the volume envelope of the miniature bulb. Therefore, it must be at least partly exterior to that envelope. The driver circuit module of the present invention comprises a small conventional printed circuit board4, circuit components (such as commercially available integrated circuits represented by elements15and17inFIG. 1), a potting layer6protecting those circuit components, a socket9for the support and conductor leads of the light emitter (LED), and pins12and14equivalent to the connector of the original incandescent bulb. (In the case of other types of miniature bulbs, the pins12and14might be instead some other type of connector, such as a standard screw or bayonet light bulb base.) The dimensions of the module for the Mini Maglite®, for example, would be about 15 mm in diameter and about 3 mm thick—larger than the original incandescent bulb.

Furthermore, if the flashlight has a lens housing which rotates, the module6provides a low friction surface in order for the reflector21to readily turn as it contacts module to preserve the focusing capability or to preserve the on-off switch capability.

Still further, the protective material of the module6must facilitate radiation and conduction of heat away from the light emitters and from the supporting circuit elements in module6. The material, for instance, may be a thermally conductive epoxy. To increase the transfer of heat from that material to the surrounding atmosphere, the module is geometrically shaped to maximize surface area within the limited volume to facilitate the radiation of heat from the emitters and the module. Besides the gross geometry of the module6, the surface of the module may be textured to increase its surface area. To increase the radiation of unwanted heat, the reflector itself could be fashioned from a thermally conductive material such as stamped aluminum. This would be particularly effective, because it directly contacts the module6in the preferred embodiment and because it has a relatively large surface area.

In flashlights like the Mini Maglite®, there would not be any available space for the driver circuit module. So, for such cases, a replacement reflector is an optional, additional element of the invention. The replacement reflector21would be essentially identical to the original reflector, except that a small rear portion is removed to account for the thickness of the driver circuit printed circuit board4and protective potting6. Assuming that the light emitting chip3occupies approximately the same optical location as the filament of the original incandescent bulb, the shape of the replacement would be equivalent to the original, except for the small portion removed from the smaller open end. (Otherwise, the replacement reflector21would be modified slightly in shape to account for the new position of the chip relative to the original position of the filament. That is, the relationship of the focal point of the new reflector to the chip would be about the same as the relationship of the focal point of the old reflector to the filament.)

An alternative embodiment is shown inFIG. 4. In it there are several smaller LEDs instead of one larger one. The disadvantage of this arrangement is that the LEDs are off the midline axis, so the light will be spread out farther than with the case ofFIG. 1. One partial remedy would be to replace the usual flat protective window of the flashlight with a (converging) lens. One advantage of multiple LEDs is that they could generate an approximation to white light by mixing the colors of several LEDs (such as that of red, green, and blue LEDs). Using a diffusing lens22(or reflector21) which has a stippled or pebbled surface would smooth the appearance of the light, especially when multiple LEDs are present.

A preferred embodiment of the driver circuit for this invention is shown in schematic diagram inFIG. 3, which shows a DC circuit used for a typical embodiment. A high frequency, low power DC-to-DC converter circuit is utilized to drive the LED302. The high frequency of operation allows components of small size to be used. A positive voltage source is introduced at +Vin312and branched to a capacitor C1316and inductor L1320and to two inputs (Vin324and EN326) of a switching circuit304. The solid-state switching circuit304regulates the input voltage Vin324to a specified value to achieve a switched output at SW328by receiving an enable signal EN326branched from Vin324. The inductor L1320is charged during the ON cycle phase of SW328and discharges in the OFF cycle phase to achieve the desired switched voltage output driving a Schottky diode D1306that in turn drives the anode side308of the output LED302and capacitor C3318which is terminated to ground. This Schottky diode D1306allows the current to flow in only one direction to the anode side308of the LED302via SW328. The Schottky diode D1306also assures that there is a quantity of rectification of the AC signal flowing through the circuit so that the LED only sees half of the AC cycle, effectively acting as a DC signal. Capacitor C3318becomes a charge reservoir, averaging out what would otherwise be a sinusoidally varying voltage with one half of the sine wave missing.

The cathode side310of the LED302is pass through ground via R-4322and branched to the feedback FB pin332of the switching circuit304through resistor R3320. The FB pin332acts as half of an operational amplifier that is comparing the voltage at R-4322above ground, to a reference voltage, (i.e., 1.23V). When the voltage at R4322reaches its reference voltage, the switching circuit304stops supplying current. The FB pin332therefore serves as feedback reference within the switching circuit304, determining the current values by comparing a feedback voltage to its internal reference and deciding whether more or less charge is needed, thereby regulating the circuit current. −Vin314, capacitors C1316and C3318, resistor R4322and the ground terminal330of the switching circuit304are all terminated to ground.

In a constant current implementation, a current sense resistor is used to provide the voltage feedback. An integrated circuit of small size, Texas Instruments TPS61040 or TPS61041 is suitable for this purpose. Although designed for DC-to-DC operation in a suitable voltage range, the circuit can be easily modified to work at higher voltages by using a zener diode resistor combination, or to operate as an AC-to-DC converter by adding a rectifier circuit. Additional operational features such as light sensors, timers, etc., could be added to provide for dimming or automatic shut-off functions. Multiple colored LEDs can be used to vary the desired colored output. Although only one LED is shown, several LEDs can be combined in a series circuit, parallel circuit or series-parallel circuit up to the limitations of the IC used. An appropriate LED may be chosen for use in this circuit to suit the particular application and sized to closely match the bulb dimensions and intensities of conventional lamps. The circuit shown inFIG. 3can be implemented in either a constant voltage output design or a constant current output design. The constant current design has advantages since light output is directly proportional to current, whereas slight variations in the LED manufacture require different operating voltages for a specific light output.

While this invention is described above with reference to a preferred embodiment, anyone skilled in the art can readily visualize other embodiments of this invention. For example, circuits other than the one described could be used. Also, other shapes for the refractive LED enclosure2could be used. Therefore, the scope and content of this invention are not limited by the foregoing description. Rather, the scope and content are delineated by the following claims.