United States Patent
`[19]
`[11] Patent Number:
`6,095,661
`
`Lebens et al.
`[45] Date of Patent:
`Aug. 1, 2000
`
`USOO6095661A
`
`[54] METHOD AND APPARATUS FOR AN L.E_D_
`FLASHLIGHT
`
`[75]
`
`Inventors: Gary A. Lebens, Chaska; Charles T.
`Eourn, Minelton‘lfafi Chilllesflltl'.
`emalre,
`pp e
`a ey, a
`0
`1nn.
`[73] Assignee: PPT Vision, Inc., Eden Prairie, Minn.
`
`[21] Appl. No.: 09/044,559
`
`7
`
`Mar. 19, 1998
`Filed:
`[22]
`..................................................... H04B 10/04
`Int. Cl.
`[51]
`.......................... 362/184; 362/183; 362/159;
`[52] U.S. Cl.
`362/249; 362/157; 362/208; 362/800; 315/224;
`315/307; 315/291; 315/312; 315/360; 315/362
`[58] Field Of Search ..................................... 362/157, 183,
`362/159> 184> 208, 800, 249; 315/224>
`307, 291, 312, 360, 362
`_
`References Clted
`U. S. PATENT DOCUMENTS
`
`[56]
`
`6/1980 Scrivo ..................................... 250/227
`4,208,579
`9/1981 SChmldt
`" 362/191
`472907095
`3132; iigiftm:
`351/3:
`$33333
`6/1986 Herman
`...... 33/366
`4:592:147
`4/1989 Spraggins ttttttttttttttttttt 446/26
`4,820,229
`
`5/1989 Nishizawa et a1.
`..
`.. 362/100
`4,831,504
`1/1990 Rowan ....................... 273/84
`4,893,815
`..... 320/48
`4,962,347 10/1990 Burroughs et al.
`..
`
`4,964,023
`10/1990 Nishizawa et a1.
`..
`362/100
`~~~~~~~~~~~~~~~~
`-~ 250/551
`479787857 12/1990 Juengel
`
`530153918
`5/1991 C°peland ‘
`""" 315/76
`" 250551
`5’065’035
`11/1991 Juengel
`1/1993 Nor ................ 320/21
`5,179,335
`
`5,279,513
`1/1994 Connelly ..
`446/219
`3/1994 Rose ............................................ 375/1
`5,299,227
`
`6/1995 Schaller et al.
`5,424,927
`......................... 362/157
`
`5,838,247 11/1998 Bladowski ........... 340/815
`........................... 362/184
`5,890,794
`4/1999 Abtahi et al.
`
`Primary Examiner—Sandra O’Shea
`Assistant Examiner—Bertrand Zeade
`Attorney, Agent,
`or
`Firm—Schwegman,
`Woessner & Kluth, PA
`[57]
`ABSTRACT
`
`Lundberg,
`
`Improved method and apparatus for hand-held portable
`illumination. A flashlight and corresponding method are
`described. The flashli ht includes a housin , a
`luralit of
`LEDs, and an electric51 Circuit that selectivelgy apghes pOZVer
`from the DC voltage source to the LED units, wherein the
`flashlight is suitable for handheld portable operation by a
`user. In one embodiment, the first electrical circuit further
`includes a control Circuit for maintaining a predetermined
`light output level of the LED units as a charge on a battery
`varies. In another embodiment, the control circuit maintains
`an average predetermined light output level of the LED units
`as the charge on the battery cell varies by changing a pulse
`width or frequency as the charge on the battery cell varies to
`maintain a given average light output. Another aspect pro-
`Vides an illumination source that includes a light-emitting
`diode (LED) housing including one or more LEDs, and a
`control circuit that selectively applies power .from a source
`of electric power to the LEDs, the control circuit substan-
`tially maintaining a light output characteristic of the LEDs
`as a voltage of the voltage source varies over a range that
`would otherwise vary the light output characteristic. Still
`another aspect provides an illumination source including a
`light-emitting diode (LED) housing including one or more
`LEDs; and a control circuit that selectively applies power
`from a source of electric power to the LEDs, thus maintain-
`ing or controlling a light output color spectrum of the LEDs.
`
`52 Claims, 11 Drawing Sheets
`
`\70
`\PULSE SYNC. SIGNAL
`
`
`POWER SUPPLY
`AND CONTROL
`
`HTC, Exhibit 1001
`
`HTC, Exhibit 1001
`
`

`

`US. Patent
`
`Aug. 1, 2000
`
`Sheet 1 0f 11
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`6,095,661
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`HTC, Exhibit 1001
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`HTC, Exhibit 1001
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`

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`US. Patent
`
`Aug. 1, 2000
`
`Sheet 2 0f 11
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`6,095,661
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`HTC, Exhibit 1001
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`HTC, Exhibit 1001
`
`

`

`US. Patent
`
`Aug. 1, 2000
`
`Sheet 3 0f 11
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`6,095,661
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`US. Patent
`
`Aug. 1, 2000
`
`Sheet 4 0f 11
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`6,095,661
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`US. Patent
`
`Aug. 1,2000
`
`Sheet 5 0f 11
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`6,095,661
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`TC, Exhibit 1001
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`

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`US. Patent
`
`Aug. 1,2000
`
`Sheet 6 0f 11
`
`6,095,661
`
`PHOTON ENERGY (eV)
`
`3.5
`
`3.0
`
`2.5
`
`INTENSITY
`
`(o.u.)
`
`WAVELENGTH (nm)
`
`0; 5
`
`HTC, Exhibit 1001
`
`HTC, Exhibit 1001
`
`

`

`US. Patent
`
`Aug. 1,2000
`
`Sheet 7 0f 11
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`6,095,661
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`

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`US. Patent
`
`Aug. 1, 2000
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`Sheet 8 0f 11
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`6,095,661
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`

`

`US. Patent
`
`Aug. 1,2000
`
`Sheet 9 0f 11
`
`6,095,661
`
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`
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`
`HTC, Exhibit 1001
`
`HTC, Exhibit 1001
`
`

`

`US. Patent
`
`Aug. 1, 2000
`
`Sheet 10 0f 11
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`6,095,661
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`HTC, Exhibit 1001
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`
`

`

`US. Patent
`
`Aug. 1, 2000
`
`Sheet 11 0f 11
`
`6,095,661
`
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`HTC, Exhibit 1001
`
`HTC, Exhibit 1001
`
`
`

`

`6,095,661
`
`1
`METHOD AND APPARATUS FOR AN L.E.D.
`FLASHLIGHT
`
`FIELD OF THE INVENTION
`
`This invention relates to the field of lighting, and more
`specifically to a method and apparatus of controlling and
`powering a solid-state light source such as a light-emitting
`diode or LED, for a portable battery-powered flashlight.
`BACKGROUND OF THE INVENTION
`
`There is a widespread need for hand-held flashlights and
`lanterns. One common flashlight includes a two-cell battery
`for power, an incandescent lamp to emit light, and a simple
`single-pole switch to connect and disconnect the battery to
`the lamp. Other flashlights use other numbers of battery cells
`in order to provide a voltage suitable for various particular
`conditions. Lanterns often use a fluorescent tube to emit
`
`light. Certain keychain fobs use a pair of hearing-aid cells
`and a red-light
`light-emitting diode (LED) in order to
`provide short-range lighting such as might be -needed to find
`a keyhole in the dark.
`Battery technology is such that as electrical power is
`withdrawn from a battery cell, the voltage available across
`a given current load will decrease. This decreased available
`voltage across the given load causes reduced light output,
`gradually dimming the light as the battery charge depletes.
`Further, LEDs have voltage, current, and power param-
`eters that must be controlled in order to maximize device
`
`life. Commonly, a current-limiting resistor is placed in series
`with an LED in order that only a portion of the voltage drop
`from the battery is across the LED and the rest of the voltage
`drop is across the resistor. This voltage drop and correspond-
`ing power loss in the resistor is dissipated as waste heat,
`which is inefficient for a flashlight which should be designed
`to emit light.
`it is awkward or difficult to determine the
`In addition,
`amount of remaining charge in a battery cell, generally
`requiring removal of the battery from the flashlight in order
`to measure the remaining charge. In addition, the cost of a
`separate measurement device can be a negative for this
`market. Some battery cells today include a built-in liquid-
`crystal indicator for the charge in the cell, but such a solution
`requires a separate measurement device/indicator for each
`battery, and requires removal of the battery from the flash-
`light in order to perform the measurement and observe the
`indication of remaining power.
`SUMMARY OF THE INVENTION
`
`The present invention provides a method and apparatus
`for an LED. flashlight or other LED illumination source. In
`one embodiment, a flashlight is described. The flashlight
`includes a flashlight housing suitable for receiving therein
`and/or mounting thereon at least one DC voltage source such
`as a battery. The flashlight also includes a light-emitting
`diode (LED) housing connected to the flashlight housing,
`the LED housing including a first plurality of LED units that
`each emit light and have a reflector for collimating the
`emitted light forwardly therefrom generally along an LED
`optical axis, the first plurality of LED units including at least
`seven individual LED units. The flashlight also includes a
`first electrical circuit that selectively applies power from the
`DC voltage source to the LED units, wherein the flashlight
`is of such compact size and low weight as to be suitable for
`single-handed portable operation by a user, the flashlight
`further having a purpose of providing general-purpose illu-
`mination.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`In one embodiment, the LED optical axes of the first
`plurality of LED units in the flashlight are substantially
`parallel to one another. In one such embodiment, the flash-
`light further includes a second plurality of LED units that
`each emit
`light and have a reflector for collimating the
`emitted light forwardly therefrom generally along an LED
`optical axis, wherein the LED optical axes of the second
`plurality of LED units converge or diverge from one another
`forwardly from the housing.
`In another embodiment, an optical spread angle of the first
`plurality of LED units in the flashlight are substantially
`equal to one another. In one such embodiment, the flashlight
`further includes a second plurality of LED units that each
`emit light and have a reflector for collimating the emitted
`light forwardly therefrom generally along an LED optical
`axis, wherein an optical spread angle of the second plurality
`of LED units are substantially equal to one another, and
`different than the optical spread angle of the first plurality of
`LED units.
`
`In yet another embodiment, the LED units are connected
`in a parallel-series configuration with at least two LED units
`coupled in parallel to one another and in series with at least
`one other LED unit, and the DC voltage source includes at
`least three battery cells connected in series.
`In still another embodiment,
`the first electrical circuit
`further includes a control circuit for maintaining a prede-
`termined light output level of the LED units as a charge on
`the battery cell varies. In one such embodiment, the control
`circuit maintains an average predetermined light output level
`of the LED units as the charge on the battery cell varies by
`increasing a pulse width or a pulse frequency as the charge
`on the battery cell decreases. In another such embodiment,
`the control circuit maintains an average predetermined light
`output level of the LED units by measuring a battery voltage
`and adjusting a pulse width or a pulse frequency or both to
`maintain the average light output at the predetermined level.
`In still another such embodiment, the control circuit main-
`tains an average predetermined light output level of the LED
`units by measuring an average light output and adjusting a
`pulse width or a pulse frequency or both to maintain the
`measured average light output at the predetermined level.
`Another aspect of the present invention provides a flash-
`light including: (a) a flashlight housing, the housing being
`suitable for at least one of receiving therein and mounting
`thereon at least one DC voltage source that includes at least
`one battery cell; (b) a light-emitting diode (LED) housing
`connected to the flashlight housing, the LED housing includ-
`ing one or more first LED units that each emit light and have
`a reflector for collimating the emitted light forwardly there-
`from generally along an LED optical axis; and (c) a first
`electrical circuit that selectively applies power from the DC
`voltage source to the LED units, the first electrical circuit
`further including a control circuit for maintaining a prede-
`termined light output level of the LED units as a charge on
`the battery cell varies; wherein the flashlight is of such
`compact size and low weight as to be suitable for single-
`handed portable operation by a user, the flashlight further
`having a purpose of providing general-purpose illumination.
`In one such embodiment, the first LED units being a first
`plurality of LED units, wherein the LED optical axes of the
`first plurality of LED units are substantially parallel to one
`another. In another such embodiment, the flashlight further
`includes a second plurality of LED units that each emit light
`and have a reflector for collimating the emitted light for-
`wardly therefrom generally along an LED optical axis,
`wherein the LED optical axes of the second plurality of LED
`units converge or diverge from one another forwardly from
`the housing.
`
`HTC, Exhibit 1001
`
`HTC, Exhibit 1001
`
`

`

`6,095,661
`
`3
`In another such embodiment, the first LED units are a first
`plurality of LED units, wherein an optical spread angle of
`the first plurality of LED units are substantially equal to one
`another.
`In yet another such embodiment,
`the flashlight
`further includes a second plurality of LED units that each
`emit light and have a reflector for collimating the emitted
`light forwardly therefrom generally along an LED optical
`aXis, wherein an optical spread angle of the second plurality
`of LED units are substantially equal to one another, and
`different than the optical spread angle of the first plurality of
`LED units.
`
`Another aspect of the present invention provides a method
`of providing general-purpose illumination of such compact
`size and low weight as to be suitable for single-handed
`portable operation by a user,
`including the steps of: (a)
`providing one or more first LED units that each emit light
`and have a reflector for collimating the emitted light for-
`wardly therefrom generally along an LED optical axis; (b)
`selectively applying power from a DC voltage source to the
`LED units; and (c) maintaining a predetermined light output
`level of the LED units as a charge on the battery cell varies
`by controlling the step (b).
`In one embodiment, the step of maintaining maintains an
`average predetermined light output level of the LED units as
`the charge on the battery cell, varies by increasing a pulse
`energy or a pulse frequency as the charge on the battery cell
`decreases. In another embodiment, the step of maintaining
`maintains an average predetermined light output level of the
`LED units by measuring a battery voltage and adjusting a
`pulse width or a pulse frequency or both to maintain the
`average light output at
`the predetermined level. In still
`another embodiment, the step of maintaining maintains an
`average predetermined light output level of the LED units by
`measuring a light output and adjusting a pulse energy or a
`pulse frequency or both to maintain an average light output
`at the predetermined level.
`Yet another aspect of the present invention provides an
`illumination source, that includes (a) a light-emitting diode
`(LED) housing including one or more LEDs; and (b) a
`control circuit that selectively applies power from a source
`of electric power to the LEDs, the control circuit substan-
`tially maintaining a light output characteristic of the LEDs
`as a voltage of the voltage source varies over a range that
`would otherwise vary the light output characteristic. In one
`such embodiment,
`the light output characteristic that
`is
`maintained is light output
`intensity.
`In another such
`embodiment, the control circuit maintains the light output
`intensity of the LED units as the voltage of the DC voltage
`source varies by increasing a pulse width, a pulse energy, or
`a pulse frequency as the voltage of the DC voltage source
`decreases. In another such embodiment, the control circuit
`maintains an average predetermined light output level of the
`LED units by measuring a voltage and adjusting a pulse
`energy or a pulse frequency or both to maintain the average
`light output at the predetermined level. In yet another such
`embodiment, the control circuit maintains an average pre-
`determined light output level of the LED units by measuring
`an average light output and adjusting a pulse width or a pulse
`frequency or both to maintain the measured average light
`output at the predetermined level.
`invention provides a
`Another aspect of the present
`battery-powered portable flashlight (100) including: a casing
`(110) suitable to hold a battery; one or more light-emitting
`devices (LEDs) (150) mounted to the casing; a switch (140)
`mounted to the casing; and a control circuit (130) coupled to
`the battery, the LEDs, and the switch, wherein the control
`circuit drives the LEDs with electrical pulses at a frequency
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`high enough that light produced by the LEDs has an appear-
`ance to a human user of being continuous rather than pulsed,
`and wherein the LEDs have proportion of on-time that
`increases as remaining battery power decreases. One such
`embodiment further includes a feedback circuit that controls
`
`the pulses so that light intensity produced by the LEDs, as
`perceived by the human user, is substantially constant across
`a greater range of battery power or voltage than a corre-
`sponding range for which light intensity is equally constant
`without the feedback circuit. In one such embodiment, the
`feedback circuit measures a light output of the LEDs.
`Another such embodiment further includes a battery-
`voltage-measuring circuit coupled to the control circuit.
`Yet another aspect of the present invention provides a
`method for driving battery-powered portable flashlight (100)
`having a casing (110), a DC power source mounted to the
`casing, one or more solid-state light-emitting device (LEDs)
`(150) mounted to the casing, the method including the steps
`of: receiving input from a user; and based on the received
`input, generating a series of pulses to drive the LEDs such
`that the LEDs have proportion of on-time that increases as
`remaining battery power decreases.
`Still another aspect of the present invention provides an
`illumination source including (a) a light-emitting diode
`(LED) housing including one or more LEDs; and (b) a
`control circuit that selectively applies power from a source
`of electric power to the one or more LEDs, the control circuit
`maintaining a predetermined light output color spectrum of
`the one or more LEDs as a voltage of the source of electric
`power varies. In one such embodiment, the one or more
`LEDs comprise one or more LEDs having a first character-
`istic color spectrum output and one or more LEDs having a
`second characteristic color spectrum output, the first char-
`acteristic color spectrum output different from the second
`characteristic color spectrum output, and the control circuit
`controls a pulse characteristic in order to control the pro-
`portion of light output having the first characteristic color
`spectrum output to that having the second characteristic
`color spectrum output. In another such embodiment, the one
`or more LEDs comprise one or more LEDs having a
`characteristic color spectrum output that varies based on
`applied current, and the control circuit controls a pulse
`current in order to control the characteristic color spectrum
`output.
`Yet another aspect of the present invention provides an
`illumination source that includes (a) a light-emitting diode
`(LED) housing including one or more LEDs; and (b) a
`control circuit that selectively applies power from a source
`of electric power to the LEDs to adjust a light output color
`spectrum of the one or more LEDs.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows one embodiment of the present invention, a
`schematic representation of a handheld LED flashlight 100.
`FIG. 2 is a circuit block diagram of an LED flashlight
`circuit 200, which circuit is used in some embodiments of
`LED flashlight 100 of FIG. 1 or LED light source in
`camcorder 500 of FIG. 5 or other devices such as machine-
`
`vision systems.
`FIG. 3 a circuit block diagram of an LED flashlight circuit
`300, which circuit is used in some embodiments of LED
`flashlight 100 of FIG. 1 or LED light source in camcorder
`500 of FIG. 5 or other devices such as machine-vision
`systems.
`FIG. 4 a circuit block diagram of an LED flashlight circuit
`400, which circuit is used in some embodiments of LED
`
`HTC, Exhibit 1001
`
`HTC, Exhibit 1001
`
`

`

`6,095,661
`
`5
`flashlight 100 of FIG. 1 or LED light source in camcorder
`500 of FIG. 5 or other devices such as machine-vision
`systems.
`FIG. 5 is a diagram showing a controlled LED light
`source is integrated into a handheld camcorder 500.
`FIG. 6 is a graph of color spectrum versus current for an
`LED to be used in one embodiment of the present invention
`FIG. 7 is circuit block diagram of an LED illumination
`device circuit 700, which circuit is used in some embodi-
`ments of LED flashlight 100 of FIG. 1 or LED light source
`in camcorder 500 of FIG. 5 or other devices such as
`machine-vision systems.
`FIG. 8 is circuit block diagram of an LED illumination
`device circuit 700 that uses a current mirror.
`
`FIG. 9 is a graph of color spectrum (photoluminescence)
`versus temperature for an LED to be used in one embodi-
`ment of the present invention.
`FIG. 10 is circuit block diagram of a machine vision
`system using an LED illumination device according to the
`present invention.
`FIG. 11 is circuit block diagram of an LED illumination
`device according to the present invention.
`DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`In the following de tailed description of the preferred
`embodiments, reference is made to the accompanying draw-
`ings that form a part hereof and in which are shown by way
`of illustration specific embodiments in which the invention
`may be practiced. It is understood that o the r embodiments
`may be utilized and structural changes may be made without
`departing from the scope of the present invention.
`The present invention takes advantage of the efficiency of
`high-intensity, light-emitting diodes (LEDs) in the visible
`spectrum and/or infra-red (IR) or ultra-violet (UV), arranged
`in various patterns,
`the low-voltage properties of CMOS
`integrated circuits and components, and the efficiency
`derived from switching the current
`to and limiting the
`duration of current to the LEDs to project light efficiently
`and with constant brightness even as the battery supply
`voltage decays over time. The invention takes advantage of
`the dynamic impedance of the LEDs which causes the
`voltage across the LED to rise rapidly relative to the current
`flow through the LED to limit the initial current flow to the
`LED, when battery voltage is highest, to prevent wire bond
`heating from causing premature failure of the LEDs. The
`present invention controls the current flow duration (pulse
`width) to limit power dissipation in the LEDs during the
`LEDs’ on state, and increasing the pulse width as the battery
`voltage decreases over time to maintain substantially con-
`stant perceived or average LED intensity over the course of
`the battery’s life. The invention controls the switching
`frequency of the pulse width to further control the LED
`intensity and power dissipation while maintaining a constant
`light output from the LEDs as perceived or visible to the
`human eye, or a light-sensing device, e.g., camera, night-
`vision scope, CMOS and CCD sensor and pixel arrays. The
`present invention provides a compact, portable light source,
`preferably sized to be readily hand-held, for illuminating an
`object, several objects, or areas for human use and/or
`machine operation. In one embodiment, the invention mea-
`sures battery voltage and in turn regulates the LED intensity.
`In another embodiment, the present invention uses a light-
`sensing device such as a light-sensing transistor or light-
`detecting diode (LDD) in proximity to the output LED(s) to
`measure the average brightness and further regulate the
`LEDs’ output.
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`Another embodiment of the present invention provides
`operator-selectable control of the pulse frequency and/or the
`pulse width to provide a reduced apparent brightness in
`order to increase battery life in situations when maximum
`brightness is not required.
`In one such pulse-frequency
`embodiment, the apparent (visible) pulse frequency would
`provide a stroboscope effect for safety or entertainment. In
`this embodiment,
`the visibly interrupted or pulsed pulse
`train may include repetitive pulses or a coded sequence as in
`Morse code “SOS” or a predetermined password or security
`string of pulses that may then be used as a key or identifier.
`A further refinement of this embodiment would provide the
`user with a method for strobing out a message. It is under-
`stood that what appears to be a single visible pulse may
`actually include a high-frequency series of pulses in order to
`increase the apparent brightness of a single pulse while also
`protecting the LEDs from excessive power dissipation. In
`yet another pulse-frequency embodiment of the invention, a
`variable or adjustable constant sequence pulse train is estab-
`lished for the accurate measurement of the velocity or
`frequency of an object in motion or vibration.
`Another embodiment of the present invention uses vari-
`ous colored LEDs for specialized purposes. In one such
`embodiment, long-wavelength LEDs, 660 nm or longer, are
`used to provide underwater divers or aquarium enthusiasts a
`light source for observing undersea life at night without
`adversely affecting the nocturnal activities of such wildlife.
`This functionality is also useful for tropical aquarium own-
`ers who also wish to observe the nocturnal activities of the
`
`occupants of their aquariums. In another such embodiment,
`short-wavelength blue LEDs are used with a UV filter to
`view fluorescing materials,
`including but not limited to:
`taggants, stamps, security codes and security seals. As UV
`LEDs become readily available (such as those announced as
`made by IBM Corporation in the Mar. 9, 1998 issue of
`Electronic Engineering Times, page 39), these could be used
`in place of the blue LEDs. In other embodiments, a suitable
`LED normally emitting in the blue spectrum, for example
`made from GaN (gallium nitride) or InGaN (indium gallium
`nitride), is pulsed by pulses of sufficiently high current to
`blue-shift the output and sufficiently short duration to not
`destroy the LED in order to maintain a constant
`light
`intensity while shifting the color spectrum from blue to
`ultraviolet. Other embodiments include IR LEDs for mili-
`
`tary or police use to enhance the usefulness of night-vision
`equipment and for friend-or-foe identification, multiple
`color LEDs to produce a white light source, and combina-
`tions of colored LEDs to enhance the ability of color-blind
`individuals to perceive colors. Other uses include LEDs
`chosen for use in photographic darkrooms wherein the LED
`wavelength is chosen to prevent undesired exposure of
`light-sensitive materials.
`Another embodiment of the present invention uses LEDs
`of various “viewing” angles to achieve wide-angle viewing
`versus narrow-angle, long-range viewing and combinations
`thereof. A further refinement of this embodiment utilizes a
`
`lens (or other lens or reflector arrangement) to
`Fresnel
`provide a focusable light source. Another embodiment uses
`polarizers to reduce specular reflections for enhanced view-
`ing or for use in machine-vision applications. Another
`embodiment utilizes quickly and easily pluggable/
`replaceable LED arrays or heads of various shapes, colors,
`and/or viewing angles for different applications.
`In yet another embodiment, the light output is momen-
`tarily interrupted repetitively, or strobed,
`to indicate low
`battery condition with some estimation of time to battery
`failure, e.g., the number of pulses could indicate the esti-
`
`HTC, Exhibit 1001
`
`HTC, Exhibit 1001
`
`

`

`6,095,661
`
`7
`mated number of minutes of battery time. As the estimation
`of time to battery failure changes, the repetition rate is varied
`to indicate impending battery failure. It is understood that
`this operational mode is easily distinguished from other
`operational modes by the duration of on time versus off time.
`In strobe mode, low battery condition is indicated by drop-
`ping pulses; e.g., every fourth output pulse is dropped, or
`three of four pulses is dropped creating an easily distin-
`guishable variance in visible output of the invention.
`In another embodiment of the invention, a switch is
`utilized to control the functions (and/or brightness) of the
`invention. A variance of this embodiment uses a thumb-
`
`wheel, or rotary switch to vary the switching characteristics
`to produce a variable light output.
`In another embodiment, a programmable microprocessor
`is utilized to provide control functionality.
`FIG. 1 shows one embodiment of the present invention (a
`schematic representation of a LED flashlight 100) having a
`case 110, a battery 120 or other portable DC power supply,
`a power supply and control circuit 130, a switch circuit 140,
`a plurality of LEDs 150, and optionally a feedback circuit
`160.
`
`In various embodiments of the present invention, feed-
`back circuit 160 (and similarly the other feedback circuits
`described herein) controls pulse width and/or frequency as a
`function of parameters such as battery voltage, LED light
`output intensity, power dissipation or device temperature, or
`LED color spectrum output.
`Case 110 is any convenient size and shape, and is typi-
`cally designed to hold the battery, provide a suitable grip to
`be handheld, and provide a housing for the circuitry and
`LEDs. In one embodiment, battery 120 includes one or more
`cells which can be any suitable technology such as alkaline
`dry cells or rechargeable cells. Alternatively, other portable
`DC electrical power sources can be used as desired in place
`of battery 120. Power supply and control circuit (PSCC) 130
`responds to switch circuit to apply electrical power from
`battery 120 to LEDs 150, controlled in order to prevent
`overloading and premature destruction of LEDs 150 while
`minimizing power dissipation within PSCC 130, thus maxi-
`mizing battery life, providing the desired accuracy or level
`of the amount of light emitted at different battery voltages or
`other environmental conditions that would otherwise vary
`the light output. Switch circuit 140 allows the user to control
`various flashlight functions such as, for example, on/off,
`setting light level, setting light color, setting pulse or strobe
`frequency, and checking battery voltage or remaining power.
`In one embodiment, PSCC 130 provides a pulse train, in
`which pulse frequency, pulse width, or pulse shape/height,
`and/or the number of LEDs that are driven, is controlled in
`order to provide a relatively constant light output level even
`as battery voltage declines and power is drained. In one
`embodiment, feedback 160 measures the light output of
`LEDs 150 (e.g., using a photo diode or other suitable light
`detecting device) and provides a signal that allows PSCC
`130 to adjust the light output to a desired level (typically
`providing a constant light output even as battery voltage
`declines as power is drained). In one such embodiment, the
`width of each pulse is adjusted to keep a constant average
`light output (widening each pulse as the intensity of light
`decreases, in order to obtain a constant light output). In one
`such embodiment, flashlight 100 is used in conjunction with
`a portable video camcorder or other video camera, and
`feedback 160 measures the overall ambient light and pro-
`vides a signal that allows generation of flashlight pulses to
`compensate for lack of light, in order to provide optimal
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`lighting for the video camera. In one such embodiment, the
`pulses to the LEDs are synchronized to the video camera
`frame rate using optional pulse synchronization (sync) sig-
`nal 170 in order that the light pulse from LEDs 150 is only
`on when the video camera shutter is collecting light
`(avoiding light output when the camera will not benefit from
`it). In another embodiment, feedback 160 measures battery
`voltage, and increases pulse width, frequency, or height as
`battery voltage or power declines.
`In yet another
`embodiment,
`feedback 160 measures the current going
`through LEDs 150, and makes the appropriate adjustment to
`pulse width or frequency in order to maintain constant or
`desired light output.
`FIG. 2 is a schematic of one embodiment of a circuit used
`
`In this embodiment, normally open,
`for flashlight 100.
`momentary contact switch 146 is momentarily closed by a
`user to activate ligh