USOO7394211B1 (12) United States Patent (10) Patent No.: US 7,394.211 B1 Kuhlmann (45) Date of Patent: Jul. 1, 2008 (54) STEP DOWN POWER MANAGEMENT 5,739,639 A 4, 1998 Johnson ....................... 315,86 SYSTEM FOR LED FLASHLIGHT 6,305,818 B1 * 10/2001 Lebens et al. ..... ... 362, 184 6,320,330 B1 * 1 1/2001 Haavisto et al. ... ... 315,291 (75) Inventor: Kurt Kuhlmann, San Jose, CA (US) 6,888,383 B1* 5/2005 Fairbanks ............ ... 327,124 7,015,654 B1* 3/2006 Kuhlmann et al. ... 315,291 7,071,630 B1* 7/2006 York ...... 315,224 (73) Assignee: Fashing Rabbit, Inc., Blachly, OR 2005/0057187 A1 3/2005 Catalano ..................... 315,291 (*) Notice: Subject to any disclaimer, the term of this * cited by examiner patent is extended or adjusted under 35 Primary Examiner Thuy V. Tran U.S.C. 154(b) by 0 days. Assistant Examiner Tung X Le (74) Attorney, Agent, or Firm Black Lowe & Graham PLLC (21) Appl. No.: 11/700,727 57 ABSTRACT (22) Filed: Jan. 30, 2007 (57) (51) Int. Cl A micro-controller and a converter circuit provide constant irosh 3702 (2006.01) current to light emitting diode array from a power Supply with greater Voltage than the forward bias Voltage of the light (52) U.S. Cl. ......... r 315/291; 315/224; . 5/362 emitting diode. A micro-controller operatively coupled with a (58) Field of Classification Search ............. 315/209 R, semiconductor Switch and the converter circuit measures the 315/224,327/514-515,540; 225, 291, 307 308, 323/222, 362; 327/175,265, 299 ability of a DC power supply to charge the inductor. Duty cycles of the semiconductor Switch are modified according to See application file for complete search history. the measurement of the Voltage across the internal resistor of (56) References Cited the semiconductor Switch so as to supply Substantially con stant current to the LED array through an inductor regardless U.S. PATENT DOCUMENTS of actual battery Voltage. 4,673,865 A * 6/1987 DeLuca et al. .............. 323,222 5,736,881. A * 4, 1998 Ortiz .......................... 327, 175 9 Claims, 5 Drawing Sheets Loop WDD cND 8 GP5/OSC1/CLKIN Pl GP4/OSC2 GP16 GP3/MCLR/VPP GP2/TOCKS Comparator Sense input 6V E. IRLML2402 24b 41 U.S. Patent Jul. 1, 2008 Sheet 1 of 5 US 7,394.211 B1 U.S. Patent Jul. 1, 2008 Sheet 2 of 5 US 7,394.211 B1 |MSD 09 ?DuDduu00?ndu|ºsu0SJO |O|| | Dy2 U.S. Patent Jul. 1, 2008 Sheet 3 of 5 US 7,394.211 B1 3. s U.S. Patent Jul. 1, 2008 Sheet 4 of 5 US 7,394.211 B1 . SW1 pressed YES Drive: Current flows through Loop 1 (Bott., L1, LED, Q1, Gnd); L1 charges; LED is on YES U5 turns Q1 off; D2 conducts Flyback: Current flows through Loop 2 (Batt., L1, LED, D2); L1 discharges; LED is on U5 turns Q1 on offer O predetermined off period FIG, 4 US 7,394,211 B1 1. 2 STEP DOWN POWER MANAGEMENT technology contemporarily advanced so as to provide semi SYSTEM FOR LED FLASHLIGHT conductor devices, including light emitting diodes (hereinaf ter occasionally “LEDs) having significantly lower current TECHNICAL FIELD drain than incandescent bulbs in a highly robust package operable at relatively low direct current voltages. In addition, The invention generally relates to portable illumination early LEDs were substantially more power efficient than devices. More specifically, the invention relates to personal, incandescent bulbs having similar current consumption char handheld flashlights having a self-contained direct current acteristics. Finally, the small physical size of LEDs permitted power Supply and one or more light emitting diodes as a light extremely efficient packaging shapes to be adopted for Such SOUC. 10 lights. U.S. Pat. No. 5,386.351 to Tabor discloses such a space efficient packaging design for a single LED flashlight. The BACKGROUND OF THE INVENTION Tabor patent discloses a two-part, Snap-fit housing incorpo rating a discoid type battery in which one leg of a two terminal Technology relating to handheld flashlights incorporating LED is employed as part of a cantilever spring Switch mecha a direct current power supply in the form of replaceable 15 nism which upon depression by a flexible button completes a batteries and low Voltage, incandescent bulbs achieved a tech direct current circuit to the LED. Unfortunately, such early nological plateau in the 1970s. Advances in the state of the stage LEDs could not provide significant light output without art typically related to methods of packaging the batteries and being driven at very high currents, in which case, the power bulbs, and reflector designs. In particular, the capabilities of efficiency of the LED with respect to the quantity of light flashlights of this type are strictly limited by inherent charac produced significantly decreased. Also, LEDs in use during teristics of the incandescent bulb itself. Initially, evacuated the period in which the Tabor patent application was filed bulbs using tungsten filaments enabled power Supplies in the were only capable of producing light in the red part of the range of 1.3V (and more when such batteries are connected in visible spectrum. These two limitations resulted in an LED series) to provide varying levels of illumination. So-called flashlight only having utility for intermittent operation or halogen bulbs permitted higher filament temperatures 25 continuous illumination over short distances. Therefore, Such increasing the output of such flashlights. Nevertheless, the personal flashlights could not Supplant conventional incan inherent inefficiency of incandescent bulbs limited the dura descent bulb flashlights which have a more linear relationship tion of operation of such flashlights to a matter of a few hours with respect to Supply Voltage and current. or less depending on the number of dry cells provided in the A high intensity incandescent bulb flashlight can be pro power supply. That is, for increased run time the batteries 30 duced by merely increasing the amount of current and/or could be connected in parallel. For increased light intensity, voltage supply to the bulb. Conventional LEDs, being non the batteries could be connected in series (for increased volt linear devices do not respond in such a linear fashion. There age) but at the expense of run time. In addition, filament bulbs fore, LEDs were often employed in lighting devices for alter are highly Susceptible to mechanical shock, breaking the fila native purposes, such as the color coded, multiple LED light ment and rendering the flashlight inoperative. In addition, 35 and key device shown in U.S. Pat. No. 4,831.504 to Nish substantial development effort was directed to switch mecha izawa et al. The Nishizawa et al. patent discloses a combina nisms for intermittently connecting the direct current power tion LED flashlight and key in which multiple LEDs having Supply to the incandescent bulb so as to render either a more different colors are driven by separate, manual Switches and/ reliable or inexpensive switch, or both. or a microprocessor to signal an appropriate light detecting U.S. Pat. No. 4,242,724 to Stone is believed to be repre 40 and demodulating device in association with a door lock or sentative of one evolutionary branch of Suchtechnology relat operating lock. Similarly, International Patent Application ing to the packaging of a disposable floating flashlight in No. WO 01/77575A1 titled, “Portable Illumination Device which the outer casing of the light itself forms a part of the published on Oct. 18, 2001, to Allen discloses a unique prod Switch mechanism which, when Squeezed, completes electri uct package for a single LED personal flashlight employing a cal continuity between two AA (1.3V each) batteries and an 45 discoid type battery in which multiple depressions of a switch incandescent bulb. The flashlight is compact, and floats if incorporated into the product housing cycles the single LED accidentally dropped into water. U.S. Pat. No. 5,134,558 to through multiple modes according to instructions stored in a Williams et al. discloses a different evolutionary branch in microprocessor within the housing. Neither the invention dis which the light output from four AA-type batteries is boosted closed by Nishizawa et al. nor the invention disclosed by by an oscillator driven transformer rectifying circuit to an 50 Allen is capable of substantially increasing the light output of intermittent high Voltage applied to a Xenon gas flashtube so the LED such that the lighting devices disclosed therein are as to provide a high intensity emergency flasher. The device adequate replacements for high intensity incandescent bulb disclosed in Williams et al. delivers significantly more illu flashlights. The principle reason for this is that light emitting mination from a direct current power Supply than does the diodes, beingjunction semiconductor devices, have a forward incandescent bulb type of flashlight disclosed by Stone. Nev 55 bias voltage which is predetermined by the physics of the ertheless, the circuitry disclosed in Williams et al. for oper semiconductor materials from which diodes are manufac ating the Xenon flashtube is expensive, bulky, and only Suit tured. The forward biased voltage of silicon-based light emit able for intermittent operation of the flashtube rather than for ting diodes is approximately 3.6 V for aqua, blue, and white providing a constant light output. Thus, the teachings of the LEDs and 1.8 V for red, yellow, and green LEDs. The voltage prior art disclosed by Williams et al. is not suitable for rem 60 current characteristics of devices of this type are such that edying the inherent limitations of the incandescent bulb type Substantially increasing the applied Voltage outside of a range flashlight technology disclosed by Stone.