LOW POWERED STROBE LIGHT

Abstract: A low power, high intensity strobe light employing light emmitting diodes (LED's). A plurality of LED's (14) are electrically connected in series and parallel in a manner to approximate the resistance of a single LED. They are mounted in a box having a reflective inner suface and an opening covered with a lens whereby the light from the LED's (14) is reflected and directed through the lens. The LED's (14) are electrically strobed by a circuit comprising a d.c. power source (10) operably connected to a triggerably constant voltage circuit (22) which in turn, is driven by a multi-vibrator circuit (32) which periodically triggers the constant voltage circuit (22) for only the time duration necessary to cause the LEDS's (14) to emit a high intensity, visually detectable pulse of light.

Description: -1- LOW POWERED. STROBE LIGHT BACKGROUND OF THE INVENTION The present invention relates to strobe Lights, and, more particularly, to a low power, h gh intensity LED circuit comprising at least one LED; a triggerable constant voltage circuit operably connected across the LED; a d.c. power source operably connected to the constant voltage circuit and the LED so that when the constant voltage circuit is triggered the LED has sufficient voltage and current applied thereto to cause it to emit light; and, u It i-vi brator circuit means connect the volt to the power source for periodically triggering the constant voltage circuit for only the time duration necessary to. cause the LED to emit a visually detectable pulse of light. Strobe lights and drivers therefor employing light emitting diodes (LED's) are well known in the art. Whereas larger strobe lamp devices are used for more permanent installations such as construction hazard modification, LED's provide a useful source of warning light for personal use such as on the body of a person or pet. For example, United States Letters Patent No. 3,944,803 describes an " i lluminated device which can comprise the collar of a pet or a bel ' t'Of a person. Patent No. 4,231,079 discloses a so-called safety hat on which LED's have been mounted. Both Patent No. 4,283,756 and Patent No. 4,523,258 show belts employing flashers thereon. Patents 4,161,018 and 4,264,845 both disclose circuits for driving a plurality of LED's when used in such devices. The problem with the prior art devices as exemplified by the above-referenced patents is that they are either of very low intensity or of very high power consumption. For any practical usefulness as a warning device, the usual choice is high intensity at a sacrifice of power consumption. In the case of the lamp strobe, de ice as used on construction sites, for example, a large battery must be employed therewith because of the semi-permanent nature of the device. In fact, automobile batteries are sometimes employed for such uses. Where the devTce is to be worn on the person, however, very small batteries must be employed. With high power " consumption, the life of such batteries is very short and, therefore, the cost of operation is very high. Wherefore, it is the object of the present invention to provide an LED strobe lighting system wherein a high intensity strobe light is produced, while, at the same time, power consumption is kept to a minimum. SUMMARY The foregoing objectives have been met by the low power, high intensity LED circuit of the present invention comprising at least one LED; a triggerable constant voltage circuit operably connected across the LED; a d.c. power source operably connected to the constant voltage circuit and the LED so that when the constant voltage circuit is triggered the LED has sufficient voltage and current applied thereto to cause it to emit light; and, multi -vibrator circuit means connectable to the power source for periodically triggering the constant voltage circuit for only the time duration necessary to cause the LED to emit a high intensity visually detectable pulse of light. In the preferred embodiment, the LED comprises a plurality of LED's electrically connected in series and parallel in a manner to minimize power consumption at a desired voltage and the multi -vibrator circuit means comprises two mono-stable pulse generators connected back to back. Additionally in the preferred embodi ent, the plurality of LED's are disposed in a box having a reflective inner surface and an opening covered with a lens whereby the light from the LED's is reflected and directed through the lens. DESCRIPTION OF THE DRAWINGS Figure 1 is a circuit diagram of the preferred circuit for driving the LED's in the present invention. Figure 2 is a timing diagram of current use by the circuit of F gure 1. Figure 3 is a plan view of an enclosure for the LED's in the present invention according to one possible e bodiment . Figure 4 is a cutaway v ew of the embodiment of Figure 3 and the plane IV-IV. Figure 5 is a plan view of a second possible embodiment for an enclosure for LED's according to the present invention. Figure 6 is a cutaway view of the embodiment of Figure 5 and plane VI-V . Figure 7 is a circuit diagram of a second embodiment of a circuit for driving the LED's in the present i nvent ion. DESCRIPTION OF THE PREFERRED EMBODIMENT The novel circu t of the present invention is shown in Figure 1. The circuit of Figure 1 comprises four major functional areas.wh ch pro ide for a high intensity strobe light pulse with low power consumption. The first major functional area is a source of d.c. power which is provided by 9-volt battery 10. Battery 10 is hooked in series with switch 12 so that the strobe lighting can be turned on and off. The second major area is comprised of the clustered LED's 14 w ich are electrically interconnected between a single anode point at 16 and a cathode point at 18 in ser es and parallel so as to mini ize power consumption at the voltage of the battery 10. The LED's 14 are then connected to the negative side of the battery 10 through a variable resistor 20 (also designated R6 ) by which the current level is se_t_. The third ma or component is a constant voltage circuit generally indicated as 22 comprising transistors 24 D and 26 (Q2), resistor 28 (R5) and zener diode (Z 1 ) . The constant voltage circuit 22 maintains a constant voltage to-annode point 16 of the LED's 14 regardless of fluctuations in the battery 10. Since the LED's 14 are fed by a constant voltage circuit, resistor 20 (R6) acts as a constant current level setting. The final ' ajor component is a mult -vibrator circuit 32 wh ch has a one second osc llation which, in turn, is used to trigger the constant voltage circuit 22 to strobe the LED's 14. A current versus time diagram for the multi-vibrator circuit 32 is shown in Figure 2. The output of the mu It i -vi brato circuit 32 (which will be discussed in- greater detail shortly) appears on the line labeled 34 which is connected to pin 9 of the integrated circuit 36. As can be seen in the upper line of Figure 2, pin 9 of the integrated circuit 36 produces narrow width pulses 38 on substantially a one-second period basis. Upon each occurrence of a negative pulse 38 on pin 9 of the integrated circuit 36, as shown in the lower line of Figure 2, an approximate 50 milli amp current pulse of 20 llisecond duration appears at the anode point 16 of the LED's 14. This, is of sufficient time duration and current level to cause the LED's to produce a strobe level intensity light emission. Turning briefly to a more detailed discussion of the mu It i -vi brator circuit 32, the integrated circuit 36 ( labeled IC1) can comprise an RCA part No. CD45388 or a Motorola part MC145388. The integrated circuit 36 (IC1) is a CMOS device containing mono-stable oscillators 40 and 42 (MONO 1 and MONO 2, respectively). The - 5 - mono-stable oscillators 40, 42 are normally used as separate units to produce pulses. As shown in the circuit diagram of Figure 1, the mono-stable oscillators 40, 42 are i nterconnec ed back-to-back in conjunction with capacitors 44 and 46 (C1 and C2, respectively) and resistors 48 and 50 (R1 and R2, respecti ely) which provide the two RC time constants to set the one second oscillator. Resistors 52 and 54 (R3 and R4, respect vely) are, of course, merely a voltage divider to provide the proper voltage level into transistor 24 ( 1 ) . Briefly, in a tested embodiment of the present invention, the value of the various components were as fo I lows : LED's - L200CWR2K (Ledt ron cs) ; R1 - 8.2 meg ohm; R2 - 220 K ohm; R3 - 4.7 K ohm; R4 - 47 K ohm; R5 - 330 ohm; R6 - 3 ohm (all resistors being one-forth watt ) ; C1 and C2 - .1 micro ferrard, 5V.D.C. tantalum; Z1 - .5 watt, 5.1 volt (dictated by the LED's emp loyed) ; Q1 - 2N2907A; and 2 - 2N6387 (Darlington, to provide for extreme high intensity, LED drive or high current ' pulse requirements) , The current (and therefore power) consumption of the mult i -vibrator circuit 32 is less than 100 microamps. The current desired (100 or more milliamps) to light the LED's is consumed during the period correspond ng to the negati e pulse 38 which is only 2 percent of the total oscillation period. Because of this low power of operation, a nine volt carbon battery was tested and lasted 350 hours before any noticeable loss of light output was perceived. The use of the Darlington transistor at Q2 would allow the same circuit to be used with, for example, -a zenon flash lamp replacing the LED's 14. As a result of the back to back interconnection of the two mono-stable oscillators 40, 42, upon application of power by closing of .switch 12, the output of transistor 24 (Q1) generates a temporary and short lived spike (positive going) lasting less than one millionth of a second. Pin 6 being tied to pin 11 of mono-stable oscillator 42 (MONO 2) generates a - positive pulse at the pin 10 output which is of a width dependent on the values of capacitor 46 (C2) and resistor 50 (R2). At the end of this pulse, the negative (falling edge) triggers a pulse out of mono-stab le oscillator 40 (MONO 1), in turn, generating a positive going pulse at pin 6. The cycle is then repeated continuously comprising a stable mu Iti-vi brator. The particular integrated circuit chosen as 36 ( IC-1 ) was chosen because it produces the desired pulses with the minimum number of added components thus keeping energy use to a minimum. Turning now to Figures 3-6, two embodiments of a special housing employed for the LED's 14 to maximize the available light produced according to the present invention will be discussed. With each of the LED's 14 according to typical products avai lable, the light intensity output is very high but confined to only a small angle (typically 10-20 ) on each side of the optical axis 56. A small_amount of light also occurs in a ring approximately 90 from the optical axis 56 and also in a direction 180 from the major output along the optical ax s 56. Normally 40 to 50 percent of the light produced by each LED 14 is lost. In the present invention, it is preferred that a plurality of LED's 14 be employed which are, as previously described, electrically interconnected in series and parallel to create the effective resistance of a single LED. It is convenient, therefore, to mount the plurality of LED' s 14 in a single enclosure in close proximity to one another to provide a single strobe light source providing almost double the avai lable light than would be avai lable from 6 LED's employed in the usual manner. Figures 3 and 4 show one possible embodiment emplo ng 6 LED's 14 whi le Figures 5 and 6 show an alternate embodiment employing 5 LED's. In both cases, a box 58 is divided having an opening 60 over which a lens 62 is affixed. The inner surfaces of the box 58 are coated with a highly reflective material 64. Whereas the typical LED is of approxi ately 1/4 inch in diameter in tested embodiments it has been found that it is convenient to make the box 58 in the form of a rectangle, as shown, approximately one inch by two inches. Both the box 58 and lens 62 are easi ly formed of a plastic such as acrylic or polycarbonate and the reflected material 64 applied thereto in any of the fi lm depositing methods well known to those ski lled in the art. Preferred operation appears to be achieved when at least one LED 14 is placed adjacent each of the corners of the box 58 and the optical axes 56 are disposed to be normal to the optical axis 66 of the lens 62. . The arrangements as shown in the embodiments of Figures 3 and 4 and Figures 5 and 6 result in the light from the LED's being reflected and di rected by the reflective material 64 and their positioning through the lens 62 to provide maximum light through the lens 62 from each i llumination of the LED' s 14. A second embodiment of the invention is shown in Figure 7. In this embodiment a log r i hi mi c current pulse is achieved by using and discharging the capacitor c-2 through the LED's by switching on amplifier Q2. Because the LED's have a logrithmic temperature versus a light output degradation curve, which are caused by instantaneous high currents, more effect ve use of current pulse operation is achieved by this alternative arrangement. * The capacitor is discharged only during a 20 milli-second per od, or less, and effectively does not use battery power _du_r_i ^ ng the discharge period because of the two stage amplifier arrangement, Q 1 and Q ? . Since the average current drain on the battery is very little, the effective ampere/hour rating of any g ven battery (9V alkaline or 7V lithium) is greatly increased, Figure 7 contains suggested values for an arrangement of the second embodiment of the invention. The disclosed values and the part numbers for the elements are provided only for illustration purposes and are not intended to be interpreted in the limiting sense,

Claims: _ 9 _ CLAIMS 1. A low power, high intensity light e itting diode circuit comp ri si ng : (a) at least one light e itting diode; (b) a triggerable constant voltage ci rcuit operably connected across said light emitting diode; (c) a d.c. power source operably connected to said constant voltage circuit and said light emitting diode so that when said constant voltage circuit is triggered said light emitting diode has sufficient voltage and current appl ed thereto to cause it to emit li ght; and (d) mult i-vibrator circuit means connectable to said power source for periodically triggering said constant voltage circuit for only the time duration necessary to cause said light emitting diode to emit a visually detectable pulse of light. 2. The circuit of claim 1 wherein: said diode comprises a plurality of light emitting diodes electrically connected in series and parallel in a manner to minimize power consumption at the voltage of said d.c. power source. 3. The c rcuit of claim 1 and additionally comp ri si ng : variable resistance means electrically connected in series with said light emitting diode for setting the level of the current through said light emitting diode. 4. The ci rcuit of claim 1 wherein: said mult i -vibrator ci rcuit means comprises two mono-stable pulse generators connected back-to-back. 5. The circuit of claim 2 wherein: said plura lity of light emitting diodes are disposed in a box having a reflective inner surface and an opening covered with a lens whereby the light from said diode is reflected and directed through said lens. - 1 0 - 6. The circuit of claim 5 wherein: said box is rectangular and a portion of said diodes are mounted adjacent respective corners of said box with their optical axes normal to the optical axis of said lens. 7. A high intensity l ght emitting diode strobe lig t comp ri si ng : (a) a box ' having a reflective inner surface and an opening covered with a lens; and (b) a plurality of light emitting diodes ' disposed within said box so as to have li ght • t heref rom reflected and di rected through said lens, said diode being electrically inner connected in series and parallel in a manner to minimize power consumption of a d.c. power means ; (c) said d.c. power means being operably connected to said diodes for periodically applying a voltage pulse to said diodes sufficient to make them emit a pulse of light. 8. The strobe light of claim 7 wherein said power means comp rises: (a) a triggerable constant voltage circuit operably connected across said light emitting diode; (b) a d.c. power source operably connected to said constant voltage circuit and said light emitting diodes so that when said constant voltage ci rcuit is triggered, said light emitting diodes have sufficient voltage and current applied thereto to cause them to emit light; and - (c) mult -vibrator ci rcuit means connectable to said power source for periodically triggering said constant voltage circuit for only the time duration necessary to cause said light emitting diodes to emit a visually detectable pulse of light. 9. The strobe light of claim 8 and additionally comp ri si ng : variable resistance means electrically connected in series with said light emitting diode for setting the level of the current through said light emitting diode. ■ 10. The strobe light of claim 8 wherein: said mu Iti -vi brator circuit means comprises two mono-stable pulse generators connected back to back. 11. The strobe light of claim 7 wherein: said box is rectangular and a portion of said diodes are mounted adjacent respective corners of said box with their optical axis normal to the optical axis of said lens. 12. A low power consumption circuit for driving a strobe light comprising: (a) a triggerable constant voltage ci rcuit operably connected across said strobe light; (b) a d.c. power source operably connected to said constant voltage circuit and said strobe light so that when said constant voltage circuit is triggered said strobe light has sufficient voltage and current applied thereto to cause it to emit light; and (c) mu Iti -v brator circuit means connectable to said power- source for periodically triggering said constant voltage circuit for only the time duration necessary to cause said strobe light to emit a visually detectable pulse of light. - 13. The circuit of claim 12 wherein: said mu 11 i -v brator circuit means comprises two mono-stable pulse generators connected back-to-back.

Inventors: BEAULEY LUCIEN H, BEAULEY, LUCIEN, H.
Applicants: NCDI INC, NCDI, INC.
Application year: 1986
Main classification: H05B37
IPC codes: H05B33