IL123123A - Illuminated sign system - Google Patents

Abstract

An illuminated sign system comprising: (a) a series-string connection of LEDs (122) including a plurality of LED groups A, B, C, D; (b) a plurality of Zener diodes (123) each said Zener diode shunting one of said LED groups (A, B, C, D) in said series-string connection of LEDs; (c) a looping layout construction of said LED groups in said series-string connection of LEDs and (d) a single current source (106) having a supply voltage providing a current to each said LED groups and to said plurality of Zener diodes.

Description

ILLUMINATED SIGN SYSTEM / ILLUM I NATED S IGN S Y STEM F I ELD AN D BAC KGROUND OF THE INVENTION The present i nvent ion relates to a general illu minated sign and signal t echnology having improved performance, i . e. high reliability but very low energy consumption and t he advantages t hat are derived thereo The signs and signals in this system are composed of discrete light sources, examples of which is the l ight emitt i ng diodes (herein-after LED's) and miniature low-voltage filament lamps. The discrete light sources are used singly or are arranged in groupings to create patterns which are observed to constitute single letters, numerals, symbols, pictures or complete signs Individual characters may be further arranged to generate complete signs. Signs may be composed of standard character elements in the field vs. typically in a sign shop, thus presenting a flexible method to compose illuminated signs of a fixed message.

The improvements in this invention derive from efficient energy use: a) light energy is only produced in the sign as is necessary for the observer to understand the message, i.e only the message itself is lit vs. illuminating the complete sign surface including the background; b) light energy produced is aimed in the direction of the observer as much as is possible; c) the energy source is properly matched to the light source through improved electrical circuitry significantly reducing energy use; and, d) light energy is produced only when needed.

As a whole, or i n part, these pri nciples enable the illumination of a myriad of sign and signaling devices heretofore impractical t o illu minate due to t he high power consumpt ion of present sign illuminating technology The invent ion provides for a new generation of reliable, energy-efficient, signs which are more readable and applicable in a variety of sign situations including: house signs, st reet signs, advertising signs, exit signs, emergency signs, signs over business, display signs, traffic signs, traffic signals, roadway i ndicators, and in any application where an improvement in readability, reliabi lity, and efficiency is desired in day-to-day use. The low power consumption makes feasible a battery back-up capability which allows address location and direct ion signs to remai n operative in extended civ il emergency situat ions, and a solar cell capability which al lows for i nstallation anywhere wit hout need for an external power su pply.

The i nvent ive features disclosed herein are t he result of the Applicant's service as an ambulance driver in the Gulf War but relates to all natural disasters such as eart hquakes, hurricanes, fires, etc.. Applicant was required to locate street and house addresses in a city, where the electrical power was interrupted, so there were no street or traffic signs. Absence of signs in times of emergency may also l o result from the use of incandescent and fluorescent light sources, which utilize fragile glass envelopes which easily break due to t he impact shock of bombs, or explosions of gas mains, during earthquakes and other natural disasters. These are the motivations for a sturdier, more reliable, low energy usage, address, direction, and traffic signal, sign system with power supply back-up. Hence, the preference for an efficient, concentrated, very long life expectancy, reliable, light source, such as 1 5 LED ' s, and also the preference for readability in daylight without electrical power. It should be appreciated that in emergency situations, the ability to locate an injured person rapidly is important to the patient's survival . No doubt emergency medical personnel anywhere would appreciate the significance of this reliability improvement . 20 PR I OR ART Four major types of illuminated sign technologies are presently in use: I ) Surface-painted signs which are illuminated by external light sources, such as floodl ights, which are generally located at acute angles to the sign. Light energy is wasted since, a) the ent ire sign su rface is illumi nated ( not just t he message ), and b ) a great percentage of the 25 l ight reflected never reaches the observer either being spilled off to the sky or ground . 2) Light box signs where a light source is placed behind a translucent surface with the message spelled out on the translucent surface, in characters contrasting to the translucent surface background Light energy is produced to provide equal luminous exitance over the entire face of the sign, including the background, as opposed to lighting only the character 5 which has to be seen. Only a small fraction of the light produced reaches the eye of the observer on the ground, as the light exits the sign in all directions including upwards, thus wasting energy. 3 ) Signs comprising light sources which themselves spell out the sign message. Neon signs and exposed incandescent filament lamp signs, are examples of this technology. When not l o lit, these signs are not readily visible (unless a paint is applied under the character or symbol) and are thus totally dependent on being illuminated to deliver the message. These signs are costly to make, operate and maintain as they are custom made for the client, of limited life span, fragile and the incandescent version is energy wasteful. 4) An improved light source sign is the LED matrix sign. LED technology is taken 15 advantage of to create changing-message signs These dynamic message signs are computer-controlled and provide interesting and attention-grabbing signs which are an excellent solution to illuminated signs with the need for a changing message. However, most signs are of a fixed message, and these signs are initially expensive and costly to operate Expensive power-supply units are required, as each addressable LED requires a 2( ) separate current-balancing resistor, so energy consumption is high These signs are relatively expensive since the complete sign area is covered with LED's. Since the LED's are located in a matrix, the LED' s are indiscernible from t heir neighbors when not excited by an electrical power source. Thus the sign must also be powered during the day.

For the purpose of comparison, we address the most similar prior art solution, which is a matrix in the "sign" consisting of a pattern of selected lamp elements in the matrix array The pattern may be selected by computer, for example, in a store display application, or in a highway sign.

The problems with the prior art are: 1) The problem of visibility of the sign in the daytime. In bright sunlight In a matrix the lamp brightness must be greater than the ambient intensity, or the illuminated LED will become invisible among the rest of the LED's in the matrix. 2) Since many signs are of a fixed message, using a selected few LED's out of a matrix to spell out a street sign or house address, the sign is more costly and complicated than need be. 3) The reliability of the sign is less since it relies on logic circuitry and a complex power supply to drive the LED matrix introducing more elements besides LED's which may cause failure.. 4) The energy-use efficiency of the matrix sign is not as good as for a fixed sign. There are many problems with the use of parallel-connected LED's, such as in a matrix sign or in prior art LED signs, which make parallel-connected LED's a poor design choice for a fixed or semi-fixed message sign application. 5) If the LED's are to be powered from a voltage source, with the current in each LED individually set, then a separate resistor is needed for each LED. This is extremely wasteful of electrical power. 6) In general, each color LED is a different semiconductor material, or a different "alloy", having its own, unique forward voltage drop, for a given light output at a given forward current For example, red LED's typically have a forward drop at about I OmA of about 1.7V, while green LED's typically have a forward drop at about 10mA of about 2.2V. Since LED's are a semiconductor diode, it is necessary to reach the conduction "knee" of the diode curve, before the LED will conduct, and emit light Thus, if one parallel connects a red and a green LED, he expects the red LED to light, and regulate the voltage across the two LED's at 1 ,7V, thereby resulting in the green LED not conducting at all. So parallel connection of LED's of different colors, in general, is a problem, requiring a separate series resistor for each LED, to balance the LED currents. 7) If many LED's of one color are to be connected in parallel, all of the parallel-connected LED's must have closely matched 1-V characteristic Again this is due to the fact that LED's are diodes, and the "current-sharing" between the parallel-connected diodes is very strongly dependent on the difference between the forward voltages of the diodes measured at a given reference current For poorly-matched diodes, very noticeable differences in intensity are expected. Thus, in production, it would be impossible to use LED's from different manufacturers, or from different production lots from one manufacturer, and one would expect to have difficulty also even with one production lot Again, balancing resistors are required.

Various attempts have been made to provide signs using LED's. A patentability search has been conducted resulting in the following patents: US 5,424,924 (filed 2 Mar 94) has characters made of LED's operating from low-voltage.

US 5,303,124 (filed 21 July 93) replaces a light bulb with a series string of LED's powered from a high-voltage (63Vnominal) rechargeable battery Normally, AC line power is used, but when the line drops, the battery provides power to the LED string. Preferably, when battery-powered, the LED's are blinking, with a conventional blinker circuit connected in series with the battery and LED's This conventional blinker circuit turns ON the LED's in order to cause the LED's to blink. This differs from the present invention in that, (a) the LED's replace a light bulb, and are not providing a character representation, and (b) the blinking circuit is different from the Applicant's light blinking circuit, which operates in parallel with the LED's, shunting current around the LED's, to cause the LED's to blink by turning OFF the LED's Further, the blinking-off circuit of the present invention may be connected to bracket a group of LED's anywhere along the series-connected string of LED's and the blinking-off circuit of the present invention is powered by the current in the series LED string, not requiring a separate power source for the operation of the blinking-off circuit US 5.0 19,438 (filed 16 Nov 89) has a design of LED's apparently operated from a low voltage battery- US 4.855,723 (filed 29 April 88) provides an outdoor building sign for emergencies. This has cards on which characters are formed from LED's in a seven-segment type arrangement, with one resistor for the string of diodes in each segment. Power is from a 22Vnominal battery. Current to each segment, for initial brightness control, is adjusted by resistor selection This sign has a blinking strobe light, not blinking LED's. Variable brightness intensity control is accomplished by varying the rate of an oscillator which is an alternative to continuous DC drive to the LED's LED's are visible when illuminated. This differs from the present invention where address is visible in daytime even when LED's are not operational and is for day to day use rather than specifically as an alarm. Cards may be slanted in viewing direction. This differs from the present approach of slanting LED's or customizing the light distribution pattern of the LED itself, as will be described below.

US 4,709,307 (filed June 86) has LED characters, battery and a control circuit which may blink the LED's US 4, 1 73,035 (filed I Dec 77) has a flexible strip with LED's mounted on it By selectively energizing the LED's the effect of a moving display can be simulated This does not form characters. A timer controlling the rate of blinking, controls the rate of apparent motion. This is not a sign, but rather a moving spot.

US 4.384,3 1 7 (filed 1 7 May 83 ) has a "light-emitting device" consisting of a series string of LED's, forming a dedicated sign, a storage battery, and a photovoltaic array, typically providing 12V, providing operation either from the battery or the photovoltaic (solar) array. The voltage required by the LED string is approximately the battery voltage Control circuitry provides the option of blinking the sign The assumption here is that the sign illumination cannot be seen in the daytime This is unlike the sign of the present invention, in which the characters of the sign are visible and readable in daylight without electrical power applied.

US 4,9 1,405 (filed 28 Aug 90) provides fiber-optic-illuminated cutout characters mounted rails which transmit either electric power or light, as a modular sign system. If the rails cany electricity, then the characters have, e . incandescent bulbs for illumination; if optical energy is transmitted, the characters have, e g., optical fibers for illumination. This also has an assumption of non-visibility of the illumination in the daytime US 4,854,062 (filed 25 Jan 88) provides a modular series-string-LED house-number sign system, transformer powered from the doorbell transformer! The characters are connected in parallel with each other and in parallel with the doorbell switch. Each character preferably has eight LED's in series.

US 4,667,277 (filed 20 Sept 85) is an dovetail-interlocking modular lamp housing.

US 4,532,579 (filed 13 April 84) provides modules which he assembled in various mechanical configurations, with one lamp illuminating each module. Again, we have the assumption that the illumination is not visible in the daytime.

US 4,471,415 (filed 20 June 83) provides a mounting bar for holding LED's on a printed-circuit board.

US 5,450,301 (filed 5 Oct 93) provides LED-array replacements for incandescent lamp display panels This uses series strings of LED's. Optionally, red and green LED's in a ratio of one red LED to two green LED's, closely packed, give the appearance at a distance of amber color A triac controller operates from the AC line to provide brightness control.

US 5,479,325 (filed 26 Dec 95) provides an electroluminescent strip to illuminate a pattern. The circuitry includes a battery, a DC/AC invertor, and "function stage", to provide visual effects, including Hashin US 4,271,408 (filed 12 Oct 79) provides a concave-mirror-ce!I surface with LED's in the concave mirrors. This is designed f r visibility 24-hrs, e , for traffic signals! He says 62 LED's may be series-connected for about 100V driving voltage, and units of this may be parallel-connected.

Further, Applicant has discovered US 5,020,253 (filed 6 February 90), which provides a modular assembly of character units, each containing a series string connection of LED's and one series resistor for the series string of LED's Each series string of LED's requires a custom-valued series current-limiting resistor to determiner the current resulting in the LED string, depending on the number of LED's in the series string, column 2, lines 64-66 The need to uniquely determine the value of the series resistor for each module is a disadvantage Further, US 5,020,253 provides 24V DC current and voltage in order to provide for forward voltage drop on each LED typically 1 ,8V for a maximum of 13 series connected LED's. In this series connection, if one of the LED's in a given character fails, then the complete character ceases to operate There is thus a widely recognized need for, and it would be highly advantageous to have, an illuminated sign system providing (a) readability in the daytime, even without electrical power applied; (b) improved readability at night, with power applied; (c) improved efficiency, whether for rechargeable battery or for operation from solar cells, or for operation from city-provided power source.

Further, new features solving problems which have not been previously identified in the prior art are: (d) improved reliability, in that readability and recognizability of the information to be provided by the sign or a portion of the sign not be lost due to failure, in an electrical open-circuit condition, of a lamp element in the sign; (e) easy adjustability of operating current in the field at the time of installation, especially when assembling a modular sign, (0 use of one power source to supply non-matching LED's, examples including LED's of many colors and LED's from various manufacturers and production lots Today, there are many signs and t raffic indicators which are not illuminated , or if illuminated, t he execution is inefficient and unrel iable. I t would be highly advant ageous to have an illuminated sign system and signal technology providing for a more functional , reliable, and efficient, illuminated sign technology.

According to the present invention, any sign, whether a street name, residential house address, business, advertising, highway, sign, etc. , would be composed of individually purchased character elements (letters, symbols spaces and/or numerals) which are adjoi ned physically or positionally to create the sign. Each character element is composed of a multitude of individual light sources either mounted above or below a support surface (where there are openi ngs for the light to exit). The i ndividual light sources may be electrically connected in parallel or in series depending on which circuit is best matched to the available power source. The character element may also be constructed in such a way that it is visible in daylight even when "unlit", i .e. , when the LED is not excited by an electric power source, and even in direct daylight (as opposed to a state of the art matrix LED sign, the message of which is only readable with the application of electrical power) The sign of the present invention may be illuminated (powered) during the clay for enhanced visibility, or only at night If the position of the sign relative to the desired audience of observers is known, then the LED' s employed may be of unique constaiction, as will be described, providing a directional light d istribut ion patt ern and ai med at the preferred viewing angles. Each numeral or letter element can be i ndi vidually affixed to the wall or hung from an arm and i ndividual ly hooked up to the electrical power or be mechanically and electrically joined to each other or to a mounting frame and then to the wal l and power supply Alt ernat ively, each character element could be battery powered with an opt ional photo-cell controlling night time operat ion, and the battery could be recharged from photovoltaic cells which could be l ocated on the charact er el ement it self on it s front and or back side or on a separate, properly aimed t owards t he sun, array Alternat ively, a cent ral ized power pack using utility power or wit h battery operat ion or back-up and photovoltaic recharging could be located in the frame or in a master character element i n the cha i n, and many charact ers powered from it . In one implementat ion of the i nvention, letter and number modules are provided, so that one may build up a custom house sign by linking modules according to the mechanical arrangements provided, such as pins, dovetails, and slots. The mechanical arrangements include provision for electrical interconnection of the modules. Street signs, direction signs, business signs, location, and advertising signs would be modularly constructed with the ability to compose t he sign at each intersection of streets or storefront from the standard letter elements.

Optionally, complete signs (as opposed to built up modular sings) custom made for a home or business would be composed in a sign factory, or may be assembled in a sign store, say, the "sign department" of a hardware store.

Due to the very low energy consumption, a number of advantages are realized, including battery back-up capability, and photovoltaic recharging allowing for use where a commercial power source i s unavailable, such as i n remote highway intersections. The reduced energy use wi ll also reduce operat ing costs and envi ronmental pollution.

Readability is improved by formation of illuminated characters in which the letters stand out on high contrast backgrounds, t he reverse of the case of t he prior art back-lit illuminated house signs ment ioned above, where t he background may cause glare at night An addit ional feature of t he LED sign system of t he present i nvention is the abi l ity for medical ( ambulance), security and service operations such as taxis to receive aid in locating an address t hrough t he blinking of LED ' s in the sign at an address to which such services have been summoned .

! O To t his end , a special circuit capable of blinking a selected group of characters in a serially-connected LED sign This is especially useful to ambulance drivers at night, and especially in blacked-out areas wit hout outside l ighting, such as i n civil disasters or wart ime but i s also useful for taxi, delivery and ot her services night and day An addit ional useful feature is t he incorporat ion of t he postal code or other location code or informat ion i n t he street and house number signs, for example, t he postal code characters which are normally not being illuminated, but being trigger-able, preferably to bl i nk for increased noticeability by remote command from an emergency vehicle, for example, say, by radio frequency or other suitable command transmission receiver incorporated in the sign.

The novel blinking-light circuit implementation of the present invention shunts a group of LED' s which form t he character of interest. The circuit operates to short out the group of LED' s, turning off the group of LED ' s to cause the group of LED ' s to blink, the reverse of the normal turning-on of lamps to blink the lamps. The blinking-off circuit is powered from the LED-st ing current, not requiring a separate power supply, and thus may be located at any position along the series string.

A further important feature is the provision of a battery back-up capability, so that if there is a temporary loss of AC power to the sign, the sign will remain illuminated for some hours. In the event of loss of AC power the battery back-up would automatically be activated. A pulser circuit is preferably included to extend the battery back-up operating time. The pulser circuit would preferably be automatically enabled when the back-up battery would be i n use and would be automatically reset upon restoration of the AC power. The pulser would also provide an AC power loss indicator function I n a modular system with battery back-up, the battery back-up pulser would be i deally located in t he power-pack module I llumination t ime may be further extended by pulsing t he power applied to t he sign, so the whole sign blinks at rates which may or may not be visible to t he eye Then t he operating time will be extended accordi ng to the pulsi ng duty ratio.

Anot her power-consumption reduct ion technique which may be employed i n parallel circuitry is t he mult i plexi ng of characters for reduced power consumption When characters are blinked at a su fficient ly-rapid rate, t he impression of constant illumination is given to t he observer. Thus, the possibi l i ty exist s of bli nki ng characters as a possible power-saving method, especially at night, when reduced i ntensity i s required for visibility, due to reduced ambient il lu minat ion, compared wit h t he dayt i me ambient . I f addit ional power saving is requi red, an extended duty cycle at very slow rates of a number of seconds on and a number o f seconds oil" would st ill leave t he sign message sufficiently recognizable I n addit ion, often street sign lighting is operated from street lighting power, which is shut off during daylight hours. I n thi s case, battery back-up may be used to power an illuminated sign during the day if desired .

The electric circuit used to drive LED or other multiple l ight source signage is optimized to match the load to the power source to obtain maximum utilization of the power source. When relatively few LED's are used in a sign, the separate current-balanci ng-resistor parallel connection of LED light sources to a low-voltage power supply - maintaining constant voltage is preferably used. Preferably, in place of the resistor, a constant current maintaining circuitry is used further increasing energy efficiency. With larger characters involving many hundreds of LED's the series connection of individual light sources is preferably used, forming letters, numerals and symbols. Parallel connection of multiple strings of series-connected light sources may be used i n all or some of the letters numerals and symbols making up the complete sign . The series connection utilizes a constant current source for each series string of LED ' s. This provides improved efficiency over parallel circuitry in such instances where the power dissipation in i ndividual parallel-LED balancing resistors becomes a factor I n an additional feature, where safety from elect rical shock is desired, such as in road signs whic h may be knocked down in a traffic accident , the cu rrent source may be limited to a safe 30 mA and it may be optionally fu sed or may alternatively i ncl ude any type of ci rcuit breaker to prov ide safer signage than previously available The features may be used in combination to realize, for example, an improved modular sign system erryman '579 discloses stackable modules containing lamps which are connected in parallel to the AC line, such that if one lamp fails, the character illuminated by that individual lamp is extinguished, but the rest of the characters remain lit. The circuitry of the present invention improves upon erryman, in that the failure of one LED does not result in the loss of readability of even one character module Further, the modules of the present invention may preferably be connected in series to a high-voltage supply with improved efficiency. The use of a current source makes the supply current lo the LED's substantially insensitive to the number of series-connected modules.

Alternatively, with a low-voltage battery supply, the modules may be supplied by individual current-mirror outputs, derived from one temperature-compensated current source.

Alternatively, a common voltage reference may be provided to each of the modules in a modular sign system, and the desired temperature coefficient for the current source in each individual module may be independently generated from the provided common voltage source.

It is important to realize that for the application of a modular system, the use of either of the current-source supplied series string connections of LED's of the present invention mentioned above is the best approach, since non-matching LED's may be readily, interchangeably used in the modules. LED's of various colors from various manufacturers and production lots may be freely assembled into interchangeable, readily-interconnectable modules. This avoids major manufacturing cost and resource difficulties. Further, temperature compensation of the LED light output versus ambient temperature may be provided by adjusting the current source temperature coefficient.

In the prior art, a disadvantage of a series connection is the continuity if one of the elements in the string fails In the present invention, a novel series power connection reliability improvement is provided by Zener diodes bracketing groups of LED' s which form the characters of the signs. Thus, if one LED in a typically series-connected stung of LED's. would fail open, only the loss of illumination of a portion of a character would result, resulting in a still-readable sign Still further sign reliability is realized by multiple Zeners bracketing strings of strategically-positioned, non-consecutively positioned, light sources comprising the character The outage of only a single section would leave t he character legible and the sign still functional. This is the "looping" connection of the present invention, described below I n this modular sign system, signs may be constructed of individual characters in the hardware-store or in the field. A current-adjustment method must be provided to obtain optimal performance as the illumination output of a LED is a function of the forward operating current of the LED, as is well-know Field adjustment of operating current is provided by a "go/no-go" current adjustment circuit. This circuit makes the use of an ammeter unnecessary for field adjustment of operating current in a series string of LED's at the time of installation of a sign Current sources are provided, including temperature-compensation for approximately constant light intensity versus temperature, with an operating temperature range centered about room temperature. The capability of economically driving multiple series strings of LED's is provided, by use of current-mirroring.

The current sources provide the capability of operation with a wide range of supply voltages, say, from 4V to 600V, without readjustment of the current-source circuitry. Thus, the current sources may be used with a wide variety of signs, containing a wide range of numbers of LED's in a series string of LED's. This is a very desirable feature, providing ease of manufacture, and interchangeability.

Both AC-line power sources and battery power sources are provided for, with efficiency-enhancement techniques. With an AC power line, the power in the bias circuitiy is reduced by use of a rectifier power supply with no filter capacitor A half-wave rectifier provides reduced power dissipation compared with a full wave rectifier. Due to the series-string LED connection, only one reverse-voltage protection diode is needed per series string, unlike the prior art parallel-connection method, in which, ideally, each diode should be provided with its own reverse-voltage protection diode This represents a significant component and assembly cost savings The reverse-voltage protection diode is required to guard against LED destruction due to reverse-polarity l ight ni ng-induced power-supply transients, and ot her AC power-l ine transients and surges, such as due t o switchi ng inductive loads, and due to motor starti ng Low power consumpt ion makes possible battery operation, preferably usi ng rechargeable batteries. Solar cel l operation and is also possible as is solar cell rechargi ng of t he batteries. The ment ioned u se of series-st ri ng connect ions of the LED ' s resu lt s in high-efficiency, low power consumption operation, as will be described in more detail below For battery-powered and battery-back-up signs, a switching power supply is provided, including an automatic adjustment feature for the voltage applied to the series string and current source, in order to maximize efficiency of the battery-powered sign system. A basic reference for the design of switching power supplies i s the book, Switching and Linear Power Supply, Power Converter Design, by Abraham 1 Pressman, Switchtronix Press, Waban, MA, copyright 77 by Hayden Book Company, rights transferred to Switchtronix Press, '87.

In photovoltaic recharging, if only the sign face is available to receive solar insolation (illumination), and the sign is facing north, for example, then such power reduction methods may be employed on an as- needed basis, determined in real time by diagnostic circuitry. Such circuitry determines the battery charge vs. time left of the night or section thereof to keep sign illuminated. The circuitry could use a preset calendar watch or analyze the daylight time subtracted from a 24 hour day to determine hours of night . Then, depending on the success of the solar cell charging of the batteries during the day, the circuitry would operate the illuminated sign in a maximum performance mode as long as possible, before switching to an energy saving operating mode. In addit ion to managing the energy use by l ight sources, the circuitry could manage the energy storage.

The LED ' s or ot her light sources are opt imized to match t he special requirements of use in signage leading to : Sign-Technology- S pecific LED and LED Assembl ies I n t he present i nvention the light sources used, where possible, are specifically adapted photomet rically, spectrally and physically, i . e. outer packaging, for sign and signal applications. Prior art L ED's are typical ly designed for use as i ndicator lamps. Directionality is generally symmetric in the vertical and horizontal The candle power distribution as a function of angle was also suited specifically to indicator lamp use The need for sign-specific LED construction will be appreciated from consideration of the following example An LED adapted for use on a sign located at six-meter height would have no light contribution above 70 degrees from the nadir, it being assumed that the viewing audience is located on the ground, and the practical viewing distance, according to the size of the letter, is not more than 16 meters In the reverse case, where a sign is located at below eye level, as on the guard rail surrounding a subway exit to the street, the distribution would be above 90 degrees.

Likewise, a highway sign to be viewed by northbound traffic would be of asymmetric light distribution also about the horizontal with light projected only towards the west.

Signs to be viewed from all directions would use wide candle power distributions, while signs located at the end of a long narrow corridor would use a very narrow candle-power distribution.

A two-sided bill-board sign located, for example, on the southwest side of an intersection having an almost 90 degrees, directly ahead viewing angle with traffic headed eastward and westward, and an almost zero-degrees angle to the parallel north south direction, can be made to have increased visibility to the parallel direction. Signs are visible at even alight (acute) viewing angles of even 20 degrees To make the sign more visible, narrow beam LED's forming the characters may be aimed to the left for the northbound traffic, and to the right for southbound traffic, to provide added light output, even during the day, in the viewing direction. Thus, if two or three LED's were used to form the width of a character, and one LED was directed perpendicular to the sign, a second LED directed at 20 degrees, and a third LED at 160 degrees, all east, north, and south-bound viewers would be getting high luminance from the sign Alternatively, a character formed of a single width of a special LED with the spatially desired candle power distribution, i.e., three candle-power peaks at 20 degrees, 90 degrees, and 160 degrees, could be used. On the westward face of the sign, different light distribution LED's with output mostly to the west and slightly to the north would be needed for traffic coming from the west.

Similarly, on a narrow street, a storefront sign located tlat above the show window could be made more visible to the pedestrians on the adjacent sidewalk by using light-sources aimed at the acute viewing angles.

Thus, signs with directional and bi-directional, non-normal, viewing angles, not perpendicular to the sign and LED mounting surface planes, may be realized.

The same technique applies to an information or directional sign mounted tlat on a wall, such as in a narrow hospital corridor. Viewing may be enhanced by aiming method .

In addition, in characters formed using a double width of light sources, different messages could be written for viewers coming from each side, approaching from each direction. For example, one could read the sign from the right, and see ENTRANCE; and from the left, and read EXIT.

An advertising sign located almost parallel to traffic could carry two different advertisements at once. Those on the way to work, eastbound, say, would see an advertisement for business computers, and for those on the way home westbound would see an advertisement for an evening news program.

An additional method of displaying two or more messages on a sign would entail the laying out of two or more separate character sets of the same or different color, which would be non-visible until illuminated, for example, due to the use of clear LED packages, and alternately illuminating one or the othe Thus, on a limited-sized sign, one could display the message "BUSSES" and then "ON LY" saving sign "real-estate", installation costs, and energy An addit ional feature, to further make signs or signals readable, would include specifically adapting the spectral power distribution of the light energy emanating from the source to fit the application This would include: (a) the use of different colors to emphasizes different parts of a message, and, ( b ) a combination of different LED's to "mix" colors to render a specifically-desired color, such as white, composed of red, green, and blue. Roadway signs or indicators, which in "normal" weather use green to deliver the message, would use red LED's to provide increased visibility in fog. A radio control signal or a fog detector could control the switch-over The discrete light sources are used singly or are arranged in groupings to create patterns which may constitute single letters, numerals, symbols, figures and pictures or complete signs. The characters are themselves constructed such that they are visible even when un-lit, i.e. not excited by an electric power source and even in direct daylight. For example, a character formed of discreet LED's is encapsulated in a plastic surround which is raised above the background surface and is shaped or molded in the shape of a character or symbol. The plastic surround is made of, or coated with, a light-reflecting material and may be opaque except where the LED light is to shine through the plastic surround or be made of a translucent material.

Another embodiment would have a light-sensitive dye within the clear plastic surround, making the plastic surround into a more visible opaque character or symbol entity during the day, and making the plastic surround clear again at night, with the LED's then providing the night-time character illumination.

The package options described may be realized in standard dual-in- line packages for through-hole printed circuit board mounting, and for non-through-hole assembly, using surface-mount technology (SMT) The packages may employ clear molding compounds, as is well known, and used in custom, proprietary, camera exposure-control integrated circuits manufactured by Cherry Semiconductor Corp., 2000 South County Trail, E. Greenwich, R.I. 02818, 401-885-3600.

Another embodiment comprises an "electronic reflector", such as may be realized by the use of a Liquid Crystal, the opacity of which liquid crystal is controlled by the application of an electric voltage control signal to cause the randomly-oriented, liquid crystal material to align in a coherent orientation over the LED's, making the characters visible during the day. At night time, without application of electrical voltage, the randomly-oriented, semi-clear liquid crystal material contained in is t he clear plastic surround, wou ld allow passage of the LED ' s l ight providing t he recognizable character or symbol I n one i mplementat ion, t he LED ' s are soldered onto a prmted-ci rcuit board I n anot her i mplementation, the LE D legs are connected one to another obviat i ng t he need for a pri nted circuit board The chai n created can then be l )fonned into free standi ng character shapes 2 )mounted into or attached onto a rigid support or 3 )become part of a flexible tape or tube. Where needed Zener diodes and power component s may be integrated into the chain.

I n another implementation, the LED' s are located on a flexible tape which contains the conductors for parallel or serial operation, with or without Zener bracketing. The tape may be formed in order to create characters or figures. The tape may come with an adhesive backing for surface attachment or alternately be placed on cloth or Velcro. The cloth could then be sewn onto the apparel of night personnel, say a roadway repair crew, making the repair crew self-illuminating and thus more visible to drivers.

I n another implementation, the LED chain or tape is built up into a round or trapezoidal shaped tube with the option adhesive tape along the broader bottom base surface, having reflective coating along the sides, and a clear or diffusing cover along the top where the LED' s may protrude through or be covered. The LED ' s may be aimed in the viewing direction and seen as individual point sources of high intensity along the tube such as for use in way out direction indication in smoke filled corridors. Alternately the LED ' s may be aimed along the tube with the tube acting as a light pipe. Specu lar and diffuse reflective surfaces can be used as required to control the amount and direction light exitance along the tube Alternately the LED ' s may be aimed totally or partially opposite to the viewing direction into a highly diffuse reflecting material to obtain a continuous light intensity along t he tubing. This reverse aiming is also ideal for the mixing of multiple individual colored LED ' s to generate uniformly a new color I n anot her embodiment t he shape of the tubing i s such that it may fit into a slot or positional holes for adherement to sign surface Power is supplied to the tubing via an edge connector which makes contact with the conductors at whichever poi nt the tube was snipped At t he opposite end, another edge connector i s supplied to close the tube and complete the electrical circuit as is necessary for a parallel or series connection.

I n anot her impl ementation the sides of the tube are covered with photocells The photocells may be of a rigid type wit h gaps left between t he phot ocells for bending, or a flexible type of phot ocel ls may be used which conti nuously bend wit h t he tube For each every-so-many LED's a rechargeable battery is provided, maki ng the product free of t he need for an external power source. This self-contained tubing may be formed into characters and figures, and attached to a wall or surface of buildings and vehicles to contrive business, traffic, advertising and many other permanent or temporary signs.

While present LED packaging is well-suited to the original LED use in indicator lights, LED's are employed, in this invention, as elements for composing characters in signs. LED junctions are packaged in shapes that allow the formation of letters, numerals and symbols based on the contiguous placement of individual LED's. Thus, in addition to the typical prior art round-shaped packages which touch one another at a point, square or rectangular shaped packages, some with angled edges to properly match up around curves in the character shape, are preferably utilized instead The package is also preferably redesigned to allow for optical features mentioned above, such as non-symmetric l ight distribution, radiation from the package at angles other than the 90-degrees angle perpendicular to the package mounting plane, and the appearance of a continuum of light rat her t han many little dots. The same technology adaptations of package shape for character format ion apply to Surface M ount Technology LED ' s as well Alt ernately, instead of forming characters from many i ndividually packed LED's, multiple LED's may be packaged together in longer shape sections.

I n a unique feature of the present invention, the "greatest- common-denominator" shapes of let ters are molded and t hen combined to form characters Thu s a " P" is made of a straight leg " I " and an arc similar to a backwards facing "c" Adding a leg at 45 degrees creates an "R" . Thus, investment in special tooling for molds is minimized Alternately, complete characters, numerals and symbols comprised of many LED junctions packaged in single unit s may be manufactured. Properly shaped and lensed, these characters would be visible during the day and would use a minimum of L ED junct ions to smoothly define the character at night The LED junctions can be aimed to directly illuminate the surface which is to be seen or by using the principles of a light tube. The LED's shine the light in to a light transmitting material where the walls are specularly mirrored except where light is to exit, thus on the back side a diffuse reflective material directs the light to exit on the front side. Such a "light bar" in the form of a character could use a minimum of LED's located along edges and be visible during the day and night.

When custom signs, i.e., those signs which are not composeable via standard character elements are required, such as in the case of "one- of-a-kind" graphics signs in advertising and business signs, a unique manufacturing technology is used In this sign manufacturing technology a specialized machine is sold to sign stores. The customer decides on the message and specific graphics of their application. The graphics are scanned into a computer or generated therein using readily available graphic programs. The graphics program would then generate silhouettes of the shapes and define the necessary placement of light sources to create the graphic. Post-processors which drive graphical plotters and computer-numerical-controlled surface-mount-technology (CNC SMT) placement machinery would then create the sign. The sign machine which would be sold to sign stores would first lay down conductors on a sign substrate surface utilizing either well-known printed circuit board masking and etching techniques, or by painting via a plotter or similar device, conductive polymers on the non-conductive substrate surface. Once the conductors are laid down in the proper graphical pattern, t he CNC SMT machine would place the LED' s, and solder or glue the LED's in place, to define t he layout of the custom sign. The machine would optionally extrude colored plastic material around the LED 's for protection and additional sign aesthetics.

Alternately, when using leg to leg connected LED chai ns, the scanned graphics would be t ranslated into coord inates for a CNC punch press which would make holes for t he LED ' s to be mounted t herein I n high volume signs, i . e. signs carryi ng a standard message, again, t he preferred manufact u ri ng t echnol ogy would be t he mass prod uct ion of complete signs as single u nits, rat her t han havi ng t he sign composed of individual character elements placed together as in the modular system mentioned earlie In this case the LED's larger signs would be connected in series strings, and the power circuitry prescribed earlier employed for significant energy and cost savings The technology of the sign system of the present invention is applied to wide range of applications using four basic packaging configurations: 1 Singular Letters, Numerals & Symbols (LNS) 2 Modular LNS a ) modular, mechanically and electrically interconnected "linked " separate modules b) modular, framed on a rigid structure Complete sign message or picture, logo, etc. , such as in an advertising sign. 4 Strings, tapes or tubes of light sources which can be formed into characters, symbols or figures 1 Singular Letter, Numeral, Symbol (LNS) or indicator elements: Single elements may be used in house number, traffic signal and highway markers LNS elements provide house st reet numbers as self-cont ained singly-packaged numerals LN S may be mounted on a solid back plate to control contrast and to give stability, or may be hollow and may be supported from t he rear I ndividual LNS element s are sel f-powered by a battery or connected to house power. An integral or separate array of photovoltaic solar sells may be used for daytime operation and for battery recharging, or the photovoltaic solar sel l s may serve as t he LNS background plate, facing out wards, to gat her light The character may be punched, cut or cast in plastic or metal or be carved out of wood or any other material typically used in house addresses. I n a brass letter holes are pu nched along a center li ne and LED' s are placed within to illumi nate or a slot along the center line is ti l led wit h a plastic LED illuminated "light bar" or "light tape or tube" as previously described . The house numeral may operate conti nuously or may be triggered by a dawn-and-dusk-sensing photocell to operate only at night . LN S may be affixed independent ly to a mounting surface such as a house surface or may mechanically be i nt er-li nked wit h ot her LN S elements.

Roadway safety can be increased using the low power usage sign and signal technology desc ribed above. A pavement marker indicator element for delineating the edge of the roadway pavement consists of reflective dots "cat-eyes" in a housing with or without a stud which is embedded or glued onto the pavement Often to see the lay of the road off at a distance the driver has to put on the high beam which blinds the oncoming traffic causing discomfort and accidents One or more directional LED' s may be added to the pavement marker which would illuminate the roadway contour at a distance without requiring use of the high beam. The LED's could be highly efficient, directional and be pulsed to minimize energy requirements allowing for pholtovoltaic recharging of batteries. The photovoltaic cells can be placed in front and or rear aperture of the marker and if necessary along the top and protected with a heavy-duty clear covering. An additional energy saving method would make use of a highly sensitive photocell which would pick up the low beam headlights of oncoming vehicles and only then trigger the flashing of the LED's I n another application, a prior art reflective (unlit) highway exit sign may be retro-fitted with self-contained LNS elements which may be affixed by adhesive or mechanical fasteners over present letters to make them more visible Further, LED' s may be aimed at angles within t he visibility range of drivers, increasing readability. Retro-fit of any sign to an illuminated sign is facilitated, since there is no need to be hooked u p to uti lity power as bringi ng power to a remote highway sign is costly. It is possible to enhance vi sibility of highway traffic signs, as wel l as indoor direction, safety and i nformation signs placed at very difficult viewi ng angles The angled LED comes to correct for the current viewing angle deficiency. S ign location on a narrow corridor wall cannot be easily viewed from the distance because of the acute angle. With LED ' s angled towards the corridor axis (rather than at 90 degrees), the viewer would easily see the message. On this sign, a viewer from the left would see one message, while one viewing from the right would see another message, since the light output from one LED angled at, say.20 degrees, would be invisible to the viewer on the other side. 2 In the modular LNS (M-LNS) there are two types of letter configurations, a stand-alone and a modular-frame type. In the modular system the function of the power supply and or mechanical securing of the individual characters is centralized a) In the stand-alone type, characters are molded 3-D in a plastic material and are visible even when not powered The lens end of the LED's extends out through the molded "cover" and shines making the letter visible even when there is no light. Alternately, the LED's are located beneath the cover surface The surface material may be clear and the light of the LED's shines through or prismatic or translucent and the LED's backlight the character. The stand-alone type of individual letters blocks are attached to a base power supply block, and letters and spaces are contiguously attached to one-another, all mechanically supported by the first block. The mechanical connection may be made using fasteners, dovetail slots, pins or other mechanical and electrical linking technology b) In the Modular Letter and Number System (M-LNS) the sign is constructed by attaching the first letter to the power pack, which is attached firmly to the wall. The second letter is attached to the fust letter with unique mechanical and electrical connections. The power pack is the physically strongest link in the modular sign system, supporting the power pack's end of the modular sign, by ruggedly mechanical mounting to the surface on which the modular sign is mounted. The last letter is optionally attached to a termination block which supports the modular sign from the termination block's end of the sign, and is similarly ruggedly mounted to the mounting surface. Alternatively, the sign may be canti-levered from one end. The circuit design allows for a very long string of symbols Typically, this type of modular sign system is suitable for house signs, street signs, and information and directional siuns.

. Complete signs as single units, rather than having the sign composed of individual character element s placed together as in the modular system mentioned earlier is t he preferred system to provide t he advert ising sign industry wit h t he flexibility to scan i nto t he computer most of the ava i lable hand-drawn or pri nt ed art work, for example, or by digit izing, as is well-known. Al ternat ively, computer-designed artwork may be di rectly used The artwork is converted by standard graphical program algorithms, into a machine parts placement program, e g. , for use by nu merical-controlled ( N-C) SMT parts placement machineiy, and into a corresponding N-C "wiring" program The N-C "wiring" machine paints the electrical circuit with a conductive polymer onto the non-conductive surface of a printed-circuit-board-type material. Then the N-C parts placement machine places the SMT parts on the surface of the electrical circuit . The LED' s are cemented to t he circuit with the conductive polymer. Utilizing one-side surface-mount technology in the sign industry provides economical sign-making technique. Alternately, holes could be punched where t hrough-hole LED' s would be placed an a placement machine from the rear would place in the positional holes an join the conducting legs and when necessary jumpers together BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 A is an LED-formed character with Zener diodes added; FIG. IB is a single group of LEDs shunted by a Zener; FIG. 1C is a "looping" LED-formed character with Zeners; FIG. ID is an electronic diagram of FIG. 1C; FIG IE is a sample "looping" character foil pattern; FIG. IF is an electronic diagram of a voltage increaser; FIG. 1G is a dual "looping" LED-formed character with two power supplies, providing redundancy; FIG. 1 H is a block diagram of redundant LED strings; FIG. 2 shows a go/no-go current adjustment circuit; FIG. 3 A illustrates a blinking-off circuit; FIG. 3B is a schematic illustration of a location-announcing sign system; FIG. 3C is a logical flow diagram of one embodiment of the location-announcing sign system; FIG. 4A is a set of battery-discharge characteristics; FIG. 4B is a corresponding plot of battery discharge time versus discharge rate; FIG. 5 A shows a current source including a current multiplier which may be used to program the operating current of a string of LED's; FIG. 5E shows a negative-temperature-coefficient current source; FIG. 5F shows a variable-temperature-coefficient current source; FIG. 5G shows a variable-temperature-coefficient current source; FIG. 5H shows two positive-temperature-coefficient current sources; FIG. 51 shows a saturation detector added to a current source; FIG. 6A shows one current source used with a current-mirror amplifier to power multiple LED strings; FIG. 6B shows one a current-mirror amplifier used as a current-splitter to power two parallel LED strings; FIG. 7A shows a power supply implementation; FIG. 7B shows an alternative power supply implementation; FIG. 8 A shows a prior art parallel-LED circuit; FIG. 8B shows a series-LED power supply implementation; FIG. 8C shows a second series-LED power supply implementation; FIG. 8D shows details of a series-LED power supply of the second type; FIG. 9A shows a directional sign, including rear solar panel; FIGS. 9B and 9C show a second sign with rear solar panel; FIG. 10 shows an LED cat's-eye type sign; FIGS. 11 A-l 1C show novel wide-viewing angle LED traffic signal; FIGS. 12A andl2B show the novel SMT LED package molding design; FIG. 13 A- 13E show a self-sufficient-character design; FIG. 14 is a modular sign system using SMT-package molded LED's; FIG. 15 A illustrates a possible custom LED package; FIG. 15B illustrates further possible custom LED packages; FIG. 16 illustrates "greatest-common-denominator" character segments.

FIG. 17A is a multiple -LED lead-frame for parallel LED connections; FIG. 17B shows a multiple-LED lead-frame for series LED connection; FIG. 17C shows a multi-colored LED sign; FIG. 17D shows a multi-alignment LED sign; FIG. 17E shows a further multi-alignment LED sign; FIG. 18 illustrates a directional sign, using custom LED's; FIG. 19 illustrates a bi-directional sign, using custom LED's.

FIG. 20 shows an LED string under command-receiver control.

D ESCRI PTI ON OF THE PREFERRED EMBODI MENTS The present invention discl oses a novel sign system suitable for use in many appl ications, accordi ng to t he features selected to be i ncluded in t he part icu lar sign for the particular application which can be realized as modular or dedicated signs The pri nci ples and operation and various features of an illuminated sign or signal according to the present invention wil l be described with reference to the drawings, to explain how to use the invention to achieve the goal of an improved sign system with respect to readability, reliability and efficiency.

The electrical circuitry will first be considered, by way of which, the design goal of an energy-efficient sign system is realized . The circuitry includes use of current sources, to provide circuitry with a very wide power-supply operating-voltage range, Zeners shunting groups of LED's in a series-string connection of LED's, for protection against loss of message in the case of an LED failing open; looping LED string layout, for use in conjunction with the Zeners; blinking-off circuitry, uniquely powered by the series-string LED current; automatic voltage- selection circuitry in a DC-DC converter for use with battery- operation.

Following this, the novel LED and LED assemblies designs, which further contribute to an energy efficient sign system, through the effective use of electrically-generated light energy, will be discussed . Novel features in the use of "greatest-common-denominator" LED-group packaging; mixed colors of LED's in one package to achieve a desired spect ral response characteristic; custom LED packages with light radiation patterns which are non-symmet ric wit h respect to the LED die center-line, and non-perpendicular (i . e. , non-normal ), wit h respect to the LED package seating plane; integral power sources, e. g. , solar cells on house signs, and on LED display strips, with backu p batteries, as well as solar-cell with batteries for remote locat ions Referring now to the drawings, Figure 1 A illustrates a letter 100 formed by connecting a string of LED's 102 The plastic lenses of LED's 102 provide readability in the daytime in ambient light. This is unlike the prior art matrix-array LED signs, in which, without electrical power applied, no character is visible Here, however, LED's 102 alone are sufficient to provide a recognizable character Each LED 102 includes an LED chip (not shown) in a preferably molded plastic lens-shaped package LED's 102 are mounted in a panel (not shown), with the packages protaiding through the panel. LED's 102 are mounted in the panel to form a pattern. The resulting pattern is recognizable in daylight without requiring application of power to the LED's 102. Readability is enhanced due to the three-dimensional structure of the package.

LED's 102 are connected in series, each group of four LED's 102 are shown to have a bracketing Zener diode 103 connected across the group of four LED's 102 in such a manner that Zener 103 is reverse biased. The forward voltage of an LED 102 is normally about 1.8V to 2.0V, depending on the color, hence specific semiconductor material which is employed in the fabrication of LED 102 The breakdown voltage of Zener 103 is chosen to exceed the maximum forward voltage drop of the string of LED's 102 to be bracketed by Zener 103. Thus, for the example of four LED's 102 bracketed by Zener diode 103, the minimum Zener breakdown voltage must be greater than, say 8V A 9V, ten per cent tolerance, Zener could therefore be used.

A current setting resistor 105 is shown connected in series with string of LED's 102. A first connection 106 and a second connection 104 are the positive and negative supply connections, respectively. In a modular system, one option would be to provide a fixed supply voltage between the supply rails Then each modular letter could have its internal dropping resistor to program the current inside the individual letter module. Thus, a module using fewer series-connected LED's 102 would have a larger dropping resistor (not shown). This would be a factory-installed resistor for the modular sign system, with pre-manufactured modules.

Figure IB shows an improved physical construction and wiring method for the character of Figure I A The improvement in Figure IB is called "looping", due to the resulting wiring pattern appearance In Figure I A, LED's 102 were physically all in a row, and wired in series according to the physical sequence If one LED 102 in a bracketed group of LED's 102 would fail, a significant portion of the character would go dark In Figure IB, however, the wiring pattern is not in the same sec]uence as the physical placement of the LED's 102. In Figure IB, we have five "regions", 111-115, of the illustrated character, each region containing four LED's 122, labeled "A" through "D" As shown in the electrical wiring diagram below the character, each group of LED's 122 labeled "A" thorough D" is connected in series and bracketed by a Zener 123 Now, from the physical arrangement, if an LED 122 in bracketed group "A" fails, the character does not lose a whole region, as would be the case in the arrangement of Figure 1 A Rather, every fourth LED 122 goes dark, resulting in a more readable and recognizable character with the arrangement of Figure IB than with arrangement in Figure 1A.

Figure 1C is a sample "looping" character foil pattern 130. Pattern 130 is designed so that all LED's 132 are inserted with similar orientation, providing ease of assembly. Pattern 130 is also designed without cross-overs, also implying low assembly cost. The reason for the choice of name "looping" is readily apparent from the figure.

Figure 1 D is a dual "looping" LED-formed character 140 with two power supplies, providing redundancy Character, 140, in Figure ID, contains two strings, 141 and 142, of LED's 155. LED's 155 of strings 141 and 142, labeled "A" and "B", respectively, alternating along the length of character 140 LED strings 141 and 142 are powered by the AC line current as a source, 146. String 141 is shown powered through a first rectifier 143, by the positive half-wave rectified half-cycle of the AC line waveform. String 142 is shown powered through a second rectifier 144 by the negative half-wave rectified half-cycle of the AC line waveform Current limiting is provided by a current-limiting resistor 145. While one resistor is shown, shared by first rectifier 143 and second rectifier 144, two separate resistors 145 (not shown) may alternatively be used Also, a pair of filter capacitors 147 and 148 are shown in Figure ID In this redundant character construction, the redundant, separately- powered, LED strings 141 and 142 assure that in the event of a failure of one of LED's 155 as an open circuit, the character will still be readable, albeit with a "density" of the illumination of one-half of the "density" of the nominal design More than two strings 141 and 142 of LED's 155 may be similarly provided, wit h separate power sources, including using all positive, or all negative, rectified power supplies, or some of each polarity If a character 140 of a wide or tat" configuration is desired, with not one. but multiple LED's 155 at each "position" along the length of a character, then the redundant strings may each contain one LED from each "position" The redundant LED strings 141 and 142 may further include series-connected strings, 141 , 142, 150, of LED's 155 in separate characters, 140a - I40n, of each character, corresponding, in effect, to a "position" of the case just described Figure 2 shows a go/no-go current adjustment circuit, 200, connected in series with character string, 206. Current adjustment circuit 200 includes a variable current-setting resistor, 205; a fixed resistor 202 in parallel with a LED 201 similar to LED 1 02 of Figure 1 A, a fixed resistor 204 in series with the parallel combination of LED 201 and resistor 202; and, an LED 203, in parallel with fixed resistor 204 in series with the parallel combination of LED 201 and resistor 202. LED 201 is selected to have a lower forward voltage than LED 203. For example, LED 201 is selected to be an AlGaAs, 6 7nm, red LED, such as Hewlett-Packard (HP) HLMP-D I O l , with a forward drop of 1 .8V at 20mA, and a voltage of about 1 .5V at I mA, and about 1 .6V at 5mA. Resistor 202 is designed for a value such that the minimum desired lamp current equals the current in LED 201 at t he forward voltage of LED 201 corresponding to the forward current, plus the current in resistor 202 with that value of LED 201 forward voltage across resistor 202 For example, choose minimum LED stung current equal to 1 5 Ma If the forward voltage of LED 201 at I mA is 1 .5V at 1 mA, and I mA will be in LED 201 , then 14mA will be flowing in resistor 202 Resistor 202 will have a value of 1 .5 V/ 1 4mA, approximately equal 100-ohin Now select LED 203, for example, HLMP- 1 52 1 , green, 569nm, GaP, with a forward drop of 2 I V at 1 0mA, and about 1 .7V at 1 mA. Select the maximum current to be 20mA. Then select resistor 204, so that with LED 203 just lit, at 1 .7V, the current in resistor 204 will be 1 9mA. Then 1 .7V across LED 204 minus 1 .6V across LED 201 gives 0 I V across resistor 204, for a current of about 20mA in resistor 204, so resistor 204 has a value of about 5-ohms.

Now. when variable current-setting resistor 205 is set to a high value, the current flowing from posit ive supply connection 106 through the current-adjustment circuit 200 and character LED string 206 to negative supply connection 104, will be less than 1 5mA, and both LED 201 and LED 204, will be off As the setting of variable resistor 205 is advanced, and the current increases, first red LED 201 will light at about 1 5mA in LED string 206, but green LED 203 will be off. As the setting of variable resistor 205 is further advanced, and the current further increases, at about 20mA in LED string 206, green LED 203 will also light. This then indicates the maximum allowed current in LED string 206 has been reached. For safe operation, the setting of variable resistor 205 is backed off until about mid-way between the points where red LED 201 came on, and where green LED 203 came on. This results in a nominal current in LED string 206, of about 17, a safe room-temperature value The example given hereinabove is merely an example and the figures are therefore approximate. In a final design, temperature variations and tolerances of the diode forward voltages and resistor tolerances must be taken into consideration in order to remain safely within the device manufacturer's absolute maximum ratings for the LED string current.

The current-adjustment circuit of Figure 2 may be used internally with each character module, or for groups of modules, in a modular sign system, or for sections of a sign in a non-modular sign system In addition, it will be appreciated that current setting resistors 105 and 205 may be either fixed resistors or variable resistors; or, a variable resistor may first be used to adjust the operating current, and then a fixed resistor of comparable value to the adjusted resistance value may be substituted for the variable resistor Figure illustrates a blinking-off circuit 300 of the present invention LED's 102 are pai of a series string of LED's 102 forming a character in the LED sign of the present invention. Now, it is desired to cause the portion of the sign represented by LED's 3 16-319 to blink on and off periodically, for increased noticeability. For example, it may be desirable to make easy the identification of the building for emergency personnel, as discussed above A switch 3 13 is closed to enable operation of bli nking circuit 300. Blinking circuit 300 uses a bli nki ng LED 31 0, such as an Everlight Model F336 family blinking LED, which i ncludes ci rcuit ry in LED package 3 10 causing LED 3 10 to bl ink at a pre-determined rate and duty ratio when blinking LED 3 10 is powered by a steady DC supply When switch 313 is closed, transistor 314 turns on, due to base current flow in a first resistor 312, which is charging an initially-discharged capacitor, 31 1 , turning off LED's 316-319. A second resistor 309 establishes a minimum turn-on threshold current requirement for the current in first resistor 3 12, i n order that transistor 314 will be turned on. First resistor 309 and second resistor 3 12 are typically 1 200-ohms and 360-ohms, respectively. The breakdown voltage of a Zener 315 is selected to assure that capacitor 31 1 , typically l microfarad, will charge to sufficient operating voltage for blinking LED 310 to operate. The minimum number of LED's 310 to be shunted to meet this requirement is about three or four LED's 310. Without capacitor 31 1 , typically l microfarad, the current in blinking LED 310, will be too small for normal blinking operation, due to the current-limiting of the base current to transistor 314, provided by series base resistor, 312.

When blinking LED 310 blinks on, capacitor 31 1 is completely discharged When blinking LED 3 1 0 turns off, first resistor 312 rapidly recharges capacitor 31 1 , so the on time of transistor 314 is only slightly longer than the on time of blinking LED 310. The on and off times of blinking LED 3 10 are determined by the circuitry in blinking LED 310. The pulse rate is about 2Hz. Once capacitor 3 1 1 has been charged to the operating voltage of bl i nki ng LED 310, the displacement current in capacitor 31 1 will be smaller than the transistor turn-on threshold current established by second resistor 30 Thu s, each time blinking LED 3 10 turns off, t ransistor 3 1 4 base current turn-on threshold requirement will not be met until blinking LED 310 internal timing circuitry turns on blinking LED 310. When capacitor 31 1 is charged to the operating voltage of blinking LED 310, blinking LED 310 operates approximately according to the data sheet frequency and duty ratio.

Zener diode 31 has a further benefit inasmuch as when the simple current-setting circuits of Figures 2 and 3 are used, by way of example, significant variations in the voltage across current-sett ing resistor 205, will not result due to the blinking-off of part and LED string by shorting some LED's 102 (Figure 3 ), resulting in blinking brighter of the other LED's 102 in the LED string. The breakdown voltage of Zener diode 315 is selected to be slightly less than the sum of the forward drops of the LED's being shunted by the blinking-off circuit, so that when transistor 314 turns on, the voltage drop across the group of LED's will be only slightly reduced, but still sufficiently reduced to extinguish the group of LED's. It is desirable for example, to simply rectify the AC power line, for example, with a half- wave rectifier 301 for the simplest off-line power supply realization, and to power the LED string in the sign system from as high a voltage as possible. Furthermore, a reverse voltage protection diode 330 is shown in Figure 3 for protecting the circuit against reverse voltage.

Figure 4A is a set of battery-discharge characteristics for a rechargeable battery. The curves shown are for Yuasa type NP valve- regulated lead-acid batteries, normalized to a one Ampere-hour battery The above batteries are also known as "sealed-lead-acid" batteries, but actually have a vent to let out gas for safety, so pressure does not build up inside the battery. Looking at the 6V battery data, for the I CA curve, the discharge curve for a discharge current in amperes equal to one times the capacity in ampere-hours, the battery voltage falls to 5.5V after about 25 minutes. At 0.6CA, the battery falls to 5.5V after about 45 minutes; at 0.4CA, about 90 minutes; at 0.2CA, about 220 minutes; for 0 I CA, about 540 minutes, for 0.05CA, about 1200 minutes.

Figure 4B is a corresponding plot of batteiy discharge time versus discharge rate for this data.

As can be seen, the batter)' capacity is available at the twenty-hour rate, and less than half the capacity is available at the one-hour rate From this, it is clear that the most efficient use of the battery results from a lower discharge rate, i.e. , from the use of a high-resistance load to increase battery capacity In a case where many LED's are to be powered, as in the LED sign application, it i s better to use batteries in series, at higher voltage and lower discharge rate, than in parallel at a low voltage and at a high discharge rate. Thus, in the sign system of the present invention, the choice is made t o operate with as high a battery voltage as possible, and to mi nimize t he voltage drop across dropping resistors 105 of Figu re I A or resistor 205 of Figure 2.

The preferred power sources for t he LED sign system of the present invention may be a battery supply, preferably using rechargeable batteries, or may be an "off-line" power supply, operating from an AC power line Additional, less-usual power sources may be a solar-powered energy source, or may even include a windmill or any other power supply driven by a force of nature.

It will be appreciated that the voltage regulation of the aforementioned power sources is not ideal Battery voltage drops as the battery' is discharged, as can be seen in Figure 4A. Improvement i n the regulation of the battery output voltage would require the additional expense of a voltage regulator (not shown). The regulation of an off-line power supply depends on the expense of the power supply. Since it is desirable to provide a low-cost sign system, it is desirable to provide a method of powering the LED's that is both efficient, and is tolerant of a poorly- regulated power supply.

Further, the light output of an LED is a function of the forward current of the LED. The LED forward current, like the forward current of any diode is a strong function of the diode forward voltage. It i s desirable therefore, to provide current regulation of the LED forward current, and not to regulate the forward voltage applied to the LED. To this end, field go/no-go current adjustment circuit 200 of Figure 2 discussed above is provided .

Recognizing the problem of the regulation of t he power sou rce to be used with an LED sign system, in view of the i mmediately preceding discussion, it is also desirable to provide a variable, adju stable current source, which will be substantially unaffected by the variations in battery voltage wit h t he st ate of discharge of the battery, or by variations in the output voltage and ripple of a poorly-regulated or poorly-filtered off-line power supply This problem is addressed by the circuitry shown i n the d rawings Figures 5A-5 I Figure 5 A shows a current source, 50/ , which may be used to program the operating current of a string of LED's. An AD592 current source 501 requires a minimum operating voltage of about 4V, and tolerates a maximum voltage drop of 30 volts. In this range, AD592 source 501 provides an output current of 1 microampere times the ambient temperature in degrees Kelvin. Thus at 25 degrees C, the output current is 298.2 Ua, nominal. The temperature coefficient of the output current is thus approximately positive one-third of one per cent per degree C, at about room temperature. The light output of LED's (not shown) operating at constant current is known to have a negative temperature coefficient. This fact is stated for example, in HP Application Brief 1-012. The temperature coefficient of light appears to be about -1%/degreeC. Thus the positive temperature coefficient output current of the AD592 is beneficial in partially temperature-compensating the LED light output versus temperature. However, the approximately 300 Ua output current at room temperature is much less than the desired, say, ten to twenty milliamperes forward current usually used with LED's (not shown). To increase AD592 source 501 current output to a more usable level, a current amplifier 510 is included in current source 501 of Figure 5 A. Current amplifier 5 JO consists of transistors 502, 503, and 505. In this circuit, a current-setting resistor 205 is adjusting the ratio of the collector currents of transistors 502 and 503. Transistor 503 has an emitter area of N times the emitter area of transistor 502. If the value of current-setting resistor 205 is zero, then the output current fed to circuits 200 and 206, will ideally be (N+l) times the output current of AD592, 501. However the output current will be less than this, since the reference collector current in transistor 502 will be reduced by the amount of the base current required in emitter-follower transistor 505. This problem can be solved by the use of a MOSFET in place of bipolar transistor, 505. This improvement is shown in Figure 5D, with a MOSFET 540 replacing transistor 505 of Figure 5A. A Zener 541 is added to protect MOSFET 540 from damage due to excessive gate-source voltage. For non-zero values of current-setting resistor 205, the output current will be the output current, Is, of AD592 current source 501 multiplied by a factor of ( 1+ N exp (R205Is q/Kt) ), where Kt/q = 0.02569 at 298K.

An alternative device to the AD592 current source 501 of Figure 5 A, is the LM134520 shown in Figure 5B The device of Figure 5B uses an external current-setting resistor Rset 205. and be programmed for a 25 degree C output current of between luA and 10mA. A positive-temperature coefficient reference voltage of 64m V at about 25 degrees C is impressed across the current-setting resistor 20 Circuit 516 works with a voltage of from IV to 40V L 134 current source 520 can be programmed to provide a larger value output current than AD592 current source 501 of Figure 5A, thereby requiring less current amplification to reach a final LED-string current in excess of 10mA.

These circuits for delivering a greatly-increased replica of an input reference current, although included in the general category of current-mirror-amplifier circuits, to be further discussed below with reference to Figures 6A and 6B, for the purpose of the claims, are herein defined as "current-multiplier" circuits.

Another alternative current source is shown in Figure 5C. Here, a junction field-effect transistor (JFET), which is a depletion-mode device has its drain current controlled by a current-setting resistor RS 205. A negative gate-source voltage IDRS is developed across RS 205 decreasing the drain current of a JFET 530 below its zero-bias value of 1DSS, the value for RS equal zero. JFET 530 may be selected for a desired 1DSS, or the drain current of a JFET with IDSS(min) greater than the maximum required LED string current may be reduced by use of RS 205. The temperature-coefficient of ID will be a function of VGS, however.

Figure E shows an especially preferred embodiment with a very stable, negative-temperature-coefficient current source Such a current source has a temperature coefficient of about -0.33%/degC, nominally, and is very insensitive to input power supply voltage variations. An AC line voltage 558 such as a 220V AC line, is rectified in a bridge rectifier 557, and filtered by a capacitor 556 to provide a high-voltage DC operating voltage to power a LED string 206. Optionally, a DC current source (not shown) may be used, thereby alleviating the need for rectifier 557 or, if desired, capacitor 556. A resistor 555, typically 330K-ohms, provides a reference current to a first diode 553, a second diode 554, and a transistor 552, as well as base current to a high breakdown voltage transistor 551 First diode 553 and second diode 554, are typically I 4007. Transistor 552 is typically 2N3904, and high breakdown voltage transistor 551 is typically a B U902 The circuit of Figure 5E provides a very stable output current of between 10 to 30 inA, for LED strings 206 consist ing of 1 0 to I 50 LED's. The circuit may be readily constructed to accommodate a power supply operating voltage range of from 4V to 600V Preferably, a fuse 548 is used to prevent electrocution. Furthermore, a resistor 549 is included to limit current entering into capacitor 556.

Figure 5F shows a current source 565 with adjustable temperature coefficient of output current, as well as adjustable nominal output current A regular "Zener" diode of 5 6V usually has a zero- temperature-coefficient breakdown voltage. This is because Zener breakdown effect, which is the breakdown mechanism below about 5.6V has a negative temperature coefficient, while avalanche breakdown effect which dominates above about 5.6 V has a positive temperature coefficient. At about 5.6V, the cross-over occurs, resulting in about zero-temperature coefficient (zero-TC) of breakdown voltage at about 5.6V. In Figure 5F, a current source 565 biases a zero-TC Zener 560, and provides sufficient base current for a transistor 561 operating at the desired LED-string current. Transistor 561 has a base-emitter voltage VBE, which has a negative temperature coefficient in the neighborhood of one-third per cent per degreeC. Thus, the voltage at the emitter of transistor 561 has a slight positive temperature coefficient. The combination of a transistor 562 with voltage-divider resistors R l 563, and R2 564, provides a "VBE-multiplier" circuit. When the values of divider resistors 563 and 564 are selected for a divider string current that is large enough to be substantially unaffected by the variations of base current of transistor 562 with initial current gain, hFE or beta, value, and with temperature variations of beta, then the collector-emitter voltage of transistor 562 will be its VB E at its operating collector current, multiplied by a factor of ( R2+ R I )/R I . Flence the name " VBE-multiplier" . The voltage at the emitter of transistor 562 may be adjusted to be much less than the voltage of Zener 560, and since the VBE-multiplier has a negative-TC voltage, as does VBE of transistor 561 , the voltage across a current setting resistor 205 can be adjusted to have a large positive temperature coefficient. The adjustment of the S VBE-multipIication ratio provides the temperature-coefficient adjustment capability. Thus resistors R l 563 and R2 564, serve as temperature-coefficient adjustment resistors in the variable temperature-coefficient current source of Figure 5 F. Current-sett ing resistor 205. then provides the init ial 25 degreeC current adjustment capability. A variation of t his circuit could employ an electronic Zener-equivalent integrated circuit, such as TL4 I , wit h a 2.5 V Zener voltage, for lower minimum operating voltage The required voltage across current-setting resistor 205 would have to be smaller also With a 5.6V Zener, about 0.8V is required across resistor 205 to provide about + l %/degreeC temperature coefficient output current. With a 2.5V Zener, about 0.4V would be required across resistor 205 to provide about + l %/degreeC temperature coefficient output current.

Although in most of the figures, a variable current-setting resistor 205 is shown, a fixed resistor may be used, with its value chosen by design, or selected based on voltage measurements in the current-source circuit. For example, in Figure 5F, the value of a fixed resistor for 205 may be chosen depending on the measured actual value of the voltage of nominally 5.6Volt Zener 560. Rl 563 and R2 564, may also be similarly selected.

An example set of component values for the circuit of Figure 5F is as follows. Zener(560) = 5.6V; transistors(561 and 562) = 2N3904; R2(564) = 1 500-ohms; R l (563) = 330-ohms; current-setting resistor(205) = 82- ohms. This provides approximately 1 0mA at about 25 degreesC, with approximately + l %/degC temperature coefficient in the temperature range of -25C to +75C.

A variation on the adjustable temperature-coefficient current source of Figure 5F is shown in Figure 5G. In Figure 5G, the VBE- multiplier is operating with a smaller collector current, hence a smaller divider current is needed. A resistor 565 programs the VBE-multiplier current while a transistor 566 carries most of the LED-st ring current . Like above, the combination of a transistor 562 with voltage-divider resistors l 563, and R2 564, provides a " VBE-multiplier" circuit. When t he values of divider resistors 563 and 564 are selected for a divider string current that is large enough to be substantially unaffected by the variations of base current of transistor 562 with initial current gain, liFE or beta, value, and with temperature variations of beta, then the collector-emitter voltage of transistor 562 wil l be its VB E at its operating collector current, multiplied by a factor of ( R2+ I )/R I Hence the name "VBE-multiplier" .

Figure 5 H illustrates another positive-temperature-coefficient current-source design approach, which is well-suited to modular applications, or to the use of LED's requiring various positive-temperature coefficients of forward current, in order to provide zero- temperature-coefficient light output . A LM 1 7-type, or similar band-gap voltage regulator 560 provides a zero-temperature-coefficient reference voltage Band-gap voltage regulator 560 is powered from an appropriate low-voltage supply, LV. An LED string 206 returns to high- voltage supply HV 106. The LED current is the collector current of a transistor 561 . Current-programming resistor Rset 205, is connected from the emitter of transistor 561 to a negative supply 104. In one implementation, the base of transistor 561 is connected directly to the zero-temperature-coefficient, I 25V-nominal output of voltage reference 560. Since the temperature coefficient of VBE of transistor 561 is about -2mV7degreeC, and VBE is about 650mV, the emitter voltage will be about 6000mV, and the temperature coefficient of LED string current, the collector current of transistor 561 , will be about 2/600=+0.33%/degreeC In the second embodiment shown in Figure 5H, the Rl and R2 resistor divider (not shown), provides a reduced voltage to transistor 561 base, of about 0.9V, therefore resulting in about 200mV at the emitter of 561 , and an LED current having a temperature coefficient of about 2/200=+ 1 %/degreeC. Figure 51 shows the addition of a saturation detection circuit 568 to a current source transistor 561 of the first Figure 5H example. Saturation detection circuit 568 consists of a differential pair of transistors P I and P2, having a series of emitter diodes Dl and D2, respectively for reverse-breakdown voltage protection for P2 provided by D2, and the resulting D2 offset-voltage cancellation provided by D l RLT provides the bias current for the differential pair. In normal operation, a supply voltage 106 will be great enough to hold the collector voltage of Q l 56 1 , above the base voltage of Q l 561. so that P2 emitter-base junction will be reverse-biased and P2 collector current will be zero If the high voltage supply voltage is too low, then for the case of the collector voltage of Q l 561 approximately equal to the base voltage of Q l 561 , P2 will conduct collector current, sourcing I output I This current may be applied to a following circuit for the control of the value of HV 106 an intermediate coupling circuit may be required, such as illustrated, in which Q2. the base of which is driven by I output I, serves as a switch to turn on Dopto 569, an LED in an optocoupler, with Rlim providing limiting of Dopto 569 LED current to an acceptable value For the case of RB=RLT.\07V/(LV-27V), the differential-pair "voltage- comparator" offset voltage will be approximately zero. The saturation detection circuit is a possible alternative to the current sensor circuit 87 in Figures 8C and 8D, below Figure 6A shows a bias-current system using one adjustable temperature coefficient current source of Figure 5G to bias a multiplicity of LED strings 206. A go/no-go current adjustment circuit 200 is used to adjust a current-setting resistor 205 to the appropriate LED-string 206 operating current at about 25 degreesC. This current flows in LED string 206. A current mirror amplifier (CMA) 600, provides additional current source outputs, using the collector current of a transistor 566 as the CMA input reference current. A transistor 601 with an emitter resistor 602, together with a transistor 603, serve as a voltage reference. The voltage from the positive supply line to the base of transistor 601 is the reference voltage. Emitter-follower transistor 603 provides a low output impedance for the voltage reference. When a transistor 604A with an emitter resistor 605A is connected across the reference voltage, then if transistor 604A is identical to transistor 601, and if resistor 605A is also identical to resistor 602, then the collector current of transistor 604A will be substantiequal to the collector current of transistor 601. However, for our current source, we desire the collector current of transistor 604A to be about 25% greater than the collector current of transistor 601 Therefore the value of resistor 605a should ideally be 0.8 times the value of resistor 602. and the emitter area of transistor 604Λ should ideally be 1.25 times the emitter area of transistor 601 If the voltage drop across resistor 602 is designed to be sufficiently large, however, the current matching error due to using the same emitter area for transistors 605A as for transistor 6 1, can be made acceptably small. For example, with about 05 volt across the emitter resistors, and equal transistor emitter areas, for an output current of 1 25 times the input current, the error shou ld ideal ly be about 1 %. I n practice, t he transistors will not be identical, and the resistors will not be identical There wi ll be additional errors due to the base current of transistor 603 "subtracting" from t he collector current of transistor 601 , and t here will be an error due to t he Early effect, i .e. , due to t he col lector-emitter voltages of the reference transistor 601 and output transistors, 604n ( not shown) not being identical . I ncreasing the drop across the emit ter resistors 602 will help to reduce t he Early voltage error. Current-mirror amplifier 600 providing multiple outputs may be used with any of the current sources described above with a current ratio of 1 : 1 , by simply inserting current -mirror amplifier 600 in series with a positive supply connection 106, of the current source which provides the reference current . Use of the current mirror 600 would be especially beneficial with of a battery power supply, in which case multiple strings of LED's 206 may be employed, operating at lower voltage than the voltage provided by AC line power supply operation.

Design considerations to be taken into account include the supply voltage and the number of LED's to be driven. It is desirable for example, to simply rectify the AC power line, for example, with a half- wave rectifier 301 , shown in Figure 3, for the simplest off-line power supply realization, and to power LED string 206 (Figure 6A) in the sign system from as high a voltage as possible. The typical 50Hz or 60Hz AC power line frequency is sufficiently high to give the appearance of continuous illumination of LED strings 206 with a non-filtered power supply. The power supply expense is minimal. Also, the lack of a filter capacitor improves safety of the circuit, since there will be no stored charge in a capacitor charged to high voltage of approximately the peak value of the AC power line voltage To maintai n efficiency, as low a voltage as possible should be dropped across the current-providing circu it ry, where the current- providing circuitry may i nclude a current-setting resistor 205. a current source, a go/no-go current adjustment ci rcuit 200, and a current-mirror amplifier 600 circuit for t he case of multiple LED strings 206.

Use of current-min or amplifier 600 to replicate the current programmed in one LED string 206 clearly represents a cost-saving, compared with the expense of providing duplicate current-providing circuitry for each of a multiplicity of LED strings 206.

Figure 6B shows a current-mirror amplifier used as a current- splitter 610 to power two parallel L ED st rings 206 For example, in a special- module application, a special module contains a module circuit ry 620 consisting of a current-splitter 610. Current-splitter 610, In turn, is a current mirror consisting a first transistor 601 and a second transistor 604 with a first emitter ballast resistor 602 and a second ballast resistor 605. Module and current- splitter input current 61 l a, is divided into current-splitter output currents 612 and 613, which tlow into the anode end of LED strings 206a and 206d, respectively. The current division ratio depends on the design of current mirror 610, according to the current mirror design principles discussed above. Current-splitter 610 output currents 612 and 613, are summed by the interconnection of the cathode ends of LED strings 206a and 206d to provide a module output current 61 1 b, of a value equal to module input current 61 l a. In an example application, two colors of LED strings 206 are to be used in one special module with each color required to operate at a different forward current, with the sum of the two currents equal the special-module system string current. The design precaution which must be observed is that for proper operation of current splitter 610, the voltage drop across LED string 206a must always be greater than the voltage drop across LED string 206b, in order that second transistor 604 will not saturate Figure 7A shows a power supply implementation incorporating a non- filtered rectifier power supply for the reference for the current source which powers LED string 206. A simple current source is shown, consisting of a transistor 561 , a current-setting resistor, 205, a reference Zener 560, and a bias resistor 703 With a 220-volt AC power line, resistor 703 must be a large-value resistor to limit the current in reference Zener 560. Due to the large voltage drop across resistor 703, there will be a large power loss in resistor 703, which therefore must also be an expensive power resistor.

The use of the non-filtered supply of Figure 7A, with a half-wave rectified voltage waveform at the top of resistor 703, results in an average voltage less than half the voltage of a capacitor-filtered supply voltage resulting in less than one- quarter of the power dissipation in resistor 703, for the same peak current in resistor 703 Current source transistor 561 will then provide a pulsating peak current to LED string 206 I f the flickering is noticeable or objectionable with the half-wave rectified current, then the addition of a rectifier 701 and a filter capacitor 702 provides smoothing for the voltage across LED string 206, and hence for the current in LED string 206. Capacitor 702 may be connected either to the negative supply line or across LED string 206, as appropriate, by connections 702a or 702b, respectively. Furthermore, a capacitor 710 may be added to provide a DC reference voltage at the base of transistor 561 , and hence to provide a DC current source to LED string 206.

Figure 7B shows an alternative power supply implementation Here a battery 704 is used to replace the high-voltage AC power source. A "switching power supply" is used in which battery 704 voltage is switched by a control circuit or oscillator 705, and applied to primary 707 of a transformer 706. Switching power supply techniques are well-known. Transformer 706 has two secondaries, a high-voltage winding, 71 1 , which replaces the high voltage AC power source, and a low-voltage winding 708. Low-voltage winding 708 provides the reference voltage for the current source which includes a transistor 561 and a current-setting resistor, 205. Use of low-voltage winding 708 eliminates the need for power resistor 703 of Figure 7A with the power loss of power transistor 703. This is especially important for battery operation In Figure 7B, the secondary voltage of winding 708 is rectified by a rectifier 709, and optionally filtered by a capacitor 710 Since typical switching power supply frequencies are much greater than the 50Hz or 60Hz AC power line frequencies, optional capacitor 702 would normally not be needed to suppress flickering of LED string 206. If capacitor 702 is included, it may be connected, as discussed above, by a connection 702a or a connection 702b.

Figure 8A shows a prior art parallel-LED circuit, with each LED 83i\ having a series dropping resistor 82n Assume 1 70 LED's, each with 1 .8V drop, operating from a 2.4V battery The efficiency depends on the design LED current, and for 7 2mA, may calculated to be about 58% due to t he power loss on the series dropping resistors Figure 8A also shows several reverse-voltage protection diodes 80a-80n Since each LED 83n has its own dropping resistor, each L ED 83n requires a separate reverse- voltage protection diode This is unlike the case of the series-st ring LED connection of the present invention, wherein one reverse-protection diode suffices for the whole series LED string. This is illustrated by reverse-voltage protection diode 330 of Figure 3 (not shown in Figure 8A).

Figure 8B shows a series-LED power supply implementation. Here, for 1 70 LED's connected in series, operating at 7.2mA, a transformer tap 84n is selected to provide approximately the required total minimum operating voltage for an LED string 206 in series with a current source 85. The efficiency of power transfer from a battery (not shown) to LED string 206 approximates the efficiency of the switching power supply, consisting of the combination of an oscillator 705 and a tapped transformer 806, which efficiency may be about 85%. The use of a tapped transformer 806 limits the power dissipation across current source 85, which is analogous to the prior art dropping resistors 82n of Figure 8 A, thus resulting in the increased efficiency, as well as reducing the required power rating and heat-sinking for the current-source output transistor.

Figure 8C shows an alternative to the configuration of Figure 8B. Here, a secondary current sensor 87, provides feedback to a selector, 86 Selector 86 automatically selects the appropriate primary tap to provide the minimum required secondary voltage to permit the desired secondary current to flow Thus, the dissipation in a current source 85 is minimized Figure 8D shows details of a preferred embodiment of a series-LED power supply of the type of Figure SC A sensor circuitry 87, as in Figure 8C, includes a secondary-current sensing resistor 871 a recti fier 872, a filter capacitor 873, and a bleeder resistor 874 The secondary current, whether DC, or including also AC components, is converted by resistor 87 1 to a corresponding voltage. A result ing rectified DC voltage is available to excite an LE D 876 contained in a optocoupler 875.

LED 876 is being used, in effect, as a switch, such that when the current is sufficient to turn on LED 876, a "digital " signal will be transferred through optocoupler 875 to a selector circuitry 86 on the primary side of a transformer 806, as in Figure SC As described, the light generated by LED 876, couples a "digital" signal through a phototransistor 877 to the primary side of transformer 806, providing a positive input to pin 1 3 , the EN ABLE input of a C D40 1 7 counter to stop counting when t he current through resistor 871 , exceeds desired threshold value, which depends on the value of resistor 871 , typically 1 75-ohms, and on the forw ard drops of diode, 872 and LED 876 When counting is ENABLED, the clock input to pin 1 4, received from a clock 705, results in the CD40 I 7 sequentially rotating a positive output level to one of the ten outputs, 0-9, on each clock 705 pulse Each output drives a buffer switch device, such as a transistor capable of carrying the required transformer primary current The connections are arranged so that each subsequent clock 705 pulse will provide a smaller number of primary turns Clock 705 thus advances the transformer primary tap connection in the direction to provide increasing transformer step-up ratio, in order to provide the lowest required secondary output voltage that will support the required secondary current How. Thus the automatic primary-tap selector circuitry of Figure 8D accomplishes the goal of Figure 8C, of reducing the power dissipation in the system, resulting in longer battery operating time Saturation detector circuitry' 568 of Figure 51 may be used for control of selector circuitry 86, of Figures 8C and 8D, when a current source, such as in Figure 5H, is used in the secondary circuit of transformer 806, to power LED string 206.

Figure A shows s sign 900 which sign 900 may include a power pack 910 with electric circuitry similar to the circuitry of Figure 5E. Optionally, pack 910 includes a battery pack option (not shown) Alternatively, sign 900 includes a solar panel 901 . Furthermore, panel 901 preferably includes a rechargeable battery 902 for illumination at nighttime as well. Battery 902 is preferably charged by solar panel 901 during light hours Sign 900 may be a remotely-located highway directional sign, relying on solar energy and rechargeable batteries for its operation Pack 910 may also serve for battery backup options. Pack 910 in an especially preferred option, includes an AC power hook-up option.

Furthermore, sign 900 includes character modules 914 or numeral modules 916, which can be arranged as the need arises, thus saving on overall costs of signage Additionally, each character module 914 or numeral module 916 can be joined to a further character module 914 or numeral module 916 by a mechanical connection. Alternatively, each character module 914 or numeral module 916 can be joined to a further character module 914 or numeral module 916 by an electrical connection. Each modules 914 or 916 can be afTixed to a wall or free hanging, such as hanging module 918 Furthermore, modules 914 or 916 can be encased in a sign shell (not shown). Figure 9 A also shows numeral modules 916 and character modules 914 of differing sizings, thereby enabling placing an emphasis on certain data or detail.

Figure 9B shows a second directional sign 920, with a rear solar panel 901 A series of light detectors 921 , have been added, for triggering a cluster of high-intensity LED's 922, such that in the daytime, the sign is visible without LED's 922, but at night, LED's 922 are required. Hence, the light-detectors 921 , which result in operating time and battery-life savings Furthermore, light detectors 921 are specifically responsive to headlights, saving battery life inasmuch as LED's 922 only illuminate when a car goes by.

Figure 1 0 shows an LED cat's-eye type pavement marker sign 1 100. This is an improvement over the prior art cat's eye highway reflectors. Sign 1 100, incorporating the present invention preferably includes a cast aluminum or plastic housing 1 101 , a solar-cell rechargeable battery power source 1 102. Optionally, a headlight detector 1 103, at least one high-power LED 1 104 and a background light-reflecting materia! 1 105. Preferably, detectors 1 103 are responsive to headlights of cars approaching sign 1 100, such that LED's 1 104 illuminate when cars approach in the night.

Figure I I shows a wide-viewing angle LED traffic sign 1200 Sign 1200 incorporates many LED's 1201 mounted on a surface 1202. Each of LED's 1201 has an individual "sunshade" 1204, with an angled front end 1205, the inside of each LED 1201 is coated with a reflective material 1206, thus providing a wide-angle-visibility traffic sign 1200, visible to drivers in vehicles located close below the traffic sign 1200.

Figure 1 2 shows an SMT LED package molding design 1400, with each LED 1401 mounted near the bottom of molding 1400, wit h an electrical connection 1402, brought out LED 1401 molding material contains a light-sensitive polarized material or a reflective material for increasing day-time readability A "lens" 1403, may be molded above the LED 1401 mounting position A tapered side shape 1404, of LED 1401 housing, and at least one tlat end 1405, of the molding 1400, provide a daylight readable shape, and the capability of adjacently mounting LED's 1401 , by automatic machinery to form characters.

Figure 1 3 shows a character 1301 consisting of a plurality of LED's 102 which may be connected in a similar way to the one shown in Figure 1 A. Furthermore, character 1301 may be mounted on a backplate structure of freestanding as shown in Figure 1 3. Preferably, character 1301 includes a reflective surface 1320 which accomplishes two objectives. First, reflective surface 1320 enhances the amount of light viewable by a viewer after the light is emitted from LED 102. Second, reflective surface 1320 facilitates visibility during day time conditions regardless of LED' s 102 being illuminated or not. A cross-section D-D exemplifies one of the possible surface mounting modes for LED 102. Namely, in D-D cross-section LED 102 is exposed. Alternatively, LED 102 having a lens 1330 is "flush mounted". Thus, LED 102 is inserted into character 1301 such that only lens 1330 protrudes therefrom, thereby further enhancing the light reflecting on a reflective surface 1320. A further construction option is shown in cross-section B-B wherein each LED 102 is electrically mounted on PCB 1324. Character 1301 , section B-B further consists of at least one light retlecting surface 1322. Preferably light reflecting surface 1322 is either opaque or translucent for enhancing the ability of LED 102 and character 1301 to be seen by the viewe Preferably, character 1301 also has a lens 1326 on the uppermost surface of character 1326 Namely, character lens 1326 is substantially above LED lens 1330 Lens 1326 can be either clear, translucent, or prismatic for diffusing light emitted by LED 102 Occasioning on reflective surface 1322 and lens 1326 being t ransparent or translucent, LED 102 can be viewed from multiple angles Furthermore, LED 102 may be constructed from material of ranging color thus further improvi ng the signal characterist ics of t he sign of the present invent ion Yet anot her possible mounting of LED' s 102 in character 1301, is shown in cross section C-C In cross-section C-C a reflect ive di ffuser surface 1328 is used for t he pu rpose of diffusing the l ight emitted by LED ' s 102 which LED ' s 102 are aimed backwards at diffuser 1328 When LED 's 102 of a varying color is used, diffuser 1328 "mixes" the color and produces a new color of desired wave length . The resulting new color depends upon the original colors of LED' s 102. Furthermore, character 1301, in cross-section C-C, also includes a transparent or semi-transparent cover 1327 such that the light returning from difFuser 1328 may be seen from several angles through cover 1327. Optionally, character 1301 may also include a larger LED 2102 for creating specialized lighting effects such as brighter areas in character 1301. Alternatively, LED 2102 may also be of a smaller size than LED 102. Further still, character 1301 may include one or more SMT' s 1401, like SMT 1401 of Figure 12 or even all of character 1301 will be built of contiguous SMT' s 1401. Further options include directly visible (no cover or background) free standing LED' s 102 (not shown) with every LED 102 having a leg 1332 connected to a leg 1332 of an adjacent LED 102. Alternatively, LED's 102 can be mounted and electrically connected via a printed circuit board (PCB - not shown) thereby facilitating selective illumination of LED's 102.

Figure 1 4 shows a modular sign system. A character shape is mounted on a module 1500 having a contrasting background 1502. A male electrical connect ion capability 1503 and a female elect rical connection 1513 are also provided. A module assembly 1550 consists of a power pack 1504, a series of modules 1500, and an end-piece termination block 1505, for completing a series st ri ng LED circuit that includes all the characters in t he sign Alternatively, each module 1550 may be individually supplied by a current from an output of a multiple-output current mirror (not shown i n Figure 1 4 ), such as current mirror 600 illustrated in Figure 6A Figu re 1 5 A illustrates a possible custom LED package 1600 for providing a light radiation patterns which is both non-symmetric with respect to a conventional LED 102 die center-tine (not shown ) Furt hermore, LED 1600 may be of a non-conventional, non-perpendicular shape with respect to LED 1600 package seating plane A custom version of a lead- frame, such as is used in i nt egrated circuit technology for the mount ing of i ntegrated circuit die in molded packages, is illust rat ed in Figure 1 Lead frame 1 600, includes a mounting pad 160 1 , a first package pinend 1 602A, and a second package pinend 1 602 Bot h first and second package pinends 1602A and 1 603Λ i nclude a wire-bonding land areas, 1603A and 1 603 B, respectively, by which connections may be made to LED die 1604. LED die 1 604 has a plurality of exposed sides 1604a-d, and an exposed top 1604e, through which light is radiated, upon the passage of an electrical current through a LED ju nction 1 605. An arrow 1609, illustrated emanating from the top surface 1604e of die 1600, is i ntended to represent the normal (perpendicular) to die 1600, and to be located at the center of die 1 600. I n Figure 1 5, LED light-emitting junction 1605, is located parallel to a top surface 1605e of die 1604, and is indicated by the dotted line along the sides of the package. Exiting light directions are indicated by the " lambda" symbols. Lead frame 1600 contains a tlat surface 1606, such as would be conventionally used for the mounting an integrated circuit die, for example, by eutectic mounting or by silver- epoxy die mounting. In a conventional lead frame (not shown), a mounting surface would be planar over the whole mounting pad area I n lead frame 1600 shown, a depression 1607 has been stamped in the center of mounting surface 1606 Depression 1607 has a plurality of side walls, 1608a-d, which may be formed in the stamping process to have any desired curvature and angle, thereby providing any desired, custom asymmet rical light radiation pattern with respect to arrow 1609, to t he surface of LED die 1604, si nce side-facet light may be directed at any angle with respect to the die normal . The package seat i ng plane surface is conventionally designed to be parallel to planar surface 1606 Further, a bottom surface 1 07f of stamped depression 1607, is illust rated to be at an angle to surface 1 606, and hence t o t he seating plane of the fi nished molded package Thus, light may be radiated at any desi red angle with respect o the package seating plane, depending on the angle of the stampling of plane 1607 The dotted projections of sidewalls 1 608a-d, below the bottom surface of stamped depression 1607, marked with "X"'s, show the projected position of the bottom of the depression if t he depression were stamped out with bottom surface 1607Γ, parallel to surface 1606 Thus, custom sign LED's 1600, with any generalized, desired, light radiation pattern and angle are provided, such as are used in directional-viewing-angle and bi-directional-viewing angle, sign applications, as described above, in the section titled, Sign-Technology-Specific LED and LED Assemblies.

Figure I 5B illustrates a group of possible configurations having a fixed angle body. A LED 1645 has a fixed angle body of substantially 45 degrees thereby facilitating creation of patterns by merely connecting a side 1648 to a side 1648 of an adjacent LED 1645. A LED 1660 having a fixed angled body of substantially 60 degrees may also be used solely with other LED's 1660 or conjunctively with LED 1645 described hereinabove above to create the desired shape of a character or a numeral. A LED 1690, having a fixed angled body of substantially 90 degrees may be used as well Like above, LED 1690 can be used solely with other LED's 1690 or in any combination with LED' s 1645 and 1660 for creating characters and numerals of any desired shape. Optionally, LED' s of any angle can be used to construct figures and characters with varying configurations.

Figure 16 shows a straight LED 1710 having a side length 1712 and a side width 1714. For the purpose of forming characters and numerals, side length 1712 is at least twice the dimension to side width 1714. A curved Led 1720 is also shown wherein curved LED 1720 is preferably of a half-circle configuration. Furthermore, curved LED width 1724 is substantially equal to straight LED width 1714 Thus by using a single straight LED 1710 and two curved LED' s 1720 a sign of the letter "B" is achieved. This curved LED's 1720 and straight LED' s 1710 of varying dimensions can be used to create virtually any numeral or character. Optionally, LED 1710 and curved LED 1720 may be constructed of several LED junctions (not shown) Figures I 7A and 17B show a plurality of LED's having differing colors of bodies in one package for achieving a desired spectral response characteristic Specifically, adapting the spectral power distribution of the light energy emanating from the source to fit the application may make signs or signals more readable. This would include, (a) the use of different colors to emphasizes different parts of a message; and, (b) a combination of different LED's to "mix" colors to render a specifically-desired color, such as white, composed of red, green, and blue; or, as disclosed in US 5,450,301, the appearance of amber results at a distance, from using closely-packed red and green L.ED's in a ratio of one red lo two green LED's The packaging of multiple, various-color LED's in one package, puts the LED's in very close proximity, so the merged-color effect will be effective from a closer viewing distance Roadway signs or indicators, which in "normal" weather use green to deliver the message, would use red LED's to provide increased visibility in fog A radio control signal or a fog detector could control the switch-over.

Figure I7A illustrates a lead frame 1801, having a die-mounting area 1802, accommodating a LED die 1803. Each of the six LED dies 1803 shown, has a wire-bond connection to a lead-frame package-pin connection wire-bonding area, 1804. LED dies 1803 are mounted, typically, with silver-epoxy, resulting in an electrical connection from the reverse of each of die 1803 to a mounting pad 1802, shown connected to two diagonally-opposite package pins Figure I7B shows a lead frame 1821 with four mounting pads 1822a-d, each accommodating an LED die 1823. This type of multiple-mounting-pad lead-frame design is required for a completely-series-string-connectable multiple-LED assembly, since the common connection of one terminal of a multiplicity of LED's implies a parallel connection Thus the Figure 17A lead-frame 1801 assembly is for parallel circuits, and lead-frame assembly 1821 such as in Figure 17B is required for use in series-string connections of the LED's contained in the package facilitating the multiple junction LED of Figure 16.

Figure 1 C shows a plurality of first colored LED strings 1830 forming a series of characters or numerals. A plurality of second colored LED strings 1840 forming additional characters or numerals are also shown. Owing to the differentiation in color between strings 1830 and 1840, a viewer may be better informed. By way of example only, first LED strings 1830 form the word "BUSSES" in Figure I7C while second LED strings 1840 form the word ONLY" thereby facilitating an intermittent illumination of strings 1830 and 1840 such that drivers will not enter a lane reserved for busses only.

A further possible mounting system is shown m Figure 1 7D wherein each character 1848 is comprised of several types of LED's. A left facing LED 1850 and a right facing LED 1860 are shown which LED' s 1850 and 1860 facilitate an altering view as a viewer approaches and passes each character 1848 Optionally, a center facing LED 1855 may also be used to create even further lighting effects A specific example of such a use is shown in Figure 1 7E wherein left facing LED's 1850 form the word EXIT" while right facing LED's 1860 form the word "ENTRANCE" Thus, a viewer approaching from the right sees the word "entrance" while a viewer approaching from the left is an indication of the whereabouts of the exit.

Figure 1 8 shows a directional sign 1900 using the lead frame of Figure 1 5. Sign 1900 has a mounting surface 1901 , on which a series of LED packages 1902 containing custom LED lead frames and having a die mounting surface 1903. Die mounting surface 1903 is angled with respect to mounting surface 1902. The resulting optimum sign 1900 viewing angle depends on the package orientation on mounting surface 1902. For example, if Figure 1 8 is a top view, then the best sign 1900 viewing angle is from the left side of the page, and it will be difficult or impossible to read the sign from the right side of the page. If, on the other hand, the right side of the page is "up", then the sign is an overhead sign, with the light output of the sign most elTectively used by being directed below, to the viewers passing under the sign. In either case, the energy put into powering the sign has most effectively been used by directing the energy in the most useful direction Figure 1 shows a bi-directional sign. Figure 19 adds alternating rows of packages 2002 between rows of packages 1902. Packages 1902 are illustrated as having the same orientation as in Figure 1 8, while packages 2002 are oriented for light radiation at an angle of 1 80- degrees to the light-radiation direction of packages 1902 If identical LED packages with identical lead frame mounting areas are used for packages 1902 and 2002, then lead frame mounting areas 2003 in packages 2002 are at the negative of the mounting angle of the lead frame mounting areas in packages 1902 In general, different angles may be provided for lead frame die mounting areas 1903 and 2003 The packages 1902 are connected together as appropriate to display a first message, and the packages 2002 are connected together to display a second message. The first message displayed using packages 1902 is optimally viewable from the first viewi ng angle, while the second message displaved bv second packages 2002 is optimally viewable from a viewing angle, thet:i2, which is the negative of the first viewing angle, theta l , for viewing angles measured with respect to the normal ( perpendicular) to the package seating plane, 2001 As mentioned above, the viewing angle, theta2, may. in general, be different from the negative of viewing angle, t hata l , if the package die mounting area, 16071', in packages 2002, has an angle different from the die mounting area angle in packages 1902 r ' Figure 20 illustrates a circuit for turning on an LED character in a sign, the character consisting of a series-string connection of LED' s, not normally being illuminated. In the absence of a +turn-on command at the base of Q2, Q2 will be non-conducting. Thus, R2 will bias Q3 on, holding off voltage reference, VR 1 . Thus, the output voltage of the voltage reference will be zero, RB will act as a safety pulldown and bleeder resistor to hold off Q l , and no current will flow in LED string, 206. Upon receipt of a +turn-on command, and while the turn-on command remains active, Q2 will be held on, holding off Q3, enabling Voltage reference, VR I to turn on and to provide the voltage VREF at the base of Q l , thereby causing a forward LED string current, 1LED, to flow, illuminating the character represented by LED string 206.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.

In particular, incandescent lamps, single crystal solid state light sources, as well as LED's may be d riven from a current source or from a current programmed according to the method and with the circuitry of the present invention. Thus, while the claims state " LED's", the claims should be understood to apply to i ncandescent lamps, also, and to any other light source which may be driven according to the present invention.

Claims (17)

123123/£ WHAT IS CLAIMED IS:

1. . An illuminated sign system comprising: (a) a series-string connection of LED's ( J 22) including a plurality of LED groups (A, B, C, D), (b) a plurali ty of Zener diodes ( 123), each said Zener diode ( 123) shunting one of said LED groups (A, B, C, D) in said series-string connection of LED's ( 122), (c) a looping layout construction of said LED groups (A, B, C, D) in said series-string connection of LED's ( 1 22), and (d) a single current source ( 106) having a supply voltage providing a current to each said LED groups (A, B, C, D) and to said plurality of Zener diodes (123).

2. The sign system of claim I , wherein said single current source ( 106) is a stable, current source.

3. The sign system of claim 2, wherein said single single current source provides for a capability of operation with a supply voltage operating in the range of 4-600V; ,

4. The sign system of one or more of claims 1 -3, further comprising: a blinking-off circuit (300) shiuiting said LED groups (A, B, C, D) in said series-string connection of LED's (122), said blinking-off circuit (300) being powered by said single current source: '

5. The sign system of one or more of claims 1 -3, further comprising a go/no-go current-adjustment circuit (200) operative!y connected to said single current source (106), said go/no-go current-adjustment circuit (200) including: a first LED indicator (201 ); a first resistor (202) wired in parallel with said first LED indicator (201), and a variable resistor (205) connected is series with said first LED indicator (201).

6. The sign system of claim 5, said go/no- go current- adjustment circuit (200) further including: a second LED indicator (203) wired in parallel with said first LED indicator (201) and in parallel with said fust resistor (202), and a second resistor wired (204) in series with said first LED indicator (201) and in series 123123/5 with said first resistor (202):

7. The sign system of claim 1 , wherein each said group (A, B C, D) is disposed within distinc t regions ( 1 1 1 - 1 15), said looping layout construct ion being designed and configured such thai if one of said LED's ( 122) fail, all of said regions ( 1 1 1 - 1 15) remain illuminated.

8. An illuminated sign system comprising: (a) a series:srrir!g 'connection of LED's ( 102; 206); (b) a single cunent source ( 106) for supplying current to said series-string connec tion of LED's ( 102; 206); and (c) a b!ink ng-off circuit (300) shunting a group of LED's in. said series-string connection of LED's (1 02; 206), said bliaking-off circuit (300) being powered by said curreni -supplied to said series-string connection of LED's ( 102; 206).

9. The sign system of claim 8, wherein said series-string connection of LED's ( 102; 206) forms at least one character, and wherein said sign system further comprises: a command receiver for receiving a remote command to trigger illumination of at least, one of said at least one character, wherein said series-string connection of LED's ( 102; 206) is normally not illuminated.

10. The sign system of claim 9, wherein said at least one character is selected from a group consisting of srreet sign characters and house address sign characters.

11. 1 1. The sign system of claim 8, the sign system further including: (d) a line voltage ( 1 0-1, 106) to which is connected S3id series-siring connection o LED's (206); (e) a first diode (553); (0 a resistor (205) for providing a reference current, said resistor (205) being elec trically connected to said first diode (553); (g) a transistor (552) electrically connected to said line voltage ( 104, 1 06); and (h) a high breakdown voltage transistor (55 1 ) electrically connected to said series-strings of LED's (206).

12. The sign system of claim 8, further comprising: a transformer (806) having a secondary winding (71 1) for providing a reference voltage 123123/5 for said single current source ( 106).

13. The sign system of claim 12, wherein said single current source (106) includes a battery operated power supply, and wherein said secondary winding- (71 1 ) of said transformer (806) is a tapped high voltage secondary winding.

14. The sign system of claim ) 3, further comprising: a multiple output current mirror (600) for receiving an input current from S3id single current source ( 106) and for providing multiple current- mirror output currents, and modules, each of said modules containing sard series- String of LED's (206), wherein each said module receives said current-mirror output current.

15. The sign system of claim 8, said single current source ( 106) for supplying current to said series-string connection of LED's (102; 206) further comprising: at least one resistor selected from the group consisting of a current-setting resistor (205 and a temperature- coeffkient-of-output-current- adjusting resistor (563 564). ;

16. The sign system of claim 15, further comprising: at least one additional circuit selected from the group consisting of a current-mirror amplifier circuit (600), a current-splitter circuit (610), and a current-multiplier circuit (563, 564).

17. The sign system of claim 8, further comprising: (c) a printed circuit board having the LED's (102; 206) mounted on said printed circuit board, the LED's (102; 206) being inserted in holes in a panel, thereby forming a pattern of LED's, representing a character; the areas surrounding the holes further being painted to represent said character represented by the LED insertion pattern, whereby said character is readable in the daytime without power applied to the LED's, and readable at night with power applied to the LED's. 1 8. The sign system of claim 17, further comprising: LED's in a hole-through or SMT molded package including molding material including light-sensitive polarized material including where such hole-through or SMT LED's are affixed to said printed circuit board. Λ DR. MAsd½RtrH)MA LT.D. PATEN T ATTO R N EYS SAMB ELO F F 3 U 1 LD1 N G 7 HftOMAN l . STR EET 678¾7 TEL - AVIV IS¾AEL