Classifications

• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
  • G09F13/00—Illuminated signs; Luminous advertising
  • G09F13/04—Signs, boards or panels, illuminated from behind the insignia
  • G09F13/0404—Signs, boards or panels, illuminated from behind the insignia the light source being enclosed in a box forming the character of the sign
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21K—NON-ELECTRIC LIGHT SOURCES USING LUMINESCENCE; LIGHT SOURCES USING ELECTROCHEMILUMINESCENCE; LIGHT SOURCES USING CHARGES OF COMBUSTIBLE MATERIAL; LIGHT SOURCES USING SEMICONDUCTOR DEVICES AS LIGHT-GENERATING ELEMENTS; LIGHT SOURCES NOT OTHERWISE PROVIDED FOR
  • F21K9/00—Light sources using semiconductor devices as light-generating elements, e.g. using light-emitting diodes [LED] or lasers
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
  • G09F13/00—Illuminated signs; Luminous advertising
  • G09F13/04—Signs, boards or panels, illuminated from behind the insignia
  • G09F13/0418—Constructional details
  • G09F13/0472—Traffic signs
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
  • G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
  • G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
  • G09F9/33—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being semiconductor devices, e.g. diodes
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
  • H05B45/37—Converter circuits
  • H05B45/3725—Switched mode power supply [SMPS]
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/40—Details of LED load circuits

Definitions

• the present invention relates to a general illuminated sign and signal technology having improved performance, i.e. high reliability but very low energy consumption and the advantages that are derived thereof.
• the signs and signals in this system are composed of discrete light sources, examples of which is the light emitting 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.
• these principles enable the illumination of a myriad of sign and signaling devices heretofore impractical to illuminate due to the high power consumption of present sign illuminating technology.
• the invention 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, street signs, advertising signs, exit signs, emergency signs, signs over business, display signs, traffic signs, traffic signals, roadway indicators, and in any application where an improvement in readability, reliability, 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 direction signs to remain operative in extended civil emergency situations, and a solar cell capability which allows for installation anywhere without need for an external power supply.
• the inventive features disclosed herein are the result of the Applicant's service as an ambulance driver in the Gulf War but relates to all natural disasters such as earthquakes, 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 result from the use of incandescent and fluorescent light sources, which utilize fragile glass envelopes which easily break due to the 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 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.
• 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 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.
• 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 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.
• An improved light source sign is the LED matrix sign. LED technology is taken 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.
• 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.
• red LED's typically have a forward drop at about 10mA of about 1.7V
• 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.
• 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.
• 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
• 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.
• 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 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 4,173,035 (filed 1 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 4,384,317 (filed 17 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 4,951,405 (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 carry electricity, then the characters have, e.g., 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 4,471,415 (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 flashing.
• US 4,271,408 (filed 12 Oct 79) provides a concave-mirror-cell surface with LED's in the concave mirrors. This is designed for visibility 24-hrs, e.g., 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.
• 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.
• 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
• 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 adjoined 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 openings for the light to exit).
• the individual 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
• the sign of the present invention may be illuminated (powered) during the day for enhanced visibility, or only at night.
• each numeral or letter element can be individually affixed to the wall or hung from an arm and individually hooked up to the electrical power or be mechanically and electrically joined to each other or to a mounting frame and then to the wall and power supply.
• each character element could be battery powered with an optional photo-cell controlling night time operation, and the battery could be recharged from photovoltaic cells which could be located on the character element itself on its front and or back side or on a separate, properly aimed towards the sun, array.
• a centralized power pack using utility power or with battery operation or back-up and photovoltaic recharging could be located in the frame or in a master character element in the chain, and many characters powered from it.
• 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 the sign at each intersection of streets or storefront from the standard letter elements.
• complete signs 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.
• Readability is improved by formation of illuminated characters in which the letters stand out on high contrast backgrounds, the reverse of the case of the prior art back-lit illuminated house signs mentioned above, where the background may cause glare at night.
• An additional feature of the LED sign system of the present invention is the ability for medical (ambulance), security and service operations such as taxis to receive aid in locating an address through the blinking of LED's in the sign at an address to which such services have been summoned.
• 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 without outside lighting, such as in civil disasters or wartime but is also useful for taxi, delivery and other services night and day.
• An additional useful feature is the incorporation of the postal code or other location code or information in the street and house number signs, for example, the postal code characters which are normally not being illuminated, but being trigger-able, preferably to blink 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 the 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-string 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 in use and would be automatically reset upon restoration of the AC power.
• the pulser would also provide an AC power loss indicator function.
• the battery back-up pulser would be ideally located in the power-pack module. Illumination time may be further extended by pulsing the power applied to the sign, so the whole sign blinks at rates which may or may not be visible to the eye. Then the operating time will be extended according to the pulsing duty ratio.
• the LED's are controlled by a power cut off controller for controlling power to the plurality of LED lamps, such that the power is alternately supplied and not supplied to the plurality of LED lamps, thereby causing the plurality of LED lamps to alternatly illuminate and not illuminate, thereby reducing power consumption.
• Another power-consumption reduction technique which may be employed in parallel circuitry is the multiplexing of characters for reduced power consumption.
• characters are blinked at a sufficiently-rapid rate, the impression of constant illumination is given to the observer.
• blinking characters as a possible power-saving method, especially at night, when reduced intensity is required for visibility, due to reduced ambient illumination, compared with the daytime ambient.
• an extended duty cycle at very slow rates of a number of seconds on and a number of seconds off would still leave the sign message sufficiently recognizable.
• often street sign lighting is operated from street lighting power, which is shut off during daylight hours. In this 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 light source signage is optimized to match the load to the power source to obtain maximum utilization of the power source.
• the separate current-balancing-resistor parallel connection of LED light sources to a low-voltage power supply - maintaining constant voltage is preferably used.
• a constant current maintaining circuitry is used further increasing energy efficiency.
• 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 in 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.
• the current source may be limited to a safe 30 mA and it may be optionally fused or may alternatively include any type of circuit breaker to provide safer signage than previously available.
• Merryman '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 Merryman, in that the failure of one LED does not result in the loss of readability of even one character module.
• modules of the present invention may preferably be connected in series to a high-voltage supply with improved efficiency.
• a current source makes the supply current to the LED's substantially insensitive to the number of series-connected modules.
• the modules may be supplied by individual current-mirror outputs, derived from one temperature-compensated current source.
• 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.
• a disadvantage of a series connection is the continuity if one of the elements in the string fails.
• a novel series power connection reliability improvement is provided by Zener diodes bracketing groups of LED's which form the characters of the signs.
• Zener diodes bracketing groups of LED's which form the characters of the signs.
• 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 the character legible and the sign still functional. This is the "looping" connection of the present invention, described below.
• 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-known.
• 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.
• 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.
• the power in the bias circuitry 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 lightning-induced power-supply transients, and other AC power-line transients and surges, such as due to switching inductive loads, and due to motor starting.
• Low power consumption makes possible battery operation, preferably using rechargeable batteries.
• Solar cell operation and is also possible as is solar cell recharging of the batteries.
• series-string connections of the LED's results in high-efficiency, low power consumption operation, as will be described in more detail below.
• a switching power supply 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 is the book, Switching and Linear
• 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.
• the circuitry could manage the energy storage.
• the LED's or other light sources are optimized to match the special requirements of use in signage leading to: Sign-Technology-Specific LED and LED Assemblies
• the light sources used are specifically adapted photometrically, spectrally and physically, i.e. outer packaging, for sign and signal applications.
• Prior art LED's are typically designed for use as indicator 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.
• 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.
• 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.
• 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.
• 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.
• a storefront sign located flat 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.
• 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 flat on a wall, such as in a narrow hospital corridor. Viewing may be enhanced by aiming method.
• An additional 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.
• 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).
• SMT surface-mount technology
• 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.
• 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.
• the randomly-oriented, semi-clear liquid crystal material contained in the clear plastic surround would allow passage of the LED's light providing the recognizable character or symbol.
• the LED's are soldered onto a printed-circuit board.
• the LED legs are connected one to another obviating the need for a printed circuit board.
• the chain created can then be l)formed into free standing 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 components may be integrated into the chain.
• 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.
• 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.
• the LED's may be aimed along the tube with the tube acting as a light pipe. Specular and diffuse reflective surfaces can be used as required to control the amount and direction light exitance along the tube.
• 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 the tubing. This reverse aiming is also ideal for the mixing of multiple individual colored
• the shape of the tubing is such that it may fit into a slot or positional holes for adherement to sign surfaces.
• Power is supplied to the tubing via an edge connector which makes contact with the conductors at whichever point the tube was snipped.
• another edge connector is supplied to close the tube and complete the electrical circuit as is necessary for a parallel or series connection.
• the sides of the tube are covered with photocells.
• the photocells may be of a rigid type with gaps left between the photocells for bending, or a flexible type of photocells may be used which continuously bend with the tube.
• a rechargeable battery is provided, making the product free of the 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.
• 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 light 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 rather than many little dots.
• optical features mentioned above such as non-symmetric light 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 rather than many little dots.
• the same technology adaptations of package shape for character formation apply to Surface Mount Technology LED's as well.
• multiple LED's may be packaged together in longer shape sections.
• the "greatest- common-denominator" shapes of letters are molded and then combined to form characters.
• 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”.
• complete characters, numerals and symbols comprised of many LED junctions packaged in single units may be manufactured. Properly shaped and lensed, these characters would be visible during the day and would use a minimum of LED junctions 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.
• 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, the CNC SMT machine would place the LED's, and solder or glue the LED's in place, to define the layout of the custom sign. The machine would optionally extrude colored plastic material around the LED's for protection and additional sign aesthetics.
• the scanned graphics would be translated into coordinates for a CNC punch press which would make holes for the LED's to be mounted therein.
• LED chain shall include LED tape in addition.
• high volume signs i.e. signs carrying a standard message
• the preferred manufacturing technology would be the mass production of complete signs as single units, rather than having the sign composed of individual character elements placed together as in the modular system mentioned earlier. 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.
• Modular LNS a) modular, mechanically and electrically interconnected "linked” separate modules b) modular, framed on a rigid structure
• LNS 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 street numbers as self-contained singly-packaged numerals. LNS may be mounted on a solid back plate to control contrast and to give stability; or may be hollow and may be supported from the rear. Individual LNS elements are self-powered by a battery or connected to house power. An integral or separate array of photovoltaic solar cells may be used for daytime operation and for battery recharging, or the photovoltaic solar cells may serve as the LNS background plate, facing outwards, to gather 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.
• LNS may be affixed independently to a mounting surface such as a house surface or may mechanically be inter-linked with other LNS elements.
• 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 pholto voltaic 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.
• 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.
• LED's may be aimed at angles within the 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 up to utility power as bringing power to a remote highway sign is costly. It is possible to enhance visibility of highway traffic signs, as well as indoor direction, safety and information signs placed at very difficult viewing angles. The angled LED comes to correct for the current viewing angle deficiency. Sign location on a narrow corridor wall cannot be easily viewed from the distance because of the acute angle.
• M-LNS modular LNS
• the function of the power supply and or mechanical securing of the individual characters is centralized
• 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.
• 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.
• M-LNS Modular Letter and Number System
• 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 first 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.
• the sign may be canti-levered from one end.
• the circuit design allows for a very long string of symbols.
• this type of modular sign system is suitable for house signs, street signs, and information and directional signs.
• the N-C parts placement machine places the SMT parts on the surface of the electrical circuit.
• the LED's are cemented to the 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 through-hole LED's would be placed on a placement machine from the rear would place in the positional holes join the conducting legs and when necessary jumpers together.
• FIG. 1 A is an LED-formed character with Zener diodes added;
• FIG. IB is a "looping" LED-formed character with Zeners;
• FIG 1C is a sample "looping" character foil pattern
• FIG. ID is a dual "looping" LED-formed character with two power supplies, providing redundancy
• FIG. 2 shows a go/no-go current adjustment circuit
• FIG. 3 illustrates a blinking-off circuit
• FIG. 4A is a set of battery-discharge characteristics
• FIG. 4B is a corresponding plot of battery discharge time versus discharge rate
• FIG. 5A 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
• FIG. 6B shows one a current-mirror amplifier used as a current-splitter to power two parallel
• FIG. 7A shows a power supply implementation
• FIG. 7B shows an alternative power supply implementation
• FIG. 8A 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
• FIG. 12 shows the novel SMT LED package molding design
• FIG. 13 shows a self-sufficient-character design
• FIG. 14 is a modular sign system using SMT-package molded LED's;
• FIG. 15A illustrates a possible custom LED package;
• FIG. 15B illustrates further possible custom LED packages
• FIG. 16 illustrates "greatest-common-denominator" character segments.
• FIG. 17 A 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
• the present invention discloses a novel sign system suitable for use in many applications, according to the features selected to be included in the particular sign for the particular application which can be realized as modular or dedicated signs.
• 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.
• 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.
• integral power sources e.g., solar cells on house signs, and on LED display strips, with back-up batteries, as well as solar-cell with batteries for remote locations.
• FIG. 1A 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 protruding 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.
• 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
• Zener 103 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.
• each modular letter could have its internal dropping resistor to program the current inside the individual letter module.
• 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 1A.
• the improvement in Figure IB is called "looping", due to the resulting wiring pattern appearance.
• 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.
• the wiring pattern is not in the same sequence as the physical placement of the LED's 102.
• each group of LED's 122 labeled "A” thorough “D” is connected in series and bracketed by a Zener 123.
• 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 1A. Rather, every fourth LED 122 goes dark, resulting in a more readable and recognizable character with the arrangement of Figure
• 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 ID 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.
• a pair of filter capacitors 147 and 148 are shown in Figure ID.
• 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, with separate power sources, including using all positive, or all negative, rectified power supplies, or some of each polarity.
• 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 - 140n, 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 102 of Figure 1A; 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 201 is selected to be an AlGaAs, 637nm, red LED, such as
• Hewlett-Packard (HP) HLMP-D101 with a forward drop of 1.8V at 20mA, and a voltage of about 1.5V at 1mA, 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 the 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 string current equal to 15 Ma. If the forward voltage of LED 201 at 1mA is 1.5V at 1mA, and 1mA will be in LED 201, then 14mA will be flowing in resistor 202. Resistor 202 will have a value of 1.5V/14mA, approximately equal 100-ohms. Now select LED 203, for example, HLMP- 1521, green, 569nm, GaP, with a forward drop of 2.1V at 10mA, and about 1.7V at 1mA. Select the maximum current to be 20mA.
• resistor 204 select resistor 204, so that with LED 203 just lit, at 1.7V, the current in resistor 204 will be 19mA. Then 1.7V across LED 204 minus 1.6V across LED 201 gives 0.1V across resistor 204, for a current of about 20mA in resistor 204, so resistor 204 has a value of about 5-ohms.
• variable current-setting resistor 205 when variable current-setting resistor 205 is set to a high value, the current flowing from positive supply connection 106 through the current-adjustment circuit 200 and character LED string 206 to negative supply connection 104, will be less than 15mA, and both LED 201 and LED 204, will be off.
• first red LED 201 will light at about 15mA in LED string 206, but green LED 203 will be off.
• 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.
• variable resistor 205 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.
• 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.
• 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.
• FIG. 3 illustrates a blinking-off circuit 300 of the present invention.
• LED's 102 are part of a series string of LED's 102 forming a character in the LED sign of the present invention.
• a switch 313 is closed to enable operation of blinking circuit 300.
• Blinking circuit 300 uses a blinking LED 310, such as an Everlight Model F336 family blinking LED, which includes circuitry in LED package 310 causing LED 310 to blink at a pre-determined rate and duty ratio when blinking LED 310 is powered by a steady DC supply.
• a blinking LED 310 such as an Everlight Model F336 family blinking LED, which includes circuitry in LED package 310 causing LED 310 to blink at a pre-determined rate and duty ratio when blinking LED 310 is powered by a steady DC supply.
• transistor 314 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, 311, turning off LED's 316-319.
• a second resistor 309 establishes a minimum turn-on threshold current requirement for the current in first resistor 312, in order that transistor 314 will be turned on.
• First resistor 309 and second resistor 312 are typically 1200-ohms and 360-ohms, respectively.
• the breakdown voltage of a Zener 315 is selected to assure that capacitor 311, typically 1 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 311, typically lmicrofarad, 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.
• Zener diode 315 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-setting 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.
• FIG. 3 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.
• 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.
• the battery falls to 5.5V after about 45 minutes; at 0.4CA, about 90 minutes; at 0.2CA, about 220 minutes; for 0.1CA, about 540 minutes; for 0.05CA, about 1200 minutes.
• FIG 4B is a corresponding plot of battery discharge time versus discharge rate for this data.
• the battery 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.
• batte ⁇ es in se ⁇ es at higher voltage and lower discharge rate, than m parallel at a low voltage and at a high discharge rate.
• the choice is made to operate with as high a battery voltage as possible, and to minimize the voltage drop across dropping resistors 105 of Figure 1 A or resistor 205 of Figure 2.
• the prefe ⁇ ed power sources for the LED sign system of the present invention may be a battery supply, preferably using rechargeable batte ⁇ es, 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 d ⁇ ven by a force of nature
• 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 is desirable therefore, to provide cu ⁇ ent regulation of the LED forward current, and not to regulate the forward voltage applied to the LED
• field go/no-go current adjustment circuit 200 of Figure 2 discussed above is provided.
• FIG. 5A shows a cu ⁇ ent source, 500, which may be used to program the operating cu ⁇ ent of a st ⁇ ng 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 cu ⁇ ent of 1 microampere times the ambient temperature in degrees Kelvin Thus at 25 degrees C, the output cu ⁇ ent is 298.2 Ua, nominal.
• the temperature coefficient of the output cu ⁇ ent is thus approximately positive one-third of one per cent per degree C, at about room temperature.
• LED's (not shown) operating at constant cu ⁇ ent 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 cu ⁇ ent of the AD592 is beneficial in partially temperature-compensating the LED light output versus temperature. However, the approximately 300 Ua output cu ⁇ ent at room temperature is much less than the desired, say, ten to twenty milliamperes forward cu ⁇ ent usually used with LED's (not shown). To increase AD592 source 501 cu ⁇ ent output to a more usable level, a cu ⁇ ent amplifier 510 is included in current source 500 of Figure 5A. Cu ⁇ ent amplifier 500 consists of transistors 502, 503, and 505.
• a current-setting resistor 205 is adjusting the ratio of the collector cu ⁇ ents of transistors 502 and 503.
• Transistor 503 has an emitter area of N times the emitter area of transistor 502. If the value of cu ⁇ ent-setting resistor 205 is zero, then the output cu ⁇ ent fed to circuits 200 and 206, will ideally be (N+l) times the output cu ⁇ ent of AD592, 501. However the output cu ⁇ ent will be less than this, since the reference collector cu ⁇ ent 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.
• Figure 5E shows an especially prefe ⁇ ed embodiment with a very stable, negative-temperature-coefficient current source.
• a cu ⁇ ent 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.
• a DC cu ⁇ ent 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 cu ⁇ ent 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 1N4007.
• Transistor 552 is typically 2N3904, and high breakdown voltage transistor 551 is typically a BU902.
• the circuit of Figure 5E provides a very stable output cu ⁇ ent of between 10 to 30 mA, for LED strings 206 consisting of 10 to 150 LED's.
• the circuit may be readily constructed to accommodate a power supply operating voltage range of from 4V to 600V.
• a fuse 548 is used to prevent electrocution.
• a resistor 549 is included to limit cu ⁇ ent entering into capacitor 556.
• Figure 5F shows a cu ⁇ ent source 565 with adjustable temperature coefficient of output cu ⁇ ent, as well as adjustable nominal output current.
• 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 5.6V 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.
• a cu ⁇ ent source 565 biases a zero-TC Zener 560, and provides sufficient base cu ⁇ ent 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.
• the voltage at the emitter of transistor 561 has a slight positive temperature coefficient.
• the combination of a transistor 562 with voltage-divider resistors Rl 563, and R2 564, provides a "VBE-multiplier" circuit.
• the values of divider resistors 563 and 564 are selected for a divider string cu ⁇ ent that is large enough to be substantially unaffected by the variations of base cu ⁇ ent 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 VBE at its operating collector cu ⁇ ent, multiplied by a factor of (R2+R1) R1.
• the name "VBE-multiplier" 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 cu ⁇ ent setting resistor 205 can be adjusted to have a large positive temperature coefficient.
• the adjustment of the VBE-multiplication ratio provides the temperature-coefficient adjustment capability.
• resistors Rl 563 and R2 564 serve as temperature-coefficient adjustment resistors in the variable temperature-coefficient cu ⁇ ent source of Figure 5F.
• Cu ⁇ ent-setting resistor 205 then provides the initial 25 degreeC current adjustment capability.
• a variation of this circuit could employ an electronic Zener-equivalent integrated circuit, such as TL431, with a 2.5V Zener voltage, for lower minimum operating voltage.
• the required voltage across current-setting resistor 205 would have to be smaller also.
• about 0.8V is required across resistor 205 to provide about +l%/degreeC temperature coefficient output current.
• about 0.4V would be required across resistor 205 to provide about +l%/degreeC temperature coefficient output cu ⁇ ent.
• variable cu ⁇ ent-setting resistor 205 a fixed resistor may be used, with its value chosen by design, or selected based on voltage measurements in the cu ⁇ ent-source circuit.
• 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.
• Zener(560) 5.6V
• transistors(561 and 562) 2N3904
• R2(564) 1500-ohms
• Rl(563) 330-ohms
• cu ⁇ ent-setting resistor(205) 82- ohms. This provides approximately 10mA at about 25 degreesC, with approximately +l /degC temperature coefficient in the temperature range of -25C to +75C.
• FIG. 5G A variation on the adjustable temperature-coefficient cu ⁇ ent source of Figure 5F is shown in Figure 5G.
• the VBE- multiplier is operating with a smaller collector cu ⁇ ent, hence a smaller divider cu ⁇ ent is needed.
• a resistor 565 programs the VBE-multiplier current while a transistor 566 carries most of the LED-string cu ⁇ ent.
• the combination of a transistor 562 with voltage-divider resistors Rl 563, and R2 564 provides a "VBE-multiplier" circuit.
• divider resistors 563 and 564 When the values of divider resistors 563 and 564 are selected for a divider string cu ⁇ ent that is large enough to be substantially unaffected by the variations of base current of transistor 562 with initial cu ⁇ ent gain, hFE or beta, value, and with temperature variations of beta, then the collector-emitter voltage of transistor 562 will be its VBE at its operating collector cu ⁇ ent, multiplied by a factor of (R2+R1)/R1. Hence the name "VBE-multiplier".
• Figure 5H illustrates another positive-temperature-coefficient cu ⁇ ent-source design approach, which is well-suited to modular applications, or to the use of LED's requiring various positive- temperature coefficients of forward cu ⁇ ent, in order to provide zero- temperature-coefficient light output.
• a LM317-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 cu ⁇ ent is the collector cu ⁇ ent of a transistor 561.
• Current-programming resistor Rset 205 is connected from the emitter of transistor 561 to a negative supply 104.
• the base of transistor 561 is connected directly to the zero-temperature-coefficient, 1.25V-nominal output of voltage reference 560. Since the temperature coefficient of VBE of transistor 561 is about -2mV/degreeC, and VBE is about 650mV, the emitter voltage will be about 6000mV, and the temperature coefficient of
• the Rl and R2 resistor divider (not shown), provides a reduced voltage to transistor 561 base, of about
• FIG 51 shows the addition of a saturation detection circuit 568 to a cu ⁇ ent source transistor 561 of the first Figure 5H example.
• Saturation detection circuit 568 consists of a differential pair of transistors PI 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 Dl.
• RLT provides the bias cu ⁇ ent for the differential pair.
• a supply voltage 106 will be great enough to hold the collector voltage of Ql 561, above the base voltage of Ql 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 Ql 561 approximately equal to the base voltage of Ql 561, P2 will conduct collector current, sourcing I outputl. This cu ⁇ ent 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 outputl, 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.
• Rlim providing limiting of Dopto 569 LED current to an acceptable value.
• 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 cu ⁇ ent adjustment circuit 200 is used to adjust a cu ⁇ ent-setting resistor 205 to the appropriate LED-string 206 operating cu ⁇ ent at about 25 degreesC. This cu ⁇ ent flows in LED string 206.
• a current minor amplifier (CMA) 600 provides additional cu ⁇ ent source outputs, using the collector cu ⁇ ent of a transistor 566 as the CMA input reference cu ⁇ ent.
• 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.
• the collector current of transistor 604A will be substantiequal to the collector current of transistor 601.
• the collector cu ⁇ ent of transistor 604A should be about 25% greater than the collector cu ⁇ ent 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 604A 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 cu ⁇ ent matching e ⁇ or due to using the same emitter area for transistors 605A as for transistor 601, can be made acceptably small.
• the e ⁇ or should ideally be about 1%.
• the transistors will not be identical, and the resistors will not be identical. There will be additional errors due to the base current of transistor 603 "subtracting" from the collector cu ⁇ ent of transistor 601, and there will be an e ⁇ or due to the Early effect, i.e., due to the collector-emitter voltages of the reference transistor 601 and output transistors, 604n (not shown) not being identical. Increasing the drop across the emitter resistors 602 will help to reduce the Early voltage e ⁇ or.
• Cu ⁇ ent-mirror amplifier 600 providing multiple outputs may be used with any of the cu ⁇ ent sources described above with a cu ⁇ ent ratio of 1:1, by simply inserting current-mirror amplifier 600 in series with a positive supply connection 106, of the cu ⁇ ent source which provides the reference cu ⁇ ent.
• Use of the cu ⁇ ent minor 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.
• 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.
• the current- providing circuitry may include a cu ⁇ ent-setting resistor 205, a cu ⁇ ent source, a go/no-go cu ⁇ ent adjustment circuit 200, and a cu ⁇ ent-mi ⁇ or amplifier 600 circuit for the case of multiple LED strings 206.
• Figure 6B shows a cu ⁇ ent-mirror amplifier used as a cu ⁇ ent- splitter 610 to power two parallel LED strings 206.
• a special module contains a module circuitry 620 consisting of a cu ⁇ ent-splitter 610.
• Cu ⁇ ent-splitter 610 is a cu ⁇ ent minor 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 cu ⁇ ent- splitter input current 611a is divided into cu ⁇ ent-splitter output cu ⁇ ents 612 and 613, which flow into the anode end of LED strings 206a and 206d, respectively.
• the cu ⁇ ent division ratio depends on the design of cu ⁇ ent minor 610, according to the cu ⁇ ent minor design principles discussed above.
• Cu ⁇ ent-splitter 610 output cu ⁇ ents 612 and 613 are summed by the interconnection of the cathode ends of LED strings 206a and 206d to provide a module output cu ⁇ ent 611b, of a value equal to module input cunent 611a.
• two colors of LED strings 206 are to be used in one special module with each color required to operate at a different forward cunent, with the sum of the two cunents equal the special-module system string cu ⁇ ent.
• the design precaution which must be observed is that for proper operation of cunent 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 cunent source which powers LED string 206.
• a simple cu ⁇ ent source is shown, consisting of a transistor 561, a cu ⁇ ent-setting resistor, 205, a reference Zener 560, and a bias resistor 703.
• resistor 703 With a 220-volt AC power line, resistor 703 must be a large-value resistor to limit the cu ⁇ ent 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.
• a rectifier 701 and a filter capacitor 702 provides smoothing for the voltage across LED string 206, and hence for the cu ⁇ ent 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.
• a capacitor 710 may be added to provide a DC reference voltage at the base of transistor 561, and hence to provide a DC cu ⁇ ent source to LED string 206.
• FIG. 7B shows an alternative power supply implementation.
• 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, 711, which replaces the high voltage AC power source, and a low-voltage winding 708.
• Low-voltage winding 708 provides the reference voltage for the cu ⁇ ent source which includes a transistor 561 and a cunent-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.
• 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 83n having a series dropping resistor 82n. Assume 170 LED's, each with 1.8V drop, operating from a 2.4V battery. The efficiency depends on the design LED cu ⁇ ent, and for 7.2mA, may calculated to be about 58% due to the power loss on the series dropping resistors.
• Figure 8A also shows several reverse-voltage protection diodes 80a-80n. Since each
• each LED 83n has its own dropping resistor, each LED 83n requires a separate reverse-voltage protection diode. This is unlike the case of the series-string 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
• Figure 8B shows a series-LED power supply implementation.
• a transformer tap 84n is selected to provide approximately the required total minimum operating voltage for an LED string 206 in series with a cu ⁇ ent 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%.
• a tapped transformer 806 limits the power dissipation across cunent source 85, which is analogous to the prior art dropping resistors 82n of Figure 8A, thus resulting in the increased efficiency, as well as reducing the required power rating and heat-sinking for the cu ⁇ ent-source output transistor.
• Figure 8C shows an alternative to the configuration of Figure 8B.
• a secondary cunent 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 cunent to flow.
• the dissipation in a cu ⁇ ent source 85 is minimized.
• FIG 8D shows details of a prefe ⁇ ed embodiment of a series-LED power supply of the type of Figure 8C.
• a sensor circuitry 87 as in Figure 8C, includes a secondary-cu ⁇ ent sensing resistor 871 a rectifier 872, a filter capacitor 873, and a bleeder resistor 874.
• the secondary cunent whether DC, or including also AC components, is converted by resistor 871 to a co ⁇ esponding voltage.
• a resulting rectified DC voltage is available to excite an LED 876 contained in a optocoupler 875.
• LED 876 is being used, in effect, as a switch, such that when the cunent is sufficient to turn on LED 876, a "digital" signal will be transfe ⁇ ed through optocoupler 875 to a selector circuitry 86 on the primary side of a transformer 806, as in Figure 8C.
• 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 13, the ENABLE input of a CD4017 counter to stop counting when the cu ⁇ ent through resistor 871, exceeds desired threshold value, which depends on the value of resistor 871, typically 175-ohms, and on the forward drops of diode, 872 and LED 876.
• each output drives a buffer switch device, such as a transistor capable of carrying the required transformer primary cunent.
• the connections are ananged 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 cunent flow.
• 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 cu ⁇ ent source, such as in Figure 5H, is used in the secondary circuit of transformer 806, to power LED string 206.
• Figure 9A shows s sign 900 which sign 900 may include a power pack 910 with electric circuitry similar to the circuitry of Figure 5E.
• pack 910 includes a battery pack option (not shown)
• sign 900 includes a solar panel 901.
• 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 prefened option, includes an AC power hook-up option.
• sign 900 includes character modules 914 or numeral modules 916, which can be ananged 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 affixed 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 9A also shows numeral modules 916 and character modules 914 of differing sizings, thereby enabling placing an emphasis on certain data or detail.
• Figure 12 shows the novel SMT LED package molding design, 1400. Each LED, 1401, is mounted near bottom of molding 1401, with electrical connections 1402, brought out.
• the LED molding material contains the light-sensitive polarized material, as described above.
• a "lens", 1403, may be molded above the LED mounting position.
• a tapered side shape 1404 of the LED 1401 housing, and one flat end 1405 of molding, 1400, provide a daylight readable shape, and the capability of adjacently mounting the LED's 1401, by automatic machinery to form characters.
• Figure 13 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 1A. Furthermore, character 1301 may be mounted on a backplate structure of freestanding as shown in Figure 13.
• 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.
• LED 102 having a lens 1330 is "flush mounted".
• 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 reflecting surface 1322.
• light reflecting surface 1322 is either opaque or translucent for enhancing the ability of LED 102 and character 1301 to be seen by the viewer.
• 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 transparent or translucent, LED 102 can be viewed from multiple angles. Furthermore, LED 102 may be constructed from material of ranging color thus further improving the signal characteristics of the sign of the present invention. Yet another possible mounting of LED's 102 in character 1301, is shown in cross section C-C. In cross-section C-C a reflective diffuser surface 1328 is used for the purpose of diffusing the light emitted by LED's 102 which LED's 102 are aimed backwards at diffuser 1328.
• 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.
• 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.
• character 1301 may also include a larger LED 2102 for creating specialized lighting effects such as brighter areas in character 1301.
• LED 2102 may also be of a smaller size than LED 102.
• 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.
• PCB printed circuit board
• FIG 14 shows a modular sign system.
• a character shape is mounted on a module 1500 having a contrasting background 1502.
• a male electrical connection capability 1503 and a female electrical 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 string LED circuit that includes all the characters in the sign.
• each module 1550 may be individually supplied by a cu ⁇ ent from an output of a multiple-output cunent minor (not shown in Figure 14), such as cu ⁇ ent minor 600 illustrated in Figure 6A.
• Figure 15 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-line (not shown). Furthermore, LED 1600 may be of a non-conventional, non- perpendicular shape with respect to LED 1600 package seating plane.
• Lead frame 1600 includes a mounting pad 1601, a first package pinend 1602A, and a second package pinend 1602. Both first and second package pinends 1602A and 1603A include a wire-bonding land areas, 1603A and 1603B, respectively, by which connections may be made to LED die 1604.
• LED die 1604 has a plurality of exposed sides 1604a-d, and an exposed top 1604e, through which light is radiated, upon the passage of an electrical cunent through a LED junction 1605.
• An anow 1609 illustrated emanating from the top surface 1604e of die 1600, is intended to represent the normal (perpendicular) to die 1600, and to be located at the center of die 1600.
• 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 flat surface
• a mounting surface would be planar over the whole mounting pad area.
• 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 asymmetrical light radiation pattern with respect to anow 1609, to the surface of LED die 1604, since side-facet light may be directed at any angle with respect to the die normal.
• the package seating plane surface is conventionally designed to be parallel to planar surface 1606.
• a bottom surface 1607f of stamped depression 1607 is illustrated to be at an angle to surface 1606, and hence to the seating plane of the finished molded package.
• light may be radiated at any desired angle with respect o the package seating plane, depending on the angle of the stampling of plane 1607f.
• the dotted projections of sidewalls 1608a-d, below the bottom surface of stamped depression 1607, marked with "X'"s, show the projected position of the bottom of the depression if the depression were stamped out with bottom surface 1607f, parallel to surface 1606.
• 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 15B 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.
• 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.
• 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.
• 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.
• curved LED width 1724 is substantially equal to straight LED width 1714.
• This curved LED's 1720 and straight LED's 1710 of varying dimensions can be used to create virtually any numeral or character.
• LED 1710 and curved LED 1720 may be constructed of several
• Figures 17A 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 LED's in a ratio of one red to two green LED's.
• FIG 17A 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 17B shows a lead frame 1821 with four mounting pads 1822a-d, each accommodating an LED die 1823.
• Figure 17C 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.
• first LED strings 1830 form the word “BUSSES” in Figure 17C 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.
• Figure 17D shows a further possible mounting system wherein each character
• FIG. 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.
• a center facing LED 1855 may also be used to create even further lighting effects.
• Figure 17E A specific example of such a use is shown in Figure 17E wherein left facing LED's
• Figure 18 shows a directional sign 1900 using the lead frame of Figure 15.
• 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 18 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 effectively 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 19 shows a bi-directional sign. Figure 19 adds alternating rows of packages
• Packages 1902 are illustrated as having the same orientation as in Figure 18, while packages 2002 are oriented for light radiation at an angle of 180- 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 viewing angle
• the second message displayed by second packages 2002 is optimally viewable from a viewing angle, theta2, which is the negative of the first viewing angle, thetal, for viewing angles measured with respect to the normal (perpendicular) to the package seating plane, 2001.
• the viewing angle, theta2 may, in general, be different from the negative of viewing angle, thatal, if the package die mounting area, 1607f, in packages 2002, has an angle different from the die mounting area angle in packages 1902.
• 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.
• Q2 will be non-conducting.
• R2 will bias Q3 on, holding off voltage reference, VR1.
• the output voltage of the voltage reference will be zero
• RB will act as a safety pulldown and bleeder resistor to hold off Ql, and no cu ⁇ ent will flow in LED string, 206.
• Q2 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, VR1 to turn on and to provide the voltage VREF at the base of Ql, thereby causing a forward LED string cunent, LIED, to flow, illuminating the character represented by LED string 206.
• incandescent lamps single crystal solid state light sources, as well as LED's may be driven from a cunent source or from a cu ⁇ ent programmed according to the method and with the circuitry of the present invention.
• LED's the claims should be understood to apply to incandescent lamps, also, and to any other light source which may be driven according to the present invention.

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• General Engineering & Computer Science (AREA)
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• 1998
  • 1998-01-29 IL IL12312398A patent/IL123123A/en not_active IP Right Cessation
• 1999
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  • 1999-01-29 EP EP99902801A patent/EP1050036A2/de not_active Withdrawn
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