CA1105161A - Numerical display using plural light sources and having a reduced and substantially constant current requirement - Google Patents

Abstract

NUMERICAL DISPLAY USING PLURAL LIGHT SOURCES AND HAVING A
REDUCED AND SUBSTANTIALLY CONSTANT CURRENT REQUIREMENT

ABSTRACT OF THE DISCLOSURE:
The present invention relates to a numerical display having a reduced dc current requirement per character display site. The invention is applicable to a variety of numerical displays including seven segment and 4 x 7 matrix displays using light emitting diodes, and low voltage incandescent segmented units designed to replace light emitting diode displays. A practical application is for displaying time in an ac powered clock or clock radio in which it is desirable to keep the dc current requirement of the display to a substantially constant minimum suitable for use with a low cost, transformerless power supply conventional with radio receivers.
The current requirement of a character display site is reduced over that of full parallel operation by selectively serializing certain light sources in a manner leaving the display control circuitry uncomplicated by permitting each light source state to be controlled by a shunt control switch sharing a common bus. Since a seven segment display may assume 27 or 128 characters and only l0 (or 11) characters are used in a full numerical font, considerable control flexibility may be sacrificed by serial segment connection before any useful characters are eliminated. A display site having a full numerical font may be reduced from 7 to 4 branches and its current reduced 43% relative to full parallel operation under shunt control. Shunt control, which diverts, rather than prevents, current flow in the display, permits the display current to remain substantially constant irrespective of the numbers displayed. When the dc current drain of a time display is comparable to that of a radio and the ac component is tolerably low, the two may be serially connected without sub-stantially increasing the dissipation over that of the clock or the radio alone.

Description

~3~ 35-EL-1403 NUMERICAL, DISPLAY USING PLURAL LI~HT SOU~CES AND HAVING A
REDUCED AND SUBSTANTL~LLY CONSTANT CURRENT REQ~MENT
. . _ BACKGROUND OF THE INVENTION-1. Field of the Invention:
The present invention relates to numerical displays using plural liyht sources and more particularly to the energization and control circuits 5 designed for such displays.

2 . Description of the Prior Art:
Visual displays consisting of characters which are formed by-the energization of various point or line element combinations are now quite common. ~uch alpha-numeric displays include the older incandescent lamp 10 matrix scoreboards and time and temperature displays as well as newer displays using light emitting diodes~ One format used frequently is a 5 x 7 rectangular matrix of points (235) which has over 34 billion potential characters of which less than 100 are normally useful, assuming both letters and numbers are to be displayed. As digital readouts find more applications 15 and continue to displace analog displays, there occur many instances of strictly numerical fonts which requirs only eleven characters or less (dei~ending on the need to generate a zero and a blank) . Since four binary elements are sufficient to generate six-teen characters (e.g. hexadecimal code), it is quite inefficient to employ seven elements having 128 possibilities 20 merely to generate these few numerals. Consumers demand a familiar font and firmly reject the use of a number system based on 16 instead of 10, so the seven line segment format is particularly popular.
The energization of a seven segment display site can be accomplished by connecting the display element branches in parallel and turning off each 25 element by means of a shunt switch causing current diversion. The current for a site is seven times that of a single segment and it does not vary greatly with the number of segments excited since the current diverted from a segment flows in the shunt switch. ~Although series control by current interruption is irequently used, thereby effecting significant dc .

3 5 -EL- 1~ 0 3 current reduction, it is normally impractical to pro~ide sufficient smoothing of the ac component for compatibility with either the desired trarlsformerless power supply or a serially connected radio rec:eiver.) Each element con-ventionally consists of a single light emitting diode creating a single visible line segment. Serial stacking of seven LED diodes (for one character site) with a shunting bipolar translstor on each segment is normally impractical. Since PNP devices would require much more area in an lntegrated form in order to handle the current for conventional LEDs, NPN devlces would be preferred. Assuming NPN devlces, the number of LEDs stacked 10 must normally be limited to avoid breaking down the emitter-base junction of the top transistor device when all other segments are "on" . Five LEDs at 1.8 volts each stack to 9.0 volts, a voltage which exceeds the maximum for most integrated NPN transistors. Thus, full serial partitioning of one character by stacking seven diodes and using bipolar control transistors is 15 normally precluded. Although a reverse current limiting diode could be employed in conjunction with each NPN, this approach would remain in-compatible with single-chip integration in the lowest cost batch fabricatlon technique currently in widespread use for production oi line operated clock/
timer ICs: MOS.
If MOSFET control devices are employed with a full serial LED
arrangement, there are comparable disadvantages which lead generally to adverse variations in brightness. The saturated MOS drain current is strongly dependent on the gate-to-source voltage, and the latter is difficult to control in the stacked arrangement. The conduction states of segments lower in the 25 stack create a wide dynamic range of source voltages for the upper MOS
switches. If brightness is controlled by current amplitude, the problems are further compoundecl.
In some display applications (e.g. line operated digital clocks and clock radios having LED readouts) a line transformer contributes significantly 30 to the total product cost. An approach which would reduce total display 5~ 3 5-EL- 1~ 0 3 current without saerificing brightness or introdueing an exeessive ae current CompOnerlt would allow a smaller, less expensive transformer or eliminate it altogether. In man~r cases, the transformer eould be omitted without inereasing the eabinet dissipation beyond aceeptable limits.
5 SUM MARY OF THE TNvENTIoN:
Accordingly, it is an object of the invention to provide an improved light emitting diode display network for a single display site.
It is a further objeet of the present invention to provide an improved numerical display using plural light sources.
It is still another object of the present invention to provide a numerical display network which requires reduced current for a single display site and uses shunt control.
It is a further objeet of the present invention -to provide a novel transformerless energization eircuit for a eloek radio using light emitting 15 diodes at four display sites for time indication.
These and other objects of the invention are achieved in a combination comprising controllable LED numerical display sites and energization and control networks for those sites. A display site displays one numerical character through a full or partial numerical font and contains a plurality of 20 light emitting diodes at positions ~a~ to "g" respectively, on a vertically elongated parallelogram with a central horizontal bar, the positions being identified as follows f ¦ ¦ b .
The diode energization and eontrol network comprises polariæed first and 25 seeond input terminals for eonnection to a unidirectional source, and a plurality of mutually parallel energization and control branches eonnected . . ~ , -' ' ': ' 5~ 35-EI,- 1~03 between the input terminals. Each branch includes a current stabillziny means, one or more forward poled diodes, and one or more switches, each returned to the second input terminal. Tal~en one branch at a time, the first branch includes a first stabillzing means and dlodes ln positions 5 a and d connected respectlvely between the first and second input termlnals, and a first switch shunting diodes ln positions a and d, whereby a dlode in position d is never on without a diode on in position a . The second branch includes a second current stabilizing means and diodes in positions c and f connected respectively between the first and second input terminals, and 10 two swltches; one shunting diodes in posi-tions c and f, and the other shunting the dlode in posltlon f, whereby a diode in posltion f is never on wlthout a diode on in position c. The third branch includes a third current stabilizing means and a diode in position b connected respectively between the first and second input terminals, and a fourth swltch shunting 15 the diode in position b. The fourth branch includes a fourth current stabilizing means and a diode in position g connected respectively between the first and second input terminals, and a fifth switch shunting the diode in position g.
When the display site is restricted to numerals from 0 to 5, the first 20 branch requires only a single switch shunting diodes in positions a and d, since the diodes in positions a and d are on or off together. In the same 0-5 display, the thlrd branch includes a diode in position e connected between the diode in position b and the second input terminal, and two switches are provided, one shunting both diodes in position b and e, and 25 the other shunting the diode in position e. The configuration causes the diode in position e never to be on without a dlode on in position b.
Wnen the display site is for numerals 0 to 9, the first branch lncludes a dlode in position e connected between the diode in position d and the second input ~erminal. The first branch also requires three switches, 30 one shuntlng dlodes in positlons a, d and e, the second shunting diodes in ~L-.' : - ~ . ~ : ;

5~ $ 35-EL- 1403 positlons d and e, and the third shunting the dlode in position e. The configuration causes the diode in position e never to be on without a diode on in position d, and the diode in position d never to be on without a diode on in position a.
In the most common display, there is one diode in each position, producing a light in a bar shape. However, the invention is also applicable to arrangements in which two or perhaps three diodes occupy each position.
In a so-called 5 x 7 display, a diode is provided at each numbered position on the parallelogram, identified as follows:
6 ~
fl ¦L
5~ g ~2 el Ic

4~ ~3 In the diode energization and control network the second branch includes a diode in position 5 connected in series between the diode in position f and said second input terminal. The second branch also includes a switch shunting diodes in positions c, f and 5, a switch shunting diodes in positions f and 5, and a switch shunting the diode in position 5. The configuration causes the diode in position 5 never to be on without a diode on in position f, and the diode in position f never to be on without a diode on in position c.
The third branch includes a diode in position 2 connected in series between the diode in position b and the second input terminal, a switch shunting diodes in positions b and 2, and a switch shunting the diode in position 2. The configuration causes the diode in position 2 never to be on without a diode on in position b. An additional fifth branch includes a fifth current stabilizing means and diodes in positions 6 and 4 connected respectivel~ between the first and second input terminals, and a switch shunting diodes in positions 6 and 4, and a switch shunting the diode in position 4. The configuration causes a diode in position 4 never to be on without a diode on in position 6 . An additional sixth branch include~s a sixth current stabilizing means and a diode ~ 5 -.

. . .

in positlon 1 connected respectively between the first and the second input terminals, and a switch shunting the diode in posltlon 1. An addltional seventh branch lncludes a seventh current stabilizing means and a diode in position 3 connected respectlvely between the first and the second input

5 terminals, and a switch shunting the diode in position 3.
In a transformerless clock radio, the LED display may be connected in series with a radio chip, and the two energized in series by a single lower power dc supply. In this application, the LED time display has four character display sites for displaying minutes, tens of minutes, hours and 10 tens of hours, and the first three of the display sites may each contain seven light emitting diodes at the previously identi:Eied positions '~a" to "g"
respectively. The energization network for the four display sites has polarized first and second input terminals, with each of the three display sites having four mutually parallel energization branches connected between 15 the input terminals . Each branch includes a current stabilizing means, and one to three forward poled serially connected light emitting diodes designed to be selectively de-energized by shunt switches. The energization network has a predetermined voltage requirement. The current requirement is sub-stantially equal to that of twelve light emitting diodes irrespective of the 20 characters displayed or the brightness adjustment. The radio integrated circuit also has a predetermined voltage requirement and a current requirement approximating that of the diode energization network. Under these conditions, the dc power supply can consist of a half wave rectifier, a filter capacitor and a voltage dropping resistor conventional to transformerless radio receivers.
25 The diode energization network and the radio integrated circuit are serially connected across the dc power supply, and the circuit is adjusted such that the output voltage of the supply is substantially equal to the sum of the voltage requirements of the energization networ~c and the radio integrated circuit at the required current. The serial connection of the radio and the 30 clock display, when the two have comparable current drains, causes no addltional power diss~pation over that of the clock or the radio alone .

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A clock timer integrated circult, normally requlrlng a much smaller current than the LED energlzation ne-twork, may be connected either directly across the dc power supply or in shunt with the LED energization network.
The invention is appllcable to a variety of displays including those using lncandescent unlts having voltage and current ratlngs comparable ~o light emitting diodes.
BRIEF DESCRIPTION OF THE DR~WINGS:
The novel and distinctive features of the invention are set forth in the claims appended to the present application. The invention itself, however, 10 together with further ob~ects and advantages thereof may best be understood by reference to the following description and accompanying drawings, in which:
Figure lA illustrates a ten character numsrical font, using seven display segments and includes a table of segment states corresponding to each character, and Figure lB is a segment position chart for the seven segment 15 dis play;
Figure 2 illustrates a seven segment display having four numerical character sites, a colon, and an AM,/PM indication for displaying time;
Figure 3 is an electrical circuit diagram for one character site of a seven segment LED display, the display being a part of a clock radio;
Figure 4 is a block diagram of a clock radio utilizing a seven segment display in which additional voltage is allocated to the display network to achieve greater constancy in display brightness;
Figure 5 is an electrical circuit diagram for part of a seven segment LED display which shows one character site capable of producing a 0 to 5 25 numerical font;
Figure 6 illustrates a ten character numerical font produced by a 4 x 7 LED display;
Figure 7A is a table of diode states of the 4 x 7 display corresponding to each numeral, and Figure 7B is a diode position chart for the 4 x 7 display;
30 and ~h~5~ 35-EL-1403 Figure 8 is an electrical circuit diagram for parl: of a ~ x 7 LED
display which shows one character site capable of produciny a 0 to 9 numerical font.
DESCRIPTION OF A PREFERRED E~BODI~IENT:
Referring now ~o Figure lA, a ten character numerical font suitable for an electrically illuminated time disp:lay is shown. ~ach character in this commonly used font may be created by selective illumination of two or more of the seven line segments which constitute the display site. (Selection of none of the segments produces a null character, which may be considered as 10 a useful eleventh character of the font.) While other light sources are known, each of the seven line segments may be illuminated by the emissions of one or more light emitting diodes (LEDs). Assuming LED illumination, the design of the individual segmsnts often involves additional optical hardware such as lenses, reflactors, filters, fiber optics and opaque stops. These measures 15 achieve greater size and contrast. The line segments ("segments~) may be of approximately equal length, and are designed to be of equal brightness when lit and to be non-visible when unlit.
The seven segments for each character display site are distributed about a vertically elongated parallelogram with a horizontal segment near 20 the center. For enhanced readability, the parallelogram may be skewed slightly, typically 8 to l0 degrees. As indicated in the segment position chart of Figure lB, the uppermost horizontal segment is marked "a", and the others, continuing clockwise around the parallelogram,bear the letters b, c, d, e, f, respectively, with the horizontal segment at the center being designated ~g~.
25 By selectively illuminating the segments a through g, as illustrated in the table of Figure IA, the numerals 0 to 9 may be selectively displayed. In the table, the lighted or ~'on" state of a segment is indicated by a ~ ', and the unlighted or '~off~l state by a "0" .
In the font illustrated in Figure lA, the following arbitrary choices ~:
30 have been elected according to common usage. The "zero" is an upper case zero, obtained by lightiny segments a through f, and leaving g unlit. The ~'one~

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3 5 -EL- 1~ 0 3 ls a right-handl~n~wlth segments b and c on, the others off. The numerals ~two", ~three~ four~ 'flve~ and ~eight~ are conventional, and are not commonly formed in a variant manner. The l~sixll ln the illustrated font has six segments with a top (a) segment present. A five segment " six" ls also 5 known with the top (a) absent. The "seven~ in the illustrated font has three (a b c) segments on and the others off, although a four (a b c f) segment~'seven'~ is also known. The "nine~'is also a six segment figure, wlth the bottom (d) segment present. A known variation is a five segment "nine" with the bottom (d) segment abs ent .
A seven segment time display having four numerical character sites is shown in Figure 2. For the purpose of displaying tlme, two of the four character sites require programming through a full font, and two through a partial font. The minutes portion of the display requires a units character which may have values from 0 to 9, and a tens character, which may have 15 values from 0 to 5. The hours portion of the display requires a units character which may have values from 0 to 9 and a tens character which has zero (or blank) and one values. A colon is used to separate the hours from the minutes (or, optionally, the minutes from the seconds) to improve the readability of -the display. Normally, a non-numerical indicator forAM and PM is provided. If 20 a 24 hour display is provided, the ~ PM indication is unnecessary, and the tens of hours character site is allowed to be zero (or blank), one, or two.
In the event that the display is used for the tuning dial of an AM radio, the rightmost site (the least significant character) may show a zero continuously, while the second and third sites may be programmable from 0 to 9. The 25 leftmost site (the most significant character) may show ~ero (or blank), or one.
Wlth a multipurpose display, all sites may be required to be programmable through a complete numerical font.
The energization and control circuit for a full font LED character site is shown in Figure 3. The drawlng shows the principal blocks of a clock radio 30 which uses the display. The energization and control circuit comprises a load ~', - .: .

circuit including an LED display and the current distribution circuitry principally located on the LED display board, a timer chip (IC2) for controlling the display, an integrated circuit radio chip (ICl), and-an ac llne operated transformerless dc power supply.
In Figure 3, the LED display for a single character site is shown in circuit symbolism and the current distribution circuitry for that site is shown. Each of the segments a through ~ for one site of the display is electrically represented as a single diode (LEDa to LED3). A sm311 arrow is associated with each of these diodes to denote the light emitting property.
The diodes are polarized in the direction indicated by the diode symbol and are designed to give off light when sufficient forward bias (normally between 1.3 and 2 volts) is present. While operable from a battery source, the light emitting diodes may also be energized by a half wave rectified ac waveform wlth or without filtering. The current distribution network for the light emitting diodes of each character site consists of four parallel branches or current paths. Each branch consists of a series string of from one to three light emitting diodes poled in the direction of easy current flow, and a large series connected impedance which acts to stabilize the current in the branch, The LED control circuit shown in Figure 3 is contained in an integrated circuit (IC2). The integrated circuit is a part of a clock timer designed to derive timing information from the 60 cycle power line by means not shown, and to provide a binary control output for the LED display at seven pads (Pa to Pg). The clock timer chip (IC2) is of the p-MOS process, and requires a -20 volt drain supply potential (-VDD) referenced to a nominally 0 volt source supply potential (VsS). ~ succession of seven p-MOS Eield effect transistors (Ta to Tg) located on the clock timer chip and all having their sources coupled to the common V5S supply bus, provide the seven binary control outputs. These field effect transistors act as shunting switches for the LED display segments, responding to a translated timing signal available at the intemal terminals (18 to 24) .
.

: ~ :

The transformerle~;s dc source in the Flgure 3 arrangement is energized from a conventional 110 volt ac power main and includes a half wave rectifier Dl, a voltage dropping impedance Rl and a filter capacitor Cl. An integrated circuit chip (ICl), which contains the active circuitry of a 5 radio receiver, forms a virtual second voltage dropping impedance for the display In addition, a second diode D2, a series resistance R2 and a large (1000 ~Ifd) "hold up" capacitor C2 are provided for the timer chip.
The dc source is connected as follows. The dc source is coupled to a llO volt 60 (or 50) hertz ac main by means of the plug ll. One pin 12 of 10 the plug is connected through the line cord to the cathode of the rectifier diode Dl and the other pin 13 is connected through the line cord to the ~Vss pad on IC2 and to the pad 14 connected to the positive LED display bus on the LED display board. The pin 13 is of nominally zero potential and by connection to the Vss pad and to the pad 14 becomes the positive source terminal for the 15 timer chip and the LED display board. The voltage dropping resistance Rl connects the pad 15 on the radio chip (ICl) to the anode of diode Dl, which draws rectified current from the load and thus provides the negative bias connection to the radio chip (ICl) . The serial order of the diode Dl and the resistance Rl may be reversed, particularly where the resistance is "fusible"
20 to self-destruct on overload. The positive bias pad (16) on the radio chip (ICl) is connected to the pad 17 connected to the negative LED display bus for serial connection of the LED display circuit and the radio chip (ICl) across the dc source. The large (100 ~1fd) filter capacitor Cl is couPled between the negative pad 15 on ICl and the positive LED display pad 14 (also pin 13) . The 25 positive terminal of the capacitor Cl may optionally be coupled to the positive pad 16 on the radio IC, in which event the voltage applied to the radio (ICl) is filtered by a lower cost capacitor having a lower vol-tage rating and the LED
supply is left unfiltered. The path for dc energization of the clock timer chip IC2 is completed through the diode D2, whose cathode is coupled .

to the negatlve radio pad 15, and whose anode is coupled through resistance R2 to the -VDD pad on the clock timer chip.
The dc source supplies low voltage bias to the LED display, the radio chip (ICl), and the clock timer chlp (IC2) . The LED display and the radio S chip are serially connected across the source. The clock timer chip (IC2) is connected in shunt with the two using a voltage dropping resistor R2. The anode of diode Dl assumes a negative polarity in respect to the voltage at the pin 13, which is the common load connection. With a current drain of 53 milliamperes, this voltage is about 72 volts (ave.). The 820 ohm resistance 10 R1 produces a further drop of about 43.5 vol-ts, so that a 28.5 volt potential difference appears at the negative radio IC pad 15 with respect to the positive display bus and common load connection. The radio chip draws approximately 50 milliamperes at a fixed voltage drop of 13.5 volts. This drop is held sub-stantially constant due to an internal voltage regulation circuit including a 15 zener diode. The LED display is also designed to conduct a substantially equal, 50 milliampere, current at the 15 volt potential difference remaining between the negative LED bus and the positive LED bus. The dc source provides three milliamperes of current at 20 volts to energize the clock timsr chip IC~ between its ~Vss and -VDD pads. Resistance R2 and the diode D2 20 produce an approximately 8.5 volt drop at 3 milliamperes from the 28.5 volts available at pad 15 of ICl with respect to the common load connection. The diode D2 prevents the "hold up" capacitor C2 from being discharged by the display when short term voltage drops occur on the ac line.
Each site of the LED display is energized by the dc potential applied 25 between the LED display buses (i.e. at pads 14 and 17~ . As noted, the LEDs for each full font site are arranged in four parallel branches, each branch including a large current stabilizing impedance. The first branch comprises the three light emitting diodes LEDe ~ LEDd and LEDa and a current stabilizing, 3100 ohm resistance (R3)~ The anode of diode LEDe is coupled to the positive 30 LED display bus, while its cathode is coupled to the anode of LEDd. The cathode of LEDd is coupled to the anode!of LEDa, and the cathode of LEDa , . .

is coupled through resistance R3 to the negatlve LED display bus. The second branch comprlses the two llght emltting dlodes LEDf and LEDC and a current stabllizlng, 3400 ohm resistance (R4). The anode of diode LEDf is coupled to the positive LED bus while its cathode is coupled to the anode of LEDC. The 5 cathode of LEDC ls coupled through resistance R4 to the negative LED bus. The third branch comPriSeS the light emltting diode LEDb and a current stabilizlng, 3700 ohm resistance (R5) . The anode of the cliode LEDb is coupled to the positive LED bus, and its cathode is coupled through resistance R5 to the negative LED bus. The fourth branch comprises the light emitting diode LEDg 10 and a current stabilizing, 3700 ohm resistance (R6). The anode of the diode LEDg is coupled to the positive LED bus and its cathode is coupled through resistance R6 to the negative LED bus. Assuming that all seven light emitting diodes in this site are lighted (as when an "eight" is displayed), each diode will draw approximately 3.5 milliamperes and produce a voltage drop of 15 approximately 2 volts. The maximum power consumPtion approximates 7 milliwatts per display segment, or 49 milliwatts per display site . The resistances R3, R4, R5 and R6 are designed to provide an approximately equal current in each segment.
The foregoing four branch energization configuration permits any one 20 of the full 0 to 9 font or a blank, if it is desired, for the display character.
Control over the excitation of the seven light emitting diodes of a single display site is achieved by the control circuit located on IC2. The control requirements of the LED display are not complicated by the consolidation of the energization circuit into four branches. Each of the seven LED diodes 25 in a display site requires the same polarity and magnitude of switching signal. In addition, the control circuit, provided that all control signals can he complemented simultaneously, may be oi the type that is usable for either series or shunt cvntrol.
The control circuit for the LED display comprises the seven MOSFET

30 transistors (Ta to Tg) formed on the timer chip (IC2) and responding to binary states existing at the in~ernal terminals 18 to 2~ of the timer chip. By shunt 3 5 - E L- 1'10 3 current control, these transistors force on and off states for indlvidual segments, as indicated in Figure lA, to produce the individual numerals of the font. The EET control transistors (Ta to Tg) are all formed on a P-channel chip with their sources all connected to the source bus (Vss) at a nominal 5 0 volts. As previously noted, the (Vss) source bus is coupled via the pad 14 to the positive LED bus and via the positive LE:D bus to the uppermost LED anode of each of the four energization branches (i.e., the anodes of LED~, LEDf, LEDb, LEDg). In short, the sources of all the FET control transistors (Ta to Tg) are connected together and to the anodes of LEDa, LEDf, LEDb and LEDg, also 10 connected together. The drains oi~ the FET control transistors ~a to Tg) are connected respectively to the pads (Pa to Pg) on the timer chip (IC2) and these pads are in turn coupled to the cathodes of the respective light emitting diodes (LEDa to LEDg). The gates of the control transistors (Te, Td, Ta, Tf, Tc, Tb, Tg) are connected respectively to the internal control terminals 18 to 24. The 15 gate control circuitry is designed to produce binary operation of the FET control transistors between high conduction and near~zero conduction states.
The FET control transistors effect a shunt control of l:he display light emitting diodes. The shunt control operation inthe simplest form may be explained by reference to the light emitting diode LED3. The anode of this 20 light emitting diode is coupled to the positive LED display (pad 14) which is also coupled to the Vss pad on the clock timer chip. The control transistor Tg, associated with LED~, which is coupled through a current s-tabiliziny impedance R6 to the negative LED display pad 17, if off, allows the lighted LED to drop 1.3 to 2 volts. If the control transistor Tg becomes conductive, the drain 25 potential approaches the source potential and the cathode potential across the LED approaches, but does not reach, zero volts. The reduction in voltage across the light emitting diode reduces its conduction to a low value thereby extinguishing its visible light emission. The current which hacl previously been flowing in the light emitting diode is now mostly diverted to the control 30 transistor. In the normal case of imperfect current stabilization, including ' .
:

the simple resistor/low voltage circuit of Figure 3, the control transistor may conduct more c-lrrent -than was flowing through the "on" diode, w~iile at the same time leaving a finite but negligible current flowlng through the "off" diode. Essential to shunt operation is that the control transistor have an adequately low saturation voltage (drain current x channel resistance product) to reduce the light output of the light emitting diode below the visible threshold.
Shunt control of the light emitting diode LED,;~ (in the fourth branch) is duplicated in the light emitting diode LEDb in the single diode third branch,but is modified for the diodes in the plural diode branches. For instance, the diodes LEDC and LEDf in the second branch are connected in a series "string".
If the control transistor Tc becomes conductive, it will bring the potential drop across both diodes LEDC and LEDE below the visible threshold, turning off both together. If the control transistor Tf becomes conductive, it will bring only the potential drop across diode LEDf below the visible threshold.
The diodès LEDa ~ LEDd and LEDe are subject to a similar mode of control .
If the control transistor Ta becomes conductive, it will bring the potential drop across all three diodes LED3, L~Dd and LEDe below the visible threshold, turning off all three. If the control transistor Td becomes conductive, it will turn off both diodes LEDd and LEDe. If only control transistor Te becomes conductive, it will turn off diode LEDe alone . The configuration tends to relax the saturation voltage specification for control transistor Ta which may result in a smaller device and, ultimately, lower ~roduction costs. This is also true !to a lesser degre~of control transistors Td and Tc .
The four parallel energization and control branches permit display of a full 0 to 9 font (including a blank) and, although many non-numeric characters are precluded, do so without complication of the control logic.
The immediate benefit of partial serializatlon of the seven diodes at a character site lnto four branches i6 a reduction in the current drain by about 43% relative to a conventlonal seven branch all parallel configuration. The .
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~L 3 5 - E L- 1~ 0 3 seven segments of an lndlvidual character site are capable of 2 or 128 dlfferent characters compared to the 11 useful characters (including the null character) required for a full numerlcal font. The objective is to analyze the combinations of segment states required for this font and, while some display 5 flexibility is lost by a less than full parallel configuration, reach a point in partial serialization at which useful characters would be eliminated by any further serializatiPn. In addition, the configuration mlst avoid complicating the control configuratlon and must permit the control devices to shunt to a terminal common to all control devices and all display branches. For shunt 10 control, we further assume energization of each branch from a substantially constant current source included in each branch, and that the control over each light emitting diode redllces the voltage across that light emitting diode to below the visible excitation level and diverts the current to an alternate path. An analysis of the font discloses that the segmsnt f is never visible 15 without the c segment also being visible. The foregoing discovery makes it possible to connect the diodes forming the c and f segments in series, with the diode f subject to the "inner" or one diode shunt control, and the diode c subject to the "outer" or two diode shunt control. This discovery precludes 32 unused characters, and eliminates one parallel current path. Further 20 analysis of the required combinations of segment states shows that the segment e is never visible without the segment d being visible. This discovery makes it possible to connect the diodes forming the e and d segments in series, with the diode e subject to the "inner" or one diode shunt control and the diode d subject to the "outer" or two diode shunt control. This discovery 25 precludes 32 unused characters (of which ~ ware precluded above) and eliminates a second current path. Further analysis of the required combinations of segmsnt states shows that the segmsnt d is never visible without segment a being visible. This discovery makes it possible to connect the diodes forming the a, d and e segm~nts in series, with the diode e being subject to the "inner"
30 or one diode shunt control, and the diode d being subJect to the "intermediate"

., . .- - . . . - . ' , :' . ': .' : . . .' . ... .: : . . .

35 -EI.- 1~03 or two diode shunt control, and the diode a being subject to the "outer~ or three diode shunt control. This discovery precludes additional unused characters and elim5nates a third separate current path. Taken together, with three serially connected diodes in the first energization and control branch, 5 two serially connected diodes in the second energization and control branch, and single diodes in each of the third and fourth energization and control branches, some 80 unused characters are precluded, permitting 4~3 characters, in which ll characters required for a full numerical font are found With the four path energization, three current paths of the seven conventionally used 10 are eliminated, resulting in a ii3% current saving for each full-font, shunt controlled seven segment display site.
The four branch energization and control network has a ma jor advantage in current saving with only a minor disadvantage in brightness "modulation~' .
The serial connection of two or three display segments occasions a change in 15 the brightness of one display segment as the other serially connected segments are switched. Assuming a 15 volt supply and a 2 volt drop in each light emitting diode, the current supplied to a single diode in a single diode branch (i.e., LEDg) is stabilized by an impedance which has a voltage drop 6-1/2 timss as great as the cliode voltage. This sets a brightness standard to wnich the other 20 segments in other branches may be referenced. In the three diode branch, the voltage drop across the current stabilizing impedance is only l-l/2 times larger than the voltage drop of the three serially connected light emitting diodes. This indiGates that the light output is likely to depart most from some standard level of brightness when the diodes in the longest series chain 25 are switched. An assumption that the shunt switch has either a zero or an inEinite resistance is unnecessarily severe. In the indicated configuration, employing FET shunt control devices, the "on" condition of the shunt device can be made to have a voltage drop in excess of one volt. Assuming 2 volt LEDs, a one volt drop in the shunt device halves the change in voltage applied 30 to the branch when the first diode (e.g. LEDe or LEDf) in the string is cut off.

' - 1 7 - ;

.,, , : .
' : . :,' , , 3 5 -EL- l ~ 0 3 In the case of equal 1.3 volt saturation voltages for both inner and intermediate shunt control transistors of the three dlode branch operated in Figure 3 from a 15 volt supply, the variation in current is approximately 28%. The reference for that branch is one in which the first LED (LEDf) in the three diode series is 5 off. When all three diodes are on, there is a drop in branch current of 7%.
When a second diode (LED~) goes off, there is an increase in current of 21%.
Should higher saturation voltages be used in the intermediate or inner shunt control devices, the variance may be further reduced. Doubling of the saturation voltage of the intermediate shunt control device ( to 2 .6 volts) in 10 this example reduces the variance to + 7% .
The foregoing assumptions used to estimate changes in brightness under different conditions are conservative and design freedom sxists to reduce the effect, if necessary, to a desired level. For example, constancy in the voltage drop across the LEDs with increased current is assumed. In 15 practice, the voltage drop in the light emitting diode increases as the current goes up, and tends to reduce the actual current increase in any remaining diode. Similarly, the voltage developed across a shunt switch has been assumed to be independent of current. The use of MOSFET switches "tumed on"
by a current-independent gate-to-source voltage bias greatly exceeding the 20 threshold voltage results in an essentially resistive drain-to-source channel, thereby providing additional negative feedback for improved current stabilization.
A second practical factor in reducing the effect of supply current variation on brightness is that the diodes may be operated near saturation. When near saturation,increases in current produce a less than proportional change in light 25 output . A third mitigating factor is the subjectiva effect on the viewer as the change in "on/off" status of soma segments within a display modulates the brightness of other segmants (typicallywithin the same character site) which remain "on" through the transition. (The worst examples of this interaction in the embodiment of Figure 3 occur when the number displayed is incremanted from 30 ~ to 7 or from 7 to 8.) Since the viewar is normally looking at the total display, : .

.

' -: . - . . . . . . .. .. .
- - , .. .

j. 35-EL-1~03 any complete turn-on or turn-off of a segment registers as a new number. In the unlikely event that one's attention is concentrated on a single segment which will remain "on" through the transitions of interest, that attention will probably be diver~ed to a nearby segment as it turns"on" or "off" . Thus, the 5 significance of this brightness modulation does not rest primarily in the time-varying nature of the brightness of a single segment, but rather in the impact which this effect has on the range of segment brightnesses to be found at any instant within a single character and, less critically, within a complete display. As such, this effect is seriously detrimental only if it significantly 10 aggravates the existing inequalities in brightness due to poor matching of LED _haracteristics and non~compensating ratio errors among current stabilizing msans. If such a problem does exist, resolution probably resides in better process control of LED Eabrication procedures and/or tighter LED
testing limits. Finally, in the event that a given circuit voltage (e.g. 15 volts) 15 allows too great a variation in the brightness of individual segments, the circuit voltage may be increased, typically to 40 volts, without exceeding the voltage breakdown limits of conventional energization or control circuitry.
The effects of a doubling or tripling of the circuit voltage are to bring about a reduction in the current variation of more than 1/2 or 2/3, respectively, and 20 to correspondingly reduce the brightness variation. Since the LED circuit voltage is normally achieved by a dissipation technique, an increase in the voltage across the paralleled energization and control circuits in order to equalize the brightness of the individual se~ments produces no additional power dissipation. In fact, since the total current for a shunt controlled 25 display is reduced while being drawn ultimately from the sarne ac line voltage, the powsr dissipation may be reduced by the same percentage as the current reduction with respect to comparable circuits.
The 43% current savings in an individual character site permits a single timsr chip to control a four character display, and permits the unit to 30 b3 powered by a lowsr power, transformerless, supply. The current requirement - 19 ~

: - .

r l D ~ ~ ~ 3 5 EL- 140 3 for four full dlgits is typically reduced from 90 to 50 milliamPeres. The control circuit dissipation is reduced as well. When a segment is off, the heat dissipation in a control transistor is about 4.55 milliwatts (1.3 volts x 3.5 milliamperes). In a conventional seven parallel circuit configuration, when 5 all segments of a site are off, th~ dissipation is 32 mllliwatts. Assuming a 12 hour display having 4 numerical sites, ~M/PM indicators and colon, the total control circuit dissipation would be about 123 milliwatts. In the present four circuit configuration, when all segments of a site are off, the comparable dissipations approach 18 milliwatts per character,or typically, 63 milliwatts 10 total. The very sizable reduction in current drain permits the combined power dissipation within the clock radio cabinet (including voltage dropping resistor dissipation, control circuit dissipation, display dissipation, current stabili~ing resistor dissipation, radio IC dissipation and loudspeaker dissipation) to fall within the 7 w3tt maximum design praference. Assuming the conditions of the 15 first embodiment, the 820 ohm resistance Rl produces a voltage drop of 43.5 volts at 53 milliamperes, and a dissipation of about 4. 37 watts . In a con-ventional 93 milliampere configuration, a like voltage drop would occasion a dissipation of about 7.6~ watts. The remaining dissipations in these examples are approximately 1.51 watts and 2 .65 watts, respectively, for total respective 20 cabinet dissipations of about 5.88 watts and 10 31 watts . This significantly reduced dissipation makes practical the replacement of the relatively expensive transformer-type power supply by the line dropping resistor-type supply.
In Figure 4 a variant arrangement is described for providing the dc bias for the LED display In this arrangement, additional voltage is provided 25 for the display to reduce the variation in brightness of individual segments as different numbers are displayed. As before, the radio chip ICl and the LED display board 26 are connected in series as a load across the dc supply, and the dc supply comprises a half wave rectifier D3 and a series voltage dropping resistance R7. A filter capacitor C3 shunts the load. With an 30 increase in values oi the current stabilizing resistances of the LED display .

~,3~
35-EL- 1~03 board, and a decrease in the value of the series voltage dropplng resistance R7, the voltage available to the LED dlsplay board 26 may be readily increased to 40 volts. This is the maximum voltage that the clock timer IC2 can be allowad to control, uslng devices made in the conventional p-MOS process. The clock 5 timer IC2 is energized in shunt vvith the LED display board in a series circuit including the chip IC~, the resistance R8, and the diode D~. The hold up capacitor C4 shunts the chip IC2. While the indi~idual switching control connections are not shown, they may take the same form as illustrated in Figure 3.
If a partial numsric font, possibly including a blank but not requlring any "six" or "seven", is desired, as for instance a 0-5 font, the LED
configuration of Figure 5 may be employed. A typical application of this partial font might be in a time display site dedicated to tens of minutes and/or tens of seconds. Here, the positive display bus is shown at 1~ and the negative 15 display bus is shown at 17. The light emitting diodes are connected in four paralleled circuits as before for energization and control, but the present arrangem3nt differs in the distribution of the light emitting diodes and the omission of a control connection. In the first energization and control circuit, the light emitting diodes LEDd, LEDa ~ and a first current stabilizing resistance 20 are connected in series in the order recited. In the second energization and control circuit, the light emitting diodes LEDE, LEDC and a second current stabilizing resistance are similarly connected in series. In the third circuit, the light emitting diodes LEDe and LEDb, and a third stabilizing impedance are similarly connected in series. In the fourth circuit,the light emitting 25 diode LEDg and a fourth current stabilizing im~edance are connected in series.
In the first circuit, there is no need to separately control the diode LEDd to achieve the desired font, and the control connection may be eliminated. In the third circuit, the serLal connection of the diodes LED3 and LEDb eliminates 32 possible characters (some of which are redundant with others already 30 elim lnated). Th a dva nta ge of this contiguration ot reduced universaiity , .

ls that it provides a more uniform brightness at a given magnitude of voltage dropped across the current stabilizing impedance than a configuration that has three diodes in series.
Shunt switching, in which total display current is held approximately 5 constant, is essential in a line operated transformerless system. The total current through one branch of the display, when a given display segrnent is on and its shunt control off, is held substantially equal to the total current through that branch when the display segment is off and its shunt device is on.
While the change in voltage drop between a lighted LED segment and an "on"
10 transistor shunt cannot be exac'cly zero, any current variation in that branch of the display is held to an acceptable minimum by design of the switching device or by use of a suitably large voltage drop across the current stabilizing resistance. If current in each branch is held constant, then that in the total display is held constant. If the total display current is not essentially constant, 15 as with series switching of a parallel connected display, a fixed resistor in the powar line is not a practical way to produce a desired display voltage because of the large current variation. In addition, without controlled display current, another load element, such as a radio IC, could not efficiently re-use the display current. Assuming a complete turn-off at the ~ED;" as in a series 20 switching arrangement, a 9 to 24 ratio of total display currents ~i.e., between the times of 1:11 and 10:08) is produced in a conventionaldisplay even when such ratio-reducing constants as two colon dots always "on" and one of the AM,~PM indicator dots always "on" are considered. Such a current variation would be too large for practical re-use of the current in a serially connected 25 radio IC.
.
Reducing the total current in the LED display by about 40% to a value which is compatible with the power-handling capability of a radio IC chip ~ - -~e.g., 55 milliamperes) permits the two to be connected in series, and permits energization of the two by a single power supply consisting of a half wave 30 recti~ier using a voltage dropping resistor and a filter capacitor. The current ~ 2 2 35-EL l~0:~

drain ln the LED display need not be exactly equal to that in the radio IC, s1nee a low cost resistance can shunt one or the other to make up any small differene-es in eurrent, particularly in the case of a radio IC lacking lnternal shunt voltage regulation. The current in the radio receiver is selected to hold power 5 dissipated within the radio eabinet to about 5 watts. The unmodified LED
display requires approximately 3.5 milliamper~ss per segment, 24 milliamperes per eharaeter, and approximately lO0 milliamperes for a four digit display. This level of eurrent is quite unaeeeptable for line cord operation and would produee a cabinet dissipation of over twelve watts. Wlth an overall reduction in curren-t lO of about 40%, attributable to the four pathenergization network and certain other eurrent eeonomies, the current in the LED display can be reduced to fit within the acceptable current range of a serially connected radio receiver. As a result, the heat previously dissipated in the series dropping resistance of the radio receiver is now dissipated in the LED display (including the energiza-lS tion and eontrol eireuitry), without increasing the total heat dissipationrequirements of the eabinet. Sinee the nominal design value of the radio IC
supply current is 42 mA., a design trade-off exists wherein display brightness may be saerifieed for deereased dissipation. In the practical embodiment of Figure 3, eabinet dissipation is allowed to inerease toward the practical 20 maximum in order to aehieve maximum brightness.
The shunt control units may be of either p-type or n-type polarity, and may be either FET devices or bipolar transistors. In the Figure 3 and Figure 4 eonfigurations, FET devices must have an adequately low ~l saturation~ voltage when turned on to reduce the visibility of the light emitting diode to the desired 25 unlit visibility. Duty cycling is preferred over other known compatible brightness eontrol teehniques for the FET embodiments described and allows the same shunt eurrent amplitude regardless of brightness ad~ustment. With two volt LEDs, the "offl' voltage is typieally higher than l. 3 volts . With lower voltage LEDs, the "off" voltage may be lower. With serial branehes, the saturation voltage of the 30 shunt eontrol eireuit may be higher on the intermediate or outer eontrol connections, and still aehieve an unlit state in the LEDs, partieularly if, whenever over-ridden, 35-EL- l 403 each shunt control clrcuit is forced to be ln its low conductlon state. With bipolar transistors, the problem of excessive saturation voltaye is normally not as severe as with FETs. If n-type control devices are employed, -the circuit connections in the display circuit board may remain as before, but 5 the polarity of the display buses should be inverted and the individual LEDs should each be kept in the same position, but wlth reversed connections.
While series resistors have been shown as the current stabilizing means in each branch of the display, it should be evident that active transistor current sources could also be employed. This causes some penalty 10 in cost unless integrated in the clock timer IC chip.
The invention is also applicable to a 4 x 7 LED display producing a O to 9 numerical font. A common 0-9 font for the 'I x 7 display is illustrated in Figure 6. The diodes of each character site are located at the intersections of a 4 x 7 matrix. Typically, there are twenty diodes and eight vacant inter-15 sections. The visual effect permitted by this number of diodes is to introduce a sense of curvature into certain of the numerical characters. The zero, for instance, by omission of the corners, appears to have a curved top and bottom.
The curved effect is present in all of the numerals except the 1, 4 and 7.
A table of the diode states for a 0 - 9 numerical font for the 4 x 7 LED
20 display is shown in Figure 7A, with the diode positions being charted in Figure 7B. Referring initially to Figure 7B, it may be seen that the diodes are disposed about an elongated parallelogram having a horizontal bar. Assuming the position designations used for the seven segment displays discussed earlier, 14 diodes are located on the line segments a, b, c, d, e, f and g, 25 and 6 diodes are locatecl at numbered locations 1 to 6 where the lettered line ..
segments adjoin. ~s i:llustrated, two diodes occupy each line segment and are designa~ed al, a2; ~ b2; cl~ c2; dl, d2; el, e2; fl~ f2; gl~ g2; P
One diode occupies each joint or "corner" and it is designated 1, 2, 3, 4, 5 and 6, respectively, proceeding clockwise around the parallelogram after 30 starting in the upper right hand corner of the character. (In a 5 x 7 display, three diodes occupy each line segment.) .
' ,:

35-EL 1~03 The diode states for each charac~er of the 0 - 9 numerlcal font shown in Figure 6 are indicated in Figure 7~. Since the lettered diodes ln the 4 x 7 display occupy the same positions that the lettered dlode occupied in the seven segment display, it is plausible that the circuit serialization achieved by ruling out unnecessary states in tlhe seven segment display can also be accomplished. The table of diode states is identical between the diode in posi~on a, for example, of the seven segment display and the corresponding diodes al, a2 also in position a of the 4 x 7 display The fourteen diodes might, obviously, form the whole display, in which event the display would be an apparently curved approximation to the angularity of the segment display. Addition of the numbered diodes enhances readability significantly .
Further analysis of the table of Figure 7A shows that the control for the numbered corner diodes can be profitably integrated with control for the lettered diodes. The diodes on segments a, d and e are essentially independent of the numbered diodes. On the other hand, diode S is never on without diodes fl~ f2 being on. This implies that diode 5 may be connected in the inner position in a branch consisting of the current stabilizing resistance Rl2, diodes LED c2, LED cl, LED f2 ~ LED fl, and LED5. Since diode 2 is never on without diodes bl, b2 being on, they may also share a branch. The diodes on segment g require their own branch. The fact that diode 4 is never Oll unless diode 6 is on implies that the two may be connected in a single branch in which a current stabilizing resistance Rl5 and diodes LED6 and LED4 are serially connected. The remaining diodes LEDl and LED3 require separate branches.
A circuit diagram for the energization and control network for a 4 x 7 diode display is shown in Figure 8. This circuit is capable of presenting the numerical font of Figure 6. The circult contains seven branches, in which the current stabilizing resistances are numbered respectively Rll to Rl7. In the first branch, althoughtheycould be serially connected, the diodes in each line segment are paralleled to reduce the supply voltage requirement. Since -.

the devlces on a llne segment are paralleled, the current in that branch ls double that ln the other branches, and the sum of dlode voltage drops tendlng to modulate the brlghtness of the a segment dlodes ls reduced to a range of from three dlodes on to one dlode on. The second branch has all five dlodes 5 connected ln serles so as to preserve a constant current in each member of the branch. The corresponding sum of diode voltage drops in thls branch varles from 5 to 4 to 2 drops. The remainder of the conflguration follows the same pattern, presenting a current draln of eight dlodes, as opposed to twenty had there been fully paralleled energlzation.
While the principal embodiments of the invention have used light emitting diodes, it should be evident that the inventlon is also applicable to other light sources. In particular, those segmented incandescent displays which are designed to replace light emitting diodes may be used. Light emitting diodes are intrlnslcally low voltage devices relative to house main 15 voltages (110-130 volts) and thus, in transformerless supplies, current conservation is essential to reasonable power dissipation. Indlvidual LED
segments at maximum brightness normally requlre voltages lying withln the range of from 1.5 to 3.5 volts. Thls voltage corresponds to the forward voltage drop in a semiconductor junction (or two in series), slightly increased 20 by the additional drop due to forward diode current flowing through the parasitic resistances in the device (or devices). The brightness in LED devices is approximately logarithmic, changing quite sharply at a ~knee" typically above two-thirds of the normal operating voltage. These devices need not be forced to a zero voltage drop to reduce the brightness below the visible range, but, 25 in most practical applications, only to a voltage in the vicinity of the ~knee~ .
The low "on" voltages and the relatively high "off" voltages permit LED
devices to be stacked in series of up to five diodes without exceeding the maximum "off" voltage, or requiring unduly high conductances, respectively, of low cost, shunt connected IC switches. The currents of LED devices 30 normally range from 0.6 milliamperes to 40 mllliamperes dependent on diode ': ' ' ~ ' ' : . . . . .

35-EI,-1403 slze, segment size and desired segment brlghtness. In consumer products .
such as the clock radios partially deplcted ln Fls~ure 3 and Figure 4, dlsplay cost is a very significant consideratlon. The display cost reduction afforded to the calculator manufacturers by means of decreased character height is not S avallable to the producer of clock radlos because the normal viewing distance is so much greater. Since decreased diode slze tends to reduce both display cost and current drain, clock radios normally use diodes which are rnuch smaller than the segments which they illumlnate. ~hs decreased maxlmum segment brightness whlch results ls acceptable prlmarily because of -the 10 relatively low ambient light level characteristic of a typical clock radio operating environment, a notable exception being the strong lighting often associated wlth point-of sale demonstrations. Inexpensively available, high-efficiency light emitters such as the 3.5 milliampere GaAsP diodes assumed in Figure 3 and Figure 4 adequately satisfy the desire for increased 15 brightness within the cost constraints of this product market. When LED
devlces having 3.5 milliampere currents are employed, a good current match is found between a four character clock tlmer display and a 50 milliampere radio chip, and the two may be serially connected as earlier discussed. When a given segment current level and maximum brightness are desired, the present 20 configuration can be used to reduce the total current drain by the 40% earlier mentioned over that of full parallel energization. Thls, in effect, permits use of a brighter LED display (or one having the same brightness but using less efficient diodes) when the current drain is fixed.
When LED devices are replaced by incandescent devices, the same 25 considerations apply. The lncandescent devices, designed for LED replacement, should be of appropriately low voltages to permit five-unit stacking without exceedlng the breakdown voltages of conventional semlconductor switching devices. Furthermore, in applications requlrlng a full-range brightness control, they should have a strongly non-linear brightness versus voltage characteristic, 30 so that they can be turned; off with relatively " poor" shunt switches . The ' present lnventive configuratlon permlts the current of such a display to be reduced 40%, thereby allowing a correspondinçl decrease in the net dlssipation of a transformerless supply. Conversely, it permlts the brightness to be greatly increased within the limits of the available current in transformerless 5 supplies. Thls increase in brightness may be used ior improved contrast in high amblent light level situations. In applicatlons which cannot benefit signlficantly from increased brightness, the unlimlted color filter selection made possible by the wideband nature oi the incandescent output spectrum comblned with the excess brightness required to compensate for filter 10 absorption provlde a saleable package in the consumer market place, where alternate display color choices are valued.

Claims (7)

35 EI. 1403 The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. The combination comprising:
(1) a controllable site capable of displaying singly numerals representing the integer numbers 0 to 9, said site containing a plurality of discrete light sources at positions "a" to "g" respectively on a vertically elongated parallelogram with a central horizontal bar, said positions being identified as follows:

(2) an energization and control network for said light sources, comprising:
A. polarized first and second input terminals for connection to a unidirectional source, and B. a plurality of mutually electrically parallel energization control branches connected between said input terminals, each branch including a current stabilizing means, one or more discrete light sources, and one or more switches each returned to said second input terminal, (a) a first of said branches including:
(1) a first current stabilizing means and light sources in said positions, a, d and e connected respectively between said first and said second input terminals, and (2) three switches: a first switch shunting said light sources in positions a, d and e, a second switch shunting said light sources in positions d and e, 35 El 1403 and a third switch shunting said light source in position e, whereby said light source in position e is on said light sources in positions d and a are on, and when said light source in position d is on said light source in position a is on, (b) a second of said branches including:
(1) a second current stabilizing means and light sources in said positions c and f connected respectively between said first and said second input terminals, and (2) two switches: a fourth switch shunting said light sources in positions c and f, and a fifth switch shunting said light source in position f, whereby said light source in position f is on said light source in position f is on said light source in position c is on, (c) a third of said branches including:
(1) a third current stabilizing means and a light source in said position b connected respectively between said first and said second input terminals, and (a) a sixth switch shunting said light source in position b, and (d) a fourth of said branches including:
(1) a fourth current stabilizing means and a light source in said position g connected respectively between said first and said second input terminals, and (2) a seventh switch shunting said light source in position g.

2. The combination set forth in claim 1, wherein each light source includes a forward-poled light-emitting diode.

3. The combination set forth in claim 2, wherein each light-emitting diode is capable of producing light in a rod-like shape.

4. The combination set forth in claim 1, wherein each light source includes two forward-poled light-emitting diodes.
5. The combination set forth in claim 1, wherein (l) said site also contains a discrete light source at each numbered position identified as follows on said parallelogram:

(2) the second branch also includes:
(i) a light source in position 5 connected in series between said light source in position f and said second input terminal, and (ii) said fourth switch shunting said light sources in positions c, f and 5, said fifth switch shunting said light sources in positions f and 5, and said second branch including an eighth switch shunting said light source in position 5, whereby when said light source in position 5 is on said light sources in positions f and c are on, and when said in position f is on said light source in position c is on, (3) the third branch also includes:
(i) a light source in position 2 connected in series between said light source in position b and said second input terminal, and (ii) said sixth switch shunting said light sources in positions b and 2, and said third branch including a ninth switch shunting said light source in position 2, whereby when said light source in position 2 is on said light source in position b is on,

Claim 5 (cont'd) (4) said network further comprises a fifth branch including:
(i) a fifth current stabilizing means and light sources in positions 6 and 4 connected respectively between said first and said second input terminals, and (ii) two switches: a tenth switch shunting said light sources in positions 6 and 4, and an eleventh switch shunting said light source in position 4 t whereby when said light source in position 4 is on said light source in position 6 is on, (5) said network further comprises a sixth branch indlucing:
(i) a sixth current stabilizing means and a light source in position 1 connected respectively between said first and said second input terminals, and (ii) a twelfth switch shunting said light source in position, 1 and (6) said network further comprises a seventh branch including:
(i) a seventh current stabilizing means and a light source in position 3 connected respectively between said first and said second input terminals, and (ii) a thirteenth switch shunting said light source in position 3.

6. The combination set forth in claim 5, wherein each light source includes a forward-poled light-emitting diode.

7. The combination set forth in Claim 6, wherein each light source at a lettered position includes at least two forward-poled light-emitting diodes.