Note: Descriptions are shown in the official language in which they were submitted.
~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
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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
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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
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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
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3 5-EL- 140 3
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
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3 5 - L- 14 0 3
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) .
.
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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
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3 5 - E L- 14 0 3
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
,
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3 5 - E L- 14 0 3
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
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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
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3 5 -EL- 14 0 3
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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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"
-- 16 --
., . .- - . . . - . ' , :' . ': .' : . . .'
. ... .: : . . .
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,
: .
- 18-
.
'
-: . - . . . . . . .. .. .
- - ,
.. .
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
- 2 0 -
.
~,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
, .
35-EL- 1403
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,
-- 2 3 -
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.)
- 24 -
.
' ,:
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
-.
- 25 -
35-EL-1403
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
- 26 -
': ' ' ~ ' '
: . . . . .
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
- 27 -
'
35-EL- 1403
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.
- 28 -
