Note: Descriptions are shown in the official language in which they were submitted.
`` ~3~
OVERLOAD PROTECTION FOR D . C. CIRCUITS
Background and Sum~mary_of the Invention
This invention relates generally to D.C. electrical
circuits and more particularly to a novel means for protection
of electrical circuits from electrical overloads and short
circuits. The invention is especially useful in automotive
electrical systems, and principles will be disclosed in
connection with automotive electrical circuits.
The number of electrical circuits in automotive
vehicles has increased over the years. In today~s passenger
cars and trucks, there are numerous electrical devices which are
used ~or various purposes such as illumination, control, power,
and instrumentation, for e~ample. While the advent of
electronics has given rise to major changes in automotive
electrical systems, converltional forms of circuit protection
devices, i.e., fuses and circuit breakexs, continue to be used,
and in increasing numbers as the number of circuits in the
electrical systems increases. The common technique for
providing protection against shorts, overloads, and other types
of electrical problems or conditions is to include a circuit
breaker or fuse in line, i.e., in series, with the wiring
circuit being protected. The protected device can be the wire
and/or electrical device. The necessity for having circuit
protection devices is well documented and need not be explained
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here. With increasing numbers of circuits, and the correlative
need for an increased number of protective d~vicec~ today's
typical automotive vehicle comprises a panel devoted essentially
exclusively to the mounting of most of these protective devices
in a single location. The panel, or fuse block as it is
sometimes called, comprises multiple compartments for the
individual protective devices. associated with these
compartments are receptacles to provide for the replaceable
mounting of the protective devices in the associated circuits.
Accordingly, the panel comprises a large number of individual
parts in assembled relationship, and it occupies a certain
amount of space in an area of the vehicle where space is
typically at a premium. A large number of wires attach to the
panel to carry current to and from the various protective
devices, and in order to serve the grouping of the protective
devlaes in ~he panel, complexities must be introduced into the
associated wiring harnesses.
Despite the advances which have taken place in the
incorporation of electrical and electronic technology into
today's automotive vehicle electrical circuits, they retain the
fuse and circuit breaker panel concept with its attendant large
number of individual protective devices to provide protection
for the various individual circuits.
There are several ways to protect an electrical device
without a circuit breaker or fuse, but most of the ways add
several parts to the circuit and typically degrade the
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performance of the electrical circuit, such as by added voltage
drop, higher power dissipation, etc. These protection methods
are not known to enjoy any significant commercial use because of
disadvantages such as those just mentioned.
The present invention relates to a novel means for
protection of D.C. electrical cicuits which affords very
significant advantages in automotive usage. One important
advantage is that the fuse and circuit breaker panel concept of
protection can be eliminated, thereby reducing the large number
of individual circuit devices (i~e., fuses and circuit breakers)
required to provide the protective function, and at the same
time, freeing space because there is no longer a need for a
separate panel.
The invention embodies the protective function in a
semiconductor device sometimes commonly known as an intelligent
æwitch. An intelligent switch comprises an internal controlled
conduction path whose conductivity is controlled by an external
control input. The switch contains another internal portion
which monitors current flow through the main controlled
conduction path and serves to internally interrupt the flow
through the path in response to incipiency of current or
temperature exceeding the rating of the main controlled
conduction path.
The invention arises through the recoynition that what
is customarily considered in the art to be an electronic switch
which has internal protection can also provide protection
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for the external components associated with it in a circuit
branch such that separate external circuit protection devices are
unnecessary in -the branch. The invention possesses not only a
generic aspect but also aspects which are specific to certain
particular circuit embodiments. Various attributes will be seen
in the several embodiments hereinafter disclosed.
The invention in one aspect pertains to a D.C.
electrical distribution system comprising a D.C. power supply and
a branch connected across the power supply, the branch comprising
an electrical load, a switch, conductors and an overload
protector all serially connected. The switch is selectively
operable to selectively control the current flow through the
brarlcll and the o~eL:I03d ;~notector ser~;e~; t:;~ sells-~ overload
associated with the ~low oE current in the branch and interrupt
the current flow upon sensing overload to thereby protect the
branch against overload. The lmprovement in the system comprises
the switch and the overload protector being embodied in a solid
state Ullit which comprises terminals via which it connects in -the
system, the unit comprising semiconductor structure which
comprises a main controlled conduction path through the uni-t
having a certain current/temperature rating and an associated
overload protector for the main controlled conduction path
responsive to incipient current or temperature exceeding the
rating to protect the main controlled conduction path from
potential damage. Two of the terminals constitute external
termination points for the main controlled conduction path via
which the main controlled conduction path connects into the
branch. At least one other of the terminals constitutes an
external termination point for connection to an input for
selectively con~rolling the conductivi.ty of the main controlled
conduction path in accordance with the input thereby selecti.vely
controlling the conductivity of the main controlled conduction
path to perform the switch function. The branch is free of
separate overload protection devices external to the unit such
that the current overload protection function within the branch
is performed entirel.y by the protection of the main controlled
conduction path within the unit by the associated overload
protector.
Another aspect of the invention pertains to an
automotive vehicle stop lamp circuit in which a stop lamp
performs stop, turn, and hazard warning signalling functions, the
ci..rcuit being powered from a D.C. power supply o:E the vehicl.e,
and a stop, turn and ha~ard warning switch means operates the
stop lamp. The improvement eomprises a semieonduetor switeh
eonneeting the stop lamp in a braneh aeross the power supply, the
semieonduetor switeh eo~prising a mai.n eontrolled eonduetion path
which has a eerta.in eurrent/temperature rating and through which
eurrent is eondueted from the power supply to the stop lamp and a
eontrol input whieh reeeives a eontrol signal Eor eontrolling the
eonduetivity of the main controlled eonduction path between
eonduetive and non-eonduetive eonditions. The semieonduetor
switeh further comprises an assoeiated internal overload
proteetion means for proteeting the main eontrolled eonduetion
path against incipient eurrent and thermal overloads exeeeding
the rating of the main eontrolled eonduetion path. The braneh is
free of separate overload proteetion deviees external to the
semieonduetor switeh sueh that the current overload proteetion
funetion within the braneh is performed entirely by the
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protection of the main controlled conduction path within the
semiconductor switch by the associated internal overload
protection means. The switch means comprises the combination of
a combined turn signal/hazard warning switch and a stop lamp
switch coac-ting to produce the control signal for causing a stop
signal to be given by the stop lamp by rendering the
semlconductor switch continuously conductive when the stop lamp
switch is operated, for causing the stop lamp to give a turn
signal by rendering the semiconductor switch intermlttently
conductive when the combined turn signal/hazard warning switch is
operated for a turn signal, and for causing the stop lamp to give
a hazard warning signal by rendering the semiconductor switch
intermlttelltly conductive when the combined turn siynal/hazard
swltch is operated for a hazard warning signal.
The foregoing features, advantages and benefits of the
invention, alon~ with add:itiorlal ones, will be seen in the
ensuing description and claims which should be considered in
conjunction with the accompanying drawings. I'he drawings
di.sclose a preferred embodiment of the invention according to the
best mode contemplated at the present time in carrying out the
invention.
Brief Description of the Drawings
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Fig. 1 is a generalized schematic diagram of circuit
embodying principles of the invention.
Fig. 2 is a schematic diagram, mostly in block diagram
form, of one of the circuit elements of Fig. 1 showing greater
detail.
Fig. 3 is a schematic diagram of a first example of
specific circuitry embodying princ~ples of the invention.
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Fig. 4 is a schematic dlagram of a second example of
speclflc circultry embodylng prlnclples of the invention. Flg. 4
is composed of Flgs. 4a and 4b.
Flg. 5 is a schematlc dlagram of a thlrd example of
specific circuitry embodying principles of the invention. Flg. 5
ls composed of Flgs. 5a and Sb.
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Fig. 6 is a schematic diagram of a fourth example of
specific circuitry embodying principles of the invention.
Fig. 7 is a schematic diagram of a fifth example of
specific circuitry embodying principles of the invention.
Descri tion of the Preferred Embodiment
Fig. 1 portrays a circuit 10 which is illustrative of
general principleæ of the invention. The circuit comprises a
D.C. power supply 12, a switch 14, and a load 16, the latter two
elements being in a series circuit across p~wer supply 12. The
power supply is illustrated as a battery having a positive
terminal 12a and a negative terminal 12b. The latter terminal
is connected to ground to make a negative ground system.
Switch 14 is the type which is commonly referred to as
an "intelligent switch". It is a semiconductor device which
contains an internal main conduction path whose conductivity is
selectively controlled by an input thereby performing a switch
function. It also comprises an internal protector section which
senses the cuxrent flowing through the main conduction path and
interrupts the current ~low through the main conduction path in
response to incipiency of current or temperature exceeding the
rating of the main conduction path, thereby endowing the device
with internal sel~-protection.
Switch 14 has a plurality of terminals via which it
connects to external circuit components. Fig. 1 shows four
terminals designated 14a, l~b, 14c, and 14d~ Terminals 14a and
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14b are associated with the main conduction path through the
device, and terminals 14c and 14d are associated with control of
the conductivity o~ the main conduction path.
Conductors such as insulated wires, printed circuits,
etc., provide the electrical connection of power supply 12,
switch 14, and load 16 in circuit. a conductor 18 connects
terminal 12a with terminal 14a; a conductor 20 connects terminal
14b with the positive side o load 16: and a conductor 22
connects the negative side of load 16 with terminal 12b.
Terminals 14c, 14d are shown connected to a control
input 24 which exercises control over the conductivity of the
main conduction path through swi~ch 1~ between the power supply
and the load. In other words control input 24 serves to turn
the current from power supply 12 to load 16 on and of~ via
switch 14.
As described earlier, external protective devices have
heretofore been required in automotive electrical circuit
branches to protect against otherwise potentially damaging
overloads or shorts in the branches. The present invention in
its several aspects ar~ses through the recognition that the
intelligent switch can provide protection not only for itself,
but in doing so, also provide protection for other circuit
elements connected in external circuit relation with it in the
branch. With this recognition, the invention further comprises
2S freeing the branch of external protective devices such that the
entire overload protection within the branch circuit connected
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130~710
across the power supply is provided solely by intelligent switch
14.
As also mentioned earlier, this reduces the number of
external components in a circuit, resulting in a significant
savings in cost, and assembly time as well, and importantly
without sacrificing circuit protection. Where a large
electrical system, such as in a car or truck, is involved, and
where the system is produced in large numbers, a substantial
cost savings is attained by the elimination of what the
invention recognizes as now-redundant external protective
devices. Accordingly, the present invention possesses
significant commercial advantages.
Fig. 2 illustrates further detail of a representative
intelligent switch 14. The Eour terminals already described are
designated accordingly; there is also a fifth terminal l~e for
supplying an output signal indicative of the switch's status.
The internal construction of switch 1~ comprises semiconductor
materials con~igured to perform particular circuit functions as
shown in the Fig. by the labelled block diagrams. The
illustrated coniguratîon is representative of a device
available from Siemens Components, Inc. and identified as a
SMT-12 "Smart-Sipmos" intelligent monolithic power switch.
Motorola, Inc. offers an equivalent device having the
designation MPC 1500, and other companies offer other equivalent
devices.
The main controlled conduction path through the device
* Trade Mark
~ 130~10
comprises a mosfet 26 whose drain 26d and source 26s are
connected respectively to terminals 14a and 14b. The mosfet's
gate 26g is connected internally of the device in association
with the several internal semiconductor circuit sections
labelled in the blocks of the drawing. Terminal 14c receives
the control input signal which acts via the several internal
circuit sections to control the mosfet, and thereby turn the
current to the load off and on according to the condition of the
input signal control. Terminal 14d is grounded and the
potential at terminal 14c is swi~ched between ground and a
higher positive voltage to selectively operate switch 14.
Terminal 14e provides the status signal.
Importantly, the internal semiconductor structure
contains a detector section 28 associated with the mosfet. This
section senses current passing through the moset between drain
26d and source 26s. In turn it exercises overriding control,
via feedback, over the control input ~ignal at terminal 14c to
render the mosfet non-conductive in response to detection of
incipient overloading o the mosfet. In so protecting its
internal mosfet, the intelligent switch also protects the
associated e~ternal circuit elements thereby eliminating the
need for separate external protection devices such as fuses,
circuit breakers, etc.
Further aspects of the invention involve the
application of the general principles to particular circuits
which are disclosed in the ensuing description with reference to
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the further drawing Figs. 3-7.
Pig. 3 illustrates an embodiment of the invention in
one circuit 30 of a truck's or highway tractor's electxical
system. The numerals 18 and 22 represent the respective
conductors from the positive and negative battery terminals 12a,
12b. Terminals 14a, 14b and 14c are the only terminals of
switch 14 portrayed in Fig. 3, and it is to be appreciated that
the remaining two terminals 14d, 14e, although not shown in Fig.
3, are in fact present, as described earlier. For clarity and
convenience in ensuing description and illustration, this same
manner of portraying intelligent switches will be employed in
subsequent Figs. as well
Terminal 14c is shown connected direc~ly to terminal
14a in Fig. 3. Accordingly, the main controlled conduction path
through the intelligent switch be~ween terminals 14a and 14b is
rendered contlnuously conductive so long as there is a positive
battery voltage on conduator 18. The positive battery voltage
is thereore transmitted through the intelligent switch so as to
be available to the several load devices which connect in
parallel fashion between terminal 14b and ground.
These load devices comprise a pair of spotlights 32 and
34 respectively, a dome light 36, a reading light 38, and a
cigar lighter 40. Associated with each of the lighting devices
32, 34, 36, and 38 is an associated switch which can be turned
on and off at the pleasure of the vehicle operator. The cigar
lighter 40 is operated in a conventional manner.
In circuit 30 the intelligent switch functions in the
manner of a circuit breaker rather than as a control switch for
intentionally switching a load on and off as desired. In
operation therefore, switch 14 provides continuous circuit
continuity between terminals 14a and 14b unless an overload
occurs. The circuit also illustrates that a number of branch
circuits can be connected to the load side of the intelligent
switch. The size of the electrical load which can be safely
connected to a single intelligent switch depends upon the
current carrying capacity of ~he switch. In functioning in the
manner of a circuit breaker, the intelligent switch of Fig. 3
functions to protect the loads and associated wiring conductors
by rendering the conductive path between terminals 14a and 14b
non-conductive when an overload is sensed.
Depending upon the specific characteristics o the
particular int~lligent switch used, the terminal 14c may not be
suited to accept the full battery voltage (typically 12 V.D.C.),
and therefore an attenuator (not shown) may be interposed
between the battery and ~erminal l~c to reduce the voltage to a
lower level.
Fig. 4 illustrates a second circuit 50 embodying
principles of the invention in one poxtion of the truck's
lighting circuit. A further portion of the lighting circuit is
contained in a portion of the circuit identified by the
reference numeral 52 in Fig. 5, and it will be appropriate to
consider both circuits 50 and 52 together.
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In both circuits of Fig. 4 and Fig. 5 the conductors
designated by the reerence n~lmerals 18 and 22 are at the
positive and negative battery potentials respectively.
Circuit 50 contains three intelligent switches 54, 56,
58 which, while identified by their own particular reference
numerals, will retain for convenience in description, the
previous terminal designations 14a, 14b, 14c. The terminal 14a
of each of the three switches 54, 56, 58 is connected directly
to conductor 18. The load for switch 54 is one portion of the
marker lamps on a trailer which is hauled by the truck or
tractor containing circuit 50. ~ence, the load terminal 14b of
switch 54 is connected to one terminal 60a of a socket 60 which
is adapted to connect with a mating plug (not shown) on the
trailer ~or the trailer marker lamps.
The load for switch 56 comprises the truck's or
tractor's own set of clearance and identification lights 62
(marker lamps) and also the remaining portion of the associated
trailer's marker lamps. Hence, the load on switch 56 branches
to lamps 62 and to a terminal 60b of the socket 60 for feeding
the remaining trailer marker lamps.
The load on switch 58 comprises two mirror lamps 64,
66, two parking lamps 68, 70 on the exterior of the vehicle, and
an illumination lamp 72 for the cigar lighter. Additional
branches leading to further loads are partially illustrated in
Fig. 4.
The terminals 14c of the three switches 54, 56, 58 are
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under the common control of a master light switch 74. The
master light switch serves to selectively connect an input
terminal 74a to three output terminals 74b, 74c, 74d, designated
off, head and tail, respectively. Terminal 74a is connected to
a positive potential reference. The head and tail terminals
74c, 74d are connected together by a diode 75 poled as
illustrated.
When the master light switch is in the off position
(74a connected to 74b), none of the switches 54, 56, 58 can be
rendered conductive. When it is in the head position (74a
connected to 74c), the positive potential reference at input
terminal 74a is transmitted to terminal 74c. This forward
biases diode 75 and renders switch 58 conductive; it also
renders switches 54 and 56 conductive via a normally closed
interrupter light switch 76 which is in the line from terminal
74d to terminal 14c ~ both swltches 54, 56. Therefore, the
lamp loads con~ected to the three switches 54, 56, and S8 are
illuminated when the master light switch is in the head
position.
The provision of the interrupter switch between master
light switch 74 and the two intelligent switches 54, 56 provides
the vehicle operator with means for giving the standard highway
signaiing feature of momentarily turning the marker lamps off
without concurrently turning off the instrument panel lamps, the
headlamps, and the tail and parking lamps.
Terminal 74d is further connected to an instrument
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panel lights portion of circuit 52 in Fig. 5 and to a headlights
portion also in Fig. 5. With switch 74 in the head position,
positive reference potential is transmitted to those two
portions of circuit 52 causing the instrument panel lamps and
the headlamps to illuminate. Details of circuit 52 will be
described later.
When the master light switch 74 is in the tail position
(74a connected to 74d), switches 54, 56, and 58 are rendered
conductive to cause the lamps of Fig. 4 and the instrument panel
lamps of Fig. 5 to illuminate; the headlamps of Fig. 5 will not
illuminate however because diode 75 is now reversed biased
preventing a feed of the positive potential reference at 74d to
a headlamp dimmer switch 78 via which control of the headlamps
in the headlamp circuit portion o Fig. 5 is efected.
Referring now also to Fig. 5, one will see that
terminal 74c of the master light switch connec~s through dimmer
sw~tch 78 to the headlamp circuits~ Dimmer switch 78 is a
two-position switch which selects either high beam or low beam
operation. The switch has an input terminal 78a; a low beam
output terminal 78b which connects both to the input terminal
l~c of a left low beam intelligent switch 80 and to the input
terminal 14c of a right low beam intelligent switch 82; and a
high beam output terminal 78c which connects to terminal 14c of
a high beam intelligent switch 84.
~ Terminals 14a of switches 80, 82, and 84 are connected
to conductor 18. Terminal 14b o$ high beam switch 84 connects
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to the high beam filaments of the two headlamps 85, 87. It also
connects to a high-beam indicator lamp 86 on the instrument
panel. Terminal 14b of switch 80 connects to the low beam
filament of the left headlamp 85 while terminal 14b of the right
low-beam switch 82 connects to the low beam filament of the
right headlamp 87.
Therefore, when the master light switch 74 is in the
head position and the dimmer switch 78 is in the low beam
position, the low beams of both headlamps are illuminated. With
the master light switch remaining in the head position,
switching of the dimmer switch to the high beam position causes
current flow to the low beam filaments of the headlamps to cease
and current flow to the high beam filaments o~ both headlamps to
begin through switch 84. High beam indication is given to the
vehicle operator by the illumination of lamp 86.
The low beam output terminal 78b o~ dimmer switch 78 is
also connected to one terminal of a normally open fog light
switch 89. The other terminal of the fog ligh~ switch in turn
connects to the terminal 14c of an intelligent swi~ch 88 whose
terminal 14a connects to conductor 18 and whose terminal 14b
connects to the right and left fog lamps 91, 93. Therefore,
when the master light switch 74 is in the head position, and the
dimmer switch 78 is in the low beam position to illuminate the
low beams, the fog lamps are rendered selectively operable
through closing of the fog li~ht switch 89.
Still referring to Fig. 5, the reader will observe
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another intelligent switch 90 whose terminal 14a connects to
conductor 18 and whose terminal 14b connects to a large number
of illumination lamps 92 for illuminating instruments on the
instrument panel. When the intelligent switch 90 is conductive,
the lamps 92 are continuously illuminated with the full battery
voltage. However, the switch is impressed with a duty cycle
type of operation via a ~ariable duty cycle timer circuit 94
which connects between terminal 74c of master light switch 74
(Fig. 4) and terminal 14c of intelligent switch 90 (Fig.5).
Timer circuit 94 comprises a potentiometer 96 and a
timer 98. The timer receives a selectable fraction of the
voltage from the master light switch as determined by the
setting of the potentiometer. The timer executes a
corresponding duty cycle of operation to thereby impose a
simi~ar duty cycle on the intelligent switch. Accordingly, the
average power input to the illumination lamps 92 is a function
o the setting o~ thc potentiom~ter. This provides the vehicle
operator with the capability of setting a desired illumination
in-tensity for the instrument panel larnps by the setting of
potentiometer 96.
Fig. 6 illustrates another circuit 110 which contains
three intelligent switches 112, 114, 116. These switches are
used in control of the stop and turn signal lamps and are
cooperatively associated with a combination hazard~turn signal
switch 117 and a stop lamp switch 118.
The highway tractor, itself, comprises left and right
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front turn signal lights 120, 122, respectively, and left and
right rear, stop, tail and turn lights 124, 126, respectively.
The components 112-126 are connected in circuit as shown in Fig.
6. The low intensity filaments of the lamps 124, 126 connect to
switch 58 of circuit 50 (Fig. 4) and illuminate when switch 58
is conductive.
Looking further at Fig. 6 one sees a socket 128 for
connecting to a mating plug (not shown) on an associated trailer
and containing a terminal 128a enabling a left stop, tail and
turn signal lamp, or lamps, on the trailer to be connected in
parallel with lamp 124. The same socket contains a terminal
128b enabling a right stop, tail and ~urn lamp, or lamps, of the
trailer to be connected in parallel with lamp 126. ~ third
terminal 128c in the socket connects to the terminal ~4b of
switch 116 and serves to feed additional stop lamps on the
trailer. The lamps 124, 126 aonnect respectively to the
terminals 14b of switches 112, 114 respectively.
The drawing illustrates switch 117 in a non-turn,
non-hazard condition. The stoplight switch 118 is connected to
a stoplight feed input terminal 117a of switch 117. With the
switch 117 in the position illustrated in the drawing figure,
closure of the stoplight switch 118 causes both switches 112 and
114 to be rendered conductive. This causes a red stop signal to
be given toward the rear by the illumination of lamps 124, 126
and the corresponding lamps on the trailer. The lamps 120, 122
are also illuminated to present an amber signal toward the
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front, an added feature.
Operation of switch 117 to either the right or the left
turn signal function disconnects the corresponding switch 112,
114 from the stoplight switch feed and connects the
corresponding switch 112, 114 to a timer circuit 136 which now
exercises control over the switch. The timer circuit
intermittently operates the corresponding switch in a
predetermined duty cycle appropriate for the turn indication
function, causing the corresponding turn signal and stop lamps
to be operated in a flashing manner independent of operation of
the stoplight switch 118.
When the switch 117 is operated to the hazard mode,
both switches 112, 114 are disconnected from the stoplight
switch feed, and are instead both connected to timer circuit 136
which causes the two switches 112, 114 to intermittently operate
in unison thereby flashing in unison the lamp loads which are
connected to them.
Fig. 7 illustrates a dual blower motor control circuit
140. This circuit comprises two blower motors 142, 144 and two
intelligent switches 146, 148. Each motor forms a load which
connects to the corresponding terminal 14b of the corresponding
switch 146, 148. The motors are of the variable speed D.C.
type, and speed control is effected by the duty cycle modulation
of battery voltage across the motors.
To achieve variable speed capability for the motors,
circuit 140 further comprises a control switch 150 and a control
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module 152. The control module comprises two timer circuits
154, 156 imparting different duty cycles of operation~ Control
switch 150 may be considered to have four inputs and a single
output. There are three input terminals 150a, 150b, and 150c
available for external connection, high, medium and low, and a
fourth input represents off position. The output terminal 150d
of the control switch is connected to terminal 14c of both
switches 146, 148. Timer circuit 156 is connected to the low
input, timer 154 circuit to the medium input, and a positive
potential reference ~s connected to the high input.
When the control switch is in the off position, the
switches 146, 148 are rendered non-conductive. When the switch
is operated to the low position, timer circuit 156 exercises
control over the duty cycle operation of the switches to produce
low speed operation or both motors. When the switch is
operated to the medium position, timer circuit 15~ exercises
control to produce a higher duty cycle mode of operation
resulting in an increased speed over the low speed. When the
switch is at the high setting, the full continuous voltage is
applied to the switches so that the switches are continuously
conductive so long as the control switch 150 remains in this
setting, and the motors run at high speed.
In the several embodiments of the invention disclosed
above, the intelligent switches provide the entire circuit
protection such that separate conventional electro-mechanical
protection devices such as fuses and circuit breakers are not
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incorporated into the circuits. Power for the various loads is
conducted from the D.C. power supply through the intelligent
switches to the loads, and not through the control circuitry.
The circuitry which controls the switching of the intelligent
switches advantageously consists of low-current, low-power
components. Such components possess cost and reliability
advantages over heretofore used mechanical switches whi~h must
be large enough themselves to carry the load currents for the
various load devices they control. The low-current, low-power
components are smaller and can be more compactly organized and
arranged in the electrical system. Attendant savings accrue in
the associated wiring harnesses both by way of simplification
and because the low-power control circuitry uses smaller
conductors and terminals.
According to a preferred implimentation of the
invention, the terminals 14a o the intelligent switches are
connected directly to a positive voltage buss from the battery.
Hence, the load on an intelligent switch and all conductors
associated w~th the load, save the buss of course, are on the
load side of the intelligent switch and are protected by the
intelligent switch.
The stop, tail, turn, and hazard signal circuit of Fig.
6 possesses significant improvemen-t over its previous
counterpart. While endowed with the advantages ~hich have been
described generally thus far, the circuit has the specific
advantage of simplifying inventory requirements in plants where
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the vehicles are built. secause different models of vehicles
may have differing numbers of lamps, several different models of
flashers have been required to handle the different loads using
the previous canterpart circuit. With the invention a common
low-power control, including timer for producing lamp flashing,
is used, and the various load requirements are handled by using
the appropriate number of intelligent swi-tches thus effectively
distributing load currents and reducing component peak currents.
The blower circuit of Fig~ 7 also afords significant
improvement over i~s prior counterpart. The prior dual-blower
heater uses two auto reset circuit breakers, a dual high-current
four-position switch, two relays, and two resistor and thermal
fuse assemblies to provide protection and the three-speed
operation. With the present invention, they are replaced by two
intelligent switches, a single low-current four-position switch,
and a dual timer~pulse width modulator circuit.
In any given design o~ system containing one or more
branch circuits embodying principles of the invention,
conventional engineering practices should be observed. The
ratin~ of an intelligent switch should be selected to correspond
with and protect the load in its branch. In many installations
the actual D.C. source, i.e. the battery, for example, will be
physically remote from the branch or branches, despite the fact
that the branch or branches are electrically across the power
source. For instance a branch could be fed from a buss, and in
such a case there could be an overload protection device
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r ~ 7~
upstream of the branch for the purpose of protecting the buss,
and it is-to be appreciated that the present invention provides
branch protection within the branch irrespective of the presence
or absence of any protection devices for protecting external
feeds to the branch, such as just described. Principles of the
in~ention in its generic aspects are independent of the
particular type electrical load being protected. Likewise the
generic aspects of the invention are not limited to any
particular type of device which exercises control of the
conductivity of the intelligent switch. Examples of
representative control devices are mechanical switches,
electronic switches, and microprocessors.
While the foregoing disclosure has portrayed general
principles of the invention in several specific embodiments, it
is to be appreciated that principles are applicable to other
embodiments with the attendant benefits of fuse and circuit
breaker elimination, a greater degree of individual circuit
protection, and savings in time, labor, and materials, as well
as space savings in the vehicles.
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