Note: Descriptions are shown in the official language in which they were submitted.
~32~08
This application is a division of cop~nding application
- 521,036, filed October 21, 1986.
The present invention relates to a single or multi
location load control system including a main control unit
and, if desired, one or more remote switching units. The
main control unit turns power on or off to one or more loa~s
in response to the receipt of a control signal generated by a
human actuable switch or appropriate automatic circuitry
(e.g. a timing circuit). The main control unit is preferably
located in a single housing adapted to fit in a standard wall
box.
:,
- one or more remote switching units are located at
positions remote from the main control unit. These positions
may be in the same room as the main control unit or in
different rooms. The remote switching units send a control
signal to the main control unit which responds to this signal
~ by either applying power to or removing power from the loads
~,! being controlled.
''J, Multi-location control systems of the foregoing type are
generally known. The most popular of these systems are
1 ~tandard single pole single throw single location and three
`~ way wall switches. More sophisticated systems wherein a
plurality of remote switches send control signals to a main
control unit which controls power to a load are also known.
;~
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-~ 25 Each of the prior art systems exhibit important
disadvantages. The present invention overcomes the
disadvantages of the prior art systems in that it can b~
mounted in standard house wall boxes, can retrofit any
existing three-way or four-way wiring, does not require a
neutral connection and has a universal load capability. ,
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1326508
According to one aspect thereof the present
`~ invention provides and claims in the parent application a
load control system, comprising: switching means having
~irst and second main terminals and a control terminal; and a
control circuit coupled to said control terminal and
controlling the operation of said switching means in response
to control signals applied to said control circuit, said
control circuit being coupled to said first and ~econd main
terminals and deriving all of its power ~rom the voltage
which appears across said main terminals of ~aid switching
means when said switching means is coupled between a source
and a load, said control circuit including: latching means
having a contact movable between an ON and OFF state, the
position o~ said contact determining whether said switching lS means is operating in an ON or an OFF state, first and second
capacitors which are arranged to be charged when the contact
is in its first or second position, the charge stored on said
capacitors being used to control the latching means as a
function of said control signals; and means for preventing
~aid capacitors from being charged as long as said control
signal is applied to said control circuit.
In another aspect thereof the present invention provides
and claims in the parent application a load control system,
comprising: switching means having first and second main
terminals and a control terminal; and a control circuit
coupled to said control terminal and controlling the
operation of said switching means in response to control
signals applied to said control circuit, said control circuit
being coupled to said first and second main kerminals and
deriving all of its power from the voltage which appears
across said main terminals of said switching means when said
switching means is coupled between a source and a load, said
control circuit inGluding: latching means having a contact
movable b~tween an ON and an OFF ~tate, the position of said
contact determining whether said switching means is operating
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in an ON or an OFF state, first and second capacitors which
. are arranged to be charged when the contact is in its first
:~ or second position, the charge stored on said capacitors
- being used to control the latching means as a function of
S said control signals, and means for charging a
predeterminedone of said capacitors whenever said contact is
stuck in a position intermediate said ON and OFF positions.
In a still further aspec~ thereof the present invention
pro~ides a load control system, comprising: A) a main
. 10 control unit including: 1) switching m~ans having first and
~ second main terminals and a control terminal; 2) a control
~!
circuit coupled to said control terminal and controlling the
~ operatio~ of said switching means in response to control
: signals applied thereto, said control circuit being polarity
insensitive and operating properly irrespective o~ whether
. the first and second main terminals of said switching means
is coupled to said load and source, respectively, or to said
:~! source and load, respectively; 3~ local means for generating
~ said control signals; and 4) a housing in which said
: 20 switching means, said control circuit and said local means is
~`' housed; B) a remote switching unit for generating said
~ control signals ~rom a location remote ~rom said main control
`' unit; and C) signal transmission means for applying said
-. control signals generated by said remote switching unit to
said control circuit.
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In another aspect thereo~ the present invention provides
~: a load control system comprising: A~ a first main control
unit including a first main control unit housing, a first
switching means located in said first main housing, a first 30 control circuit located in said first main housing and
controlling the operation of said first switching means in
response to control signals applied thereto, and ~irst lo¢al
means located in said first main housing for generating qaid
control signals and applying them to said first control
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Gircuit; B) a second main control unit including a second
main control unit housing, a second switching means located
in said second main housing~ a second control circuit located
in said second main housing and control3.ing the operation of
said second switching means in response to control signals
applied thereto and second local means lociated in said second
main housing for generating said control signals and applying
them to said second control circuit; r) a :re~ote switch unit
ineluding a remote switch unit housing a first and second
human operable switches located in said housing for
.. generating control signals in rasponse to the human actuation
thereof; and D) signal trans~ission means for applying
i control signals generated by said first human operable F~witch
to said first control circuit and for applying control
signals generated by said second human actuable switch to
said second control circuit.
In a further aspect thereof the present invention
provides a load control system, comprising- an electronic
switching means operable in a conductiv~ and a non-conductive
~ 20 state, said switching means including ~irst and second power
.~ leads connectable to a source and load, respectively; a
control circuit for controlling the operation of said
i ~witching means whenever power is applied to said control
' circuit and as a function of control signals applied to said
;? 25 control circuit, said control circuit including memory means
;~ for storing the state of said switching means immediately
.. , before power is cut off from said control circuit and for
returning said switching means to said stored state when
power is returned to said control circuit.
In yet a further aspect thereof the present invention
provides a load control system, comprising: a
bidirectionally conductive electronic switching element
having first and second main terminals and a control
terminal, said electronic switching element being operable in
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a conductive and non-conductive mode as a function of
enabling signals applied to said ~ontrol terminals; and a
control circuit coupled to said control te~inal and con-
trolling the operation of said switching means in response to
periodic conkrDl signals applied thereto, said conkrol
circuit being operable in an ON mode and an OFF mode, said
control circuit causing said electronic switching element to
~, be non~conductive whenever said control circuit is in said
`l OFF ~ode and causing said electronic switching element to be'~ 10 conductive ~or at least 95% of each hal~ cycle of an AC wave
foxm applied across said first and second main terminals
~, whenever said control circuit is in said ON state and said
electronic switching element is coupled between an AC source
~` and a load.
`1. 15 In the presently preferred embodiment of the invention,
a bidirectionally conductive electronic switching device
I (preferably a triac) is located in series between a power
~-3 supply and a load and controls the application of power to
the load. A latching contxol circuit, which may be either an
electronic, mechanical or magnetic circuit, controls the
operation of the triac and thereby application of power to
the load. The control circuit alternatively turns the triac
on and o~f (and thereby applies power to or removes p~wer
from the load) in respon~e to a control signal applied
thereto. In order to ensure that power is supplied to khe
control circuit when the triac is on, the control circuit
fires the triac shortly after each zero crossing of the
svurce AC wave form with the result that the portion of the
AC
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132~08
,
wave form preceding the instant at which the triac is
~ fired can be used to power the control ~ircuit.
-, In the preferred e~bodiment, the power
. require~ents of the cvntrol circuit are such that the
; triac can be fired after a time period corresponding to
~ o ~ore than approximately 5% of each hal~ cyole of the
~ wave form. As will be explained in greater dq~ail below,
this can be achieved as a result of the characteristics of
the reset capacitor charging circuit~ of the presently,
.ji preferred embodiment. By ensuring that the triac can be
fired shortly after each zero crossing of the AC wave ~orm,
~ the present invention assures that a substa~tially sinusoidal
;;` wave form is applied to the load and thereby permits the
:; control circuit of the present inventio~ to be utilized with
resistive, capacitive and/or inductive loads.
he con~xol circuit has a bistable operation
.l and preferably switches between an ON and OFF position
:~ each time a control signal is applied theretoO Whenever
:1) the contro~ circuit is in the ON position it will enable
the triac shortly after each zero crossing of the source
AC wave form and thereby apply power to the load7 When-
ever the control circuit is in the OFF position it will
disable ~he triac thereby removing power from the load.
I . The control signal is preferably ~enerated by a
j~ human actuable switch. If desired, the control signal
can be generated by a timer circuit or any other control
apparatus.
The heart of the control circuit is a bis~able
. latch w~ich switches between the ON and OFF conditions
.;, each time the con~rol signal is generated.. The position
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of the latch co~trols the condition of the aontrol cir-
~ cuit.
:~3 In the presently preferred embodiment, the
:.~
latch is a ~agnetic latching relay including set and
~1 reset coils and a contac~ which moves between an O~ and
an OFF position every ti~e a predetermined level of cur-
rent flows through the set and r~se~ coils, respectively.
The contact is magnetically la~ched into the ON or OFF
position by respective per~anent magnet~ whenever there
!~ is no cl~rrent flow through the set and reset c0115. Set
`j and reset capacitors are associated with the set and
reset coils. Set and reset capacitor charging circuits
are provided for charging the set and reset capacitors,
~ respectively, when the contact of the relay is in the
i OFF and ON positions f respectively. The charging cir-
cuit preferably includes a current re~ulator which en-
1 ables the use of low value charging resistor$ which en-
;, sure that the capacitors are charged quickly. The
i charged capacitor will discharge ~hrough its associated
coil in response to th~ application of a control signal
1 to the control circuit thereby causing the position of
the latch (and thereby the operation of the triac) to
change. ~he charging circuits are disabled as long as
the control signal is applied to the control circuit to
~` ensure that current does not inad~ertently flow through
'~ the wrong coil while the control signal is generated.
A control sign~l is preferably generated by a
manual~y ~perable short-throw, light-force switch of the type
shown in applicants U.S. Patent No. 4,S43~592. The human
actuable switch is preferably located in the same housing as
the control circuit, the entire housing being
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received in a standard wall box A plurallty of remote
switches can also be used for the purpose of generating
the control signal. Remote switches are also preferably
short-throw, light-force switches which are located in
i, respective housings, each housing preferably being sub-
stantially identical in appearance to the bousîng in
~: which the control c:ircuit is located.
If desired, a plurality of load control systems
can be provided, e~ch controlling the operation of a
different set of loads. Each control system will include
. its own main control unit wherein the controllably con-
ductive switching device, control circuit and main human
. actuable switch is provided. In order to permit two or
I more of the load control systems to be operated from a
.1 single remote location, a plurality of human actuab:le
.~ switches may be located in a single remote housin.g, each
of~the human actuable switches belng coupled to the con-
: trol circuit of a respective one of the load control
systems and thereby generatin~ the control signal for
that system.
While the control signal is preferably
J~: generated by a human actuable switch, an automatic timing
circuit can be provided for the purpose of generating the
con~rol signal. Wireless remote control devices such as
infrared, radio frequency, ultra sonic or sonic devices
could also be used.
BRIEF DESCRIPTION OE THE DRAWINGS
For the purpose of illustrating the invention,
there is shown in the drawing several forms which are
presently preferred, it being understood, however, that
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,3~6508
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j the invention is not limited to the precise arrangemients
-~ and instrumentality shown.
.;;;'; Figure 1 is a circuit diagram of a load control
system in accordance with a flrst embodi~ent of the
`, present invention.
~i Figure 2 is a series of wavs forms appearing at
:..
various locations in the circ.uit of Figure 1.
~, Figure 3 is a wave diagram illustrating the
. manner in which the current lags the voltage when the
:j present invention is used in connection with inductive
,i loads.
Figure 4 is a schematic diagram ill~strating
:~ the ~Zanner in which two control systems constructed in
,~ accordance with the priDciple of the present invention
can be controlled from a single remote control unit.
,...
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~rl DETAI:LED DESCRIPTION OF TH~3 INVENTION
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Referring now to Fig. 1, there i5 illustrated a
presently preferred embodiment of a load controL system
constructed in accordance with the principles of the
present invention and designated generally as 10. Load
control system 10 is connected between a power source 12
and one or more loads 14. While the load 14 is illus-
trated as being a~ incandescent lamp, load control system
10 may be: used in conDection with other loads including
capacitive and inductive loads. To control the applica-
tion of power from source 12 to load 14, control system
10 preferably includes both a manually controlled air gap
switch 16 and a bidirectionally conductive electronic
switching element 18 which is polarity insensitive (each
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o~ i~s ~ain terminals can be applied to the source 12 or
load 14 withou~ affecting the operation of the element~
~he ~peration of electxonic switching element 18 is con-
trolled by a latching control circuit 20 in response to
the receipt of a control signal generated by either the
local push button switch Pb or any of the remote switch
units 22. Latching control circui$ 20 is also polarity
insensitive and includes a bi-stable latch whi~h switch-
es between the ON and O~F state each time a local p~sh
button switch Pb (preferably located in the sa~e housing
as control circuit 20) or a push button switch Pb' (lo-
cated at one of the remote switch units 22) is de-
pressed. In the OFF state, control circuit 20 removes
gate current from electronic s~itching element 18 (pref-
erably a triac) thereby removing power from load 14. In
the ON state, control circuit 20 fires triac 18 shortly
after each zero crossing of the AC wave form Vs (Fig. 2)
generated by source 12 with the result that a substan-
tially sinusoidal wave form is applied to load 14.
The contrvl circuit 20 and associated push button
switch Pb are preferably located in a single housing adapted
to b~ installed in a standard wall box. One such housing is
illustrated in Figures 11-14 of applicants U.S. Patent No.
4,543,592. This housing incorporates a short-throw, light-
force push button switch which has a highly pleasing tactile
feel and needs only be depressed a short distance to move it
from its normally open to its momentarily closed position.
~hile the present invention is not limited to the use of such
a switch (other mechanical, touch plate, beam break and
re~ote control switches say be used), the use oL a short-
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throw, light force switch is preferred. Such a switch may be
.l 5 used with the present invention because the push button
~? switches Pb, Pb' are subject to low magnitude control
voltages and not full line voltages and load currents.
,,
In the U.S. Patent 4,563,594, issued January 7, 1986,
~, 10 only the push button switch is located in the remote housing
,! .
~' When the structure of Figures 11-14 of the foregoing patent
' is used in connection with control circuit 20 of the present
: invention, the control circuit 20, as well as the triac 18
and air gap switch 16, are all preferably located within the
~ 15 ~ingle housing. The air gap switch 16 is manually controlled
:~ by the operator of system 10, for example by toggle switch
located in the lower right hand corner of the face plate.
. .
~j~ Each of the remote switching units 22 includes a push
.'. 20 button æwitch Pb' in series with a po~itive temperature ~.
coefficient resistor 36 whi~h protect~ the push button switch
<;, Pb' from high currents in the event that the remote switching
.~ unit 22 is improperly wirsd. As with the main control unit,
. each remote switch unit 22 pre~erably takes the form
illustrated in Figures 11-14 of applicants U.S. Pate~t No.
4,5~3,592. These wall plate units are located at locations
~ remote from control circuit 20 and send a control signal to
j ¢ontrol circuit 20 wheneYer one of the push button switche~
Pb' is depressed. This low voltage control sig~al causes the
latching control circuit 20 to toggle from its present state
(e.g. the ON state) to the opposite state (e.g. the OFF
~- state).
Latching control circuit 20 can be either an electronic,
electromagnetic, or mechanical bistable
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latching circuit. In the presently preierred embodi-
ment, an electromagnetic latching ~ircuit is used. The
heart of latching control circuit 20 is a latching relay
comprising a bi-stable contact 24 t a set coil 26 and a
reset coil 28. Whenever surrent is pulsed through set
coil 26, contact 24 switches to ~he ON position. Whenev-
er current is pulsed through the reset coil 28, contact
24 switches to the OFF position. The contact 24 i.3 main-
tained ln the ON and OFF positions by permanent magnets.
The po ition of contact 2~ defines the state of operation
of the latching control circuit 20 and thereby the mode
of operation of triac 18. When contact 24 is in the ON
position, control circuit 20 gates triac 18 shortly af-
ter zero crossing of each half cycle of the AC wave form
~s of source 12 with the result that a substantially
sinusoidal voltage Vl (Fig. 2) is applied to load 14.
When contact 24 is in the OFF position, gate current is
removed from triac 18 and the triac is cut off thereby
removing power from loa~ 14.
The operation of control circuit 20, and
thereby the operation of triac 18 t is va~ied as a func-
tion of the position o relay 24. Relay 2~ is toggled
from ~he ON o the OFF position whenever capacitor Cl
discharges through the reset coil 28 and toggles from the
OFF to the ON position whenever capacitor C2 discharges
through set coil 26. The charging o~ capacitors C} and
c2 is controlled by reset capacitor charging circuit 32
and set capacitor charging circuit 34, respectively~ The
discharging of capacitors Cl, C2 is controlled by tran-
sistor Q3 which is turned on by the control signals ap-
plied to its bas~ by local push button switch Pb and/or
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132~0
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remote control circuits 22. The operation of reset ca-
pacitor charging circuit 32 will be described first.
When contact 24 is in the 0~ position, the
voltage at node A will attempt to follow the source volt-
ag~ Vs . This sine wave is illustrated in ~igure 2.
Node A (Fig. 1) is coupled to the gate of triac 18 via
contact 24, resistor Rl and silicon bilateral switches
30, 31 (any suitable bilateral break over device can be
used). The silicon bilateral switches 30, 31 are de-
signed to break over whenever the magnitude of the volt-
age across the switch exceeds a predetermined level. The
magnitude of the break over voltage is chosen to be ~uf-
ficiently small to ensure that the voltage applied to
load 14 is substantially a sinusoidal voltage while at
the same time sufficiently large to provide charging
current to capacitor Cl. A break over voltage of approx-
imately:l5 volts has been found to be suitable. This
provides ~for a off time of approximately one hundred
microseconds for the triac 18 yet provides sufficient
charging voltage to capacitor Cl. As a result of the
silicon bilateral switches 30, 31, the voltage Vg be-
tween nodes A and ~ will be a pulsed voltage having a
short.duration and having a maximum value equal to the
level to which capacitor Cl is to be charged. This volt-
age Vg i~ illustrated in Figure 20
While the maximum value of Vg is sPt to be
equal to the desired maxi~um voltage level to which ca-
pacitor Cl charges, the duration of the Vg pulse is very
short (preferably no more t~an about 5% of one half cycle
o~ the AC wave form Vs). The use of such a short pulse
is required to ensure that the load voltage applied by
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~ 1326~08
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... ~ triac 18 will be substantially sinusoidal thereby permitting
~, the system lO to control capacitive loads. The short off
.. time also serves to mini~ise incidental radio frequency
interference, acoustic noise which may be generated by lamp
or transformer loads controlled by the system, and inrush
current stresses in the switching device. While such a short
pulse duration is desirable in texms o~ the wave form ~pplied
to the load, it provides a very bri2f time period during
which source 12 can supply power to control circuit 20. The
design of control circuit 20 makes this possible by requiring
a very small amount of power--the power required to maintain
sufficient charge on either the capacitor Cl or C2 (depending
~`, upon the position of contact 24~ at a level sufficient to
drive the reset and set coils 28, 26, respectively.
. . .
It is desirable to charge the res~t capacitor Cl quickly
~ since the operator of system 10 has to wait until capacitor
,i Cl charges before the system can be switched to the OFF
; state. In order to ensure that cap~citor Cl can be charged
to the required value in a short period of time (typically
~ 100 to 200 milliseconds), it is necessary that the resistor
- R6 through which the charging current to capacitor Cl flows
: have a low value. The use of such a resistor could, however,
create problems once capacitor Cl has charged to the desired
level. Since capacitor Cl will charge in such a short period
~ of time due to the use of the lsw value resistor R6, it is
`~ quite possible, indeed likely, that the operator of system 10
will still be depressing one of the push button switches Pb,
;Z Pb' after the capacitor Cl has charged to its maximum value
`!, 30 (~etermined by Zener diode Dl). Since the push button switch
~, Pb, Pb' is still closed, transistor Q3 will be on and current
would be permitted to flow directly through resistor R6 into
the reset coil 28 thereby inadvertently toggling the control
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~326508
-12-
:.~. circuit 20 back into the OFF position. To avoid this
problemJ reset capacitor charging circuit 32 includes the
~`~ transistor Ql which acts as a current regulator. Whenever Q3
`~, 5 is o~f (this will occur whenever push buttons Pb, Pb' are all
. open) and relay contact 24 is in the ON position, tr~nsistor
~":
~, Ql allows current to flow into capacitor Cl. Whenever
. transistor Q3 is on (this will occur whene~er any one of the
~ push button switches Pb, Pb' is closed), transistor Ql will
,,'!~ 10 be cut-off (this is described in greater detail below) and
will prevent current fro~ ~lowing directly to the reset coil
., 28.
,,
once the operator of system lO has released the push button
switch Pb, Pb' he had originally depressed and capacitor Cl
has charged he can switch control circuit 20 to the OFF mode
by depressing any of the push button switches Pb, Pb'.
Whenever any of these switches are closed, base driv~ ~the
: control signal to control circuit 10) will be available to
transistor Q3 and the transistor will turn on. This provides
a discharge path for the voltage across capacîtor Cl through
reset coil 28, diode Dll and transistor Q3. The current
pulse passing through reset coil 28 causes the contazt 24 to
switch to the OFF position. This cuts off triac 18 and once
the push button switches Pb, Pb' have been released initiates
the charging of capacitor C2.
In the OFF state, the entire supply voltage Vs is available
across nodes A and B. As soon as the push button switch Pb,
Pb' which~initiated the transfer of operation of the latching
control circuit 20 from the ON to the OFF mo~e has been
released, transistor Q2 will turn ON and rharging current
will flow through the diode~
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~` D10, the resistor R~ and the transistor Q? to the capaci-
~, tor C2. If capacitor C2 were permitted to charge to the
full source voltage, the current which would pulse
`j through set coil 26 when one of the push buttons switches
Pb, Pb' was subsequently depressed could destroy the
coil. To avoid this problem, a Zener diode D2 is placed
in series with a diode V5 between node B and the base of
i"
transistor Q2. As soon as the voltage acros~ capacitor
C2 reaches the break over level of Zener diode D2, tran-
sistor Q2 will turn OFF and the current flow to capaci-
tor C2 will cease. At this time, capacitor C2 will be
free to discharge through diode D7, set ~oil 26 and tran-
~istor Q3 the next time one of the push button switches
Pb, Pb' is depressed.
When control circuit 20 is in the OFF mode,
triac 18 is OFF and current flow to load 14 is stopped.
In this mode, it is extremely important that the leakage
current through the control circuit 20 be minimized. The
transistor Q2 carefully regulates the flow of current
during the OFF mode of control circuit 20 to prevent any
signiicant leakage current. A5 soon as the push button
switch Pb, Pb' which initiated the transfer of operation
of the latching control circuit 20 from the ON to the OFF
mode has been released transistor Q2 turns ON and sup-
plies current to capacitor C2 via diode D10 and resistor
R4. Since this current is being used to charge capacitor
C2, there will be some leakage current. Once capacitor
C2 has charged to the voltage driven by diode D2~ tran-
sistor Q2 shuts off but current continues t~ flow through
diode D10, resistor R3 and Zener diode D2. The reverse
leakage current through Zener diode D2 is relatively
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;~. small and is reduced even further by the high value re-
`. sistor R3 (e.g. 560K ohm). If a~ attempt was made to
reduce leakage ~urrent by using a high resistance for ~.
resistor R~ and omitting transistor Q2, the charging
time of capacitor C2 would be extremely slow (as long as
one seco~d). This would be highly undesirable ~ince it
would prev~nt the latching control circuit 20 fxom being
switched back to the ON condition for a period of at
least one second. By steering the current in the manner
described above, the transistor Q2 avoids this problem.
As discussed above, transistor Ql ensures that
: current will not flow from the source 12 to the reset
coil 28 while a push button switch Pb, Pb' is depressed
(i.e. while the control signal is being applied to con~
trol circuit 20). The transistor Q2 which forms part of
- the set coil charging circuit 34 serves a similar pur-
;l pose.
:1 Assuming that contact 24 is initially in the
ON position and push button:switch Pb is depressed, ca-
pacitor Cl will discharge through Dll, reset coil 28 and
.~l transistor Q3 causing contact 24 to switch to the OFF
.~i position. If transistor Q2 were permitted to be on at
this time ~or if the transistor were omitted~ charging
current could immediately~f}ow from source 12 to capaci-
tor C2. While this would be acceptable, a signi~icant
!~ problem could occur once capacitor C2 had accumulated a
significant amount of charge. As tbe voltage across the
3` capacitor C2 increases, so does the voltage available to
energize set coil 26. If the push bu~ton switch Pb con~
~3 tinues to be depressed, transistor Q3 will be on and
current will be free to flow through coil 26. If this .is
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permitted to occur it will cause contact 24 to return to
the ON position. The process can repea~ itself as ~ong
as switch Pb is closed and a toggle situation can occur.
To avoid this proble~, the base of ~ransistors
Ql, Q2 are coupled to the emitter of translstor Q3 via
respective diodes D4, D6~ Whenever a push button switch
Pb, Pb' is depressed, transistor Q3 re~oves base drive
~ro~ transistors Ql and Q2 via D4 and D6 ~hereby turning the
tran~istors off. This di~ables aharging circuits 3~, 34
during the period that any of the push button switches Pb,
Pb' are depressed and prevents current from ~ource 12
from passing through coils 26, 28. While this also de-
lays the charging of capa~itor Cl, C2, this is acceptable
since the appropriate capacitor will be charged very
quickly when the push button Pb, Pb' is released due ~o
the current regulating characteristics of the transis-
tors Ql, Q2.
Summarizing the foregoing, the interaction of
contact 24, low value resistors R6, R4, and transistors
Ql-Q3 ensures that the appropriate capacitor Cl, C2 is
charged only after the push button switch Pb, Pb' which
had been closed is returned to the open position (so that
the coils 26, 28 cannot accidentally ~e energized) and
that the capacitors Cl, C2 are quickly charged when the
push buttvn switch Pb, Pb' is releas~d (to ensure that
the sys~em can intentionally bé switched betw~en the O~F
and the O~ ~ode very quickly).
While ~he above described structure ensures
that the capacitors Cl, C2 are charged very quickly (e.g.
in 100 milliseconds), it is possible that two push but-
ton switches Pb, Pb' will be ~uccessively closed in such
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a short time interval that the charge in the appropriate
ca.pacitor Cl, C2 would not reach a suficien~ level to
fully energize its associated coil 26, 28~ In such a
case, it is possible that the contact 24 would be stuck
between the O~ and OFF positions (i.e. the contact would
be in an intermediate position between the ON terminal
and the OEF terminal). In this event, charging current
will not be available to either capacitor C1 or capaci-
tor C2 with the result that the switching system would be
effectively stuck in the OFF condition.
In order to avoid this problem, control circuit
20 in~ludes a bootstrap circuit including transistor Q4,
for automaticaliy charging capacitor C2 in the event that
:'
-J relay contact 24 is stuck between the ON and OFF posi-
;- . tions. One of the push buttons Pb, Pb' can then be
;i depreased to discharge capacitor C2 through set coil 26
and thereby move relay contact 24 to the ON position.
:~ When contact 24 is stuck between the ON and OFF
positions, transistor Q4's base drive current path is
from node A into the emitter of transistor Q4, out the
~ - base of transi~tor Q4, through R10 and R7. Note that
.i node A i~ on the opposite side of triac 18 from the lower
end of R7. It is the voltage acr~ss triac 18 which
provides the drive for transistor Q4's base current.
Transistor Q4 can receive hase drive whenever Vs ~ VCl
.1 ~the voltage across Cl). It is not necessary for VCl - 0
,j for transistor Q4 to turn on. Thus whenever transistor
Q~ has base drive and Vs > VC2 (the voltage across C2),
transistor Q~ will turn on and charge C2 up to a voltage
~,j limited by Zener diode D2 ~e.g., 18V~. Resistors R10 and
3 R7 are
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, chosen such that when transistor Q4 is om, C2 will charge
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:.i fully in lecs than one second which shou:ld be unnotice-
i able to the user.
-j The last part of the bootstrap circuit is
i r~sistor R9 which functions purely as bleeder resistor.
The value of resistor R9 is chosen such that any leakage
:^~ or noise current through transistor Q4 when it should be
of will not charge capacitor C2 but will pass through
:: resistor R9. Resistor R9 is also large enough that it
will not significantly discharge capacitor C2 under nor-
~ mal conditions.
.~ . In order to protect control circuit 20 from
. ;~
excess voltages due to improper wiring of the control
circuit during installation of switching system 10, a
positive temperature coefficient resistor 42 is placed in
series with Diode D12 in the control line ~0. The diode
D12 makes it possible ~o have a single remote switch
coupled to a plurality of load control systems, each
controlling the operation o different sets of loads, and
to have that single remote switch operate as a control
.,,
:i switch for each of the control systems. This is
;y described in greater detail in application Serial No.
541,368 except that in the foregoing application the
;,: diodes are external to the control circuits7
A snubber circuit comprising re~istor Rll and d
capacitor C4 are placed in p~rallel wit~ triac 18 to
~;i limit the rate of rise of voltage across the triac so as
to protect the same when i~ is use~ in connection with
~: inductive loads.
~' Under normal conditions, the charging voltage
` . to capacitor Cl is the low duty cycle pulsed voltage Vg
illustrated in Figure 2. This voltage is typically no
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.~ more than 15 volts. Xn the event that the contact 24 is
:: toggled ~rom the OFF to the ON position at some poin~ other
than the voltage z~ro crossing of the AC source 12, a
relatively large vol~age could appear batween nodes A and B
before triac 18 is fired. To protect the transi~tor Ql in
:`~ the event of ~uch a large voltage, a Zener diode Ds is placed
parallel with the collector and emitter of transistor Ql.
`~ As noted above, the switching syste~ 10 is
designed for inductive as well as resisti~e loads. When
used with an inducti~e load, the current lagæ the voltage
as shown in Figure 3. Referring to Fig. 3, the current
goes to zero at time ~ and the triac 18 ~urns OFF. The
triac 18 needs a gate pulse to begin conducting in the
``'J opposite direction. The voltage available across the
. triac 18 depends on how inductive the load is but can
.` easily be as high as 130V. This would cause the gate to
fire instantaneously which would provide no time to
Y, charge capacitor Cl. To avoid this problem, a capacitor
.~3 C3 is placed in parallel with the series connection con-
sisting of the silicon bilateral switches 30 and 31 and
the gate of triac 18, and delays the instant at whieh
~? triac 18 turns O~ by a short.period of time sufficient to
allow capacitor Cl to charge but short enough to pre~
. serve the desired essentially sinusoidal wave form ap-
i~y plied to load 14.
While the capacitor C3 ensures that capacitor
Cl will charge even with highly inductive loads, the
delayed firtng of triac 18 results in voltages across
j nodes ~ and B of greater than the 15 volts to which the
~i capacitor Cl is designed to be charged. For this reason,
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a Zener diode Dl is placed in parallel wi~h capacitor Cl
to li~it the charge o~ capacitor Cl to ~afe level~.
~;The presently preferred value~ of the
resistors, capacitors and Zener diodes of Figure 1 is ~et
fort~ in table 1 b~low.
.,
~ TABLE 1
., . - .
: VAW E VALUE IN VALUE -
~ RESISTOB IN O~MS CAPACITOR ICRO FARADS 2ENER IN VOLTS
,,
Rl 150 Cl 68 Dl 22
. R2 22k C2 68 D2 18
: R3 560k C3 0.22 D9 22
- R4 2.2k C40.047
.. i R5 3.3k
. R6 47
R7 390k
:, R8 47k
$ R9 390k
.: R10 l.ZM
. Rll lk
~`......... All diodes are type lN4004. Triac 18 is an MAC224-5.
Transistor Ql is an MPS-A13, transistor Q2.is a 2N6517,
~;~ transistor Q3 is an MPS-A56 and transistor Q4 is an MPS-
:,, A92.
The load control system 10 o~ the foregoing
embodi~ents has several advantages. Because the only power
needed for the control circuit 20 i~ the power re~uired to
charge and ~aintain the charge on the capacitors Cl and C2,
the triac 18 can remain on for substantially the ~ull AC wave
~orm. This makes it possible to utilize the control system
10 with capacitive loads. The time required to charge the
capacitor Cl and C2 to the
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required level can be very short due to the use of the
low value charging resistors R6 and R40 These resistors
can be used due to the OperatioD of the capacitor charg-
ing cixcuits 32, 34 which make it possible to use low
charging re~istors while at the same time preventing
high leakage currents and the possibility that the con-
tact 24 would go into a toggle state while the push
button switch Pb is depressed.
Another major advantage o the present
invention is the control circuit 20 is powered by the
voltage across triac 18 ~both in the ON and OFF condition
of control circuit 20) alone. As a result, the control
circuit need only be connected between the sburce 12 and
the load 14 and does not have to be connected to neu-
tral.
Another significant advantage of the present
invention is that it is polarity insensitive; the nodes A
and B can be connected to the source 12 and load 14,
respectively, or to the load 14 and source 12, respec-
tively.
Another major advantage of the present
invention is that it inherently contains a power off
memory in which the control circuit 20 remembers whether
it was in the ON or the OFF state when power is removed
from the control circuit 20. When the power is returned,
the control circuit will either enable or disable the
triac 18 as determined by the original condition of the
control circuit. The power off memory function is
achieved as a result of the use of the bistable latch.
If an electronic latch was used for this purpose, a
lithium battery or similar power source would be supplied
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to maintain the latch in its original position before the
~C power to control oircuit 20 was xemoved.
Figure 4 is a schematic diagram illustrating
the manner in which two load control systems 10-l, 10-2
constructed in accordance with the present inventlon can
share remote control swi~chesO The first contral ~ystem
lO-l includes a main housin~ 38 (which hous~s a triac 18,
a control circuit 20 and the local push button switch Pb)
and three remote control switch housings 42, 44 and 46
the housings 44 and 46 also formîng part of the control
system 10-2 as described below). The housing 42 is
substantially identical in external appearance to hous-
ing 38 and houses a single remote switching circuit Z2
including the push button switch Pb'. The housings ~4,
46 are also substantially identical in appearance to the
housing 38 except that they each include a pair of re~ote
control switching circuits 22, each of which includes a
respective push bùtton switch Pb'-1~ Pb'-2. The combined
ize and shape of the~push button witches Pb'-l and Pb'~
2 are approximately equal to the overall size:and shape
,
of the single push button switch Pb' in main housing 38.
The push button switch Pb'-l in each of the housings 44,
46 is coupled to the control circuit 20 of main housing
38 and~applies a control signal to control circuit 20
whenever depressed.
The push button switches Pb'-2 of housings 4
and 46 are coupled to the mair housing 40 of the load
control system lQ-2. Like housing 38, the main housing
40 houses the control circuit 20, the triac 18 and the
push button Pb of the load control circuit 10-2~ Whenev-
er one of the push button switche~ Pb'-2 is depressed, it
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applies a control signal to the control circuit 20 located in
housing 400 As such, the single housing 44 (as well as the
single housing 46), includes a pair o~ pus,h button switches,
~: one for each o~ the load control systems 10-1, 10-2 and
~ thereby makes it possible to control two sets o~ loads from a
:~ . single remote location.
",10
In the embodiment illustrated, the load control system
.` 10-2 also includes a housing 48 which houses a Gin~le remote
i switching unit 22 including the push button switch Pb'.
While each load control system 10-1~ 10-2 is shown as having
three remote units, two of which are located in the same
housing as the remote unit for the other load control system,
~i the invention is not so limited and other combinations can be
used.
.~
In the foregoing description of Figure 4, the control
plates at the front of each of the housings 38-46 are
referred to as push button switches. In fact, each push
butgon switch is located internally of the housing and the
element viewed from the front of the housing is an actuator
~,125 plate coupled to the push button switch. This is described
in more detail in U.S. Patent ~,563,594. As used în the
'1 appended claims, the term 'lactuator plate" refers to the
plate labeled Pb, Pb', Pb'-l and Pb'-~ in Figure 4.
.'30 In the foregoing description, the bidirectionally
conductive switching element 18 is shown as triac. Other
bidirectional devices can be used. Additionally, hybrid
circuits which effectively operate as a bidirectionally
conductive switching means (e.g. a pair of back to hack SCRS)
can also be used.
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~ The present invention may be embodied in other
" speciic forms wi~hout departing from the spirit or es-
'.5sential attributes thereof and, accordin~ly, reference
~1,should be made to the appended claims, rather than to the
foregoing specification, as indicating the scope of th*
invention.
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