CA1326508C - Load control system - Google Patents
Load control systemInfo
- Publication number
- CA1326508C CA1326508C CA000616223A CA616223A CA1326508C CA 1326508 C CA1326508 C CA 1326508C CA 000616223 A CA000616223 A CA 000616223A CA 616223 A CA616223 A CA 616223A CA 1326508 C CA1326508 C CA 1326508C
- Authority
- CA
- Canada
- Prior art keywords
- control circuit
- load
- control system
- control
- switching means
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
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- Electronic Switches (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A load control switching system includes a switching element adapted to be coupled between a power source and a load. The switch element is operable in an ON state wherein its supplies power from the source to load and an OFF state wherein it cuts off power from the source to the load. A
control circuit controls operation of the witching element in response to the actuation of one or more short-throw, light-force switches which are each movable between a normally open and a momentarily closed position. The control circuit alternates the state of the switching element each time the short-throw, light-force switch is momentarily closed.
A load control switching system includes a switching element adapted to be coupled between a power source and a load. The switch element is operable in an ON state wherein its supplies power from the source to load and an OFF state wherein it cuts off power from the source to the load. A
control circuit controls operation of the witching element in response to the actuation of one or more short-throw, light-force switches which are each movable between a normally open and a momentarily closed position. The control circuit alternates the state of the switching element each time the short-throw, light-force switch is momentarily closed.
Description
~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. , ,, ": .
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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: ~2~8 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 - 2b -.
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: ' 1~265~8 `, 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
- 2c -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.
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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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`:, ~ 5 -:, 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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`;''',, 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.
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~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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i '! ' 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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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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... ~ 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.
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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 :.~. 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 J
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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 ~, :.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 3~ 8 ~ - 20 -:. , 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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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. , ,, ": .
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 . . . ~ .
:
: ~2~8 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 :~ .
: - 2a -132~08 ~ .
,, 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 - 2b -.
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: ' 1~265~8 `, 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
- 2c -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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`:, ~ 5 -:, 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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`;''',, 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.
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~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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i '! ' 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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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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... ~ 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 :.~. 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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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 J
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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 ~, :.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 3~ 8 ~ - 20 -:. , 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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Claims
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A load control system, comprising: an electronic switching means operable in a conductive and a non-conductive state, said switching means including first and second power leads connectable to a source and load, respectively: a control circuit for controlling the operation of said switching means whenever power is applied to said control circuit and as a function of control signals applied to said control circuit, said control circuit including memory means for storing the state of said switching means immediately before power is cut of from said control circuit and for returning said switching means to said stored state when power is returned to said control circuit.
2. The load control system as claimed in claim 1, wherein said memory means is a bistable latch forming part of said control circuit, said latch having an ON state and an OFF
state, said control circuit causing said electronic switching means to operate in said conductive state when said latch is in said ON state and causing said electronic switching means to operate in said non-conductive state when said latch is in said OFF state.
3. The load control system as claimed in claim 2, wherein said bistable latch is an electronic latch having an energy storage source associated therewith which powers said electronic latch when power is cut off from said control circuit.
4. The load control system as claimed in claim 2, wherein said bistable latch is a mechanical latch.
5. The load control system as claimed in claim 2, wherein said bistable latch is a magnetic latch relay having set and reset coils and a contact movable between ON and OFF
positions, the position of said contact determining the condition of said latch.
6. The load control system as claimed in claim 5, wherein said control circuit further includes: set and reset capacitors associated with said set and reset coils, respectively; means for charging said set and reset capacitors when said contact is in the ON and the OFF
position, respectively; and means for discharging said charged capacitor through its associated coil in response to the application of said control signal to said control circuit.
7. The load control system as claimed in claim 6, further including means for charging a predetermined one of said capacitors whenever said contact is stuck in a position intermediate said ON and OFF positions.
8. The load control system as claimed in claim 6, further including means for disabling said charging means as long as said control signal is applied to said control circuit.
9. The load control system as claimed in claim 8, wherein:
said charging means includes a first current regulator which supplies current to said set capacitor when said contact is in said OFF position and a second current regulator which supplies current to said reset capacitor when said current is in said ON position; and said disabling means disables said current regulators whenever said control signals applied to said control circuit.
10. The control system as claimed in claim 1, wherein said electronic switching means and said control circuit are all located in a single housing.
11. The load control system as claimed in claim 10, further including a local human actuable switch housed in said housing.
12. The load control system as claimed in claim 11, further including at least one remote switch, each of said remote switches being housed in a respective remote switch housing, each of said remote switches generating control signals which are applied to said control circuit.
13. The load control system as claimed in claim 12, wherein the external appearance of said main and remote switch housings are substantially identical.
14. The load control system as claimed in claim 1, wherein said electronic switching means is bidirectionally conductive and has first and second main terminals and a control terminal and wherein said control circuit derives 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 and wherein said control circuit is polarity insensitive and operates properly irrespective of whether the first and second main terminals of said switching means is coupled to said load and said source, respectively, or to said source and load, respectively.
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A load control system, comprising: an electronic switching means operable in a conductive and a non-conductive state, said switching means including first and second power leads connectable to a source and load, respectively: a control circuit for controlling the operation of said switching means whenever power is applied to said control circuit and as a function of control signals applied to said control circuit, said control circuit including memory means for storing the state of said switching means immediately before power is cut of from said control circuit and for returning said switching means to said stored state when power is returned to said control circuit.
2. The load control system as claimed in claim 1, wherein said memory means is a bistable latch forming part of said control circuit, said latch having an ON state and an OFF
state, said control circuit causing said electronic switching means to operate in said conductive state when said latch is in said ON state and causing said electronic switching means to operate in said non-conductive state when said latch is in said OFF state.
3. The load control system as claimed in claim 2, wherein said bistable latch is an electronic latch having an energy storage source associated therewith which powers said electronic latch when power is cut off from said control circuit.
4. The load control system as claimed in claim 2, wherein said bistable latch is a mechanical latch.
5. The load control system as claimed in claim 2, wherein said bistable latch is a magnetic latch relay having set and reset coils and a contact movable between ON and OFF
positions, the position of said contact determining the condition of said latch.
6. The load control system as claimed in claim 5, wherein said control circuit further includes: set and reset capacitors associated with said set and reset coils, respectively; means for charging said set and reset capacitors when said contact is in the ON and the OFF
position, respectively; and means for discharging said charged capacitor through its associated coil in response to the application of said control signal to said control circuit.
7. The load control system as claimed in claim 6, further including means for charging a predetermined one of said capacitors whenever said contact is stuck in a position intermediate said ON and OFF positions.
8. The load control system as claimed in claim 6, further including means for disabling said charging means as long as said control signal is applied to said control circuit.
9. The load control system as claimed in claim 8, wherein:
said charging means includes a first current regulator which supplies current to said set capacitor when said contact is in said OFF position and a second current regulator which supplies current to said reset capacitor when said current is in said ON position; and said disabling means disables said current regulators whenever said control signals applied to said control circuit.
10. The control system as claimed in claim 1, wherein said electronic switching means and said control circuit are all located in a single housing.
11. The load control system as claimed in claim 10, further including a local human actuable switch housed in said housing.
12. The load control system as claimed in claim 11, further including at least one remote switch, each of said remote switches being housed in a respective remote switch housing, each of said remote switches generating control signals which are applied to said control circuit.
13. The load control system as claimed in claim 12, wherein the external appearance of said main and remote switch housings are substantially identical.
14. The load control system as claimed in claim 1, wherein said electronic switching means is bidirectionally conductive and has first and second main terminals and a control terminal and wherein said control circuit derives 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 and wherein said control circuit is polarity insensitive and operates properly irrespective of whether the first and second main terminals of said switching means is coupled to said load and said source, respectively, or to said source and load, respectively.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000616223A CA1326508C (en) | 1985-10-25 | 1991-11-12 | Load control system |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US791,318 | 1985-10-25 | ||
| US06/791,318 US4833339A (en) | 1983-10-13 | 1985-10-25 | Load control system |
| CA 521036 CA1298871C (en) | 1985-10-25 | 1986-10-21 | Load control system |
| CA000616223A CA1326508C (en) | 1985-10-25 | 1991-11-12 | Load control system |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 521036 Division CA1298871C (en) | 1985-10-25 | 1986-10-21 | Load control system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1326508C true CA1326508C (en) | 1994-01-25 |
Family
ID=25671132
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000616223A Expired - Fee Related CA1326508C (en) | 1985-10-25 | 1991-11-12 | Load control system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1326508C (en) |
-
1991
- 1991-11-12 CA CA000616223A patent/CA1326508C/en not_active Expired - Fee Related
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |