Light Switch

U.S. Pat. No. 3,898,516, entitled "Lighting Control System For Incandescent Lamps," by Henry H. Nakasone, Aug. 8, 1975;

U.S. Pat. No. 4,008,416, entitled "Circuit For Producing A Gradual Change In Conduction Angle," by Henry H. Nakasone;

U.S. application Ser. No. 768,544, entitled "Momentary Contact Light Switch," by Bruce D. Jimerson and Henry H. Nakasone, filed Feb. 14, 1977;

U.S. application Ser. No. 768,547, entitled "Soft Switch With Rapid Recovery Circuit," by Henry H. Nakasone, filed Feb. 14, 1977.

1. Field of the Invention

The invention relates to soft switches which can be used with existing household wiring arrangements to effect control from any other number of separate stations. The contents of the above Patents and Patent Applications are incorporated herein by reference for the purpose of providing background information.

2. Description of the Prior Art

The concept of soft switching, i.e., gradual "turn-on" and "turn-off," has been disclosed in previous Patents by one of the Inventors (e.g. U.S. Pat. Nos. 3,898,516 and 4,008,416) and at least one circuit has been proposed by the same Inventors for producing a momentary contact soft switch.

These prior art circuits, however, cannot be used to effect multiple station control, unless the facility is already specially wired for standard three way operation, i.e., in addition to the wire between each station and one of the lamp terminals, both sides of the AC line must be brought to each of the stations. Thus, in situations where one wishes, for example to operate a table lamp which is plugged into an outlet controlled by a single wall switch, one would have to add additional household wiring to be able to turn the lamp "on" or "off" from the wall switch or the lamp switch. Moreover, if one wished to control a lamp from more than two locations using momentary contact switches, an arrangement like that shown in application Ser. No. 768,544, would not suffice even where the existing wiring was adequate) because such a configuration is inherently limited to a maximum of two stations.

Accordingly, a primary object of the invention is to provide a momentary contact light switch which can be used to replace a conventional mechanical toggle switch at any number of control stations.

Another object of the invention is to provide a momentary contact light switch which does not utilize relays or other mechanical devices to effect a change in the state of the system.

A further object of the invention is to provide a switch which can be added to any existing wiring configuration to effect control from more than one station.

Another object of the invention is to provide a momentary contact switch which can be wired in series with any number of similar momentary contact switches so that each switch is capable of controlling the application of power to a load independent of every other switch.

Another object of the invention is to provide a momentary contact switch which will eliminate the need for 3-way (or more) household wiring arrangements to effect control of a light from a plurality of separate stations.

Another object of the invention is to provide a gradual change in the amount of AC power applied to a load following the depression of any one of a plurality of series connected momentary contact switches.

Another object of the invention is to provide gradual turn-on and turn-off of a lamp from one or more momentary contact switches which are series interconnected with the lamp and AC power source.

Other objects and advantages of the present invention will be obvious from the detailed description of a preferred embodiment given hereinbelow.

The aforementioned objects are realized by the present invention which comprises one or more normally closed momentary contact switches, each of which is bypassed by a diode. The control circuit, (which may physically be located at one of the switch stations) comprises a low current power supply, a Schmidt trigger, a bistable multi-vibrator (or Flip Flop) and a variable conduction angle circuit. The low current power supply generates a DC voltage for operating the Schmidt trigger and Flip Flop. Depression of any series switch momentarily removes one input polarity which causes the Schmidt trigger to temporarily change state. This, in turn, compliments the Flip Flop which functions to allow the variable conduction angle circuit to commence a progressive increase (if the lamp was initially "off" or to abruptly cut off conduction during one polarity followed by a gradual decrease in the conducting angle during the other polarity (if the lamp was initially "on").

The Figure shows a schematic diagram of a preferred embodiment of the invention.

Adverting to the Drawing, there is shown a control circuit together with a lamp L.sub.1 and four control switches S.sub.1, S.sub.2, S.sub.3 and S.sub.4. It will be understood, however, that any number of control switches could be utilized, and that each would be located at a separate station. Each switch is normally "closed" so that AC power is applied to the lamp L.sub.1 and control circuit until one of the switches S.sub.1 - S.sub.4 is momentarily depressed. When this occurs, only the positive fraction of each AC cycle is applied to the lamp L.sub.1, and circuitry. The momentary interruption of the negative half cycle operates in a manner to be described below to gradually turn the lamp from "off" to "on" or from "on" to "off" as the case may be. Each switch (S.sub.1 - S.sub.4), therefore, is capable of effecting the same transition, and hence any number of switches could be so connected so as to operate the lamp L.sub.1. Since only one control circuit is required for any number of switches, it can be located at any station (for example, it may be incorporated in the same structure as that used to house S.sub.4) or it may be built into an adaptor at the Lamp L.sub.1, or located at any point in-between switch stations, whatever.

Referring now to the particular components of the control circuit, there is shown a Schmidt Trigger 200, [comprising Resistors R.sub.9, R.sub.10, R.sub.11, R.sub.12 and R.sub.13 ; and transistors Q.sub.2 and Q.sub.3 ], a Flip flop 300 [comprising transistors Q.sub.4, and Q.sub.5 ; Resistors R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.17 and R.sub.18 commutating capacitors C.sub.4 and C.sub.5 ; bypass capacitor C.sub.6 ; and steering diodes D.sub.14 and D.sub.15 ]. Both the Schmidt trigger and Flip Flop are supplied with an operating voltage (line 50) from a DC power supply 100, [comprising capacitors C.sub.8 and C.sub.9 ; Transistor Q.sub.1 ; Diodes D.sub.6, D.sub.7, D.sub.8 and D.sub.9 ; Resistor R.sub.16 and Zener Diode Z.sub.1.] The output of the Flip Flop 300 (line 54) is coupled to the input of a variable conduction angle circuit 400 through Diode D.sub.13. This latter circuit functions in a manner analogous to the circuit shown in Application Ser. No. 768,547, cited hereinabove. Its operation may be briefly described as follows: If the charge on accumulating capacitor C.sub.3 is low, capacitor C.sub.2 (being effectively connected to ground through the low impedance of D.sub.10 during the negative half cycles and through D.sub.11 and C.sub.3 during the positive half cycles) functions to delay the phase of the voltage applied through resistor R.sub.2 so as to reliably prevent the potential on line 52 from exceeding that which is required to breakdown Diac X.sub.1. As long as this condition remains, Triac T.sub.1 does not fire during either the positive or negative half cycle of the AC input which appears on line 53. If, however, the state of Flip Flop 300 is such that Q.sub.4 does not conduct, line 54 will be positive, and hence C.sub.3 will be charged through R.sub.2, C.sub.2 and D.sub.11, during each positive half cycle of the AC source. As C.sub.3 charges the phase shifting effect of C.sub.2 is reduced, and the voltage on line 52 will reach a magnitude which exceeds the breakdown voltage of Diac X.sub.1 near the end of each half cycle. When this occurs, X.sub.1 will conduct, discharging C.sub.1 through the gate of T.sub.1, thus causing T.sub.1 to conduct during the latter part of each half cycle. As C.sub.3 continues to charge, during each positive half cycle, the conduction duration of T.sub.1 increases (i.e., T.sub.1 fires at an earlier time during each successive half cycle) until the lamp L.sub.1 is fully turned "on." It will thus be seen that the intensity of Lamp L.sub.1 is dependent upon the charge on C.sub.3. With this background, an explanation of the operation of the entire circuit can be undertaken.

Assume, for example, that as an initial condition, all switches S.sub.1, S.sub.2, S.sub.3 and S.sub.4 are in their normal position and that Flip Flop 300 is in the "off" state (Q.sub.4 conducting) so that line 54 is approximately at ground. C.sub.3 will be assumed to be at zero volts, and hence T.sub.1 is not conducting, so that the full value of the AC source appears on line 53. In this condition, C.sub.3 is kept discharged by the negative current flowing through D.sub.5, resistor R.sub.1 and the 1/4 watt neon indicator lamp N.sub.1 (which breaks down whenever the magnitude of the negative half of the voltage on line 53 exceeds 80 volts). The positive waveform applied to R.sub.2 is clamped by Diode D.sub.13, so that virtually no current flows through Diode D.sub.11. The potential at point 56 remains near zero because of the combined positive current flowing through D.sub.16 and R.sub.15 and the negative current flowing through R.sub.14 and D.sub.5 . As a consequence, Q.sub.2 is "off" and Q.sub.3 is "on". In this condition, the power supply 100 will output approximately 65 volts on line 50, the value of C.sub.9 being chosen (in conjunction with the load requirements of Flip Flop 300 and Schmidt trigger 200) such that the average potential on C.sub.8 will exceed the breakdown voltage of Z.sub.1 (as a consequence Q.sub.1 will be cut-off so that very little power will be dissipated by the power supply 100).

In order to change from the quiescent "off" state described above, any one of the switches (S.sub.1 - S.sub.4) can be actuated to temporarily interrupt the negative half cycle. Assume, for example, that S.sub.3 is momentarily depressed, the voltage on C.sub.7 will immediately begin to increase positively; [preferably, the components R.sub.15 and C.sub.7 will be chosen such that the voltage on C.sub.7 will rise to a point to cause Q.sub.2 to conduct in approximately 6 cycles or about 1/10 ssecond]. When this occurs, Schmidt trigger 200 fires, causing the collector of Q.sub.2 to abruptly fall to ground. This negative transition is coupled through trigger capacitor C.sub.10 causing Flip Flop 300 to change state. Q.sub.4 thus stops conducting, so the positive half of the AC cycle is no longer clamped to ground by D.sub.13. C.sub.3 thus commences to charge through R.sub.2, C.sub.2 and D.sub.11 as previously explained.

When the quiescent "on" state is reached, most of the input AC source will be dropped across the lamp L.sub.1 (i.e., the waveform on line 53 will follow the input AC source until T.sub.1 fires, at which point it will be abruptly reduced to nearly zero). Since the value of R.sub.2 and the value of C.sub.1 will preferably be chosen to obtain as large a conduction angle as possible, the maximum potential on line 53 will be reduced to less than 60 volts, and the duration of each positive and negative excursion will be approximately one millisecond.

Because of the reduced amplitude and duration of the voltage on line 53, the capacitor C.sub.9 will be unable to supply sufficient current to maintain the charge on C.sub.8. As a consequence, the voltage on C.sub.8 drops until Q.sub.1 becomes conductive, i.e., whenever the potential on C.sub.8 drops below the breakdown voltage of Zener Z.sub.1, transistor Q.sub.1 will conduct to maintain the charge on C.sub.8. Thus, C.sub.9 function is to charge C.sub.8 when the lamp is "off" and Q.sub.1 functions to charge C.sub.8 when the lamp is "on."

Once the circuit is triggered to the "on" state, it will remain until one of the switches S.sub.1 -S.sub.4 is depressed. C.sub.3 will charge to a peak value approximately equal to the voltage on line 50. In this state, only a very small current flowing through R.sub.2 will be required to maintain the charge on C.sub.3 since: (1) the maximum potential on 53 is reduced to less than that required to ionize neon N.sub.1, and, (2) the potential on line 54 is approximately equal to that on C.sub.3, so that almost no current flows through resistor R.sub.3 (typically 500K or larger). Before considering "turn off" it will be assumed that Schmidt trigger 200 returned to its original state (Q.sub.2 "off") immediately after the actuating switch S.sub.3 was released, and that it is now in readiness to be retriggered by a second momentary interruption of the negative half cycle of the AC power source.

In order to initiate "turn-off," any one of the switches S.sub.1 -S.sub.4 may be actuated. Assume, for example, that S.sub.1 is depressed so as to momentarily interrupt the negative half cycle of the AC source. The power applied to will immediately drop by 50%, and C.sub.7 will commence charging positively through R.sub.15 and D.sub.16. Since the average positive voltage available on line 53 is now considerably less than that available to charge C.sub.7 when initiating "turn-on," more time will be required to raise the potential on line 56 to a level sufficient to operate Schmidt trigger 200. Thus, if 20 cycles are required, the Schmidt 200 will be triggered in 1/3 of a second. Flip Flop 300 is then complemented so that Q.sub.4 conducts. The positive portion of the AC waveform will then be clamped through D.sub.13, and C.sub.3 will begin to discharge through D.sub.12 and R.sub.3. Upon release of S.sub.1, the negative half of the source becomes available to trigger T.sub.1. This occurs, however, at a progressively later time during each negative half cycle due to the gradual discharge of C.sub.3. When the conduction of T.sub.1 is delayed to a point such that the magnitude of the negative waveform at 53 is sufficient to ionize N.sub.1, the rate of discharge of C.sub.3 is increased rapidly, causing the intensity of the lamp to abruptly diminish.

To recapitulate, momentary depression of S.sub.1, actuates Schmidt trigger 200, which in turn complements Flip Flop 300, the latter functioning: (1) to abruptly reduce the lamp intensity by clamping the positive gating signal at 52 through D.sub.13 ; and (2) to continue thereafter, to gradually discharge C.sub.3 through D.sub.12 and R.sub.3 so as to cause the light intensity to decrease slowly until it is abruptly extinguished by the rapid discharge of C.sub.3 via neon N.sub.1. The rate at which the lamp intensity rises during "turn-on," is determined primarily by the value of C.sub.3. Thus, for a 2 to 3 seconds fade-in, a value of 10.mu.f can be used. It will be understood, however, that a large value is not necessary for the purpose of extending lamp life, and that the life expectancies of common incandescent lamps can be greatly extended even though "turn-on" appears to occur almost instantaneously. In a like manner, the "turn-off" time can be controlled, so as to be instantaneous or gradual. One advantage of gradual decay lies in the fact that the operator is instantly informed of the fact that actuation has taken place (by the 50% decrease in intensity), yet there is sufficient light for several seconds to permit safe departure. Although the invention has been illustrated with the aid of a particular embodiment, it will be understood that the basic concepts are not limited thereto, and that numerous changes, modifications and substitutions may be made without departing from the spirit of the invention.