US3902080A

US3902080A - Switching device

Info

Publication number: US3902080A
Application number: US483286A
Authority: US
Inventors: Clair Raymond Edward St; Melvin A Hughes
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-06-26
Filing date: 1974-06-26
Publication date: 1975-08-26
Anticipated expiration: 1992-08-26

Abstract

A switching assembly wherein a triac is controlled by a magnetically-operated reed switch. The reed switch is in turn operated by a magnet attached to a slidable button. The circuitry includes a zero crossing detector which operates to interconnect a load through the triac when the switch is operated at an instant when the instantaneous value of A.C. line voltage is less than about 30 volts (in an initial half-cycle) and otherwise limits current flow (if the switch is turned on at a time when the line voltage is above about 30 volts) for the remainder of a first half-cycle, thus in both instances reducing undesired initial abnormal current flow when a typical load is switched ''''on''''.

Description

United States Patent [1 1 St. Clair et al.

[ Aug. 26, 1975 SWITCHING DEVICE [76] Inventors: Raymond Edward St. Clair, Rt. 2,

Box 154; Melvin A. Hughes, Rt. 2, Box 95, both of New Market, Ala. 35761 [22] Filed: June 26, I974 [21} Appl. No.: 483,286

[52] US. Cl. 307/252 B; 307/252 UA; 315/199; 3l5/DIG. 7

[51] Int. Cl. H03k 17/72 [58] Field of Search 307/252 B, 252 UA, 308; 315/DIG. 7, 194, 199, 200 R [56] References Cited UNITED STATES PATENTS 3,594,59l 7/197l Lampman 307/252 B 4 WIT Primary Exuminer.lames B. Mullins [57] ABSTRACT A switching assembly wherein a triac is controlled by a magnetically-operated reed switch. The reed switch is in turn operated by a magnet attached to a slidable button. The circuitry includes a Zero crossing detector which operates to interconnect a load through the triac when the switch is operated at an instant when the instantaneous value of AC. line voltage is less than about 30 volts (in an initial half-cycle) and otherwise limits current flow (if the switch is turned on at a time when the line voltage is above about 30 volts) for the remainder of a first half-cycle, thus in both instances reducing undesired initial abnormal current flow when a typical load is switched on".

9 Claims, 4 Drawing Figures I20 VAC.

PATENTEB AUG 2 6 I975 SWITCHING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to switches, and particularly to a new and improved switch which offers both improved safety and economy.

2. General Description of the Prior Art There are two principal considerations in determining the safety of a switch. One is the safety of the environment with respect to the switch, and the other is the safety of the user of the switch. In the first category is the matter of exposure of an environment to a spark or actual fire which might damage or destroy the environment. In the second category is the matter of possible shock to the user. In the past, switches particularly directed to the matter of safety to an environment have been rather elaborate with substantial coverings, mak ing them both bulky and relatively expensive. Much the same can also be said for switches particularly adapted to provide safety to a user. As an example, switches for use in wet areas or outdoors where there is likely to be conduction between the surface of the switch contacted by the user and an electrical conductor of the switch have required elaborate sealing structures and substantial housings.

In both instances, the resulting switch is both bulky and expensive. In addition to the matter of safety, the present invention attacks the problem of economy, economy from the point of view of the life of electrical devices, particulary incandescent electrical lamps. In the past, the principal approach to extending bulb life has been to use bulbs rated at 100 to 150 volts on 115- volt lines. While this will extend the life of a bulb somewhat, the problem has been that light output is significantly reduced. While efforts have been made to produce electronically-operated switches to limit initial current flow to a bulb, these devices have been too expensive to enable their general usage.

SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide an improved switch which provides both safety to an environment and to the user and which may be safely used in most any environment.

It is a further object of this invention to provide an improved switch wherein power provided by the switch to a load is substantially reduced during the first halfcycle of operation, thus substantially improving equipment life.

In accordance with the invention, a switch, or switching assembly, is constructed wherein a triac is controlled by an electronic circuit including a single-pole, single throw switch. The circuitry includes a unique zero-crossing detector employing a pair of parallel opposite-type transistors connected across the gate circuit of a triac, and wherein the parallel bases of the transistors are powered by a voltage dividing circuit which for low voltage turn ons (instantaneous voltage less than a selected value, say 30 volts) transistors do not operate and the triac is allowed to immediately turn on. However, where the switch is turned on at an instance when the instantaneous voltage is greater than this value, one of the transistors turns on before the triac can turn on, preventing and pulling gate voltage on the transistor down to essentially zero and preventing it from operating during the initial half-cycle. Thus, the triac cannot fire until a zero crossing of the line voltage occurs.

In accordance with the second aspect of the invention, a switching assembly is constructed as described wherein, in addition, the switch is operated by a sliding button. The sliding button houses a small magnet which is moved to and away from a reed switch, which forms the single-pole, single-throw switching function. The components of the circuit are mounted on one side of a printed circuit board with only two terminals (the operating terminals) protruding. Power connections are made by wire to these terminals and then a potting compound is poured into a container surrounding the board and components, totally sealing the switching assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical schematic illustration of an embodiment of the invention.

FIG. 2 is an exploded pictorial view of the mechanical details of the invention.

FIG. 3 is a partial pictorial view of certain of the mechanical details as assembled.

FIG. 4 is a Waveform useful in explaining the operation of the circuit of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, there is shown an electrical schematic diagram of an embodiment of the invention as it would be connected to energize electrical load 10, such as an incandescent lamp bulb from a volt A.C. source. One switch lead or terminal 12 is connected through load 10 to anode-cathode terminal 14 of triac 16. It is further connected through normally open magnetically-operated reed switch 18 to one lead of

resistors

20 and 22. Resistor 22 is connected to the parallel-connected collectors of PNP transistor 24 and NPN transistor 26 and to gate terminal 28 of triac 16. The other lead of resistor 20 is connected to the parallel connected bases of

transistors

24 and 26 and through resistor 30 to opposite switched terminal 32.

Resistors

20 and 22 are typically of comparable value, e.g. 510 ohms for resistor 20 and 470 ohms for resistor 22. Actually, a range of values for resistor 20 would typically be from 20 to 5000 ohms, and for resistor 22, from 50 to 800

ohmsResistors

20 and 30 form a current divider network with resistor 30 having a typical value on the order of 20 ohms or l/25 of the value of resistor 20. It can, with an appropriate transistor, have a range of values from 1 to 200 ohms or a range of ratios of l/20th to 1/30th with respect to resistor 20. The parallelconnected emitters of the transistors are also connected to switched terminal 32 as is the second anodecathode terminal 34 of triac 16. By use of

opposite polarity transistors

24 and 26, a voltage of sufficient amplitude of either polarity will turn on one of them as required. An optional capacitor 27 is connected between gate terminal 28 of triac l6 and switched terminal 32. It is employed when because of the particularly fast turn on ofa particular triac that it is necessary to decrease the rise time of the voltage at the gate of the triac OFF an instant longer so that the transistor can fire before the triac does. The voltage will thus be sustained at the gate by capacitor 27 for the finite time that it takes it to be discharged through one of the transistors.

The electrical components of the invention are mounted on one side of printed circuit board or card 36 and are installed as shown in FIGS. 2 and 3. Printed card 36 is then placed in an essentially rectilinear opening 38 formed through housing 40. Printed card 36 is supported within guide slots 42 formed in

opposite walls

44 and 46 of opening 38 and is inserted within the opening so that upper edge 48 of card 36 is just below the upper surface of the housing. Triac 16 is attached to circuit card 36 in a position so that heat dissipating tab 50 mates with raised longitudinal surface 52 within opening 38 and to which it is secured through matching holes in tab 50 and housing 40 by rivet 54. This is more clearly shown in FIG. 2. Connections are made to the switch by externally connecting leads 56 which are internally connected to the anode-cathode junction of triac 16 and extend out lower end 58 of housing 40. Once the switch is assembled as shown in FIG. 2, opening 38 is completely filled with heat conductive potting compound 60. Cover plate 62 of nonferrous material contains usual mounting holes 64 and 66, adapting it to be employed in place of existing-type wall switches. Slide button assembly 68 consists of resilient slider portion 70 and button 72 with magnet 74 positioned in opening 76 of button 72. Slide button assembly 68 is held to a selected operating range of movement by rectangular opening 77 through which button 72 extends when assembled. Slider portion 70 of button assembly 68 is dimensioned to freely slide within slot 78 provided in housing 40 and is provided with flexible prong 80, which frictionally engages one side 82 of slot 70 when in a position other than on. When in the on" position, it is more substantially supported by detent 84, which engages semi-circular notch 86 formed near upper end 88 of slot 78. This condition is illustrated in in FIG. 2 which shows button 68 positioned in the on position. When assembled, cover plate 62 is supported by notches 90 formed in housing 40. It is typically positioned permanently by pins (not shown) which are inserted through cover plate 62 and housing 40. Finally, when the switch is mounted, an outer cover plate (not shown) would be connected by conventional means to cover plate 62.

The function and operation of the invention is as follows. When button 72 is pushed upward (as shown in FIG. 2), magnet 74 in slider 70 is essentially positioned over reed switch 18. This causes this switch to close and a circuit is completed through load 10. Now, depending upon whether the instantaneous voltage of the applied 120 volt A.C. source is above or below approximately 30 volts, power would be applied to load in either one or the other of two modes. First, assume initially that switch 18 would be closed at a time when the instantaneous value of the applied source is at 100 volts (point A), as illustrated on curve 92 of FIG. 4 showing 120 volts (R.M.S.) AC. input voltage. In such case, the current flow through resistor and the base emitter path of transistor 26 is such as to turn transistor 26 on before triac 16 can fire. (If the polarity of input had been negative, transistor 24 would have turned on). This effectively shorts out any significant voltage to gate 28 of triac 16. Thus, triac 16 does not switch on at this instant to provide power to load 10. Instead, there exists relatively high impedence paths through

resistors

20 and 22, which limit peak current flow during the balance of the positive half-cycle of curve 92 to between 600 and 700 milliamperes. Thus, current flow through load 10 which would otherwise typically be several amperes (e.g. an incandescent -watt bulb would draw a peak current during the first half-cycle of approximately 10 amperes) would be initially substantially limited. The condition of limited current flow or preheat current through load 10 continues until the voltage drops at point B (FIG. 4) to zero at the end of the first half-cycle. At this point, the voltage is removed from transistor 26 and it would open.

As the supply voltage increases in a negative direction, the posture of the circuit is as follows. Initially, both transistors are off and triac 16 is off, and thus the voltage at the gate of triac 16 rises with little delay. Capacitor 27 having a value of, for example 0.1 Mfd, does not significantly slow the rise time of the 60 cycle current which is applied. This voltage corresponds closely to the full source voltage until there is significant current flow through one of the current paths, a transistor or through gate 28 of triac 16. On the other hand, the voltage on the base of transistor 24 initially rises at a slower rate because of the voltage divider input circuit, wherein the voltage input on a transistor is essentially 1/25 of the source input voltage. The result is that triac 16 is fired before the transistor (in this case transistor 24) can significantly turn on and before it can saturate. When this occurs, the voltage across triac 16 and

transistors

24 and 26 drops to less then one volt, and transistor turn on cannot occur. Actually, triac 16 fires when the supply voltage has risen to about 30 volts and stays on until the supply voltage goes through zero again, at which point the operation just described repeats. With this mode of turn on, the peak current is limited, being limited to about one-half normal peak for the turn on half-cycle.

If, however, switch 18 is turned on at a time when the source voltage is less than 30 volts, we have the same posture as described above following source voltage passing through zero and rising in either a positive or negative direction. In such case, triac 16 will fire first because the gate voltage reaches a triac firing potential before base voltage on one of the transistors can cause the transistor to saturate.

It will be thus appreciated from the foregoing description that the present invention provides a simple and inexpensive electronic structure wherein power can be applied to a load gradually. Typically, the inrush current during the first half-cycle of power applied to an incandescent light bulb rises to approximately 100 milliseconds of operation. In the applicants device, tests have shown that it rises to no greater than five times the normal operating value. The result is that by limiting the initial application of current in this manner, it has been found that the life of electrical devices in general can be extended. With respect to incandescent lamp bulbs, bulb life can be extended from a minimum of about five times to a maximum of about 10 times. It is thus obvious that the potential savings from the applicants device are enormous. While other current limiting devices have been devised in the past, in view of their complexity and expense, it does not appear that they have enjoyed any significant acceptance. The applicants device, on the other hand, reduces the circuitry substantially, and thereby has made possible substantial net savings to a user.

Whatis claimed is:

' 1. An electrical switching assembly comprising:

first and second electrical terminals to be selectively opened and closed;

a solid state A.C. switch having a gate lead and first and second controlled leads;

a PNP transistor and NPN transistor with emitters and collectors commonly connected in parallel between said gate lead and said first controlled lead, respectively;

a control switch having an input terminal connected to said second controlled lead and an output terminal;

a current-limiting resistor connected between said switch output terminal and said gate lead and collector leads of said transistors;

a voltage divider comprising a first resistor and second resistor, wherein said first resistor has a resistance value substantially greater than said second resistor;

a first terminal of said first resistor being connected to said output terminal of said control switch, a second terminal of said first resistor being connected to a first terminal of said second resistor and to the bases of said transistors, and a second terminal of said second resistor being connected to said emitters to said transistors and to said first controlled lead and to said second electrical terminal;

whereby upon the application of an A.C. potential through a load across said first and second electrical terminals, switching operation occurs upon the closing of said control switch with said solid state A.C. switch providing a closed circuit in the event that closure of said control switch occurs when a source switching potential is below a selected discrete voltage, and when said control switch is closed when said source voltage is above a selected discrete voltage, one of said transistors turns on before said solid state A.C. switch can turn on, applying initially a reduced current flow through a said load.

2. A switching assembly as set forth in claim 1 wherein said selected discrete voltage is 30 volts.

3. A switching assembly as set forth in claim 1 wherein said control switch is a magneticallycontrollable reed switch.

4. A switching assembly as set forth in claim 1 wherein said solid state A.C. switch is a triac.

5. A switching assembly as set forth in claim 4 further comprising:

a metal enclosure having exterior heat emitting ribs;

a printed circuit card and said triac, control switch, re-

sistors and transistors being mounted on said printed circuit card; and

said enclosure includes a slot for mounting therein said printed circuit card with said triac in heat conductive contact with said enclosure.

6. A switching assembly as set forth in claim 5 comprising switch operating means including a slide button assembly comprising: an operating slidable button;

a magnet attached to said button; and

a supporting sliding surface adapted to enable said button and magnet to be moved on the outer face of said enclosure, whereby said magnet is moved toward and away from said magnetically-controlled switch, and thereby said switching assembly selectively operated 7. A switching assembly as set forth in claim 6 wherein said slide button assembly comprises a nonmetallic plastic material and wherein there is included a contractable arm having a notch thereon, and a notch in said housing and adapted to receive and latch said button assembly when it is positioned in an on" position.

8. A switching assembly as set forth in claim 7 wherein said magnet is positioned within said plastic material.

9. A switching assembly as set forth in claim 8 wherein the range of ratios of ohmage values for the resistance of said second resistor divided by the resistance of said first resistor is in the range of 1/20 to l/30.

Claims

1. An electrical switching assembly comprising: first and second electrical terminals to be selectively opened and closed; a solid state A.C. switch having a gate lead and first and second controlled leads; a PNP transistor and NPN transistor with emitters and collectors commonly connected in parallel between said gate lead and said first controlled lead, respectively; a control switch having an input terminal connected to said second controlled lead and an output terminal; a current-limiting resistor connected between said switch output terminal and said gate lead and collector leads of said transistors; a voltage divider comprising a first resistor and second resistor, wherein said first resistor has a resistance value substantially greater than said second resistor; a first terminal of said first resistor being connecteD to said output terminal of said control switch, a second terminal of said first resistor being connected to a first terminal of said second resistor and to the bases of said transistors, and a second terminal of said second resistor being connected to said emitters to said transistors and to said first controlled lead and to said second electrical terminal; whereby upon the application of an A.C. potential through a load across said first and second electrical terminals, switching operation occurs upon the closing of said control switch with said solid state A.C. switch providing a closed circuit in the event that closure of said control switch occurs when a source switching potential is below a selected discrete voltage, and when said control switch is closed when said source voltage is above a selected discrete voltage, one of said transistors turns on before said solid state A.C. switch can turn on, applying initially a reduced current flow through a said load.

3. A switching assembly as set forth in claim 1 wherein said control switch is a magnetically-controllable reed switch.

5. A switching assembly as set forth in claim 4 further comprising: a metal enclosure having exterior heat emitting ribs; a printed circuit card and said triac, control switch, resistors and transistors being mounted on said printed circuit card; and said enclosure includes a slot for mounting therein said printed circuit card with said triac in heat conductive contact with said enclosure.

6. A switching assembly as set forth in claim 5 comprising switch operating means including a slide button assembly comprising: an operating slidable button; a magnet attached to said button; and a supporting sliding surface adapted to enable said button and magnet to be moved on the outer face of said enclosure, whereby said magnet is moved toward and away from said magnetically-controlled switch, and thereby said switching assembly selectively operated.

7. A switching assembly as set forth in claim 6 wherein said slide button assembly comprises a non-metallic plastic material and wherein there is included a contractable arm having a notch thereon, and a notch in said housing and adapted to receive and latch said button assembly when it is positioned in an ''''on'''' position.

9. A switching assembly as set forth in claim 8 wherein the range of ratios of ohmage values for the resistance of said second resistor divided by the resistance of said first resistor is in the range of 1/20 to 1/30.