US3446991A

US3446991A - Alternating current switch

Info

Publication number: US3446991A
Application number: US536886A
Authority: US
Inventors: Edward K Howell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1966-03-23
Filing date: 1966-03-23
Publication date: 1969-05-27
Anticipated expiration: 1986-05-27

Description

May 27, 1969 E. K. HOWELL ALTERNA'IING CURRENT SWITCH Sheet Filed March 23. 1966 FIG. 1

FIG. 2

)X/QZIw/e. A/E/TI-I HOWELL av 20M A 7' TORA/EV E. K. HOWELL ALTERNAIING CURRENT SWITCH May 27, 1969 Filed um 23. 1966 Sheet United States Patent US. Cl. 307-252 28 Claims This invention relates to an alternating current switch which includes a semiconductive bidirectional device having at least one gate terminal, as the current interrupting element. More specifically it relates to an alternating current switch including a semiconductive bidirectional device as the current interrupting element, and a circuit associated with the gate terminal for causing the device to assume its low impedance characteristic, and to indefinitely retain this characteristic, until it is again desirable for the device toassume its normal or high impedance characteristic.

A relatively recent addition to the growing family of semiconductive devices broadly referred to as semiconductors, are the bidirectional triode P-N-P-N switches. These bidirectional triode switches are provided with two main current carrying terminals and at least one gate or trigger terminal. Current flow from the two main current carrying terminals through the bidirectioanl triode switch in either direction can be controlled by the application of a low voltage, low current pulse between a gate terminal and one of the load current terminals. These devices have some similarity to the earlier developed silicon-controlled rectifiers. They are similar in their blocking current and voltage characteristics. But, unlike silicon-controlled rectifiers, they can switch load current of either polarity. For a more complete discussion of the bidirectional triode P-N-P-N switches reference may be made to an article entitled: Bi-Directional Triode P-N-P-N Switches, Gentry, F. E., et al., in the Proceeding of the IEEE, volume 53, No. 4, April 1965, pp. 355-369. Bidirectional triode P-N-P-N switches are also discussed in a book entitled: Semiconductor Controlled Rectifiers Principles and Applications of P-N-P-N Devices by Gentry, F. E., et al., published by Prentice-Hall, Inc., Englewood Cliffs, N.J., 1964.

This invention is particularly directed toward utilizing a semiconductive bidirectional device such as a bidirectional triode P-N-P-N switch as an A.C. switch. An A.C. switch which would eliminate the need for mechanically movable contacts to interrupt a load current would be highly desirable in some applications. The combination of a semiconductive bidirectional device having two main current carrying terminals and at least one additional gate terminal and a circuit arrangement which provides at the desired time a low voltage, low current signal to the gate terminal, would provide such an A.C. switch. That is, an arrangement whereby an initiating signal is applied to the gate of a bidirectional triode, to cause the triode to conduct, a signal is maintained on the gate, such that the bidirectional triode will continue to conduct through an indefinite number of full cycles of alternating current even though the initiating signal which initially turned on the triode is removed, and the signal maintained on the gate is removed to cause the triode to stop conducting.

It is therefore an object of this invention to provide a novel and improved A.C. switch utilizing a semiconductive bidirectional device having two main current carrying terminals and at least one additional gate terminal, in a circuit arrangement whereby a momentary signal may be provided to cause the bidirectional device to assume its low impedance characteristic and to retain this low impedance characteristic after the removal of the momentary signal.

It is another object of this invention to provide an alternating current switch having two main current carrying terminals and at least one additional gate terminal, including a semiconductive bidirectional device in a circuit arrangement whereby a first momentary signal will cause the bidirectional conducting device to assume its low impedance characteristic, thereby conducting current, and whereby the bidirectional device may be returned to its high impedance state by a second momentary signal.

It is a further object of this invention to provide a control 'means for energizing a load from an A.C. supply including in a circuit arrangement a semiconductive bidirectional conducting device having two main current carrying terminals and at least one additional agate terminal, and the load, such that the variation of a first variable impedance will cause the semiconductive device to assume its low impedance characteristic and such that the device will continue to exhibit its low impedance characteristic until the impedance of a second variable impedance device is varied, at which time the device will again assume its high impedance characteristic.

These objects are accomplished in accordance with this invention, in one form thereof, by providing a circuit arrangement including therein a semiconductive bidirectional device having two main current carrying terminals and at least one additional gate terminal. The main current carrying terminals are connected in series with a circuit energized by an A.C. source. Typically the device will be connected in series with a load, the energization of which is to be controlled by the conductive state of the device. The circuit arrangement further includes a control circuit including a variable impedance device and energy storage means connected in series. This control circuit is connected in parallel with the device such that the A.C. source simultaneously energizes both the device and the control circuit. The junction of the variable impedance and the energy storage means is connected by :a gate circuit to the gate terminal of the device.

With the variable impedance in a high impedance state, insufiicient current is conducted through the variable impedance and the gate circuit to apply a signal of greater than a predetermined level which is necessary to cause the device to assume its low impedance characteristic. A decrease in the impedance of the variable impedance below a predetermined level, will permit a signal greater than the predetermined level to be applied to the gate of the device, thereby causing the device to assume its low impedance characteristic. While the device is in its low impedance state, the energy storage means will receive energy through the gate terminal and the gate circuit from the A.C. source. As the A.C. source passes through a voltage zero, which would also be a current zero in the case of a resistive load, the current flowing through the energy storage means, the gate circuit, and the gate terminal, will be of a magnitude sutficient to provide a signal of greater than the predetermined magnitude to the gate of the device such that the device will retain its low impedance characteristic during the following half cycle. This current flow in the gate circuit during supply voltage zeros is due to the fact that the energy storage means causes the current flow in the gate circuit to be out of phase with the A.C. source voltage. Due to this out of phase current flow, the device maintains its low impedance characteristic as long as the circuit connections to the A.C. source are uninterrupted. Thus, a momentary decrease below a predetermined level of the impedance of the variable impedance will cause the device to be latched in its low impedance characteristic.

A second variable impedance is provided to dissipate the energy in the energy storage means when it is desirable for the device to again assume its high impedance characteristic. Reducing this second variable impedance below a predetermined level will cause the energy in the energy storage means to be dissipated below the level which provides a gate signal of greater magnitude than the predetermined magnitude necessary for the device to maintain its low impedance state.

Other objects and further details of that which is believed to be novel and the invention will be clear from the following description and claims taken with the accompanying drawings wherein:

FIGURE 1 is a circuit diagram of a first embodiment of this invention employing a capacitor as the energy storage means.

FIGURE 2 is a circuit diagram of a second embodiment of this invention employing an inductor as the energy storage means.

FIGURE 3 is a circuit diagram of the first embodiment of this invention modified to employ a different arrangement of the variable impedance means.

FIGURE 4 is a circuit diagram of the first embodiment of this invention modified to employ an arrangement of the variable impedance means differing from those shown in FIGURES l and 2.

FIGURE 5 is a circuit diagram of the first embodiment of this invention modified to employ an arrangement of the variable impedance means differing from those shown in FIGURES l, 3, and 4.

Referring to the circuit diagram of FIGURE 1 the operation of an A.C. switch or as it may be referred to, a control circuit for energizing a load from an A.C. supply will be described. The control circuit shown enclosed within the dotted lines 2 is energized by connecting its two external terminals 4 and 6 to an A.C. supply.

Terminals

8 and 10 representing an A.C. supply (not shown) are connected to terminals 4 and 6 with a control switch 12 interposed between terminals 4 and 8. The control circuit includes a semiconductive bidirectional device 14 connected in series with an impedance 16 between terminals 4 and 6. The semiconductive bidirectional device is shown as having main current carrying

terminals

18 and 20, and a gate or trigger terminal 22. The device shown is commonly called a triac and by International Electrotechnical Commission standards named a bidirectional triode thyristor. While this particular device is shown, which will hereinafter be referred to as a triac, any other semiconductive bidirectional device which has at least one gate terminal, may be employed. It is only necessary that the semiconductive bidirectional device which is employed exhibit a high impedance characteristic in the absence of a signal of a predetermined amplitude at its gate, and that it exhibit a low impedance characteristic in the presence of a signal of a magnitude greater than the predetermined amplitude at its gate.

The gate terminal 22 of the triac 14 is energized by a gate circuit which is in turn energized by a control circuit. The control circuit is shown as including a resistor 24, a switch 26, and a capacitor 28 connected in series between the terminals 4 and 6. The series circuit comprising resistor 24 and switch 26 may be replaced by any variable impedance means. Such a variable impedance might be a semiconductive device such as a transistor or a semiconductor controlled rectifier. An embodiment of this invention utilizing a semiconductor controlled rectifier will be discussed later. The capacitor 28 may be replaced by any other energy storage means which it might be desirable to utilize, such as an inductor. As shown in FIGURE 1, the gate circuit comprises a resistor 30 connected between the control terminal 22 and a junction 32 between the switch 26 and the capacitor 28. The gate circuit may be a direct connection as will be discussed in another embodiment of this invention.

Before setting forth the operation of the circuit just described, a typical use of the circuit as a control circuit will be set forth. In a typical application, the impedance 16 may be a resistive load such as a lamp in a single luminaire, or it may be representative of all the lamps in all the luminaires and a room or hall. The control circuit and load 16 shown enclosed within the dotted lines 2 would in the case of a single lamp be contained within the outlet box on which is mounted the socket for the lamp. Terminals '4 and 6 would be connected to the A.C. supply system represented by

terminals

8 and 10. Terminal 4 being connected to terminal 8- through a wall switch 12 and terminal 6 being directly connected to terminal 10.

Assuming that the wall switch 12 has been open, the triac 14 will remain in its high impedance state uponthe closing of wall switch 12 if switch 26 remains in its normally opened position. Switch 26, the contacts of which wouldbe in the outlet box, would in the usual case be remotely actuated. Examples of such remote means for closing the switch 26 will be further discussed in the following embodiments. Closing the switch 26 will cause a signal of greater than the predetermined amplitude to be applied to gate 22 through resistor 30. With the application of this control signal, the triac 14 assumes its low impedance characteristic, i.e., is turned on so as to conduct. With the triac 14 turned on, the load 16 is energized from the A.C. supply.

The triac 14 would normally revert to its high impedance characteristic, i.e., turn off, during the next succeeding current zero of the supply if the switch 26 were only closed momentarily. But, the arrangement of the control circuit and gate circuit as shown in FIGURE 1 insures that the triac will continue to conduct until the switch 12 is open. This is due to the fact that a signal of greater than the predetermined amplitude is maintained on'the gate 22 by the control and gate circuits. Current limiting 24 protects the capacitor 28 from the damaging effects of an excessive charging current which it would draw from the AC. supply on the closing of switch 26. After the triac begins conducting load current between its main

current carrying terminals

18 and 20, the gate current will also flow between main terminal 18 and gate terminal 22. This gate current which flows through resistor 30 to charge capacitor 28, results from the voltage appearing across the triac 14 and the load 16. This voltage is essentially the A.C. supply voltage, most of which appears across the load 16. This gate current is limited by resistor 30 in the gate circuit. With a highly resistive load 16, the gate current, due to the capacitor 28, will be out of phase with the load current.

Sufficient energy in the form of a charge on capacitor 28 is stored during the period load current is flowing, to assure a gate signal of greater than the predetermined magnitude after the supply passed through a zero, so as to cause the triac to conduct during the succeeding half cycle. Due to the bidirectional nature of the device, the capacitor 28 will continue to supply gate signals greater than the predetermined amplitude to the gate 22 through resistor 30 during succeeding load current zeros, such that the triac 14 will be latched on to continuously conduct between its main current carrying terminals without need for additional closures .of switch 26. Thus, it is only necessary that switch 26 be closed momentarily to latch the triac in its low impedance characteristic.

The load 16 may be deenergized by opening switch 12 or, if it is desirable to be able to remotely deenergize the load 16, an additional variable impedance turn-off circuit may be provided. This circuit, which is shown as comprising a switch 34, is connected between the junction point 32 and a second junction point 36 between one terminal of the load 16 and main terminal 20 of the triac. Switch 34 is normally open, would be remotely actuated in the same manner as switch 26. Closing the contacts of switch 34 causes capacitor 28 to be discharged through the load 16, such that an insufficient charge is retained thereon to supply a gate signal of greater than the predetermined value after the next succeeding current zero. Thus, the triac will return to its right impedance characteristic at the next succeeding current zero, thereby deenergizing the load 16.

Considering now the circuit diagram of FIGURE 1 as representing an A.C. switch, the impedance 16 will no longer represent the load. Rather, a load (not shown) and an A.C. supply (not shown) are connected in series between the

terminals

8 and 10. The impedance 16 rather than being a load, is a very small impedance. With impedance 16 very small, as is the impedance of triac 14 when conducting, the current fiow between terminals 4 and 6 is determined by the TC. supply voltage and the load impedance. For a predetermined load and a predetermined A.C. supply voltage, a predetermined current will flow through the triac 14 and the very small impedance 16. The impedance 16 is chosen such that the voltage developed across it due to the current flowing therethrough will, along with the voltage developed across the triac 14 between the gate terminal 22 and main current carrying terminal 20, produce a suflicient voltage across the series circuit comprising the triac gate 14, resistor 30, and capacitor 28, to charge capacitor 28 to a sufiicient level to provide a gate signal greater than the predetermined amplitude to maintain the triac 14 in its low impedance state after switch 26 has been closed momentarily. In this arrangement, it is necessary to determine the impedance value of impedance 16 for a given load current, so as to insure sufficient energy storage in the capacitor 28 to provide a gate signal of greater than the predetermined amplitude. Since the voltage appearing across the series circuit comprising the resistor 30 and the capacitor 28 is greatly reduced in this arrangement, the resistor 30 may be of a very small value or replaced by a conductor.

In still aonther embodiment of the A.C. switch, the impedance 16 may be made negligible, that is replaced by a conductor. In this arrangement the resistor 30 is also replaced by a very small impedance or a conductor. The charging current for the capacitor 28 through the gate terminal is derived from the voltage drop appearing across the triac between the

terminals

18 and 20. The gate terminal 22 assumes the voltage of main current carrying terminal 18 while the triac is in its low impedance state, such that the voltage drop between main

current carrying terminals

18 and 20 due to load current appears between gate terminal 22 and main current carrying terminal 20. Due to the small voltage available for charging capacitor 28, the triac 14 must be responsive to a very low voltage, low current gate signal.

Referring now to FIGURE 2, an alternate embodiment of the invention is shown in which the energy storage means shown as capacitor 28 in FIGURE 1 is replaced by an inductor 28. Also, the gate circiut is shown as comprising a direct connection between the control terminal 22 of the triac 14 and junction 32. The operation of this alternate embodiment of the invention is quite similar to that shown in FIGURE 1.

Assuming that the switch 12 has been open, the triac 14 will remain in its high impedance state upon the closing of switch 12 if switch 26 remains in its normally open position. Closing the contacts of switch 26 will apply a control signal having a greater amplitude than the predetermined amplitude to gate terminal 22. This control signal will turn triac 14 on, thereby energizing the load 16 from the A.C. supply.

As did the capacitor 28 in FIGURE 1, inductor 28' will store suflicient energy due to gate current flow to provide a gate signal of greater than the predetermined magnitude immediately after a supply voltage zero so as to cause the triac to coninue to conduct after the supply voltage passes through a voltage zero. A resistor 30 is not needed in the gate circuit, since the inductor 28' will itself limit the gate current.

As was discussed with respect to FIGURE 1, the portion of the circuit included within dotted line 2 may be considered an A.C. switch when the load (not shown) and an A.C. supply (not shown) are connected in series between

terminals

8 and 10. Again, the impedance 16 may be very small or replaced by a negligible impedance that is, a conductor.

Referring now to FIGURE 3, an embodiment of the invention in which the switch 26 in the control circuit and the switch 34' in the turn-off circuit are remotely controlled will be described. In this embodiment, the switches 26' and 34 are made responsive to a carrier frequency imposed on the A.C. supply (not shown) represented by the

terminals

8 and 10. More particularly, the switch 26 is a pair of normally open contacts of a relay 38 which also includes an actuating coil 40. Similarly, switch 34' is a pair of normally open contacts of a relay 42 which also includes an actuating coil 44. The actuating coil 40 of relay 38 is connected in series with a capacitor 46 between terminals 4 and 6. The capacitance of the capacitor 46 is chosen such that the series circuit including actuating coil 40 and capacitor 46 is resonant at a first predetermined frequency. Similarly, the actuating coil 44 of relay 42 is connected in series with a capacitor 48 between terminals 4 and 6. The capacitance of capacitor 48 is chosen such that the series circuit including actuating coil 44 and capacitor 48 is resonant at a second predetermined frequency.

While relays 38 and 42 may be of many varied types, resonant reed relays, and relays formed of reed switches and actuating coils would be particularly suitable. The resonant reed relays would be chosen to have resonant frequencies corresponding to the first and second predetermined frequencies. Relays formed of reed switches and actuating coils would be designed such that the read switches would only be actuated in response to the increased resonant current flows at the first and second predetermined frequencies.

The first and second predetermined frequencies are chosen to be substantially higher than the supply frequency, such as are commonly referred to as a carrier frequencies. The switch 12 is not necessary for operation of the control circuit shown in FIGURE 2 but, may be provided for manual deenerigaztion of the load 16. With the switch 12 closed, imposing a carrier frequency signal corresponding to the first predetermined frequency on the A.C. supply represented by

terminals

8 and 10 will energize the actuating coil 40 to a sufficient level to close contacts 26', thereby causing triac 14 to turn on as previously discussed with respect to FIGURE 1. To close contacts 34', thereby turning off triac 14, a carrier frequency signal corresponding to the second predetermined frequency is imposed on the A.C. supply represented by the

terminals

8 and 10. The carrier frequency signals corresponding to the first and second predetermined frequencies need be maintained only momentarily to turn the triac 14 on or off respectively. If it is desirable to provide for only remote energization of the load 16, the relay 42 including contacts 34 need not be provided. The load 16 may be deenergized by opening the switch 12.

The circuit modification shown in FIGURE 4 is similar to that shown in FIGURE 3, in that the

switches

26 and 34 are normally open contacts of relays 38 and 42 respectively. In the circuit modification shown in FIG- URE 4, the relays 38 and 42 are remotely controlled in response to sonic and supersonic vibrations of a gaseous medium surrounding the control circuit. Typically this gaseous medium would be the air in the room in which the control circuit is utilized. The operation of the circuit'shown in FIGURE 4 is similar to that of FIGURE 3, but for the manner in which the relay actuating coils 40 and 44 are energized.

A transducer 50 is provided to convert vibration of a gaseous medium into an electrical output signal. The transducer 50 is provided with a pickup device 52 which is eifective to provide an electrical signal to leads 54 and 56 in response to sonic and supersonic vibrations of the surrounding air. The pickup device 52 might be a microphone which is responsive to both sonic and supersonic vibrations. An amplifier and filter circuit 58 of conventional design is energized through leads 60 and 62 from the AG. supply. Leads 54 and 56 from the pickup device 52 provide the input to the amplifier and filter circuit 58. The output of the amplifier 58 appears on output leads 64 and 66. The series resonant circuit comprising actuating coil 40' of relay 38, and capacitor 46, and the series resonant circuit comprising actuating coil 44 of relay 42, and capacitor 48, are connected in parallel between output leads 64 and 66.

In the presence of a sonic or supersonic vibration of the air surrounding transducer 50, it will produce an electrical output signal on leads 64 and 66 having a frequency proportional to the sonic or supersonic vibration frequency. Thus, the resonant frequency of the series resonant circuit comprising actuating coil 40 and capacitor 46 can be chosen such that it is energized at its resonant frequency when a sonic or supersonic vibration of a first predetermined frequency occurs in the air surrounding transducer 50. Similarly, the resonant frequency of the series resonant circuit comprising actuating coil 44 and capacitor 48 can be chosen such that it is energized at its resonant frequency when a sonic or supersonic vibration of a second predetermined frequency occurs in the air surrounding transducer 50.

Thus, it is possible to turn the triac 14 on and off in response to sonic and supersonic vibrations in the air surrounding the transducer 50. Such vibrations might be audible sounds produced by a person, or supersonic sounds produced by a mechanical whistle. Further, the sonic or supersonic vibrations of the air might be created by a transducer driven by an electronic oscillator. By installing the control circuit and load 16 enclosed within the dotted lines 2 within a lighting fixture, it is possible to provide for the energization and deenergization of the lamp in response to a sonic or supersonic vibration of the air in the room.

Referring now to FIGURE 5, still another modification of the first embodiment of this invention will be described. Again, those components of the control circuit which are similar to those shown in FIGURE 1 are associated with the same reference numeral. In this circuit, the

switches

26 and 34 are shown as semiconductor controlled rectifiers 26" and 34". A typical semiconductor controlled rectifier is the silicon controlled rectifier (SCR). SCR 26" is turned on by applying a signal to its gate electrode 68. Similarly, SCR 34" is turned on by applying a signal to its gate electrode 70. While many arrangements might be provided for applying a signal to the

gate electrodes

68 and 70 of SCRs 26" and 34", respectively, pulse transformers 72 and 74. Pulse transformer 72 includes a primary winding 76 and a secondary winding 78. Similarly, pulse transformer 74 includes a primary winding 80 and a secondary winding 82. The secondary winding 78 of pulse transformer 72 is connected between the gate electrode 68 and anode 84 of SCR 26". Similarly, secondary winding 82 of pulse transformer 74 is connected between gate 70 and anode 86 of SCR 34".

A circuit arrangement for energizing primary windings 76 and 80 includes a signal transformer 88. Signal transformer 88 comprises a primary winding 90 and a secondary winding 92. Primary winding 90 is energized from the AC. supply through

conductors

94 and 96. Primary winding 76 of pulse transformer 72 is connected in series with the secondary winding 92 of signal transformer '88 through a switch 98 and a current limiting resistor 100. Similarly, primary winding 80 is connected in series with secondary winding 92 of signal transformer 88 by a switch 102 and a current limiting resistor 104.

In setting forth the operation of the circuit shown in FIGURE 5, it will be assumed that the load 16 is deenergized, with the

switches

12, 98, and 102 in their open positions. Closing switch 12 will energize the control the signals are applied as shown in FIGURE 5 by circuit shown enclosed within the dotted lines 2. Until a signal is applied to gate 68 of SCR 26", it will not conduct, and therefore signal will not be applied to trigger 22 of the triac 14, so as to turn it on. Closing switch 98 will cause primary winding 76 of pulse transformer 72 to be energized, whereupon a signal will appear in secondary winding 78. This signal is applied to gate 68 of SCR 26", thereby turning it on. As previously discussed, this will cause triac 14 to begin conducting and continue to conduct until it is turned-off in response to the turn-on of SCR 34" The turn-on of SCR 34 is brought about by the closing of switch 102. Closing switch 102 energizes primary winding of pulse transformer 74, such-that a signal appears in its secondary winding 82. This signal is applied to gate 70 of SCR 34-", thereby turning it on. As previously discussed, the turn-on of SCR 34" will cause capacitor 28 to be discharged through the load 16, such that triac. 14 will turn off at the next succeeding load current zero. Switch 98 need only be closed momentarily, so as to turn on triac 14, since the latching feature of this circuit, as previously described with respect to FIGURE 1, will maintain the triac 14 in its low impedance characteristic, even though the SCR 26" is turned on only momentarily.

While use of silicon controlled rec-tifiers as switches 26" and 34" has been shown, other types of semiconductor controlled rectifiers may also be used. Further, other types of semiconductive devices could be substituted. for SCRs 26" and 34". For instance, NPN and PNP transistors. The transistors could be used in either a switching mode or continuously variable control mode.

As particularly set forth with respect to FIGURES 1 and 2, this invention is directed toward the use of a semiconductive bidirectional device as an AC. switch or a control circuit. To aid in describing the circuit shown in FIGURE 1, the portion of the circuit included within dotted lines 2 was set forth as a control circuit wherein the impedance 16 was the load, the energization of which was being controlled. Further, with a load connected in series with an.A.C. supply between

terminals

8 and 10, (neither of which are shown), and with impedance 16 being an impedance of small or negligible magnitude, the portion of the circuit included within the dotted line was set forth as an AC. switch.

These characterizations of the circuit arrangement of this invention are used only as an aid in describing the invention. In the broader aspects of this invention the circuit location of a load, the energization of which is controlled by the conductive characteristic of the semiconductive bidirectional device, is immaterial. Further, the circuit arrangement of this invention may be utilized in a circuit not including a series connected load. For instance, it might be used to shunt a high impedance A.C. supply to lower its output voltage.

I claim:

1 1. A control means for energizing a load from an AC. supply comprising:

(a) a semiconductive bidirectional device having two main current carrying terminals and at least one additional gate treminal, said device normally exhibiting a high impedance characteristic between said two main terminals and exhibiting a low impedance characteristic between said two main terminals in response to application of a control signal having at least a predetermined amplitude to said gate terminal, a first of said main terminals and'a first terminal of the load connected to a first junction point, a second of said main terminals and a second terminal of the load connected to the A.C. supply,

(b) a control circuit comprising an energy storage means having at least two terminals and a variable impedance means having at least two terminals, a first terminal of said energy storage means 'and'a first terminal of said variable impedance means connected to a second junction point, a second terminal of said energy storage means connected to said second terminal of said load, and a second terminal of said variable impedance means being connected to said second main terminal, and

(c) a gate circuit connecting said second junction point to said gate terminal, whereby when the impedance of said variable impedance means is reduced below a predetermined level, the voltage appearing across said energy storage means, which is applied to said gate through said gate circuit exceeds the predetermined amplitude so as to cause said device to exhibit a low impedance characteristic, said energy storage means being effective in response to a subsequent increase of the impedance of said variable impedance means above said predetermined level to thereafter supply gate signals in excess of said predetermined amplitude derived from the voltage developed across the load to said gate terminal through said gate circuit, whereby said device thereafter exhibits a low impedance characteristic so that the load is energized by the A.C. supply through said device.

2. The control means defined in claim 1 wherein said variable impedance means comprises an additional semiconductive device having two main current carrying terminals and at least one additional control terminal, said additional semiconductive device normally exhibiting a high impedance characteristic between its two main terminals an dexhibiting a low impedance characteristic between its two main terminals in response to application of a control signal having at least a predetermined amplitude to said control terminal, such that said semiconductive bidirectional device exhibits a low impedance characteristic so that the load is energized by the A.C. supply through said semiconductive bidirectional device.

3. The control means defined in claim 1 comprising in addition,

(d) a variable impedance turn-off circuit connecting said first junction point to said second junction point, said turn-elf circuit normally exhibiting a high impedance, said turn-ofi circuit being caused to exhibit a low impedance to dissipate the energy in said energy storage means such that said energy storage means is no longer effective to supply gate signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic thereby deenergizing the load.

4. The control means defined in claim 3 wherein said variable impedance turn-off circuit comprises an additional semiconductive device having two main current carrying terminals and at least one additional control terminal, said additional semiconductive device normally exhibiting a high impedance characteristic between its two main terminals and exhibiting a low impedance characteristic between its two main terminals in response to application of a control signal having at least a predetermined amplitude to said control terminal such that the impedance of said variable impedance turn-off circuit is reduced, so as to exhibit a low impedance to dissipate the energy in said energy storage means such that said energy storage means is no longer effective to supply gate signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic thereby deenergizing the load.

5. The control means defined in claim 1 wherein said variable impedance means is a pair of contacts of a resonant reed relay, said resonant reed relay comprising said pair of contacts and an actuating coil, said actuating coil actuating said contacts in response to the application thereto of a signal of a predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic.

' a capacitor being addition, a transducer responsive to sonic and supersonic vibrations of a gaseous medium to produce an alternating current output the frequency of which is proportional to the frequency of the vibrations, said actuating coil being energized by the alternating current output, said trans ducer providing an output of said predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic.

7. The control means defined in claim 1 wherein said variable impedance means is a pair of contacts of a relay including also an actuating coil, said actuating coil and connected in series across the A.C. supply, said actuating coil and said capacitor being tuned to a predetermined frequency substantially higher than the A.C. supply frequency, such that when a signal of said predetermined frequency is impressed on the A.C. supply, said actuating coil is energized to actuate said pair of contacts, whereby said device is caused to exhibit a low impedance characteristic.

8. The control means defined in claim 3 wherein said variable impedance means comprises a first pair of contacts of a first resonant reed relay, said first resonant reed relay comprising said first pair of contacts and a first actuating coil, said first actuating coil actuating said first contacts in response to the application thereto of a signal of a first predetermined frequency, and said variable impedance turn-off circuit comprises a second pair of contacts of a second resonant reed relay, said second resonant reed relay comprising said second pair of contacts and a second actuating coil, said second actuating coil actuating said second contacts in response to the application thereto of a signal of a second predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic when a signal of the first predetermined frequency is applied to said first actuating coil, said device thereafter exhibiting a low impedance 6. The control means defined in claim 5, comprising in characteristic so that the load is energized by the A.C. supply through said device until a signal of the second predetermined frequency is applied to said second actuating coil, causing said second pair of contacts to 'be actuated, such that the energy stored in said energy storage means is dissipated such that said energy storage means is no longer elfective to supply gate signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic thereby deenergizing the load.

9. The control means defined in claim 3 wherein said variable impedance means comprises a first pair of contacts of a first relay including also a first actuating coil, a first capacitor, a first series circuit comprising said first actuating coil and said first capacitor connected across the A.C. supply, said first series circuit being tuned to a first predetermined frequency substantially higher than the A.C. supply frequency and, said variable impedance turn-off circuit comprises a second pair of contacts of a second relay including also a second actuating coil, a second capacitor, a second series circuit comprising said second actuating coil and said second capacitor connected across the A.C. supply, said second series circuit being tuned to a second predetermined frequency substantially higher than the A.C. supply frequency, such that when a signal of said first predetermined frequency is impressed on the A.C. supply, said first actuating coil is energized to actuate said first pair of contacts, causing said device to exhibit a low impedance characteristic, said device thereafter exhibiting a low impedance characteristic so that the load is energized by the A.C. supply through said device until a signal of said second predetermined frequency is impressed on the A.C. supply, such that said second actuating coil is energized to actuate said second pair of contacts to dissipate the energy in said energy storage means such that said energy storage means is no longer eifectiveto supply gate signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic thereby deenergizing the load.

10. The control means defined in claim 8 comprising in addition, a transducer responsive to sonic and supersonic vibrations of a gaseous medium to produce an alternating current output the frequency of which is proportioned the frequency of the vibrations, said first and second actuating coils being energized by the alternating current output, seaid transducer providing an output of said first predetermined frequency in response to the presence of vibrations of a first predetermined frequency, and an output of said second predetermined frequency in response to the presence of vibrations of a second predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic when a signal of the first predetermined frequency is applied to said first actuating coil, said device thereafter exhibiting a low impedance characteristic so that the load is energized by the A.-C. supply through said device until a signal of the second predetermined frequency is applied to said second actuating coil, causing said second pair of contacts to be actuated, such that the energy stored in said energy storage means is dissipated such that said energy storage means is no longer eltective to supply gate signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic thereby deenergizing the load.

11. The control means defined in claim 1 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is a capacitor, and said variable impedance means comprises a resistor and a switch connected in series.

12. The control means defined in claim 3 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is a capacitor, said variable impedance means comprises a resistor and a switch connected in series, and said variable impedance turn-off circuit is a switch.

13. The control means defined in claim 1 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is an inductor, said variable impedance means comprises a resistor and a switch connected in series.

14. The control means defined in claim 3 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is an inductor, said variable impedance means comprises a resistor and a switch connected in series, and said variable impedance turn-off circuit is a switch.

15. An alternating current switch comprising a semiconductive bidirectional device having two main current carrying terminals and at least one additional gate terminal, said device normally exhibiting a high impedance characteristic between said two main terminals such that the switch is normally open in the absence of a control sig nal, and exhibiting a low impedance characteristic between said two main terminals such that the switch is closed in response to application of a control signal having at least a predetermined amplitude to said gate terminal, a control circuit including in series an energy storage means and a variable impedance means, a gate circuit having terminals connected respectively to said gate terminal and to a point in said control circuit intermedi ate said storage means and said variable impedance means, and a second circuit including said main terminals and an impedance traversed by current traversing said main terminals, said second circuit being connected in parallel with said control circuit, said gate terminal receiving a control signal in excess of said predetermined amplitude through said variable impedance means and through said gate circuit when the impedance of said variable impedance means is reduced below a predetermined level to cause said device to exhibit a low impedance characteristic to develop a voltage across said impedance, said energy storage means being effective in response to a subsequent increase of the impedance of said variable impedance means above said predetermined level to thereafter supply control signals in excess of said predetermined amplitude derived from the voltage developed across said impedance to said gate terminal through said gate circuit.

16. The alternating current switch defined in claim 15 wherein said variable impedance means comprises an additional semiconductive device having two main current carrying terminals and at least one additional control terminal, said additional semiconductive device normally exhibiting a high impedance characteristic between its two main terminalsand exhibiting a low impedance characteristic between its two main terminals in response to application of a control signal having at least a predetermined amplitude to said control terminal, whereby said semiconductive bidirectional device exhibits a low impedance characteristic between its two main terminals such that the switch is closed.

:17. The alternating current switch defined in claim 15 comprising in addition, a variable impedance turn-ofi circuit connected in circuit with said energy storage means, said turn-off circuit normally exhibiting a high impedance, said turn-off circuit being caused to exhibit a low impedance to dissipate the energy in said energy storage means such that said energy storage means is no longer elfective to supply control signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic, such that the switch is opened.

18. The alternating current switch defined in claim 17 wherein said variable impedance turn-ofi' circuit comprises an additional semiconductive device having two main current carrying terminals and at least one additional control terminal, said additional semiconductive device normally exhibiting a high impedance characteristic between its two main terminals and exhibiting a low impedance characteristic between its two main terminals in response to application of a control signal having at least a predetermined amplitude to said control terminal such that the impedance of said variable impedance turn-off circuit is reduced, so as to exhibit a low impedance to dissipate the energy in said energy storage means such that said energy storage means is on longer effective to supply gate signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said bidirectional device again exhibits a high impedance characteristic thereby opening the switch.

19. The alternating current switch defined in claim 15 wherein said variable impedance means is a pair of contacts of a resonant reed relay, said resonant reed relay comprising said pair of contacts and an actuating coil, said actuating coil actuating said contacts in response to the application thereto of a signal of a predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic between its two main terminals such that the switch is closed.

-20. The alternating current switch defined in claim 19 comprising in addition, a transducer responsive to sonic and supersonic vibrations of a gaseous medium to produce an alternating current output the frequency of which is proportional to the frequency of the vibrations, said actuating coil being energized by the alternating current output, said transducer providing an output of said predetermined frequency in response to the presence of vibrations of a predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic between its two main terminals such that the switch is closed.

21. The alternating current switch defined in claim 15 adapted for use with an alternating current supply, wherein said 'variable impedance means is a pair of contacts of a relay including also an actuating coil, a capacitor,

said actuating coil and said capacitor being connected in series across the alternating current supply, said actuating coil and said capacitor being tuned to a predetermined frequency substantially higher than the alternating current supply frequency, such that when a signal of said predetermined frequency is impressed on the alternating current supply, said actuating coil is energized to actuate said pair of contacts, whereby said device is caused to exhibit a low impedance characteristic between its two main terminals such that the switch is closed.

22. The alternating current switch defined in claim 17 wherein said variable impedance means comprises a first pair of contacts of a first resonant reed relay, said first resonant reed relay comprising said first pair of contacts and a first actuating coil, said first actuating coil actuating said first contacts in response to the application thereto of a signal of a first predetermined frequency, and said variable impedance turn-off circuit comprises a second pair of contacts of a second resonant reed relay, said second resonant reed relay comprising said second pair of contacts and a second actuating coil, said second actuating coil actuating said second contacts in response to the application thereto of a signal of a second predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic when a signal of the first predetermined frequency is applied to said first actuating coil, said device thereafter exhibiting a low impedance characteristic so that the alternating current switch is closed until a signal of the second predetermined frequency is applied to said second actuating coil, causing said second pair of contacts to be actuated, such that the energy stored in said energy storage means is dissipated such that said energy storage means is no longer elfective to supply control signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic, such that the switch is opened.

'23. The alternating current switch defined in claim 17 adapted for use with an alternating current supply, wherein said variable impedance means comprises a first pair of contacts of a first relay including also a first actuating coil, a first capacitor, a first series circuit comprising said first actuating coil and said first capacitor connected across the alternating current supply, said first series circuit being tuned to a first predetermined frequency substantially higher than the alternating current supply frequency and, said variable impedance turn-off circuit comprises a second pair of contacts of a second relay including also a second actuating coil, a second capacitor, a second series circuit comprising said second actuating coil and said second capacitor connected across the alternating current supply, said second series circuit being tuned to a second predetermined frequency substantially higher than the alternating current supply frequency, such that when a signal of said first predetermined frequency is impressed on the alternating current supply, said first actuating coil is energized to actuate said first pair of contacts, causing said device to exhibit a low impedance characteristic between its two main terminals, said device thereafter exhibiting a low impedance characteristic so that the switch is closed until a signal of said second predetermined frequency is impressed on the alternating current supply, such that said second actuating coil is energized to actuate said second pair of contacts to dissipate the energy in said energy storage means such that said energy storage means is no longer effective to supply control signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby of said first predetermined frequency in response to the presence of vibrations of a first predetermined frequency, and an output of said second predetermined frequency in response to the presence of vibrations of a second predetermined frequency, whereby said device is caused to exhibit a low impedance characteristic when a signal of the first predetermined frequency is applied to said first actuating coil, said device thereafter exhibiting a low impedance characteristic so that the alternating current switch is closed until a signal of the second predetermined frequency is applied to said second actuating coil, causing said second pair of contacts to be actuated, such that the energy stored in said energy storage means is dissipated such that said energy storage means is no longer effective to supply control signals in excess of said predetermined amplitude to said gate terminal through said gate circuit, whereby said device again exhibits a high impedance characteristic, such that the switch is opened.

25. The alternating current switch defined in claim 15 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is a capacitor, and said variable impedance means comprises a resistor and a switch connecter in series.

26. The alternating current switch defined in claim 17 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is a capacitor, said variable impedance means comprises a resistor and a switch connected in series, and said variable impedance turn-off circuit is a switch.

27. The alternating current switch defined in claim 15 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is an inductor, said variable impedance means comprises a resistor and a switch connected in series.

28. The alternating current switch defined in claim l1'7 wherein said semiconductive bidirectional device is a bidirectional triode thyristor, said energy storage means is an inductor, said variable impedance means comprises a resistor and a switch connected in series, and said variable impedance turn-off circuit is a switch.

References Cited UNITED STATES PATENTS 3,238,390 3/1966 Pinckaers 315-196 XR 3,335,291 8/ 1967 Gutzwiller. 3,3 60,713 12/1967 Howell. 3,388,269 6/1968 Bertioli 32881 XR OTHER REFERENCES G.E. Application note titled Triac Control for AC Power, written by E. K. Howell, dated May 1964, pp. 4-6.

ARTHUR GAUSS, Primary Examiner. STANLEY T. KRAWSZEWICZ, Assistant Examiner.

US. Cl. X.R. 307-305; 315196

Claims

1. A CONTROL MEAND FOR ENERGIZING A LOAD FROM AN A.C. SUPPLY COMPRISING: (A) A SEMICONDUCTIVE BIDIRECTIONAL DEVICE HAVING TWO MAIN CURRENT CARRYING TERMINALS AND AT LEAST ONE ADDITIONAL GATE TERMINAL, SAID DEVICE NORMALLY EXHIBITING A HIGH IMPEDANCE CHARACTERISTIC BETWEEN SAID TWO MAIN TERMINALS AND EXHIBITING A LOW IMPEDANCE CHARACTERISTIC BETWEEN SAID TWO MAIN TERMINALS IN RESPONSE TO APPLICATION OF A CONTROL SIGNAL HAVING AT LEAST A PREDETERMINED AMPLITUDE TO SAID GATE TERMINAL, A FIRST OF SAID MAIN TERMINALS AND A FIRST TERMINAL OF THE LOAD CONNECTED TO A FIRST JUNCTION POINT, A SECOND OF SAID MAIN TERMINALS AND A SECOND TERMINAL OF THE LOAD CONNECTED TO THE A.C. SUPPLY, (B) A CONTROL CIRCUIT COMPRISING AN ENERGY STORAGE MEANS HAVING AT LEAST TWO TERMINALS AND A VARIABLE IMPEDANCE MEANS HAVING AT LEAST TWO TERMINALS, A FIRST TERMINAL OF SAID ENERGY STORAGE MEANS AND A FIRST TERMINAL OF SAID VARIABLE IMPEDANCE MEANS CONNECTED TO A SECOND JUNCTION POINT, A SECOND TERMINAL OF SAID ENERGY STORAGE MEANS CONNECTED TO SAID SECOND TERMINAL OF SAID LOAD, AND A SECOND TERMINAL OF SAID VARIABLE IMPEDANCE MEANS BEING CONNECTED TO SAID SECOND MAIN TERMINAL, AND (C) A GATE CIRCUIT CONNECTING SAID SECOND JUNCTION POINT TO SAID GATE TERMINAL, WHEREBY WHEN THE IMPEDANCE OF SAID VARIABLE IMPEDANCE MEANS IS REDUCED BELOW A PREDETERMINED LEVEL, THE VOLTAGE APPEARING ACROSS SAID ENERGY STORAGE MEANS, WHICH IS APPLIED TO SAID GATE THROUGH SAID GATE CIRCUIT EXCEEDS THE PREDETERMINED AMPLITUDE SO AS TO CAUSE SAID DEVICE TO EXHIBIT A LOW IMPEDANCE CHARACTERISTIC, SAID ENERGY STORAGE MEANS BEING EFFECTIVE IN RESPONSE TO A SUBSEQUENT INCREASE OF THE IMPEDANCE OF SAID VARIABLE IMPEDANCE MEANS ABOVE SAID PREDETERMINED LEVEL TO THEREAFTER SUPPLY GATE SIGNALS IN EXCESS OF SAID PREDETERMINED AMPLITUDE DERIVED FROM THE VOLTAGE DEVELOPED ACROSS THE LOAD TO SAID GATE TERMINAL THROUGH SAID GATE CIRCUIT, WHEREBY SAID DEVICE THEREAFTER EXHIBITS A LOW IMPEDANCE CHARACTERISTIC SO THAT THE LOAD IS ENERGIZED BY THE A.C. SUPPLY THROUGH SAID DEVICE.