US3644754A

US3644754A - Circuit for the contactless control of thyristors

Info

Publication number: US3644754A
Application number: US760528A
Authority: US
Inventors: Peter Dosch; Emil Benz
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-09-20
Filing date: 1968-09-18
Publication date: 1972-02-22
Anticipated expiration: 1989-02-22
Also published as: FR1597507A; GB1176307A; JPS4836074B1; CH484563A; DE1763928A1

Abstract

Circuit for contactless control of thyristor is response to approachment of predetermined electromagnetic field influencing means; input means are provided for supplying input pulses to said circuit and control means are coupled to thyristor for operating same in response to input pulse in predetermined amplitude range; translating means are coupled to the input means and control means for applying the input pulses to control means, the translating means includes circuit electromagnetic means operable in response to approachment of said influencing means to establish said input pulse in said predetermined amplitude range.

Description

United States Patent Dosch et al.

[54] CIRCUIT FOR THIB CONTACTLESS CONTROL OF THYRISTORS [72] Inventors: Peter Dosch, Rankstrasse l5; Emil Benz, Iarchenstrasse 10, both of Canton of St. Gall, Switzerland 22 Filed:. Sept. 18,1968

211 Appl.No.: 760,528

[30] Foreign Application Priority Data Sept. 27, 1967 Switzerland ..13 136/67 [52] US. Cl. ..307/252 N, 307/287, 307/288, 307/324, 317/D1G.'2, 328/5, 331/65 [51] Int. Cl. ..H0lh 36/00, H031; 17/70, I-I03k 17/72 [58] Field of Search ..307/247, 262, 287, 288, 305, 307/324; 317/123 P, 146, 123, DIG. 2; 328/5;

[56] References Cited UNITED STATES PATENTS 2,985,848 5/1961 Raffaelli ..317/146 3,147,408 9/1964 Yamamoto et al.. 317/123 3,161,759 12/1964 Gambill et a1. 307/287 3,195,043 7/1965 Burig et a1. 340/258 Feb. 22, 1972 Galloway J. I-I., Using the Triac for Control of AC Power, 3/66 pp. 5- 19. G. E. Transistor Manual; p. 312- 316, 320- 333, Copyright 1964.

Primary ExaminerDonald D. Forrer Assistant Examiner-L. N. Anagnos AttorneyWard, McElhannon, Brooks & Fitzpatrick 57] ABSTRACT Circuit for contactless control of thyristor is response to approachment of predetermined electromagnetic field influencing means; input means are provided for supplying input pul- 3,197,658 7/ 1965 Byrnes et al.. 317/12 ses to said circuit and control means are coupled to thyristor 3'200305 8/1965 Atkms, 317/123 for operating same in response to input pulse in predeter- 3201'679 8/1965 Buchanan" "307/287 mined amplitude range; translating means are coupled to the 3,201,774 8/1965 Uemura ..317/ 123 input means and control means applying the input pulses 3,206,696 9/1965 Wright." 331/ 1 1 to control means, the translating means includes circuit elec- 3,215,950 11/1965 Re nerm. 331/11 tromagnetic means operable in response to approachment of 3,223,352 12/1965 wright 307/287 said influencing means to establish said input pulse in said 3,254,313 5/1966 Atkins et al ..317/123 predetermined amplitude 3,255,380 6/1966 Atkins et a1 ..317/123 3,265,991 8/1966 Ferguson ..331/ l 1 1 13 Claims, 9 Drawing Figures PATENTEDFEBZZ I972 3, 44,754

SHEET 3 BF 3 l N VENTURS Para/e LbscH BY 671/4 560 CIRCUIT FOR THE CONTACTLESS CONTROL OF THYRISTORS This invention relates to switching circuits and, more parcontrol of thyristors.

Most known proximity switching circuits, sometimes referred to as contactless initiators, operate in accordance with the principle wherein a magnetic or like field set up by the switching circuit, is influenced by the approachment of a metallic object to change the impedance of the switching circuit, and thus change the voltage/current relationship of the circuit to indicate the presence of the object. Thus for example, in one known arrangement a coil is arranged in a balanced bridge circuit which is energized with a high frequency source; and, upon the approachment of the metallic object, the bridge is unbalanced by the disturbance of the magnetic field set up by the coil. In another arrangement, the coil is incorporated as a part of an oscillator circuit and the approachment of the metallic object within the vicinity of the magnetic field set up by the coil distunes or dampens the oscillator thereby changing the amplitude of the output signal of the oscillator. In both of these described arrangements, a signal indicating the proximity of the metal object to the circuit is produced from the output signals of these described switching arrangements in a suitable output circuit.

Proximity switching circuits are used, by way of example, to provide an indication of the relative position of a metallic object or the like without using any contacts; and very often are made part of a very simple regulating circuit wherein the proximity switching circuit senses, for example, the turning of a measuring instrument, or the position of an element indicating the actual value of a regulating path (e.g., a membrane) to provide a control signal. Usually, this control or output signal is then used to control a relay which in turn controls a regulating circuit or the like. As those skilled in the art appreciate, the use of a relay, and thus contacts, at the output of a proximity switching circuit is, however, subject to many drawbacks. In order to avoid the use of contacts at this point the relay could be replaced with a contactless switching circuit controlled or switched by the output signal of the proximity switching circuit. Typical contactless switching circuits may include a thyristor switching element, two thyristors in antiparallel relationship, a thyristor controlled bridge, a triac or the like.

The substitution of a contactless switching circuit for a relay at the output of the proximity circuit, however, has the disadvantage that the coil in the proximity switch must be energized with a high-frequency source to provide a first control signal, and then a direct voltage signal must be produced from this control signal. Thereafter, this direct voltagesignal must again be converted into a high-frequency signal for providing the ignition pulse for the contactless switching circuit. Obviously this method of eliminating contacts is very complicated and costly.

The present invention provides a very simple and inexpensive means for eliminating contacts at the output of a proximity switching circuit and avoids many of the drawbacks of the solution discussed above.

In accordance with one aspect of the present invention, there is provided a switching circuit for controlling a thyristor operated circuit in response to the approachment in the vicinity of switching circuit of a predetermined electromagnetic field influencing means, such as a metallic object or the like. The switching circuit constructed in accordance with the present invention comprises input means for supplying at least one electrical input pulse, and preferably a train thereof, to said switching circuit and control means coupled to the gate electrode of the thyristor for controlling the operation thereof in response to an applied pulse in a predetermined amplitude range. Translating means are coupled to said input means and said control means for applying said input pulse to said control means. The translating means includes circuit electromagnetic means, such as an induction coil or the like, operable in response to the approachment of the said influencing means, to establish said input pulse in said predetermined amplitude range.

In accordance with another aspect of the present invention, the thyristor operated circuit includes a thyristor having a gate electrode and two other electrodes having conduction therebetween when said thyristor is in the on-state, and an output load and alternating power supply input means connected between said two other electrodes. The input means of the switching circuit and the alternating power supply input means of said thyristor operated circuit are synchronized, and preferably energized from a common alternating power source. Thus, the inputmeans of the switching circuit may include an RC charging circuit energized by said alternating power supply input means of said thyristor operated circuit and a trigger circuit connected to said charging circuit and said translating means to provide the necessary input pulses. In addition, the control means may also comprise a suitable trigger circuit operable in response to said pulses in said predetermined amplitude to control saidthyristor. The trigger circuits utilized in both the input means and the control means may include voltage breakdown triggering elements, transistor switching circuits or the like.

In accordance with another aspect of the present invention, the control means maintains the thyristor in substantially nonconductive state when its applied signal is within said predetermined amplitude range and places said thyristor in the conductive state when the applied signal is within a second amplitude range. Of course, in this arrangement, the input pulse supplied by said input means is within said second amplitude range such that the thyristor is placed in the conductive state when the electromagnetic field influencing means is not in said vicinity and is maintained in the nonconductive state when said influencing means is within said vicinity.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several aspects of the invention. It is important therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

Certain specific applications of the invention have been chosen for purposes of illustration, and are shown in the accompanying drawing forming a part of the specification wherein:

FIG. 1 shows in schematic form a circuit constructed in accordance with the present invention for controlling a thyristor and utilizing voltage breakdown triggering elements;

FIG. 2 shows in schematic form another circuit, similar to that shown in FIG. 1, for regulating the output load of the thyristor;

FIG. 3 shows a modified form of the circuit shown in FIG. I which is especially suitable for utilizing triggering elements having similar triggering voltages;

FIG. 4 shows a modified form of the circuit shown in FIG. 3 and utilizing unijunction transistors;

FIG. 5 shows wave forms schematically illustrating the temporary course of the ignition voltage and of the ignition voltage threshold of the unijunction transistor utilized in FIG. 4',

FIG. 6 shows a modified form of the circuit shown in FIG. 1, using transistor switching circuits instead of trigger elements;

FIG. 7 shows in schematic form another circuit constructed in accordance with the present invention;

FIG. 8 shows still another schematic version of a circuit constructed in accordance with the present invention; and

FIG. 9 shows a modified form of the circuit shown in FIG. 1 and adapted for utilizing coupled transformers as the electromagnetic influenced element.

thyristor controlled output circuit, shown generally at 14, in-

cluding a thyristor l6 and an'output load 18 coupledin series across the alternating power source 20. The thyristor 16 comprises a gate electrode 22and two

other electrodes

24 and 26 having conduction therebetween when the thyristor is in the on-state, and which are connected to the output load 18 and to one terminal of the alternating power source 20. In addition, the circuit includes input means, shown generally at 28, for supplying electrical input pulses through the circuit. The input means 28 includes an RC charging circuit comprising resistor 30 and capacitor 32 connected in series across the alternating power source 20, and a trigger circuit 34 comprising a voltage breakdown triggering element, such as the diac 36 and a resistor 38 shown in FIG. 1. Translating circuit means, shown generally at 40, is connected between the resistor 38 and one side of the alternating power source'20, and functions to translate the input pulses supplied by the input circuit 28 to a control circuit 42 coupled to the thyristor 16. As shown in FIG. 1, the translating circuit means 40 includes circuit electromagnetic means, such as the coil 44, the magnetic field of which is influenced by the approachment of the vane 12. The control circuit 42 comprises a voltage breakdown trigger element, such as the diac 46 shown in FIG. 1, which is connected between the translating circuit means 40 and the gate electrode 22 of the thyristor 16.

In operation, the voltage supplied by the alternating power supply 20 charges the capacitor 32 via the resistor 30 until the voltage breakdown value of the diac 36 is reached, thus igniting the same. Upon ignition of the diac 36, pulse current flows through same, the resistor 38, and the coil 44 to produce a pulse of the shape shown in FIG. 1 which is applied to the control circuit 42. It will be appreciated that by suitably choosing the RC time constant t" of the capacitor 32 and the resistor 30, the exact moment at which this pulse is applied to the control circuit 42 and thus diac 46 may be fixed. Preferably, when the vane 12 is not within the vicinity of circuit 10, the pulse applied to the control circuit 42 will be so intense or within a predetermined amplitude range, that it will ignite the diac 46. The ignition of the diac 46 will, of course, in turn ignite the thyristor 16 toconnect the output load 18 across the alternating power source 20. When the vane 12 is within the vicinity of the circuit 10, however, the vane influences'the magnetic field of the coil 44, and thus its voltage current relationship, to dampen the amplitude of the input pulses passing through the translating means 40 to a second amplitude range which does not trigger diac 46. Thus, as the vane 12 moves closer and closer to the circuit 10, and thus to the coil 44, the coil is dampened and the pulse produced thereacross to the control circuit 42 gradually becomes smaller and smaller until it is below the ignition voltage of the diac 46. At this position, and upon any subsequent further approachment of the vane 12 to the circuit 10, the thyristor 16 is not ignited, and thus the output load 18 is switched off from the alternating input power supply 20. Stated another way, the thyristor 16 is placed in the onstate when the object is not within the vicinity of the circuit,

and is maintained in the off-state when the metallic vane is within its vicinity.

. The output load 18 does not have to be connected to the full supply voltage of the input power supply 20 and may be controlled in a manner shown schematically in FIG. 2. The circuit 48 shown in FIG. 2 is constructed and operates substantially the same as that described in connection with FIG. 1 except for the use 'of an additional RC charging circuit, shown generally at 50, and an additional voltage breakdown triggering circuit, such as the diac 52 shown therein. The RC charging circuit comprises a resistor 54 and a capacitor 56 connected in series across the input power supply 20. The diac 52 is connected at one end to the juncture of resistor 54 and capacitor 56 and to the gate electrode 22 of the thyristor 16. The time constant of the RC charging circuit 50 is made larger than that of the RC charging circuit defined by the resistor 30 and the capacitor 32 described in connection with FIG. 1. Thus, in operation, and simultaneously with the operation of the circuit as otherwise described above, the capacitor 56 of the charging circuit 50 is charged via the resistor 54 until the ignition voltage of the diac 52 is reached. At this voltage, the diac 52 is ignited and thus also the thyristor 16. When the vane 12 is not within the vicinity of the circuit, and since the time constant of the charging circuit 50 is longer than that of RC charging circuit of the input means 28, the thyristor 16 is ignited by the input pulse supplied by the coil 44 through the control circuit 42. If, however, the vane 12 is in the vicinity of the circuit, the ignition of the diac 46 of the control circuit 42 will not take place, but the thyristor 16 will still be ignited upon the delayed ignition of the diac 52. Thus, it will be appreciated by regulating the charging time of the two noted charging circuits, the phase cutout of the basic and full load may be selected to selectively determine the power load at output circuit 18. This described ignition circuit may be provided in all of remaining circuits described hereinafter.

It will be appreciated from the above discussion in connection with FIGS. 1 and 2 that the amplitude of the pulse translated by coil 44 will be smaller than the breakdown voltage of the diac 36 and thus a suitable diac having a voltage breakdown value smaller than that of diac 36 must be utilized as diac 46. The circuit 60, shown generally in FIG. 3, is a modified form of the circuit shown in FIG. 1 wherein the breakdown voltage of the

diacs

36 and 46 are substantially the same. The circuit 60 is arranged substantially similar to that shown in FIG. 1, except that the coil 44 is coupled to diac 46 via a charging capacitor 62. In addition, a voltage

divider comprising resistances

64 and 66 is connected across the charging capacitor 32, and a diode 68 is connected between the voltage divider and diac 46 in the manner shown in FIG. 3. The values of

resistances

64, 66 and capacitor 62 are chosen such as that during the charging of the RC charging circuit of the input means 28, the capacitor 62 is charged to a value which when added to the amplitude of the pulse produced'across the coil 44 during the ignition of the diac 36, produces a value sufficient to trigger the diac 46. Thus, during normal operation of the circuit 60, the RC charging circuit of the input means 28 proceeds to charge to a value sufficient to ignite the diac 36, and the capacitor 62 similarly charges through the

resistances

64,66 and the diode 68 to its mentioned value. When the voltage across the capacitor 32 has reached that value sufficient to ignite the diac 36, the latter is ignited and a pulse is coupled through the capacitor 62 and supplemented with the charging voltage thereon to ignite the diac 46. Upon the ignition of the diac 36, the diode 68 is back-biased to prevent the capacitor 62 from being quickly discharged. Thus, when the vane 12 is not within the vicinity of the circuit 60, the pulse translated through the capacitor 62 is of a sufficient amplitude to trigger the diac 46, but when the vane 12 is within the vicinity of the circuit, the pulse produced via the coil 44 is reduced in amplitude sufficient that the resultant pulse coupled via the capacitor 62 is no longer of an amplitude sufficient to trigger the diac 46.

While the circuits described in connection with FIGS. 1, 2 and 3 utilize diacs as trigger elements, obviously other known voltage breakdown triggering elements may be utilized such as for example trigger diodes, four layer diodes, glowlamps and unijunction transistors. For example, FIG. 4 shows in schematic form a circuit 70 which utilizes

unijunction transistors

72 and 74 in lieu of

diacs

36 and 46 described in connection with FIGS. l-3. As shown therein, a Zener diode 76 is connected through a resistance 78 and charging resistor 30 to the power supply 20 and during the positive excursion of the power input voltage builds a voltage thereacross. The capacitor 32 proceeds to charge to this latter voltage through resistance 79 until the ignition voltage of the unijunction transistor 72 is reached. At this voltage the unijunction transistor 72 is ignited and a pulse is coupled through the resistance 38 across the coil 44 to the unijunction transistor 74. Simultaneously, as in the embodiment described in connection with FIG. 3, the condenser 62 is charged via the voltage divider consisting of

resistors

64 and 66 to a voltage which is lower than the ignition voltage of the unijunction transistor 74. In normal operation when the vane 12 is not in the vicinity of the circuit 70, the voltage buildup on the condenser 62 and the amplitude of the pulses transmitted therethrough from the coil 44 are sufficient to reach the ignition voltage of the unijunction transistor 74, and thus also sufficient to trigger the thyristor 16 and connect output load 18 to the alternating power supply 20. In this regard, a resistance 80 may be provided between one of the emitters of the unijunction transistors 74 and one side of the power supply 20 to prevent current surges from damaging the respective elements. Upon the approachment of the vane 12, (not shown) the electromagnetic field of the coil 44 is changed so that the sum of the condenser voltage 62 and the amplitude of the transmitted pulses is not sufficient to ignite the unijunction transistor 74.

' The schematic representation of the operation of the circuit shown in FIG. 4 may be best understood by reference to FIG. 5. There is shown therein in schematic form, the wave forms of the ignition voltage and the ignition voltage threshold for the unijunction transistor 74 of the circuit in FIG. 4. The ignition threshold voltage of the unijunction transistor 74 is represented by curve 82. As shown in FIG. 5, the voltage rapidly rises from zero until such time as the Zener diode 76 becomes conductive, thereafter the voltage remains substantially constant and follows perhaps a slightly bent curve created by the dynamic inner resistance of the Zener diode 76 and the additional resistance 78 connected in series with the Zener diode 76. Toward the end of the half cycle of the alternating power supply input, the ignition threshold voltage is rapidly reduced to zero and then repeats itself as described above. The voltage buildup on condenser 62 during the operation of the circuit 70 is represented in FIG. 5 by the curve 84. As shown therein, the curve 84 indicates that the voltage across condenser 62 follows the ignition threshold voltage shown in curve 82, but at a certain predetermined lag caused by the time constant which is produced by the resistances of the voltage

divider comprising resistances

64 and 66 and the condenser 62, This time lag causes the differences between the ignition threshold voltage 82 and the condenser voltage 84 to become smaller and smaller in the course of the half cycle of the alternating input power source 20.

As discussed above, the voltage 84 of the capacitor 62 is superimposed with the input pulse voltage of the coil 44, represented in FIG. 5 by the needlelike pulses 86. It will be appreciated that the

voltage divider resistances

64 and 66 are preferably adjusted so that the first impulse provided by the coil 44 adds to the condenser voltage 84 to exceed the ignition threshold voltage 82, and thus ignite the thyristor 16 in the manner discussed above. Upon the approachment of the vane 12 near the circuit 70, the pulses translated by the coil 44 becomes small such that the initial pulse of the resultant ignition voltage across condenser 62 is insufficient to ignite the unijunction transistor 74. In this instance, the first ignition of the unijunction transistor 72 is followed by a recharging of the condenser 62 through the resistance 78, and after the lapse of time, a second pulse is provided across the coil 44 by the reignition of the unijunction transistor 72 during the subsequent cycle of the input power source 20. The resultant voltage level .across the capacitor 62 may now bring about the ignition of the unijunction transistor 74 and, therefore also of the thyristor 16. If the vane 12 is brought closer to the coil 44, then perhaps only the third, fourth, fifth, sixth, etc., pulse produced by the unijunction transistor 72 may bring about ignition of the unijunction transistor 74. Therefore, the thyristor 18 is ignited later and later, and thus the arrangement may be used as a discontinuously working proportional regulator whose proportional range is selected by appropriate choice of resistance 80 and the time constant resulting from the condenser 62 and of the

resistors

64 and 66.

The circuit 90 schematically shown in FIG. 6 utilizes transistor switching circuitry in lieu of

diacs

36 and 46 as in FIGS. 1-3. Thus, transistors 92 and 94 are circuit arranged such that each are in off state during the time that the capacitor 32 is charged in a manner described heretofore. Thus, by including

resistances

96 and 98 in series with a Zener diode 100 and connected to transistors 92 and 94 as shown in FIG. 6, as long as the voltage buildup across capacitor 32 is below the zener voltage of the Zener diode 100, no conduction is made between this series connection therethrough and thus the transistors 92 and 94 are maintained in off state. As soon as the voltage across capacitor 32 exceeds the Zener voltage of the Zener diode 100, however, the Zener diode 100 becomes conductive and a voltage drop appears across the

resistances

96 and 98 which bring transistors 92 and 94 into the conductive range. As soon as one of the transistors 92 and 94 becomes conductive, its base to collector impedance effectively short circuits Zener diode 100 to thereby further increase the voltages drop across the

resistances

96 and 98, and thus further turn on the transistors 92 and 94. Accordingly, a very quick change in state of transistors 92 and 94 is obtained. Consequently, a very rapidly increasing current pulse is fed through the resistor 38 to produce a triggering pulse in the coil 44. During this time, the capacitor 62 is charged via the diode 68 to approximately the Zener voltage of the Zener diode 100.

Transistors

102 and 104 are also additionally arranged within the circuit such that they are also in off state during the latter described charging time. Thus, the voltage

divider comprising resistances

106 and 108 are selected such that the emitter of the transistor 102 is maintained at a very high potential with respect to its base and thus reversed biased. Since there is no voltage across the resistance 110 by reason of the reverse bias of the transistor 102, transistor 104 is also in off state. If, however, the amplitude of the pulse appearing across coil 44 is higher than the voltage supplied by the

voltage divider

106, 108 to the emitter of transistor 102, the transistor 102 is made conductive through the'resistance 111. This, of course, produces a voltage drop across resistance 110 which also brings the transistor 104 into conduction so that an ignition pulse is fed therethrough to the thyristor 16 via the resistance 112 to ignite the same. A diode 114 may be provided between the collector and base of the

transistors

104 and 102 respectively to prevent the thyristor 16 from being directly ignited by the pulse of the coil 44.

Based on the above disclosure, it will be apparent that other modifications may be made to produce other significant electrical functions. Thus, as shown in FIG, 7, the electric circuit shown in FIG. 1 as well as the other electric circuits described hereinabove, may be operated during both halves of the input alternating power supply 20 by the use of a diode bridge 116. It will be appreciated, as shown by the wave form of FIG. 7, that the output load 18 is fed by a double wave direct voltage 118. In another circuit, an alternating voltage output load may be inserted as shown in FIG. 7 to provide an alternating load output. Also, as shown in FIG. 8 the circuit of FIG. 1 as well as all the other circuits heretofore described, may utilize a pulse transformer 122 connected as shown in FIG. 8 to indirectly control thyristors or other triac configurations. Lastly, as shown in FIG. 9, a transformer 124 may be used in lieu of the coil 44 described above. It will be noted that in this case, no series resistance 38 is necessary.

Thus, it will be seen from the above that the present invention provides a simple and very inexpensive proximity switching circuit which does not have contacts at its output.

Having thus described the invention with particular reference to the preferred forms thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding the invention, that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the claims appended hereto.

What is claimed as new and desired to be secured by Letters Patent is: i

1. A circuit for the touchless control of a thyristor in response to the approachment in the vicinity of said circuit of a predetermined electromagnetic field influencing means, said circuit comprising a thyristor controlled output circuit including a thyristor having a gate electrode and two other electrodes having conduction therebetween when said thyristor is in the conductive state, alternating power sourceinput means connected across said two other electrodes, pulse circuit means connected to and synchronized by said alternating power source input means for providing a triggering pulse at a predetermined time 'after the beginning of each alternation of said alternating power source, control means coupled to said gate electrode of said thyristor for controlling the operation thereof in response to anapplied pulse in a predetermined amplitude range, and translating means coupled to said pulse circuit means for applying said triggering pulse to said control means, said translating means including touchless electromagnetic circuit means operable in response to the approachment of said influencing means to establish said input pulse in said predetermined amplitude range. I

2. A circuit as in claim 1 wherein said control means maintains said thyristor in substantially nonconductive state when said applied signal is within said predetermined amplitude range and places said thyristor in conductive state when said applied signal is within a second amplitude range, and wherein the amplitude of said triggering pulse is within said second amplitude range whereby said thyristor is placed in the conductive state when said influencing means is not in said vicinity and is maintained in the nonconductive state when said influencing means is within said vicinity.

3. A circuit as in claim 2 wherein said electromagnetic circuit means comprises a coil and said influencing means comprises means for affecting the magnetic field of said coil.

4. A circuit for indicating the position within a given vicinity of an object having electromagnetic field'influencing properties, said circuit comprising a thyristor controlled output circuit including a thyristor having a gate electrode and two other electrodes having conduction therebetween when said thyristor is in the conductive state, an output load and alternating power supply input means connected between said two other electrodes; pulse circuit means connected to and synchronized by said alternating power source input means for providing a triggering pulse at a predetermined time after the beginning of each alternation of said alternating power source, control means coupled to said gate electrode of said thyristor for controlling the operation thereof in response to applied pulses in a predetermined amplitude range; and translating said applied signal is within said predetermined amplitude range and places said thyristor in the conductive state when said applied signal is within a second amplitude range, and wherein the amplitude of said triggering pulse is within said second amplitude range whereby said thyristor is placed in the conductive state when said influencing means is not in said vicinity and is maintained in the nonconductive state when said influencing means is within said vicinity.

6. A circuit as in claim 5 wherein said electromagnetic circuit means includes a coil. I

7. A circuit as in claim 5 wherein said electromagnetic circuit means includes a transformer.

8. A circuit as in claim 5 wherein said control means comprises a trigger circuit having a voltage breakdown triggering element.

9. A circuit as in claim 5 wherein said control means includes trigger circuit means comprising transistors.

10. A circuit as in claim 4 wherein said pulse circuit means includes a first RC charging circuit coupled across said alternating power supply input means and a trigger circuit connected to said first RC charging circuit whereby said pulse circuit means provides a trigger pulse at a predetermined time after the beginning of each alternation of said alternating power supply.

11. A circuit as in claim 10 wherein said trigger circuit comprises a transistor switching circuit.

12. A circuit as in claim 10 wherein said trigger circuit comprises a first voltage breakdown triggering element and wherein said control circuit comprises a second voltage breakdown triggering element having a breakdown voltage smaller than said first voltage breakdown element.

13. A circuit as in claim 10 wherein said trigger circuit comprises a first voltage breakdown triggering element and wherein said control circuit comprises a second voltage breakdown triggering element having substantially the same breakdown voltage as said first voltage breakdown element and wherein a second RC charging circuit is provided between said first RC charging circuit and said control circuit and in additive combination with the output of said translating circuit applied to said control means.

Claims

1. A circuit for the touchless control of a thyristor in response to the approachment in the vicinity of said circuit of a predetermined electromagnetic field influencing means, said circuit comprising a thyristor controlled output circuit including a thyristor having a gate electrode and two other electrodes having conduction therebetween when said thyristor is in the conductive state, alternating power source input means connected across said two other electrodes, pulse circuit means connected to and synchronized by said alternating power source input means for providing a triggering pulse at a predetermined time after the beginning of each alternation of said alternating power source, control means coupled to said gate electrode of said thyristor for controlling the operation thereof in response to an applied pulse in a predetermined amplitude range, and translating means coupled to said pulse circuit means for applying said triggering pulse to said control means, said translating means including touchless electromagnetic circuit means operable in response to the approachment of said influencing means to establish said input pulse in said predetermined amplitude range.

4. A circuit for indicating the position within a given vicinity of an object having electromagnetic field influencing properties, said circuit comprising a thyristor controlled output circuit including a thyristor having a gate electrode and two other electrodes having conduction therebetween when said thyristor is in the conductive state, an output load and alternating power supply input means connected between said two other electrodes; pulse circuit means connected to and synchronized by said alternating power source input means for providing a triggering pulse at a predetermined time after the beginning of each alternation of said alternating power source, control means coupled to said gate electrode of said thyristor for controlling the operation thereof in response to applied pulses in a predetermined amplitude range; and translating means coupled to said pulse circuit Means for applying said triggering pulse to said control means, said translating means including electromagnetic circuit means operable in response to the approachment of said object to establish said input pulses in said predetermined range whereby the average power presented to the output load current of said output circuit indicates the presence and absence of said object within said vicinity.

5. A circuit as in claim 4 wherein said control means maintains said thyristor in substantially nonconductive state when said applied signal is within said predetermined amplitude range and places said thyristor in the conductive state when said applied signal is within a second amplitude range, and wherein the amplitude of said triggering pulse is within said second amplitude range whereby said thyristor is placed in the conductive state when said influencing means is not in said vicinity and is maintained in the nonconductive state when said influencing means is within said vicinity.

6. A circuit as in claim 5 wherein said electromagnetic circuit means includes a coil.