Synchronous switching circuit

Claim 2

A switching circuit for controlling the application of an A.C. source to a load, comprising switching thyristor means having a pair of load terminals and a control terminal and having a bidirectional switching characteristic, said load terminals being connected in series with the A.C. source and the load, control thyristor means having a pair of load terminals and a control terminal, detector means for providing pulses indicative of the zero voltage crossings of said A.C. source, current supply means, means for selectively applying at leasT one of said pulses to the control terminal of said control thyristor means for triggering the same and for supplying continuous latching current thereto from said current supply means for succeeding cycles of said A.C. source once said control thyristor means becomes conductive, and means for coupling the control terminal of said switching thyristor means to one of said load terminals thereof through the load terminals of said control thyristor means.

Claim 3

The circuit of claim 1 wherein said coupling means comprises rectifier means for appropriately steering currents from the control terminal of said switching thyristor means, through said control thyristor means, to said one load terminal of said switching thyristor means for each polarity of the A.C. source.

Claim 4

The circuit of claim 2 wherein said rectifier means provides a rectified D.C. voltage for operating said detector means.

Claim 5

The circuit of claim 3 wherein said detector means comprises transistor means responsive to said rectified D.C. voltage to provide an output pulse whenever the rectified D.C. voltage is below the cut-off level of said transistor means, said output pulses being indicative of the zero voltage crossings of said source.

Claim 6

The circuit of claim 4 wherein said current supply means is also coupled to the output of said transistor means.

Claim 7

The circuit of claim 5 wherein said means for selectively applying said pulse and said latching current comprises a switch serially connecting the output of said transistor means to control terminal of said control thyristor means.

Claim 8

The circuit of claim 5 comprising circuit means for causing said transistor means to become nonconductive in response to said control thyristor becoming conductive.

Claim 9

The circuit of claim 2 wherein the load terminals of said control thyristor means are coupled across the output of said rectifier means.

Claim 10

The circuit of claim 8 wherein said rectifier means comprises a full wave bridge rectifier circuit having one input coupled to one terminal of said A.C. source and the other input coupled to the other terminal of the A.C. source and to the control terminal of said switching thyristor means.

Claim 11

A switching circuit for controlling the application of an A.C. source to a load, comprising switching thyristor means having a pair of load terminals and a control terminal and having a bidirectional switching characteristic, circuit means coupled to said load terminals for connecting the A.C. source to the load, control thyristor means having a pair of load terminals and a control terminal, detector means for providing a signal indicative of the zero voltage crossings of said A.C. source, means for, at will, enabling said control thyristor means to be responsive to said signal so that it is triggered into a conductive state at a zero voltage crossing of the source, means for supplying latching current to the control terminal of said control thyristor means for succeeding cycles of said A.C. source after said control thyristor means becomes conductive, and means for coupling the control terminal of said switching thyristor means to one of said load terminals thereof through the load terminals of said control thyristor means to maintain said switching thyristor means conductive.

Claim 12

A switching circuit for controlling the application of an A.C. source to a load, comprising switching thyristor means having a pair of load terminals and a control terminal and having a bidirectional switching characteristic, circuit means coupled to said load terminals for connecting the A.C. source to the load, control thyristor means having a pair of load terminals and a control terminal, detector means for providing a signal indicative of the zero voltage crossings of said A.C. source, means for, at will, enabling said control thyristor means to be responsive to said signal so that it is triggered into a conductive state at a zero voltage crossing of the source, means for supplying latching current to the control terminal of said control thyristor means for succeeding cycles of said A.C. source after said control thyristor means becomes conductive, and means for coupling the control terminal of said switching thyristor means to one of said load terminals thereof through the load terminals of said control thyristor means to maintain said switching thyristor means conductive.

Claim 13

The circuit of claim 10 comprising rectifier means for providing a full-wave rectified voltage to said detector means, said detector means including a transistor circuit having a transistor responsive to said rectified voltage for providing said signal when said rectified voltage is below the cut-off level of the transistor and said control thyristor means is enabled to be responsive to said signal.

Claim 14

The circuit of claim 11 wherein said rectifier means is also connected across the load terminals of said control thyristor means so that said transistor remains non-conductive when said control thyristor means becomes conductive, reducing the rectified voltage to the detector means below said cut-off level.

Claim 15

The circuit of claim 12 comprising means coupled to said transistor for supplying said latching current only when said transistor is nonconductive.

Claim 16

The circuit of claim 13 including means for applying said rectified voltage to the base circuit of said transistor, and means for applying said signal to the control terminal of said control thyristor means when said transistor becomes nonconductive.

Claim 17

The circuit of claim 14 comprising rectifier means for supplying said latching current to the control terminal of said control thyristor means when said transistor is nonconductive, the emitter and collector of said transistor being connected in shunt circuit relation to the control terminal of said control thyristor means and across said latching current supply.

Claim 18

A synchronous switching circuit for controlling the application of an A.C. source to a load, comprising a triac having an anode, cathode and gate; circuit means coupled to the triac anode and cathode for switching the A.C. source to the load when the triac is in its conductive state; a silicon controlled rectifier having an anode, cathode and gate; a rectifier circuit having four diodes interconnected in a general bridge arrangement to provide a pair of input terminals for the application of an A.C. voltage thereto and a pair of output terminals to provide a full-wave D.C. voltage therefrom; conductive means for coupling the A.C. source across said pair of input terminals, for coupling the triac gate to one of said input terminals, and for coupling the other of said input terminals to the triac anode; said pair of output terminals being connected across the anode and cathode of said silicon controlled rectifier and poled with respect to the diodes of said rectifier circuit so that a direct conductive path is provided between the gate and anode of the triac through the silicon controlled rectifier when the latter is in its conductive state; a transistor circuit having base input means connected across said pair of output terminals for rendering the transistor nonconductive when the full-wave D.C. voltage is below the cut-off level of the transistor, said cut-off level being sufficiently low so that the periods of nonconduction are indicative of the zero voltage crossings of the A.C. source; means coupled to the output of said transistor circuit and to the gate of the silicon controlled rectifier for selectively enabling the silicon controlled rectifier to be triggered into a conductive state at a zero voltage crossing of the A.C. source; and means coupled to the gate of the silicon controlled rectifier for supplying a latching signal thereto for succeeding cycles of the A.C. source after said silicon controlled rectifier becomes conductive.

Claim 19

A synchronous switching circuit for controlling the application of an A.C. source to a load, comprising a triac having an anode, cathode and gate; circuit means coupled to the triac anode and cathode for switching the A.C. source to the load when the triac is in its conductive state; a silicon controlled rectifier having an anode, cathode and gate; a rectifier circuit having four diodes interconnected in a general bridge arrangement to provide a pair of input terminals for the application of an A.C. voltage thereto and a pair of output terminals to provide a full-wave D.C. voltage therefrom; conductive means for coupling the A.C. source across said pair of input terminals, for coupling the triac gate to one of said input terminals, and for coupling the other of said input terminals to the triac anode; said pair of output terminals being connected across the anode and cathode of said silicon controlled rectifier and poled with respect to the diodes of said rectifier circuit so that a direct conductive path is provided between the gate and anode of the triac through the silicon controlled rectifier when the latter is in its conductive state; a transistor circuit having base input means connected across said pair of output terminals for rendering the transistor nonconductive when the full-wave D.C. voltage is below the cut-off level of the transistor, said cut-off level being sufficiently low so that the periods of nonconduction are indicative of the zero voltage crossings of the A.C. source; means coupled to the output of said transistor circuit and to the gate of the silicon controlled rectifier for selectively enabling the silicon controlled rectifier to be triggered into a conductive state at a zero voltage crossing of the A.C. source; and means coupled to the gate of the silicon controlled rectifier for supplying a latching signal thereto for succeeding cycles of the A.C. source after said silicon controlled rectifier becomes conductive.

Claim 20

The circuit of claim 16 wherein said means for providing a latching signal comprises means for providing a direct current derived from the A.C. source, and said output of said transistor circuit is interconnected with said immediately aforementioned means for permitting said latching current to be supplied to the gate of the silicon controlled rectifier only when said transistor is nonconductive.