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, 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 pulses indicative of the zero-voltage crossings of said a.c. source, current supply means including resistance means connecting one of said control thyristor load terminals to the control terminal of said control thyristor, 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 permitting current flow thereto from said current supply means through said resistance means for succeeding cycles of said a.c. source once said control thyristor means becomes conductive, and circuit 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, and including means coupled to said detector means for driving said detector means when said control thyristor means is nonconductive and for serving as said current supply means when said control thyristor means is conductive.

Claim 3

The circuit of claim 1 wherein said coupling circuit 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 full-wave 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 be enabled to provide an output pulse under the condition that said full-wave d.c. voltage is below the cut-off level of the transistor means, said output pulse being indicative of a zero-voltage crossing of said source.

Claim 6

The circuit of claim 4 wherein said rectified d.c. voltage is applied to the base circuit and the emitter-collector circuit of said transistor means, said emitter-collector circuit including a series resistor connected therein, and said emitter-collector circuit being connected across the output terminals of said rectifier means so that said output pulse is generated at one end of said resistor under the condition that said transistor means becomes nonconductive.

Claim 7

The circuit of claim 5 wherein said control thyristor means comprises a silicon controlled rectifier having anode and cathode load terminals and a gate control terminal, said anode and cathode being connected across the output of said rectifier means and the gate being responsively coupled to said output pulses from said transistor means so that the silicon controlled rectifier will be triggered to its conductive state at the zero-voltage crossing of said source and will be latched in said conductive state by said resistor coupled between the gate and anode of said controlled rectifier.

Claim 8

The circuit of claim 6 comprising a selectively operable, normally closed switch connected between the gate and cathode of the silicon controlled rectifier, normally disabling the operation of said detector means and said silicon controlled rectifier, but enabling said operation upon being opened so that the controlled rectifier will be triggered into conduction by the first output pulse from the detector means.

Claim 9

The circuit of claim 2 wherein said rectifier means has one input connected to said one load terminal of said switching thyristor means, and the other input resistively coupled to the control terminal of said switching thyristor means, said one load terminal being connected to one a.c. source terminal, and said control terminal being resistively coupled to a further terminal for connection to the other a.c. source terminal through the load.

Claim 10

The circuit of claim 1 wherein said means for selectively applying at least one of said pulses to the control terminal of said control thyristor means comprises a switch connected in said circuit means for selectively closing and opening a circuit 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 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 a zero-voltage crossing 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 current to the control terminal of said control thyristor means through a resistance means coupling the control terminal to one load terminal thereof 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, said last named means including in common therewith said means for supplying current to the control terminal of said control thyristor means through said resistance means.

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 a zero-voltage crossing 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 current to the control terminal of said control thyristor means through a resistance means coupling the control terminal to one load terminal thereof 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, said last named means including in common therewith said means for supplying current to the control terminal of said control thyristor means through said resistance means.

Claim 13

The circuit of claim 10 wherein said enabling means comprises a switch for selectively closing and opening a circuit of said coupling means.

Claim 14

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 recifier 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 non-conductive 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, said last named means comprising a resistor connected between the gate and anode of the silicon controlled rectifier.

Claim 15

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 recifier 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 non-conductive 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, said last named means comprising a resistor connected between the gate and anode of the silicon controlled rectifier.

Claim 16

The circuit of claim 10 wherein saud means coupled to the output of said transistor circuit and to the gate of the silicon controlled rectifier comprises switching means for normally shunting the gate and cathode of the silicon controlled rectifier.

Claim 17

The circuit of claim 10 wherein said resistor is also connected in the collector circuit of said transistor.

Claim 18

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 thyristor load terminals for connecting the a.c. source to the load; an operating circuit for said switching thyristor means comprising a full-wave rectifier circuit having input and output terminals, a control thyristor having anode, cathode and gate terminals, and a transistor zero-voltage crossing detector circuit; means conductively connecting the output terminals of the rectifier circuit across the anode and cathode terminals of the control thyristor, the load terminals of the transistor circuit, and the control terminal of the transistor circuit; means for conductively connecting the output load terminal of the transistor circuit to the gate of the control thyristor; the control terminal of the switching thyristor means being coupled to one input terminal of the rectifier circuit and resistively coupled to one load terminal of said switching thyristor means, and the other load terminal of said switching thyristor means being connected to the other input terminal of the rectifier circuit; and means for selectively enabling the control terminal of said switching thyristor means to be coupled to said other load terminal thereof through the anode and cathode of said control thyristor so as to permit the latching of said switching thyristor means in a conductive state.

Claim 19

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 thyristor load terminals for connecting the a.c. source to the load; an operating circuit for said switching thyristor means comprising a full-wave rectifier circuit having input and output terminals, a control thyristor having anode, cathode and gate terminals, and a transistor zero-voltage crossing detector circuit; means conductively connecting the output terminals of the rectifier circuit across the anode and cathode terminals of the control thyristor, the load terminals of the transistor circuit, and the control terminal of the transistor circuit; means for conductively connecting the output load terminal of the transistor circuit to the gate of the control thyristor; the control terminal of the switching thyristor means being coupled to one input terminal of the rectifier circuit and resistively coupled to one load terminal of said switching thyristor means, and the other load terminal of said switching thyristor means being connected to the other input terminal of the rectifier circuit; and means for selectively enabling the control terminal of said switching thyristor means to be coupled to said other load terminal thereof through the anode and cathode of said control thyristor so as to permit the latching of said switching thyristor means in a conductive state.

Claim 20

The circuit of claim 15 wherein said enabling means comprises a selectively operable, normally closed switch connected between the gate and cathode of the control thyristor.

Claim 21

The circuit of claim 15 wherein said enabling means comprises a selectively operable, normally open switch connected between said control terminal of the switching thyristor means and said other load terminal thereof.

Claim 22

The circuit of claim 15 wherein said enabling means comprises a selectively operable, normally open switch connected between said control terminal of the switching thyristor and said one input terminal of said rectifier circuit.