Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
175 words
An electronic switching circuit for controlling a supply of alternating current electricity to a load, including a bi-directional rectifier combination comprising first and second thyristors connected in parallel with opposite polarities, each thyristor having a trigger electrode; first and second direct current trigger voltage supplies of equal magnitude and polarity but electrically isolated from each other; a first switchable semiconductor device connected in series between the first direct current trigger voltage supply and the trigger electrode of the first thyristor; a second switchable semiconductor device, connected in series between the second direct current trigger voltage supply and the trigger electrode of the second thyristor; control means for rendering both first and second switchable semiconductor devices conductive simultaneously from the next zero voltage instant of the alternating current supply after the onset of a control signal; detection means for detecting when either of the thyristors has failed open-circuit; and inhibiting means controlled by the detection means for inhibiting the control signal whenever an open-circuit failure of either of the thyristors is detected by the detection means.
Claim 2
Dependent Claim
175 words
An electronic switching circuit for controlling a supply of alternating current electricity to a load, including a bi-directional rectifier combination comprising first and second thyristors connected in parallel with opposite polarities, each thyristor having a trigger electrode; first and second direct current trigger voltage supplies of equal magnitude and polarity but electrically isolated from each other; a first switchable semiconductor device connected in series between the first direct current trigger voltage supply and the trigger electrode of the first thyristor; a second switchable semiconductor device, connected in series between the second direct current trigger voltage supply and the trigger electrode of the second thyristor; control means for rendering both first and second switchable semiconductor devices conductive simultaneously from the next zero voltage instant of the alternating current supply after the onset of a control signal; detection means for detecting when either of the thyristors has failed open-circuit; and inhibiting means controlled by the detection means for inhibiting the control signal whenever an open-circuit failure of either of the thyristors is detected by the detection means.
Claim 3
Dependent Claim
28 words
An electronic switching circuit as claimed in claim 1 and wherein the first and second switchable semiconductor devices are photo-transistors of first and second opto-electronic isolator devices respectively.
Claim 4
Dependent Claim
61 words
An electronic switching circuit as claimed in claim 1 and wherein the first and second switchable semiconductor devices are first and second transistors respectively and the control means includes a first opto-electronic isolator device connected to control the switching operations of the said first transistor and a second opto-electronic isolator device connected to control the switching operations of the second transistor.
Claim 5
Dependent Claim
99 words
An electronic switching circuit as claimed in claim 1 and wherein the control means includes a full-wave rectifier circuit connected in parallel with the said thyristors, and a third switchable semiconductor device connected to receive a control signal on one input and the unsmoothed output waveform of the full-wave rectifier circuit on another input so that it will conduct only when the control signal is on and the rectifier output is substantially at zero voltage and means for rendering the said first and second switchable semiconductor devices conductive in response to the conduction of the third switchable semiconductor device.
Claim 6
Dependent Claim
52 words
An electronic switching circuit as claimed in claim 4 and wherein the control means also comprises a third direct voltage supply and a third opto-electronic isolator device connected to control the supply of a direct voltage from the third direct voltage supply to the third switchable semiconductor device as a control signal.
Claim 7
Dependent Claim
83 words
An electronic switching circuit as claimed in claim 4 wherein the detection means comprises a fourth opto-electronic isolator device responsive to the output waveform developed across the full-wave rectifier circuit when either of the thyristors fails open-circuit, and wherein the inhibiting means comprises an edge-triggering bistable circuit having a setting input connected to receive the control signal, a resetting input connected to the output of the fourth opto-electronic isolator device, and a set output connected to control the said third opto-electronic isolator device.