Protective switching circuit for providing power to a load from an alternating current source having peak to peak excursions within or above a given range

Claim 2

A protective switching circuit for limiting the supply of power to a load from an alternating current source having peakto-peak excursions within or above a given range comprising: a thyristor having first and second main terminal electrodes and a gate electrode; a first triggering circuit connected in circuit with said thyristor electrodes for providing a triggering signal to the gate electrode of said thyristor in response to said alternating current source when said excursions are within said given range; and a second triggering circuit connected in circuit with said thyristor electrodes for providing a triggering signal to the gate electrode of said thyristor in response to said alternating current source when said excursions are above said given range.

Claim 3

A switching circuit comprising: a thyristor adapted for connection to an alternating current source having peak-to-peak excursions within or above a given range, said thyristor having first and second main terminal electrodes and a gate electrode; means for connecting said main terminal electrodes in circuit with a load to be supplied from said alternating current source, the conduction state of said thyristor determining the supply of power to said load; a first time constant circuit for controlling the conduction state of said thyristor when the peak-to-peak excursions of said alternating current source are within said given range; means for charging said first time constant circuit from said alternating current source when said excursions are within said range; a second time constant circuit for controlling the conduction state of said thyristor when the peak-to-peak excursions of said alternating current source are above said given range; and means for charging said second time constant circuit from said alternating current source when said excursions are above said range, said thyristor being triggered into conduction by a triggering signal applied to said gate electrode from said first time constant circuit when said excursions are within said range and via a triggering signal applied to said gate electrode from said second time constant circuit when said excursions are above said range.

Claim 4

A switching circuit comprising: a thyristor adapted for connection to an alternating current source having peak-to-peak excursions within or above a given range, said thyristor having first and second main terminal electrodes and a gate electrode; means for connecting said main terminal electrodes in circuit with a load to be supplied from said alternating current source, the conduction state of said thyristor determining the supply of power to said load; a first time constant circuit for controlling the conduction state of said thyristor when the peak-to-peak excursions of said alternating current source are within said given range; means for charging said first time constant circuit from said alternating current source when said excursions are within said range; a second time constant circuit for controlling the conduction state of said thyristor when the peak-to-peak excursions of said alternating current source are above said given range; and means for charging said second time constant circuit from said alternating current source when said excursions are above said range, said thyristor being triggered into conduction by a triggering signal applied to said gate electrode from said first time constant circuit when said excursions are within said range and via a triggering signal applied to said gate electrode from said second time constant circuit when said excursions are above said range.

Claim 5

A switching circuit as defined in claim 2 further comprising means for preventing said first time constant circuit from providing a triggering signal to said gate electrode when the peak-to-peak excursions of said alternating current source are above said given range.

Claim 6

A switching circuit as defined in claim 3 wherein said preventing means comprises a threshold device, said device becoming conductive when said excursions exceed said given range.

Claim 7

A protective switching circuit for limiting the power supplied to a load from an alternating current source having peak-to-peak excursions within or above a given range comprising: a thyristor having first and second main terminal electrodes and a gate electrode; means for connecting the main terminal electrodes of said thyristor in circuit with the load to be supplied, the conduction state of said thyristor determining the supply of power to said load; first and second time constant circuits connected in circuit with said thyristor electrodes; means for charging said first and second time constant circuit from said source; means for effectively disabling said first time constant circuit when the peak-to-peak excursions of saiD source exceed said given range, said thyristor being triggered into conduction by a triggering signal applied to said gate electrode from said first time constant circuit when said excursions are within said range and via a triggering signal supplied to said gate electrode from said second time constant circuit when said excursions exceed said range.

Claim 8

A protective switching circuit for limiting the power supplied to a load from an alternating current source having peak-to-peak excursions within or above a given range comprising: a thyristor having first and second main terminal electrodes and a gate electrode; means for connecting the main terminal electrodes of said thyristor in circuit with the load to be supplied, the conduction state of said thyristor determining the supply of power to said load; first and second time constant circuits connected in circuit with said thyristor electrodes; means for charging said first and second time constant circuit from said source; means for effectively disabling said first time constant circuit when the peak-to-peak excursions of saiD source exceed said given range, said thyristor being triggered into conduction by a triggering signal applied to said gate electrode from said first time constant circuit when said excursions are within said range and via a triggering signal supplied to said gate electrode from said second time constant circuit when said excursions exceed said range.

Claim 9

A switching circuit comprising: a triac having first and second main terminal electrodes and a gate electrode, said triac adapted for connection to an alternating current source having peak-to-peak excursions within or above a given range; means for connecting said main terminal electrodes in circuit with a load to be supplied from said source, the conduction state of said triac determining the supply of power to said load; a first time constant circuit having a charge path of a first time constant including an energy storage device and having a discharge path of a second time constant including said energy storage device; means for charging said storage device over said time constant circuit charge path only when said alternating current source is of a given polarity; means connected to the gate electrode of said triac for discharging said storage device over said time constant circuit discharge path and into said gate electrode; means for preventing said energy storage means from discharging into said gate electrode when said peak-to-peak excursions exceed said given range; a second time constant circuit including a further energy storage device; means for charging said further energy storage device from said alternating current source; and means for discharging said further energy storage device into said gate electrode when said excursions exceed said given range; whereby said triac is triggered into conduction by the first time constant circuit when said excursions are within said range and by the second time constant circuit when said excursions exceed said range.

Claim 10

A switching circuit comprising: a triac having first and second main terminal electrodes and a gate electrode, said triac adapted for connection to an alternating current source having peak-to-peak excursions within or above a given range; means for connecting said main terminal electrodes in circuit with a load to be supplied from said source, the conduction state of said triac determining the supply of power to said load; a first time constant circuit having a charge path of a first time constant including an energy storage device and having a discharge path of a second time constant including said energy storage device; means for charging said storage device over said time constant circuit charge path only when said alternating current source is of a given polarity; means connected to the gate electrode of said triac for discharging said storage device over said time constant circuit discharge path and into said gate electrode; means for preventing said energy storage means from discharging into said gate electrode when said peak-to-peak excursions exceed said given range; a second time constant circuit including a further energy storage device; means for charging said further energy storage device from said alternating current source; and means for discharging said further energy storage device into said gate electrode when said excursions exceed said given range; whereby said triac is triggered into conduction by the first time constant circuit when said excursions are within said range and by the second time constant circuit when said excursions exceed said range.

Claim 11

A switching circuit as defined in claim 6 wherein said discharge prevention means includes a threshold device which becomes conductive when said excursions exceed said given range.

Claim 12

In a circuit which includes a load in circuit with the main terminal electrodes of a thyristor and which circuit is adapted to be operated by an alternating voltage source connected across said circuit, a circuit for limiting the power supplied to said load comprising: first circuit means responsive to said alternating voltage when its peak-to-peak excursions are within a given range for providing a control signal to the gate electrode of said thyristor to cause power at an average level not greater than a given value related to the maximum voltage within said range to be applied to the load; means responsive to said alternating voltage when its peak-to-peak excursions extend above said given range for effectively disconnecting said first circuit means from said thyristor; and second circuit means responsive to said alternating voltage when its peak-to-peak excursions extend beyond said given range for providing a control signal to said gate electrode so phased relative to said alternating voltage to cause power at an average level not greater than said given value to be delivered to the load.

Claim 13

In a circuit which includes a load in circuit with the main terminal electrodes of a thyristor and which circuit is adapted to be operated by an alternating voltage source connected across said circuit, a circuit for limiting the power supplied to said load comprising: first circuit means responsive to said alternating voltage when its peak-to-peak excursions are within a given range for providing a control signal to the gate electrode of said thyristor to cause power at an average level not greater than a given value related to the maximum voltage within said range to be applied to the load; means responsive to said alternating voltage when its peak-to-peak excursions extend above said given range for effectively disconnecting said first circuit means from said thyristor; and second circuit means responsive to said alternating voltage when its peak-to-peak excursions extend beyond said given range for providing a control signal to said gate electrode so phased relative to said alternating voltage to cause power at an average level not greater than said given value to be delivered to the load.

Claim 14

The invention as defined in claim 8 wherein said first circuit means comprises a rectifier circuit for providing DC signals to the gate electrode of the thyristor.

Claim 15

The invention as defined in claim 8 wherein said first circuit means comprises an oscillator circuit for providing a train of pulses having a frequency greater than the frequency of the alternating current source to the gate electrode of the thyristor.

Claim 16

The invention as defined in claim 8 wherein said second circuit is a phase delay circuit.

Claim 17

The invention as defined in claim 11 wherein said phase delay circuit comprises a resistor-capacitor timing circuit and a threshold device responsive to the charge on said caPacitor for providing said phased control signal to said gate electrode.

Claim 18

The invention as defined in claim 8 wherein said disconnecting means comprises a threshold circuit responsive to alternating voltage signals having peak-to-peak excursions beyond said given range.

Claim 19

The invention as defined in claim 13 wherein said threshold circuit comprises a threshold device connected in circuit with the base electrode of a transistor, said device becoming conductive to provide base current to said transistor when the peak-to-peak excursion of the alternating voltage signals exceeds said given range, said transistor thereby operating to effectively disable said first circuit means.