Interference suppression circuits

Claim 2

In a switching circuit comprising a thyristor adapted for connection to an alternating current source and a load to be supplied from said alternating current souRce; means for connecting said thyristor in circuit with said load and said alternating current source; a time constant network responsive to said alternating current source and connected in circuit with said thyristor for controlling the phase angle at which said thyristor is switched into conduction; and a filtering network connected in circuit with said thyristor for the suppression of interference generated by the switching action of said thyristor, the improvement comprising: circuit means coupled to said thyristor and responsive to the collapse of load current through said thyristor for preventing said thyristor from commutating into an off state during midcycle.

Claim 3

The invention as defined in claim 1 wherein said filtering network comprises an inductor-capacitor circuit with forms a resonant discharge circuit with said triac that is dependent upon the impedance of said load for damping, the Q of said resonant circuit being above a critical level such that the oscillating current of said resonant discharge circuit would be sufficient to cause said triac to commutate into an off state during midcycle.

Claim 4

The invention as defined in claim 2 wherein said thyristor comprises a triac having first and second main terminal electrodes and a gate electrode, and wherein said inductor is connected at one end thereof to a given one of said main terminal electrodes and at the other end thereof through said circuit means to said gate electrode.

Claim 5

The invention as defined in claim 3 wherein said circuit means comprises a resistor-capacitor circuit.

Claim 6

A switching circuit for controlling the supply of power to a load from a source of alternating current comprising: a triac having first and second main terminal electrodes and a gate electrode; means for connecting said first and second main terminal electrodes in circuit with said alternating current source and said load; a time constant network responsive to said alternating current source and connected in circuit with said triac electrodes for controlling the phase angle at which said triac switches into conduction; an interference suppression network comprising an inductor-capacitor circuit connected in circuit with said main terminal electrodes of said triac, said suppression network and said triac forming a resonant discharge circuit which is dependent upon the impedance of said load for damping, the Q of said resonant circuit being above a critical level such that the oscillatory current of said resonant discharge circuit would be sufficient to cause said triac to commutate into an off state during midcycle; and circuit means connected on one end thereof to said gate electrode and at the other end thereof to a given one of said main terminal electrodes through the inductor of said suppression network, wherethrough the energy stored in said inductor is applied to said gate electrode in response to the collapse of load current through said triac main terminal electrodes to prevent said triac from commutating off during midcycle.

Claim 7

A switching circuit for controlling the supply of power to a load from a source of alternating current comprising: a triac having first and second main terminal electrodes and a gate electrode; means for connecting said first and second main terminal electrodes in circuit with said alternating current source and said load; a time constant network responsive to said alternating current source and connected in circuit with said triac electrodes for controlling the phase angle at which said triac switches into conduction; an interference suppression network comprising an inductor-capacitor circuit connected in circuit with said main terminal electrodes of said triac, said suppression network and said triac forming a resonant discharge circuit which is dependent upon the impedance of said load for damping, the Q of said resonant circuit being above a critical level such that the oscillatory current of said resonant discharge circuit would be sufficient to cause said triac to commutate into an off state during midcycle; and circuit means connected on one end thereof to said gate electrode and at the other end thereof to a given one of said main terminal electrodes through the inductor of said suppression network, wherethrough the energy stored in said inductor is applied to said gate electrode in response to the collapse of load current through said triac main terminal electrodes to prevent said triac from commutating off during midcycle.

Claim 8

A switching circuit as defined in claim 5 wherein said circuit means comprises a series resistor-capacitor network.

Claim 9

In a switching circuit comprising a triac having first and second main terminal electrodes and a gate electrode; means for connecting said main terminal electrodes in circuit with an incandescent lamp load and an alternating current source; a time constant network responsive to said alternating current source and connected in circuit with said triac electrodes for controlling the phase angle at which said triac is switched into conduction; and a radio frequency interference suppression network comprising an inductor and a capacitor connected in circuit with said main terminal electrodes, wherein said suppression network and said triac form a resonant discharge circuit which is dependent upon the impedance of said incandescent lamp load for damping, and wherein the Q of said resonant circuit is above a critical level such that the oscillatorY current of said resonant discharge circuit would be sufficient to cause said triac to commutate into an off state during midcycle thereby causing said lamp load to flicker, the improvement comprising: a resistor-capacitor network connected in circuit with said inductor between said gate electrode and a given one of said main terminal electrodes to provide therethrough an output current to said gate electrode in response to the collapse of load current through said triac to prevent said triac from commutating into an off state during midcycle, whereby said lamp load is prevented from flickering.

Claim 10

In a switching circuit comprising a triac having first and second main terminal electrodes and a gate electrode; means for connecting said main terminal electrodes in circuit with an incandescent lamp load and an alternating current source; a time constant network responsive to said alternating current source and connected in circuit with said triac electrodes for controlling the phase angle at which said triac is switched into conduction; and a radio frequency interference suppression network comprising an inductor and a capacitor connected in circuit with said main terminal electrodes, wherein said suppression network and said triac form a resonant discharge circuit which is dependent upon the impedance of said incandescent lamp load for damping, and wherein the Q of said resonant circuit is above a critical level such that the oscillatorY current of said resonant discharge circuit would be sufficient to cause said triac to commutate into an off state during midcycle thereby causing said lamp load to flicker, the improvement comprising: a resistor-capacitor network connected in circuit with said inductor between said gate electrode and a given one of said main terminal electrodes to provide therethrough an output current to said gate electrode in response to the collapse of load current through said triac to prevent said triac from commutating into an off state during midcycle, whereby said lamp load is prevented from flickering.

Claim 11

In a circuit which includes a thyristor having main electrodes and a gate electrode, a load in circuit with said thyristor, connections for a source of power coupled to said load and thyristor, and an inductor-capacitor network in circuit with the thyristor and load forming a resonant therewith, and which circuit tends to be driven into oscillation at a frequency substantially higher than the power frequency when said thyristor is turned on by a turn-on signal applied to said gate electrode, said oscillations being at an amplitude sufficient intermittently to turn off said thyristor, a circuit for lessening said tendency of said thyristor intermittently to turn off comprising: a feedback path which exhibits a relatively low impedance at the frequency of said oscillations and a relatively high impedance at the power frequency, said feedback path being connected in circuit with said inductor between said gate electrode and a given one of said main electrodes to provide therethrough a signal to said gate electrode in response to the collapse of load current through said thyristor which signal tends to maintain said thyristor in its conducting state when an oscillation across said main electrodes tends to drive said thyristor to cut off.

Claim 12

In a circuit which includes a thyristor having main electrodes and a gate electrode, a load in circuit with said thyristor, connections for a source of power coupled to said load and thyristor, and an inductor-capacitor network in circuit with the thyristor and load forming a resonant therewith, and which circuit tends to be driven into oscillation at a frequency substantially higher than the power frequency when said thyristor is turned on by a turn-on signal applied to said gate electrode, said oscillations being at an amplitude sufficient intermittently to turn off said thyristor, a circuit for lessening said tendency of said thyristor intermittently to turn off comprising: a feedback path which exhibits a relatively low impedance at the frequency of said oscillations and a relatively high impedance at the power frequency, said feedback path being connected in circuit with said inductor between said gate electrode and a given one of said main electrodes to provide therethrough a signal to said gate electrode in response to the collapse of load current through said thyristor which signal tends to maintain said thyristor in its conducting state when an oscillation across said main electrodes tends to drive said thyristor to cut off.

Claim 13

In a circuit as set forth in claim 8, said feedback circuit comprising a resistor of relatively low value in series with a capacitor.

Claim 14

In a circuit as set forth in claim 8, the means for turning on said thyristor comprising a phase delay network coupled to said connections and a triggering device connected between said phase delay network and said gate electrode, said feedback path being connected between said inductor and a circuit point intermediate said triggering device and said gate electrode.