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 conduction state of 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 which forms a resonant discharge circuit with said thyristor that is dependent upon the impedance of said 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 thyristor to commutate into an off state during midcycle.

Claim 4

The invention as defined in claim 1 wherein said thyristor comprises a triac having first and second main terminal electrodes and a gate electrode, and wherein said circuit means comprises a further time constant network connected between a given one of said main terminal electrodes and said gate electrode.

Claim 5

The invention as defined in claim 3 wherein said further time constant network 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 is switched into conduction; an interference suppression network 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 between a given one of said main terminal electrodes and said gate electrode, said circuit means operating to provide current to said gate electrode in response to a rate of change of voltage of greater than a critical value across said given terminal electrode and said gate electrode 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 is switched into conduction; an interference suppression network 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 between a given one of said main terminal electrodes and said gate electrode, said circuit means operating to provide current to said gate electrode in response to a rate of change of voltage of greater than a critical value across said given terminal electrode and said gate electrode 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 between a given one of said main terminal electrodes and said gate electrode, said network operating in response to a rate of rise of greater than a given value of the voltage across said gate electrode and said given terminal electrode to provide current to said gate electrode 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 between a given one of said main terminal electrodes and said gate electrode, said network operating in response to a rate of rise of greater than a given value of the voltage across said gate electrode and said given terminal electrode to provide current to said gate electrode 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 reactive elements in circuit with the thyristor and load forming a resonant circuit 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, connected between a main electrode of said thyristor at which said oscillations appear and said gate electrode, for feeding back to said gate electrode a signal which 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 reactive elements in circuit with the thyristor and load forming a resonant circuit 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, connected between a main electrode of said thyristor at which said oscillations appear and said gate electrode, for feeding back to said gate electrode a signal which 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 from said main electrode to a circuit point between said triggering device and said gate electrode.