Thyristor gating circuits

Claim 2

A gating circuit for controlling the operation of a thyristor, including an output circuit, and circuit means operable to apply to said output circuit a control pulse having an initial peaked portion of one polarity for firing said thyristor, a second portion of substantially constant current and of said one polarity for maintaining conduction in said thyristor, a third portion of substantially constant current and of reverse polarity for maintaining the thyristor cutoff during a required period of nonconduction of the thyristor. said circuit means including a resistor and two transistors connected in series between opposite polarity power supplies, and a capacitor shunting said resistor with said control pulse being derived from a junction in the series circuit intermediate the transistors.

Claim 3

A circuit according to claim 1 in which said circuit means includes at least one network for developing said initial peaked portion of said control pulse, first and second supply means for providing said constant current of said one polarity and said other polarity, respectively, and switching means operable to select the required one of said supply means for connection to the output circuit.

Claim 4

A circuit according to claim 2, in which said switching means includes first and second switching devices connected, respectively, between said output circuit and said first supply means and between said output circuit and said second supply means, and in which two of said networks are connected, respectively, in the circuits of the switching devices.

Claim 5

A circuit according to claim 3, in which each said network comprises a RC network.

Claim 6

A circuit according to claim 3, in which said switching means includes a bistable circuit which operates said switching devices alternately.

Claim 7

A gating circuit for applying an operating pulse to a thyristor, including an output circuit, control means for developing first and second control signals, a bistable circuit operable to assume one or other states of conduction in dependence on the first and second signals respectively, pulse shaping means effective to apply to said output circuit an initial peaked portion of said operating pulse for firing said thyristor, a constant current stage operable in response to said one state of the bistable circuit to apply to the output circuit a substantially constant current second portion of said operating pulse for maintaining conduction in the thyristor, and operable in response to said other state of the bistable circuit to apply to the output circuit a substantially constant current third portion of said operating pulse, said third portion being of reversed polarity to maintain the thyristor cutoff during a required period of nonconduction of the thyristor, and control means to apply said first and second signals to the bistable circuit so that said initial, second and third portions together from a continuous control pulse.

Claim 8

A gating circuit for applying an operating pulse to a thyristor, including an output circuit, control means for developing first and second control signals, a bistable circuit operable to assume one or other states of conduction in dependence on the first and second signals respectively, pulse shaping means effective to apply to said output circuit an initial peaked portion of said operating pulse for firing said thyristor, a constant current stage operable in response to said one state of the bistable circuit to apply to the output circuit a substantially constant current second portion of said operating pulse for maintaining conduction in the thyristor, and operable in response to said other state of the bistable circuit to apply to the output circuit a substantially constant current third portion of said operating pulse, said third portion being of reversed polarity to maintain the thyristor cutoff during a required period of nonconduction of the thyristor, and control means to apply said first and second signals to the bistable circuit so that said initial, second and third portions together from a continuous control pulse.

Claim 9

A circuit according to claim 6, in which sAid constant current stage includes two transistor switching circuits for selecting the polarity of the output of said stage, and in which the pulse shaping means includes two RC networks connected, respectively, in the transistor switching circuits.