Gate drive for thyristors at high potentials

Claim 2

A circuit for driving the gate of a controllable element, said circuit comprising an energy transferring means, said energy transferring means isolating the potential of the energy receiving components from the energy supplying components, switching means which controls the energy transferred to the gate of said controllable element from said energy transferring means, said switching means comprising solid state amplifying elements which are powered from energy transferred by said energy transferring means, activating means for activating said switching means, said activating means comprising a source of electromagnetic radiation and a means for detecting electromagnetic radiation, a gating network having a first and a second state, said network being switched from the first state to the second state by said switching means, said gating network providing during the first state a voltage across the gate which is being driven which will permit conduction of the controllable element, and said gating network providing during the second state a reverse bias voltage across the gate which is being driven which will prohibit conduction of the controllable element.

Claim 3

The circuit of claim 1 wherein the energy transferring means comprises a first and a second current transformer, said transformers each having a prImary or high current winding and a secondary or low current winding, said primary windings of said first and second transformers being electrically connected, said secondary winding of said first transformer being connected to means creating a substantially constant current through said secondary winding of said first transformer, said secondary winding of said second transformer being center tapped and connected to rectifying means.

Claim 4

The circuit of claim 1 wherein the means for detecting electromagnetic energy comprises a photosensitive diode.

Claim 5

The circuit of claim 2 wherein the means creating a substantially constant current through said secondary winding of said first transformer comprises a magnetic frequency multiplier, inductive and capacitive elements serially connected across the output of said magnetic frequency multiplier, said secondary winding of said first transformer being connected across said capacitive element.

Claim 6

The circuit of claim 2 wherein the gating network comprises a first and a second current path, said first path being between the positive potential terminal of the rectifying means and the center tap of the secondary winding of the second transformer, said second path being between the center tap of the secondary winding of the second transformer and the negative potential terminal of the rectifying means, said first path having two intermediate terminals, an avalanche diode and the gating electrode of the controllable element being serially connected between said intermediate terminals of said first path, the switching means being connected between said intermediate terminals of said first path, said switching means providing a current path which bypasses the gating electrode and said avalanche diode when the switching means is activated, said second path having two intermediate terminals, a diode and the gating electrodes of the controllable element being connected in parallel between said intermediate terminals of said second path, said intermediate terminals of said second path having a voltage therebetween which reverse biases the controllable element when the switching means is not activated.

Claim 7

A circuit for driving the gate electrode of a controllable element, said circuit comprising a magnetic frequency multiplier having input and output terminals, a first inductor and a capacitor serially connected across said output terminals, a first current transformer having a low current and a high current winding, said low current winding being connected across said capacitor, a second current transformer with a low current and a high current winding, said high current windings of said first and second current transformers being connected together, said low current winding of said second current transformer having two output terminals and a center tap terminal, a full wave bridge rectifying means connected between said output terminals thereby providing a positive potential terminal and a negative potential terminal, a circuit connected between said positive potential terminal and said center tap terminal, said circuit connected between said positive potential terminal and said center tap terminal comprising the combination of a second inductor, a first resistor and an avalanche diode connected in series with each other and in series circuit relationship with a parallel circuit comprising a diode and the gating electrode of said controllable element, a second resistor connected between said negative potential terminal and a terminal between said avalanche diode and said parallel combination of the diode and the gating electrode of the controllable element, switching means comprising a cascade transistor circuit which derives its operating power from the DC voltage provided by said rectifying means, said switching means having two output terminals, one of said output terminals being connected to said center tap terminal, the other said output terminal being connected to a terminal between said avalanche diode and said first resistoR, and said switching means comprising a photosensitive diode which is irradiated by electromagnetic energy to control the activation of said switching means.

Claim 8

A circuit for driving the gate electrode of a controllable element, said circuit comprising a magnetic frequency multiplier having input and output terminals, a first inductor and a capacitor serially connected across said output terminals, a first current transformer having a low current and a high current winding, said low current winding being connected across said capacitor, a second current transformer with a low current and a high current winding, said high current windings of said first and second current transformers being connected together, said low current winding of said second current transformer having two output terminals and a center tap terminal, a full wave bridge rectifying means connected between said output terminals thereby providing a positive potential terminal and a negative potential terminal, a circuit connected between said positive potential terminal and said center tap terminal, said circuit connected between said positive potential terminal and said center tap terminal comprising the combination of a second inductor, a first resistor and an avalanche diode connected in series with each other and in series circuit relationship with a parallel circuit comprising a diode and the gating electrode of said controllable element, a second resistor connected between said negative potential terminal and a terminal between said avalanche diode and said parallel combination of the diode and the gating electrode of the controllable element, switching means comprising a cascade transistor circuit which derives its operating power from the DC voltage provided by said rectifying means, said switching means having two output terminals, one of said output terminals being connected to said center tap terminal, the other said output terminal being connected to a terminal between said avalanche diode and said first resistoR, and said switching means comprising a photosensitive diode which is irradiated by electromagnetic energy to control the activation of said switching means.

Claim 9

Alternating current tap changing apparatus comprising the gate electrode driving circuit of claim 6, a transformer having a tapped winding, controllable rectifying elements connecting said tapped winding to a load, at least one of said controllable rectifying elements being gated by said gate driving circuit.