Thyristor overvoltage protective circuit

Claim 2

An improved overvoltage triggering scheme for turning on at least a first main thyristor, said thyristor including a pair of main electrodes and a gating means, said main electrodes being adapted to be connected in an electric power circuit where they are periodically subjected to a forward bias voltage (anode potential positive with respect to cathode), said thyristor when forward biased being adapted to be turned on if either a trigger signal is applied to its gating means or the instantaneous magnitude of the forward bias voltage increases to a level sufficiently above a normally applied peak forward blocking voltage to cause a voltage breakover, wherein the improvement comprises: a. overvoltage sensing means; b. energy storing means; c. means for connecting said overvoltage sensing means and said energy storing means in series with each other and in parallel with said thyristor; and d. means for coupling the gating means of said thyristor to the juncture of said sensing and storing means; e. said overvoltage sensing means comprising at least one unidirectional conducting device poled to conduct current in the same direction as said main thyristor, said sensing means having a normal high-resistance state and being operative to switch abruptly to a low-resistance, current conducting state in high-speed response to the forward bias voltage on said thyristor attaining an overvoltage magnitude which is higher than said peak forward blocking voltage and lower than said breakover level; f. said energy storing means being arranged momentarily to impede any current increase therein when said sensing means first switches to its conducting state in response to an overvoltage condition, whereupon most of the current initially conducted by said sensing means is forced to supply said trigger signal for said gating means and said first main thyristor is quickly turned on by a sharp gate punch before its forward bias voltage can attain said breakover level.

Claim 3

The improvement of claim 1 in which said overvoltage sensing means has negligible capacitance.

Claim 4

The improvement of claim 1 in which said coupling means comprises a conductive connection including a resistor.

Claim 5

The improvement of claim 3 in which said overvoltage sensing means comprises an inductor connected in series with said unidirectional conducting device.

Claim 6

The improvement of claim 3 in which said energy storing means comprises a capacitor connected in series with an inductor.

Claim 7

The improvement of claim 5 in which said energy storing means is shunted by a resistor.

Claim 8

The improvement of claim 1 in which said unidirectional conducting device comprises a PNPN semiconductor element.

Claim 9

The improvement of claim 7 in which a plurality of PNPN semiconductor elements are serially interconnected in polarity agreement with one another to form said overvoltage sensing means.

Claim 10

The improvement of claim 7 in which said PNPN semiconductor element comprises: a. a semiconductor body having four layers arranged in succession with contiguous layers being of different conductivity types, whereby rectifying junctions are formed between contiguous layers of the body; b. a main current-carrying contact; c. means for connecting said contact to a predetermined end layer of said body; d. said predetermined end layer comprising a central main region joined to said contact, a first auxiliary region disposed adjacent to the lateral border of said main region, and a second auxiliary region disposed outboard with respect to Said first auxiliary region, all of said regions being contiguous with the intermediate layer of said body that adjoins said predetermined end layer; e. a ring of electroconductive material spaced apart from said contact and connected to said first auxiliary region; f. said second auxiliary region being characterized by a lateral resistance appreciably higher than the resistance between said ring and said contact; and g. said semiconductor body being so constructed and arranged that, when said overvoltage condition occurs, leakage current triggers a peripheral area thereof.

Claim 11

The improvement of claim 1 in which said overvoltage sensing means comprises a plurality of unidirectional conducting devices which are serially interconnected in polarity agreement with one another.

Claim 12

The improvement of claim 10 in which at least one of said unidirectional conducting devices comprises an auxiliary thyristor.

Claim 13

The improvement of claim 1 in which the gating means of said thyristor is adapted to be coupled to an external source of periodic trigger signals.

Claim 14

The improvement of claim 12 in which said coupling means comprises a conductive connection including an isolating diode in series with a resistor.

Claim 15

For triggering a switch having characteristics similar to those of a thyristor including a pair of main electrodes and control means adapted to receive a trigger signal, a circuit which comprises: a. a first terminal adapted to be connected to one of said main electrodes, a second terminal adapted to be connected to the other main electrode, and a third terminal; b. means for coupling said third terminal to the control means of said switch; c. a capacitor connected in series with an inductor between said second and third terminals; and d. at least two auxiliary thyristors serially interconnected in polarity agreement with one another between said first and third terminals, said auxiliary thyristors being arranged to turn on in a voltage breakover mode in response to forward bias voltage across the main electrodes of said switch increasing to a predetermined magnitude.

Claim 16

For triggering a switch having characteristics similar to those of a thyristor including a pair of main electrodes and control means adapted to receive a trigger signal, a circuit which comprises: a. a first terminal adapted to be connected to one of said main electrodes, a second terminal adapted to be connected to the other main electrode, and a third terminal; b. means for coupling said third terminal to the control means of said switch; c. a capacitor connected in series with an inductor between said second and third terminals; and d. at least two auxiliary thyristors serially interconnected in polarity agreement with one another between said first and third terminals, said auxiliary thyristors being arranged to turn on in a voltage breakover mode in response to forward bias voltage across the main electrodes of said switch increasing to a predetermined magnitude.

Claim 17

The triggering circuit of claim 14 wherein said switch comprises at least one main thyristor and said auxiliary thryistors are so selected that said predetermined voltage magnitude is lower than the level of forward bias voltage that can cause damage to said main thyristor.

Claim 18

An improved triggering scheme for turning on at least a first main thyristor having relatively large dimensions, said thyristor including a pair of main electrodes and a gating means, said main electrodes being adapted to be connected in an electric power circuit where they are subjected to a forward bias voltage which, if allowed to increase to a sufficiently high level, can cause a voltage breakover of said main thyristor, wherein the improvement comprises: a. voltage sensing means; b. energy storing means comprising a capacitor connected in series with an inductor; c. means for connecting said voltage sensing means and said energy storing means in series with each other and in parallel with said thyristor; and d. means for coupling the gating means of said thyristor to the juncture of said sensing and storing means; e. said voltage sensing means comprising a plurality of normally non-conductive overvoltage triggered controlled switching elements which are serially interconnected in polarity agreement with one another, each of said elements being smaller in size than said main thyristor and being operative to switch abruptly to a low-resistance, current conducting state in high-speed response to the voltage across that element reaching a value which is a predetermined fraction of the voltage existing across said sensing means when the forward bias voltage on said main thyristor attains a predetermined magnitude which is not as high as said breakover level.

Claim 19

An improved triggering scheme for turning on at least a first main thyristor having relatively large dimensions, said thyristor including a pair of main electrodes and a gating means, said main electrodes being adapted to be connected in an electric power circuit where they are subjected to a forward bias voltage which, if allowed to increase to a sufficiently high level, can cause a voltage breakover of said main thyristor, wherein the improvement comprises: a. voltage sensing means; b. energy storing means comprising a capacitor connected in series with an inductor; c. means for connecting said voltage sensing means and said energy storing means in series with each other and in parallel with said thyristor; and d. means for coupling the gating means of said thyristor to the juncture of said sensing and storing means; e. said voltage sensing means comprising a plurality of normally non-conductive overvoltage triggered controlled switching elements which are serially interconnected in polarity agreement with one another, each of said elements being smaller in size than said main thyristor and being operative to switch abruptly to a low-resistance, current conducting state in high-speed response to the voltage across that element reaching a value which is a predetermined fraction of the voltage existing across said sensing means when the forward bias voltage on said main thyristor attains a predetermined magnitude which is not as high as said breakover level.

Claim 20

The improvement of claim 16 in which said elements are auxiliary thyristors, at least two of Said auxiliary thryistors having forward voltage breakover values which differ from each other, and the sum of the individual voltage breakover values of all of said auxiliary thyristors being equal to 100 percent of the voltage existing across said sensing means when the forward bias voltage on said main thyristor attains said predetermined magnitude.

Claim 21

For protecting at least two duplicate main thyristors from overvoltage, said thyristors each having a pair of main electrodes and a gating means, with the corresponding main electrodes s of the respective thyristors being directly interconnected to form a parallel array of similarly poled thyristors, said array being adapted to be connected in a high-current electric power circuit where said thyristors are subject to voltage breakover if the instantaneous magnitude of forward bias voltage on said array increases to a sufficiently high level, the improvement comprising: a. overvoltage sensing means; b. energy storing means; c. means for connecting said overvoltage sensing means and said energy storing means in series with each other and in parallel with said array; and d. means for coupling the gating means of all of said thyristors to the juncture of said sensing and storing means; e. said overvoltage sensing means comprising at least one unidirectional conducting device poled to conduct current in the same direction as said main thyristors, said sensing means having a normal high-resistance state and being operative to switch abruptly to a low-resistance, current conducting state in response to the forward bias voltage on said array of thyristors attaining a predetermined overvoltage magnitude which is lower than said breakover level; f. said energy storing means being arranged momentarily to impede any current increase therein when said sensing means first switches to its conducting state in response to an overvoltage condition, whereupon most of the current initially conducted by said sensing means is forced to supply a trigger signal for said gating means and at least a first one of said main thyristors is quickly turned on by a sharp gate punch before its forward bias voltage can attain said breakover level, said energy storing means being further arranged to serve as a source of current which sustains said trigger signal after said first one of said thyristors is turned on, thereby generating a trigger signal of sufficient magnitude and duration to ensure successful turn-on of all of the thyristors in said array.

Claim 22

For protecting at least two duplicate main thyristors from overvoltage, said thyristors each having a pair of main electrodes and a gating means, with the corresponding main electrodes s of the respective thyristors being directly interconnected to form a parallel array of similarly poled thyristors, said array being adapted to be connected in a high-current electric power circuit where said thyristors are subject to voltage breakover if the instantaneous magnitude of forward bias voltage on said array increases to a sufficiently high level, the improvement comprising: a. overvoltage sensing means; b. energy storing means; c. means for connecting said overvoltage sensing means and said energy storing means in series with each other and in parallel with said array; and d. means for coupling the gating means of all of said thyristors to the juncture of said sensing and storing means; e. said overvoltage sensing means comprising at least one unidirectional conducting device poled to conduct current in the same direction as said main thyristors, said sensing means having a normal high-resistance state and being operative to switch abruptly to a low-resistance, current conducting state in response to the forward bias voltage on said array of thyristors attaining a predetermined overvoltage magnitude which is lower than said breakover level; f. said energy storing means being arranged momentarily to impede any current increase therein when said sensing means first switches to its conducting state in response to an overvoltage condition, whereupon most of the current initially conducted by said sensing means is forced to supply a trigger signal for said gating means and at least a first one of said main thyristors is quickly turned on by a sharp gate punch before its forward bias voltage can attain said breakover level, said energy storing means being further arranged to serve as a source of current which sustains said trigger signal after said first one of said thyristors is turned on, thereby generating a trigger signal of sufficient magnitude and duration to ensure successful turn-on of all of the thyristors in said array.

Claim 23

The improvement of claim 18 wherein each of said main thyristors has an anode and a cathode, and a first common heat sink is provided for the anodes of all of said main thyristors and a second common heat sink is provided for the cathodes of all of said main thyristors.

Claim 24

For protecting a plurality of main thyristors from overvoltage, said thyristors each having a pair of main electrodes and a gating means, with the main electrodes of the respective thyristors being interconnected in a series string which is adapted to be connected in a high-voltage electric power circuit, the improvement comprising an equal plurality of overvoltage triggering circuits respectively associated with said main thyristors, each of said circuits comprising: a. overvoltage sensing means; b. energy storing means; c. means for connecting said overvoltage sensing means and said energy storing means in series with each other and in parallel with the associated main thyristor; and d. means for coupling the gating means of said associated thyristor to the juncture of said sensing and storing means; e. said overvoltage sensing means having a normal high-resistance state and being operative to switch abruptly to a low-resistance, current-conducting state in response to forward bias voltage across the main electrodes of said associated thyristor increasing to a predetermined overvoltage magnitude; f. said energy-storing means being arranged momentarily to impede any Current increase therein once said sensing means first switches to its conducting state in response to an overvoltage condition, whereupon most of the current initially conducted by said sensing means is forced to supply a trigger signal for the gating means of said associated thyristor which is consequently turned on by a sharp gate punch.

Claim 25

For protecting a plurality of main thyristors from overvoltage, said thyristors each having a pair of main electrodes and a gating means, with the main electrodes of the respective thyristors being interconnected in a series string which is adapted to be connected in a high-voltage electric power circuit, the improvement comprising an equal plurality of overvoltage triggering circuits respectively associated with said main thyristors, each of said circuits comprising: a. overvoltage sensing means; b. energy storing means; c. means for connecting said overvoltage sensing means and said energy storing means in series with each other and in parallel with the associated main thyristor; and d. means for coupling the gating means of said associated thyristor to the juncture of said sensing and storing means; e. said overvoltage sensing means having a normal high-resistance state and being operative to switch abruptly to a low-resistance, current-conducting state in response to forward bias voltage across the main electrodes of said associated thyristor increasing to a predetermined overvoltage magnitude; f. said energy-storing means being arranged momentarily to impede any Current increase therein once said sensing means first switches to its conducting state in response to an overvoltage condition, whereupon most of the current initially conducted by said sensing means is forced to supply a trigger signal for the gating means of said associated thyristor which is consequently turned on by a sharp gate punch.