Gate turnoff thyristor control circuit with shorted gate detection
First Claim
1. A system for responding to a shorted gate in a gate turnoff thyristor to which alternative turn on and turnoff signals are applied, the turnoff signal being supplied by means of a controllable switch connected between the gate electrode of the thyristor and a control voltage terminal having a negative potential with respect to the cathode potential of the thyristor, the controllable switch having a control terminal coupled to control means that in normal operation causes the switch to conduct negative gate current from the thyristor gate to the control voltage terminal in response to a thyristor turnoff command and to not conduct such current in response to a thyristor turn on command, the control means comprising:
- first means coupled to the controllable switch and having alternative first and second output states, the first output state being true if negative gate current being conducted by the switch exceeds a predetermined threshold magnitude that is less than a lowest peak magnitude needed to turn off the thyristor but greater than a magnitude normally conducted after the thyristor is turned off, the second output state being true otherwise;
second means, operatively connected to the control means, for causing the switch to stop conducting negative gate current in response to the first output state of the first means being true; and
third means, operatively connected to the control means, for delaying operation of the second means until the end of a predetermined interval following the start of the thyristor turnoff command, thereby ensuring that the control means continues to cause the switch to conduct negative gate current throughout the interval.
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Accused Products
Abstract
For responding to a shorted gate in a gate turnoff thyristor the gate electrode of which is connected by means of a controllable switch to a control voltage terminal having a negative potential with respect to the cathode potential of the thyristor, the controllable switch being arranged to conduct negative gate current in response to a thyristor turnoff command, voltage comparing means is coupled to the controllable switch for detecting when the switch is conducting negative gate current of relatively high magnitude, timing means is active for a predetermined interval following the start of said thyristor turnoff command, and logic means is operative to cause the switch to stop conducting negative gate current if the voltage comparing means detects high gate current at the end of such interval.
19 Citations
14 Claims
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1. A system for responding to a shorted gate in a gate turnoff thyristor to which alternative turn on and turnoff signals are applied, the turnoff signal being supplied by means of a controllable switch connected between the gate electrode of the thyristor and a control voltage terminal having a negative potential with respect to the cathode potential of the thyristor, the controllable switch having a control terminal coupled to control means that in normal operation causes the switch to conduct negative gate current from the thyristor gate to the control voltage terminal in response to a thyristor turnoff command and to not conduct such current in response to a thyristor turn on command, the control means comprising:
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first means coupled to the controllable switch and having alternative first and second output states, the first output state being true if negative gate current being conducted by the switch exceeds a predetermined threshold magnitude that is less than a lowest peak magnitude needed to turn off the thyristor but greater than a magnitude normally conducted after the thyristor is turned off, the second output state being true otherwise; second means, operatively connected to the control means, for causing the switch to stop conducting negative gate current in response to the first output state of the first means being true; and third means, operatively connected to the control means, for delaying operation of the second means until the end of a predetermined interval following the start of the thyristor turnoff command, thereby ensuring that the control means continues to cause the switch to conduct negative gate current throughout the interval. - View Dependent Claims (2, 3, 4)
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5. A system for responding to a shorted gate in a gate turnoff thyristor to which alternative turn on and turnoff signals are applied, the turnoff signal being supplied by means of a controllable switch connected between the gate electrode of the thyristor and a control voltage terminal having a negative potential with respect to the cathode potential of the thyristor, the controllable switch having a control terminal coupled to control means that in normal operation causes the switch to conduct negative gate current from the thyristor gate to the control voltage terminal in response to a thyristor turnoff command and to not conduct such current in response to a thyristor turn on command, the control means comprising:
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first means coupled to the controllable switch and having alternative first and second output states, the first output state being true if the voltage across the switch exceeds a predetermined magnitude and the second output state being true otherwise, the predetermined magnitude being attained whenever the switch is conducting negative gate current of relatively high magnitude; second means, operatively connected to the control means, for causing the switch to stop conducting negative gate current in response to the first output state of the first means being true; and third means also, operatively connected to the control means, for delaying operation of the second means until the end of a predetermined interval following the start of the thyristor turnoff command, thereby ensuring that the control means continues to cause the switch to conduct negative gate current throughout the interval.
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6. A gate turnoff thyristor control circuit comprising:
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a gate turnoff thyristor operatively connected between a source of electric power and an electrical load circuit and having alternative first and second states, in its first state the thyristor having negligible resistance in the path of load current and in its second state being effective to decouple the source from the load circuit; control means for changing the thyristor from first to second states in response to a turnoff command being received by the control means and for returning the thyristor to its first state in response to an alternative turn on command being received (;
), the control means including a controllable switch connected between the gate electrode of the thyristor and a control voltage terminal having a negative potential with respect to the cathode potential of the thyristor, during normal operation the controllable switch conducting negative gate current from the thyristor gate to the control voltage terminal in response to the turnoff command and not conducting such current in response to the turn on command;comparing means coupled to the controllable switch and having alternative first and second output states, the first output state being true if the voltage across the switch exceeds a predetermined magnitude and the second output state being true otherwise, the predetermined magnitude being attained only when negative gate current being conducted by the switch has a threshold magnitude that is less than a lowest peak magnitude needed to turn off the thyristor but greater than a magnitude normally conducted when the thyristor is in its second state; and logic means coupled to the comparing means and effective only when the control means is receiving the turnoff command for indicating whether or not the first output state of the comparing means is true. - View Dependent Claims (7, 8)
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9. A method for responding to a turn-off failure of a gate turnoff thyristor having an anode, a cathode, and a gate electrode, the gate electrode being connected by means of a controllable switch to a control voltage terminal having a negative potential with respect to the thyristor'"'"'s cathode potential, comprising the steps of:
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normally responding to a thyristor turnoff command by turning on the controllable switch; detecting when the switch is conducting gate current of relatively high magnitude; and indicating the coexistence of high gate current and the thyristor turnoff command. - View Dependent Claims (10, 11)
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12. A system for responding to a turn-off failure of a gate turnoff thyristor having an anode, a cathode, and a gate electrode, the gate electrode being operatively connected to a control voltage terminal by a controllable switch, the control voltage terminal having a negative potential relative to the thyristor'"'"'s cathode potential, the system comprising:
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means for normally responding to a thyristor turnoff command by turning on the controllable switch; means, operatively connected to the responding means, for detecting when the switch is conducting gate current of relatively high magnitude; and means, operatively connected to the detection means, for indicating the coexistence of high gate current and the thyristor turnoff command. - View Dependent Claims (13, 14)
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Specification