Anti crow bar current interrupter for microwave tube transmitters
AssigneeThe United States of America as represented by the Secretary of the Air Force
InventorsWalter E. Milberger, Franklin B. Jones, Charles S. Kerfoot
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Abstract
A high-speed high-voltage FET current interrupter which opens the cathode circuit of microwave tubes when internal tube arcing occurs. By removing the detrimental fault current which causes degradation to the microwave tube body and grid, the longevity of the microwave tube and the pulse energy storage capacitor is greatly increased over those transmitters which use dissipative crow bar circuits. Even more important is that the transmitter reset time after an arc occurs is orders of magnitude faster than transmitters using crow bars or primary power interrupters when arcing occurs--an important feature when engaged in a "dog fight".
Claims10
Circuit protection apparatus for arc suppression in a system in which a high-voltage power supply has a storage capacitor connected across a pair of output terminals, with one of the output terminals coupled to a microwave tube for supplying several thousand volts to the tube, with fault current detector means including current sensor means connected in series between the power supply and said tube, for actuating the circuit protection apparatus upon detection of a fault current due to arcing in the microwave tube;
- the improvement wherein the circuit protection apparatus comprises switching means including high-speed high-voltage transistor means used as a current interrupter which opens the circuit between said storage capacitor and said tube in response to a signal from said fault current detector means upon detection of a fault current due to arcing in the microwave tube, with means for limiting the current through the switching means;
- wherein said switching means comprises a plurality of high-voltage field effect transistors (FETs), each FET having a source, a drain and a gate terminal, the FETs being connected in series, with the drain terminal of each FET except a first one connected to the source terminal of the next, each FET having a resistor connected between its source and drain electrodes, and a resistor connected between its gate and source electrodes;
- gate control means comprising transformer means having a plurality of ferrit toroidal cores with primary winding means contained in quartz glass tubing through a plurality of the toroidal cores, and a plurality of secondary windings, each wound on one of the toroidal cores, the secondary windings being coupled to the source and gate terminals of the FETs of said switching means to control the switching means to the On or Off state;
- wherein said fault current detector means comprises a threshold detector coupled to the current sensor means, and trigger means having an input coupled to an output of the threshold detector and having outputs coupled to the primary winding means of the gate control means.
Circuit protection apparatus for arc suppression in a system in which a high-voltage power supply has a storage capacitor connected across a pair of output terminals, with one of the output terminals coupled to a microwave tube for supplying several thousand volts to the tube, with fault current detector means including current sensor means connected in series between the power supply and said tube, for actuating the circuit protection apparatus upon detection of a fault current due to arcing in the microwave tube;
- the improvement wherein the circuit protection apparatus comprises switching means including high-speed high-voltage transistor means used as a current interrupter which opens the circuit between said storage capacitor and said tube in response to a signal from said fault current detector means upon detection of a fault current due to arcing in the microwave tube, with means for limiting the current through the switching means;
- wherein said switching means comprises a plurality of high-voltage field effect transistors (FETs), each FET having a source, a drain and a gate terminal, the FETs being connected in series, with the source terminal of each FET except a first one connected to the source terminal of the next, each FET having a resistor connected between its gate and drain electrodes, and a resistor connected between its gate terminal and the source terminal of the preceeding FET, the FETs being inner laced to provide a boot strap switch which is independent of all auxiliary bias and control circuits for its operation and is a normally on switch;
- wherein said fault current detector means is coupled to only the gate and source terminals of said first one of the FETs so that the switching means is automatically latched off when faults occur;
- wherein the microwave tube has a cathode to which said power supply is coupled via said switching means, wherein said fault current detector means is a d-c overload sensor circuit which causes the switching means to open when fault currents occur, the current sensor means being a current sense resistor connected between the source electrode of said first one of the FETs and said power supply, said fault current detector means also including an NPN and a PNP bi-polar transistor which causes the switching means to become a constant current source prior to latch up that causes the switching means to open.
Dependencies are inferred from the claim text.