# US 4,400,755 A · Overvoltage protection circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,400,755 A - Document ID: US4400755A - Status: Granted - Kind: A - Application number: 06/284,070 - Filed: 1981-07-16 - Granted: 1983-08-23 - Earliest claimed: 1981-07-16 - Assignees: General Electric Company - Inventors: Georges R. E. Lezan - Web page: https://patentgrep.com/patent/US4400755A ## CPC - H03K 17/0824: {in thyristor switches} - H02H 3/20: responsive to excess voltage - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) ## Abstract An overvoltage protection circuit for a circuit array including one or more semiconductor devices such as thyristors derives its energization solely from the voltage across the array. A unidirectional current is developed to respond to that voltage and this current is utilized to develop an electrical charge of not more than a predetermined magnitude. The unidirectional current is also utilized to develop a signal which is proportional to the voltage across the array. When this signal reaches a predetermined level, indicative of an overvoltage condition of the array, a switching current is rendered operative to cause the stored charge to be applied to the gating electrodes of the array semiconductor devices to thereby render each such device conductive. ## Claims ### Claim 1 An overvoltage protection circuit for a circuit array comprised of one or more semiconductor devices each having anode, cathode and gate electrodes, said array being connected intermediate a source of electrical power and a load and serving, upon the application of gating pulses to the gate electrodes, to deliver electrical power from the source to the load, said overvoltage protection circuit comprising: (a) means to provide a unidirectional current proportional to the instantaneous voltage across the array; (b) change storage means responsive to said unidirectional current to develop an electrical charge of a predetermined magnitude; (c) means responsive to said unidirectional current to develop a signal proportional to the instantaneous voltage across the array; and, (d) switch means, responsive to said signal, operative to discharge said charge storage means to thereby develop a firing signal for rendering each device of the array conductive. ### Claim 2 (depends on 1) The invention in accordance with claim 1 wherein said charge storage means includes a capacitor. ### Claim 3 (depends on 2) The invention in accordance with claim 2 wherein said switch means includes; (a) a cascade arrangement of first, second and third transistors; (b) diode means having a predetermined reverse breakdown voltage connecting said signal developing means to said first transistor to thereby render it conductive in response to said signal; (c) means interconnecting said first, second and third transistors whereby said second and third transistors are rendered conductive in response to the conduction of said first transistor; and, (d) latch circuit means innerconnecting said second and third transistors to provide a holding current to said third transistor. ### Claim 4 An overvoltage protection circuit for a circuit array comprised of one or more semiconductor devices each having anode, cathode and gate electrodes, said array being connected intermediate a source of electrical power and a load and serving, upon the application of gating pulses to the gate electrodes, to deliver electrical power from the source to the load, said overvoltage protection circuit comprising: (a) means connected across said circuit array for providing a unidirectional current as a result of the instantaneous voltage existing across the circuit array by virtue of the array's connection to the source of power; (b) charge storage means; (c) means for delivering said current to such charge storage mean whereby an electrical charge is developed and stored therein; (d) means for limiting the magnitude of said electrical charge; (e) signal developing means responsive to said current to develop a signal proportional thereto; and, (f) switch means responsive to a predetermined magnitude of said signal for discharging said charge storage means to thereby generate a gating signal for application to the gate electrodes of each semiconductor device of the array to thereby render each such device capable of conduction. ### Claim 5 (depends on 4) The invention in accordance with claim 4 wherein said means for limiting the magnitude for said charge includes a diode having a predetermined reverse breakdown voltage connected in a basically parallel relationship with said capacitor. ### Claim 6 (depends on 5) The invention in accordance with claim 5 wherein said diode is a Zener diode. ### Claim 7 (depends on 5) The invention in accordance with claim 5 wherein said signal developing means comprises resistive means connected in series with said diode. ### Claim 8 An overvoltage protection circuit for a plurality of series connected semiconductor devices comprising: (a) means to provide a unidirectional current proportional to the instantaneous voltage across the series connected semiconductor devices; (b) means including charge storage means responsive to said unidirectional current to develop a charge of a predetermined magnitude; (c) means responsive to said unidirectional current to develop a control signal proportional to the instantaneous voltage across the semiconductor devices; and, (d) switch means responsive to said control signal operative to discharge said charge storage means to thereby develop a firing signal for rendering each of said semiconductor devices conductive. ### Claim 9 An overvoltage protection circuit for a plurality of series connected semiconductor devices, each having a gate electrode, adapted to be rendered conductive by single firing pulse operative to apply simultaneous gating pulses to the individual gate electrodes of the semiconductor devices comprising: (a) means to provide a unidirectional current proportional to the instantaneous voltage across the series connected semiconductor devices; (b) charge storage means responsive to said unidirectional current to develop an electrical charge of a predetermined magnitude; (c) means responsive to said unidirectional current to develop a control signal proportional to the instantaneous voltage across the semiconductor devices; and, (d) switch means, responsive to said control signal, operative to discharge said charge storage means to thereby develop a firing signal for rendering of said semiconductor devices conductive.