# US 2018/0172734 A1 · Current sense overload limiting circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0172734 A1 - Document ID: US20180172734A1 - Status: Published application - Kind: A1 - Application number: 15/846,543 - Filed: 2017-12-19 - Published: 2018-06-21 - Earliest claimed: 2016-12-21 - Assignees: QualiTau, Inc. - Inventors: James Borthwick - Web page: https://patentgrep.com/patent/US20180172734A1 ## CPC - G01R 1/36: Overload-protection arrangements or circuits for electric measuring instruments - H02H 1/0007: {concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445)} - H02H 9/04: responsive to excess voltage (lightning arrestors H01C7/12, H01C8/04, H01G9/18, H01T) - G01R 31/31924: {Voltage or current aspects, e.g. driver, receiver} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - 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 A voltage limiting circuit for limiting the voltage developed across a current sensing circuit and a method are disclosed. The voltage limiting circuit includes an input terminal configured to receive an input signal from the current sensing circuit, and an output terminal configured to receive an output signal from the current sensing circuit. A voltage sense circuit is connected to the input terminal and output terminal to detect that a predefined threshold voltage is developed between the input terminal and output terminal. An activation circuit receives a signal from the voltage sense circuit to activate the voltage limiting circuit, and a level shifting circuit interfaces the voltage sense circuitry to the activation circuitry and other circuits by level shifting signals to required levels. ## Claims ### Claim 1 A voltage limiting circuit for limiting the voltage developed across a current sensing circuit, the voltage limiting circuit comprising: an input terminal configured to receive an input signal from the current sensing circuit; an output terminal configured to receive an output signal from the current sensing circuit; a voltage sense circuit configured to detect that a predefined threshold voltage is developed between the input terminal and output terminal; a level shifting circuit configured to level shift signals; and an activation circuit configured to activate the voltage limiting circuit. ### Claim 2 (depends on 1) The voltage limiting circuit of claim 1, wherein the level shifting circuit comprises a first and second optoisolator configured to shift voltage levels of signals. ### Claim 3 (depends on 1) The voltage limiting circuit of claim 1, wherein the input terminal and output terminal are connected in parallel to a resistor network. ### Claim 4 (depends on 3) The voltage limiting circuit of claim 3, wherein the resistor network is configured to provide current sense elements for a multi-decade current sensing circuit. ### Claim 5 (depends on 3) The voltage limiting circuit of claim 3, wherein the voltage limiting circuit limits the voltage generated across the resistor network in an overload condition. ### Claim 6 (depends on 1) The voltage limiting circuit of claim 1, wherein the voltage sense circuit comprises one or more programmable threshold field effect transistors configured to conduct current at a predetermined threshold voltage. ### Claim 7 (depends on 1) The voltage limiting circuit of claim 1, further comprising a latch circuit configured to latch a state of the voltage limiting circuit. ### Claim 8 (depends on 7) The voltage limiting circuit of claim 7, wherein the latch circuit latches in accordance with a current through the voltage limiting circuit exceeding a predetermined threshold. ### Claim 9 (depends on 1) The voltage limiting circuit of claim 1, wherein the activation circuit comprises first and second shunting transistors. ### Claim 10 (depends on 9) The voltage limiting circuit of claim 9, wherein the first and second shunting transistors are also used with circuitry not related to the voltage limiting circuit. ### Claim 11 A method of limiting voltage developed across a current sensing circuit using a voltage limiting circuit, the method comprising: receiving at an input terminal an input signal from the current sensing circuit; receiving at an output terminal an output signal from the current sensing circuit; detecting by a voltage sense circuit that a predefined threshold voltage is developed between the input terminal and output terminal; level shifting signals; and activating the voltage limiting circuit to shunt current from the current sensing circuit. ### Claim 12 (depends on 11) The method of claim 11, wherein the input terminal and output terminal are connected in parallel to a resistor network. ### Claim 13 (depends on 12) The method of claim 12, wherein the resistor network is configured to provide current sense elements for a multi-decade current sensing circuit. ### Claim 14 (depends on 13) The method of claim 13, wherein the voltage limiting circuit limits the voltage generated across the resistor network in an overload condition. ### Claim 15 (depends on 11) The method of claim 11, wherein the voltage sense circuit comprises a programmable threshold field effect transistor configured to conduct current at a predetermined threshold voltage. ### Claim 16 (depends on 11) The method of claim 11, further comprising latching a latch circuit in accordance with a current through the voltage limiting circuit exceeding a predetermined threshold. ### Claim 17 (depends on 16) The method of claim 16, wherein latching the latch circuit provides a constant bias to a photovoltaic isolator.