Solid-state ground-fault circuit interrupter

A ground-fault circuit interrupter for use between a single-phase electrical supply (101), having a line hot (103) and a line neutral (104), and, a two- terminal electrical load (806) connected from line hot to line neutral, the ground-fault circuit interrupter comprising:

• a) a switch (301) located in the line hot between the electrical supply and a first terminal of the load, and,
• b) the switch controlled by a switch controller (303), and,
• c) a first current sensor (201) located in the line hot in series with the first switch, and,
• d) a second current sensor (202) located in the line neutral between a second terminal of the load and the electrical supply, and,
• e) a microprocessor (206), programmed to receive a digital signal from each of the first current sensor and the second current sensor, and, to compare the digital signal from the first current sensor with the digital signal from the second current sensor, and, if the digital signals have a difference greater than a first pre-selected value, to determine a ground fault condition, and, to send a first fault signal to the switch controller, and, causing the switch controller to open the switch, and, thereby disconnect the electrical supply from the load, and,
• f) an AC to DC converter (205) providing power to the ground-fault circuit interrupter, and,
• g) wherein the switch comprises first (802) and second (803) series connected MOSFET devices, each MOSFET device having a drain terminal, a source terminal and a gate terminal, wherein the drain terminal of the first MOSFET device comprises an input terminal of the switch and the drain terminal of the second MOSFET device comprise an output terminal of the switch, and, the source terminals of the first and second MOSFET devices are interconnected at a first control point and the gate terminals of the first and second MOSFET devices are interconnected at a second control point, and a first control switch (1101) is interconnected between the first control point and the second control point, and a bias terminal (808, 810) is connected to the second control point through a second control switch (1102), and, a voltage regulator device (811) is connected between the bias terminal and the first control point, and, a capacitor (1003) is connected in parallel to the voltage regulator device, and, a first rectifier device (808) is connected from the input terminal to the bias terminal through a first current limiting resistor (807), and, a second rectifier device (810) is connected from the second terminal of the load to the bias terminal through a second current limiting resistor (809), and, the switch controller controls the first control switch and the second control switch such that the first control switch is closed when the second control switch is open and vice versa.

An electrical-fault circuit interrupter for use between a single-phase electrical supply (101), having a line hot (103)and a line neutral (104), and, a two-terminal electrical load (806), having a type of load, connected from line hot to line neutral, the electrical-fault circuit interrupter comprising:

• a) a switch (301) located in the line hot between the electrical supply and a first terminal of the load, and,
• b) the switch controlled by a switch controller (303), and,
• c) a first current sensor (201) located in the line hot between the electrical supply and the switch, the first current sensor producing a first digital waveform signal proportional to a current flowing through line hot, and,
• d) a second current sensor (202) located in the line neutral between a second terminal of the load and the electrical supply, the second current sensor producing a second digital waveform signal proportional to a current flowing through line neutral, and,
• e) a first voltage sensor (203) connected between line hot and line neutral and located between the electrical supply and the switch, the first voltage sensor producing a third digital waveform signal proportional to the voltage of the electrical supply, and,
• f) a second voltage sensor (204) connected between line hot and line neutral and located between the switch and the load, the second voltage sensor producing a fourth digital waveform signal proportional to the voltage at the load, and,
• g) a microprocessor (206), programmed to receive the digital waveform signals from each of the first current sensor, the second current sensor, the first voltage sensor, and, the second voltage sensor, the waveforms all sampled at frequencies optimized for detection of the type of load, and,
• h) to compare the digital waveform signals, and, to determine from that comparison at least one of:
• i) whether the difference in current through line hot and line neutral exceed a first pre-selected limit, thereby indicating a first fault condition, and, to send a first fault signal to the switch controller, causing the switch controller to open the switch and disconnect the load from the electrical supply, and,
• ii) whether the current through the load exceeds a second preselected limit, thereby indicating a second fault condition, and, to send a second fault signal to the switch controller, causing the switch controller to open the switch and disconnect the load from the electrical supply, and,
• i) wherein the switch comprises first (802) and second (803) series connected MOSFET devices, each MOSFET device having a drain terminal, a source terminal and a gate terminal, wherein the drain terminal of the first MOSFET device comprises an input terminal of the switch and drain terminal of the second MOSFET device comprise an output terminal of the switch, and, the source terminals of the first and second MOSFET devices are interconnected at a first control point and the gate terminals of the first and second MOSFET devices are interconnected at a second control point, and a first control switch (1101) is interconnected between the first control point and the second control point, and a bias terminal (808, 810) is connected to the second control point through a second control switch (1102), and, a voltage regulator device (811) is connected between the bias terminal and the first control point, and, a capacitor (1003) is connected in parallel to the voltage regulator device, and, a first rectifier device (808) is connected from the input terminal to the bias terminal through a first current limiting resistor (807), and, a second rectifier device (810) is connected from the second terminal of the load to the bias terminal through a second current limiting resistor (809), and, the switch controller controls the first control switch and the second control switch such that the first control switch is closed when the second control switch is open and vice versa.