A direct current (DC) circuit breaker for power transmission or distribution system includes a current sensor for sensing current of a system, a controller, a physical switch, and multiple switch modules. The multiple switch modules are electrically coupled to the current sensor and the physical switch in series. Each switch module includes multiple base elements electrically coupled in parallel. Each base element includes a first silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) and a second SiC MOSFET electrically coupled in an opposite series connection mode. The first and second SiC MOSFETs are configured in a synchronous rectification mode by channel reverse conduction control. The controller controls the multiple switch modules to connect current in the system, and break current of the multiple switch modules according to sensed current signals from the current sensor.

A relay circuit, including a solid state relay switch, connected to a first relay line and to a charging capacitor, and connected to a second relay line. The relay circuit may also include a solid state relay control circuit, coupled between the charging capacitor and the solid state relay switch. The solid state relay control circuit may include a voltage detection circuit, having an input coupled to an output of the charging capacitor, and having an output arranged to generate a LOW voltage signal when a voltage level of the charging capacitor is below a low threshold value. The solid state relay control circuit may also include a zero crossing circuit, coupled to the first relay line and the second relay line, and having an output to generate a clock signal when a zero crossing event takes place between the first relay line and the second relay line.

A power switching device includes a primary power source, a backup power source, and a power switching circuit, and the power switching circuit can switch rapidly between the two or more power sources. The power switching circuit includes a first switching module, a second switching module, and a control module. The first switching module includes first through fourth relays, and first through fourth driving units. The first switching module also includes a first bidirectional thyristor and a second bidirectional thyristor. A power switching circuit is also provided.

A power switching device includes a primary power source, a backup power source, and a power switching circuit, and the power switching circuit can switch rapidly between the two or more power sources. The power switching circuit includes a first switching module, a second switching module, and a control module. The first switching module includes first through fourth relays, and first through fourth driving units. The first switching module also includes a first bidirectional thyristor and a second bidirectional thyristor. A power switching circuit is also provided.

A power supply unit for use with thermostats or other like devices requiring power. A power supply unit may be designed to keep electromagnetic interference emissions at a minimum, particularly at a level that does not violate governmental regulations. A unit may be designed so that there is enough power for a triggering a switch at about a cross over point of a waveform of input power to the unit. Power for triggering may come from a storage source rather than line power to reduce emissions on the power line. Power for the storage source may be provided with power stealing. Power stealing may require switching transistors which can generate emissions. Gate signals to the transistors may be especially shaped to keep emissions from transistor switching at a minimum.

A power supply unit for use with thermostats or other like devices requiring power. A power supply unit may be designed to keep electromagnetic interference emissions at a minimum, particularly at a level that does not violate governmental regulations. A unit may be designed so that there is enough power for a triggering a switch at about a cross over point of a waveform of input power to the unit. Power for triggering may come from a storage source rather than line power to reduce emissions on the power line. Power for the storage source may be provided with power stealing. Power stealing may require switching transistors which can generate emissions. Gate signals to the transistors may be especially shaped to keep emissions from transistor switching at a minimum.

An electrical switch comprises a first terminal, a second terminal, a third terminal, a solid-state AC switch connected in an electrical path between the first terminal and the second terminal, and a microcontroller configured to control operation of the solid-state AC switch to control power flow between the first terminal and the second terminal. The microcontroller is configured to communicate with a second electrical switch over a data line that is connected to the third terminal of the electrical switch and to the second electrical switch, to implement multi-way switch control for controlling power to a load. The microcontroller is configured, upon power up, to perform a master/slave self-identification process to determine whether to operate the electrical switch in a master mode or a slave mode, based on sensing a voltage level on the data line that is connected to the third terminal of the electrical switch.

An electrical switch comprises a first terminal, a second terminal, a third terminal, a solid-state AC switch connected in an electrical path between the first terminal and the second terminal, and a microcontroller configured to control operation of the solid-state AC switch to control power flow between the first terminal and the second terminal. The microcontroller is configured to communicate with a second electrical switch over a data line that is connected to the third terminal of the electrical switch and to the second electrical switch, to implement multi-way switch control for controlling power to a load. The microcontroller is configured, upon power up, to perform a master/slave self-identification process to determine whether to operate the electrical switch in a master mode or a slave mode, based on sensing a voltage level on the data line that is connected to the third terminal of the electrical switch.

A thyristor switch is constituted of a pair of arms connected in anti-parallel, each of the arms including a plurality of thyristors connected in series. A controller includes a phase detecting unit configured to detect a phase of a power supply voltage supplied from an alternating-current power supply, and a gate signal generating unit configured to interrupt a gate signal when an open command is provided to the static switch and the phase of the power supply voltage detected by the phase detecting unit matches a target phase. The target phase is set outside of a phase range where interruption of the gate signal is prohibited, the phase range being set so as to include a zero crossing point at which a load current is switched in polarity.

Light-dimming device includes: first and second terminals; switch including switching device connected between terminals; adjuster for varying conduction angle of switch; controller for controlling switch and power supply module for supplying power to controller. Controller includes zero-cross detection circuit for detecting zero-cross of AC voltage, control circuit for generating PWM signal of on-duty ratio corresponding to conduction angle from adjuster, and driver circuit for turning device on and off by PWM signal. Controller allows device to conduct and then turn off within variable period of time, from start of half cycle of AC voltage, shorter than half cycle. Circuit starts generation of pulse in PWM signal when prescribed period of time, shorter than variable period of time, from zero-cross of voltage elapses.