Switching circuit having delay for inrush current protection

A two-wire switching circuit for controlling the power delivered from an AC power source to an electrical load, the switching circuit comprising:

• a mechanical air-gap switch adapted to be coupled in series electrical connection between the AC power source and the electrical load;
• a controllably conductive device having a control input, the controllably conductive device operable to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in a first position;
• a delay circuit coupled in parallel electrical connection with the controllably conductive device and in series electrical connection with the mechanical air-gap switch;
• and
• a latching circuit coupled to the control input of the controllably conductive device for controlling the controllably conductive device to be conductive, the latching circuit responsive to the delay circuit to control the controllably conductive device to be conductive after a first predetermined time from when the mechanical air-gap switch changes to the first position.

A two-wire switching circuit for controlling the power delivered to an electrical load from an AC source voltage of an AC power source, the switching circuit comprising:

• a mechanical air-gap switch adapted to be coupled in series electrical connection between the AC power source and the electrical load;
• a delay circuit coupled in series electrical connection with the mechanical air-gap switch when the mechanical switch is in a first position, the delay circuit operable to conduct a control current through the mechanical switch when the mechanical switch is in the first position;
• and
• a controllably conductive device having a control input and coupled in parallel electrical connection with the delay circuit, the controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the controllably conductive device operable to become conductive in response to the control current to conduct the load current through the mechanical switch when the mechanical switch is in the first position;
• wherein when the mechanical air-gap switch is in the first position, substantially all of the AC source voltage is provided to the load.

A load control device for controlling the power delivered from an AC power source to an electrical load, the load control device comprising:

• a mechanical air-gap switch adapted to be coupled in series electrical connection between the AC power source and the electrical load;
• an actuator operable to actuate the mechanical air-gap switch;
• a turn-on delay circuit adapted to be coupled in series electrical connection with the mechanical air-gap switch when the mechanical switch is in a first position, the turn-on delay circuit operable to conduct a control current through the mechanical air-gap switch when the mechanical switch is in the first position;
• a controllably conductive device having a control input and coupled in parallel electrical connection with the turn-on delay circuit, the controllably conductive device adapted to be coupled in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position, the controllably conductive device operable to change from a non-conductive state to a conductive state in response to the turn-on delay circuit after a first predetermined time from when the mechanical air-gap switch changes to the first position;
• and
• a latching circuit coupled to the turn-on delay circuit and the control input of the controllably conductive device, the latching circuit responsive to the turn-on delay circuit to control the controllably conductive device to the conductive state after the first predetermined time from when the mechanical air-gap switch changes to the first position, such that the controllably conductive device stays latched in the conductive state;
• wherein the mechanical air-gap switch and the first controllably conductive device are operable to conduct the load current when in the first position.

A method for controlling the power delivered to an electrical load from an AC power source, the method comprising:

• switching a mechanical switch to a first position;
• beginning to conduct a control current through the mechanical switch in response to switching the mechanical switch to the first position;
• coupling a first controllably conductive device in series electrical connection between the AC power source and the electrical load when the mechanical switch is in the first position;
• controlling the first controllably conductive device to a conductive state after a first predetermined time from the beginning of the conduction of the control current through the mechanical switch;
• subsequently conducting a load current through the mechanical switch;
• and
• latching the first controllably conductive device in the conductive state such that the first controllably conductive device is subsequently maintained conductive each half-cycle of the AC power source.