Dimmer switch for use with lighting circuits having three-way switches

A dimmer switch adapted to be coupled to a circuit including an AC power source, a load, a first single-pole double-throw switch, and a second single-pole double-throw switch, the first three-way switch comprising a first fixed contact, a second fixed contact, and a movable contact adapted to be coupled to the power source, the second three-way switch comprising a first fixed contact, a second fixed contact, and a movable contact adapted to be coupled to the load, the first and second three-way switches each having a first state in which the movable contact is contacting the first fixed contact and a second state in which the movable contact is contacting the second fixed contact, the dimmer switch comprising:

• a first load terminal adapted to be coupled to the first fixed contact of the first three-way switch;
• a second load terminal adapted to be coupled to the second fixed contact of the first three-way switch;
• a third load terminal adapted to be coupled to the first fixed contact of the second three-way switch;
• a fourth load terminal adapted to be coupled to the second fixed contact of the second three-way switch
• a controllably conductive device electrically coupled between the first load terminal and the third load terminal for conducting a load current to the load;
• a first sensing device coupled between the first load terminal and the second load terminal and adapted to carry the load current through the second load terminal, the first sensing device operable to sense a first electrical characteristic associated with the second load terminal;
• a second sensing device coupled between the third load terminal and the fourth load terminal and adapted to carry the load current through the fourth load terminal, the second sensing device operable to sense a second electrical characteristic associated with the fourth load terminal;
• and
• a controller operably coupled to the controllably conductive device and to the first and second sensing devices for controlling the controllably conductive device in response to the first and second electrical characteristics;
• wherein the controller is operable to control the amount of power delivered to the load by controlling the controllably conductive device to conduct the load current through the first load terminal when the first three-way switch is in the first state, through the second load terminal when the first three-way switch is in the second state, through the third load terminal when the second three-way switch is in the first state, and through the fourth load terminal when the second three-way switch is in the second state.

A method for controlling a load in a circuit comprising a power source, the load, a dimmer switch, and a single-pole double-throw three-way switch, the three-way switch comprising a first fixed contact, a second fixed contact, and a movable contact adapted to be coupled to either the power source or the load, the three-way switch having a first state in which the movable contact is contacting the first fixed contact and a second state in which the movable contact is contacting the second fixed contact, the method comprising the steps of:

• providing a first load terminal on the dimmer switch, the first load terminal adapted to be coupled to either the power source or the load to which the three-way switch is not coupled for conducting a load current through the load;
• providing a second load terminal on the dimmer switch, the second load terminal adapted to be coupled to the first fixed contact of the three-way switch;
• providing a third load terminal on the dimmer switch, the third load terminal adapted to be coupled to the second fixed contact of the three-way switch;
• electrically coupling a first controllably conductive device between the first and second load terminals, such that the first controllably conductive device is operable to conduct the load current through the second load terminal when the three-way switch is in the first state;
• electrically coupling a second controllably conductive device between the first and third load terminals, such that the second controllably conductive device is operable to conduct the load current through the third load terminal when the three-way switch is in the second state;
• and
• controlling the first and second controllably conductive devices between the conductive state and the non-conductive state, so as to control the amount of power delivered to the load.

A system for supplying power from an AC power source to a load comprising:

• a first single-pole double-throw three-way switch comprising a first fixed contact, a second fixed contact, and a first movable contact adapted to be coupled to the power source, the first three-way switch having a first state in which the first movable contact is contacting the first fixed contact and a second state in which the first movable contact is contacting the second fixed contact;
• a second three-way switch comprising a third fixed contact, a fourth fixed contact, and a second movable contact adapted to be coupled to the load, the second three-way switch having a third state in which the second movable contact is contacting the third fixed contact and a fourth state in which the second movable contact is contacting the fourth fixed contact;
• and
• a dimmer switch comprising a first load terminal coupled to the first fixed contact of the first three-way switch, a second load terminal coupled to the second fixed contact of the first three-way switch, a third load terminal coupled to the third fixed contact of the second three-way switch, and a fourth load terminal coupled to the fourth fixed contact of the second three-way switch;
• wherein the dimmer switch is operable to control the power delivered to the load.