Dual bimetal power control switching arrangement for electronically controlled appliances

A power control switching arrangement for selectively coupling a power signal from an external power supply to an electrical load in response to trigger signals from an external controller, said arrangement comprising:

• a first semiconductor switch means for coupling the power signal from the external power supply to the load, having a gate terminal, and being switched into conduction by a trigger signal at its gate terminal from the external controller;
• a first bimetal switch member operative to move when heated from a normally open position to a closed position;
• a second bimetal switch member operative to move when heated from a normally closed position to an open position;
• said first and second bimetal members being electrically connected in parallel circuit with said first semiconductor switch means to shunt said first semiconductor switch member when both bimetal members are in said closed positions;
• first heater means arranged for electical connection electrically connected in parallel circuit with the load operative when energized to heat said first bimetal member;
• second heater means electrically connected in series circuit with a second semiconductor switch means, and arranged for electrical connection across the power supply, operative when energized to heat said second bimetal member, said second semiconductor switch means having a gate terminal and being switched into conduction by a trigger signal from the controller applied to its gate terminal;
• whereby a trigger signal at the gate of said first semiconductor switch means enables energization of the load and said first heater means, causing said first bimetal member to move to its closed position thereby shunting said first semiconductor switch means, and a trigger signal applied to the gate terminal of said second semiconductor switch means enables energization of said second heater means causing said second bimetal member to move to its open position thereby de-energizing the load, and de-energizing said first heater means to enable said first bimetal element to return to its normally open position.

A power control switching arrangement for selectively coupling a power signal from an external power supply to an electrical load in response to ON and OFF signals from an external controller, said arrangement comprising:

• first and second input power terminals for electrical connection to the external power supply;
• first and second output terminals for electrical connection across the load to be controlled;
• a pair of control terminals comprising an ON terminal and an OFF terminal for receiving ON and OFF control signals respectively from the external controller;
• manually operable main power ON/OFF switch means electrically connected at one side to said first power input terminal;
• a first power control triac electrically connecting the other side of said power switch means to said first output terminal, said first triac including a gate terminal electrically connected to said ON control terminal;
• a first bimetal switch member electrically connected at one side to the other side of said power switch, said first bimetal member being operative when heated to move from a normally open position to a closed position;
• a second bimetal switch member electrically connected at one side to said first output power terminal, said second bimetal member being operative when heated to move from a normally closed position to an open position;
• said first and second bimetal members being positioned to electrically connect said other side of said power switch means directly to said first power output terminal, thereby shunting said first semiconductor switch means when each bimetal member is in its closed position;
• first heater means electrically connected across said first and second power output terminals operative when energized to heat said first bimetal member;
• second heater means electrically conected in series with a second power control triac between said other side of said power switch means and said second output terminal, operative when energized to heat said second bimetal member;
• said second triac having a gate terminal electrically connected to said OFF input terminal;
• whereby when said power switch is actuated, an ON signal from the external controller enables energization of said first heater means causing said first bimetal member to move to its closed position effectively shunting said first triac until an OFF signal enables energization of said second heater means causing said second bimetal member to move to its open position thereby de-energizing the load and de-energizing said first heater means, enabling said first bimetal member to return to its normally open position where it remains until the next ON signal from the controller.