Resettable safety circuit for PTC electric blankets and the like
First Claim
1. A safety-assuring control device for an electric alternating current appliance which includes a heater having first and second heater feed conductors, said first heater feed conductor being connected to a protective fuse and connectable therethrough to an ungrounded pole of a source of electric alternating current and said second heater feed conductor being connected to an electrically controllable heater switch and connectable therethrough to a grounded pole of said source of electric alternating current, said first and second heater feed conductors, at respective ends remote from said fuse and from said heater switch, being respectively connected to primary and secondary safety link return conductors which lead towards respective connections thereof in said control device, said primary safety link conductor being connected with said secondary safety link conductor, said control device comprising:
- an integrated circuit microcontroller unit including;
a first safety circuit input,a second safety circuit input, andan output connected to a control input of said electrically controlled heater switch;
a safety circuit including;
at least one gas discharge current breakdown element connected between said primary safety link return conductor and said first safety circuit input, and producing;
a voltage drop when said at least one gas discharge current breakdown element conducts so as to produce, at said first safety input, a voltage clamped at a steady potential during half waves of one polarity of said alternating current of said alternating current source and at ground potential during half waves of another and opposite polarity of said alternating current, andan open circuit when said at least one gas discharge current breakdown element fails to conduct such that an input signal is supplied to said first safety circuit input which indicates whether there is a first type of fault in said heater, anda first connection between said second safety circuit input and said secondary safety link return conductor such that an input signal is supplied to said secondary safety circuit input which indicates whether there is a second type of fault in said heater; and
said microcontroller unit including;
preliminary fault detection means for supplying a limited power test signal in a test mode to said heater for a predetermined period of time prior to a full power operation of said heater, andmeans for;
controlling operation of said microcontroller unit to terminate supply of current to said heater if at least one fault is detected by said microcontroller at least one of said first and second safety circuit inputs during said predetermined period of time, andcontrolling operation of said microcontroller unit to supply current to said heater in said full power operation if no fault is detected during said predetermined period of time.
3 Assignments
0 Petitions
Accused Products
Abstract
A safety-assuring control device for an electric blanket which includes a PTC heater includes an integrated circuit microcontroller unit having first and second safety circuit inputs and an output connected to a control input of an electrically controlled heater switch. A neon tube is connected between the primary safety link return conductor of the heater and the first safety circuit input, to indicate whether there is a first type of fault in the PTC heater. A connection between the second safety circuit input and the secondary safety link return conductor of the PTC heater is provided which indicates whether there is a second type of fault in the heater. The microcontroller unit includes a preliminary fault detection circuit for supplying a limited power test signal in a test mode to the heater for a predetermined period of time prior to a full power operation of the heater. The microcontroller unit also includes a circuit for controlling operation of the microcontroller unit to terminate supply of current to the heater if at least one fault is detected by the microcontroller at least one of the first and second safety circuit inputs during the predetermined period of time, and for controlling operation of the microcontroller unit to supply current to the heater in the full power operation if no fault is detected during the predetermined period of time.
53 Citations
35 Claims
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1. A safety-assuring control device for an electric alternating current appliance which includes a heater having first and second heater feed conductors, said first heater feed conductor being connected to a protective fuse and connectable therethrough to an ungrounded pole of a source of electric alternating current and said second heater feed conductor being connected to an electrically controllable heater switch and connectable therethrough to a grounded pole of said source of electric alternating current, said first and second heater feed conductors, at respective ends remote from said fuse and from said heater switch, being respectively connected to primary and secondary safety link return conductors which lead towards respective connections thereof in said control device, said primary safety link conductor being connected with said secondary safety link conductor, said control device comprising:
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an integrated circuit microcontroller unit including; a first safety circuit input, a second safety circuit input, and an output connected to a control input of said electrically controlled heater switch; a safety circuit including; at least one gas discharge current breakdown element connected between said primary safety link return conductor and said first safety circuit input, and producing; a voltage drop when said at least one gas discharge current breakdown element conducts so as to produce, at said first safety input, a voltage clamped at a steady potential during half waves of one polarity of said alternating current of said alternating current source and at ground potential during half waves of another and opposite polarity of said alternating current, and an open circuit when said at least one gas discharge current breakdown element fails to conduct such that an input signal is supplied to said first safety circuit input which indicates whether there is a first type of fault in said heater, and a first connection between said second safety circuit input and said secondary safety link return conductor such that an input signal is supplied to said secondary safety circuit input which indicates whether there is a second type of fault in said heater; and said microcontroller unit including; preliminary fault detection means for supplying a limited power test signal in a test mode to said heater for a predetermined period of time prior to a full power operation of said heater, and means for; controlling operation of said microcontroller unit to terminate supply of current to said heater if at least one fault is detected by said microcontroller at least one of said first and second safety circuit inputs during said predetermined period of time, and controlling operation of said microcontroller unit to supply current to said heater in said full power operation if no fault is detected during said predetermined period of time. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method for testing the safety of an electric alternating current appliance prior to full power operation thereof, said appliance including a heater having first and second heater feed conductors, said first heater feed conductor being connected to a protective fuse and connectable therethrough to an ungrounded pole of a source of electric alternating current and said second heater feed conductor being connected to an electrically controllable heater switch and connectable therethrough to a grounded pole of said source of electric alternating current, said first and second heater feed conductors, at respective ends remote from said fuse and from said heater switch, being respectively connected to primary and secondary safety link return conductors which lead towards respective connections thereof in said control device, said primary safety link conductor being connected with said secondary safety link conductor, said method comprising the steps of:
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supplying a limited power test signal in a test mode to said heater for a predetermined period of time prior to a full power operation of said heater; terminating supply of current to said heater if at least one fault is detected by said microcontroller at least one of said first and second safety circuit inputs during said predetermined period of time; and supplying current to said heater in said full power operation if no fault is detected during said predetermined period of time. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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Specification