Electric blanket control circuit

• US 4,034,185 A
• Filed: 09/02/1975
• Issued: 07/05/1977
• Est. Priority Date: 09/02/1975
• Status: Expired due to Term

• Current Assignee: Northern Electric PLC (Berkshire Hathaway Incorporated)
• Original Assignee: Northern Electric PLC (Berkshire Hathaway Incorporated)
• Inventors: Crowley, George C.
• Primary Examiner(s): Hickey, Robert J.
• Application Number:
  US05/609,243
• Time in Patent Office: 672 Days
• Field of Search: 317/18 R, 317/18 A, 317/9 A, 317/9 D, 317/40 R, 317/41, 317/124, 317/132, 317/40 A, 219/212, 219/494, 219/504, 219/505, 340/228
• US Class Current: 219/212
• CPC Class Codes: H02H 3/044 Checking correct functioning of protective arrangements, e.g. by simulating a fault for differential current circuit breakers H02H3/335
• CPC Class Codes: H02H 5/043 the temperature dependent resistor being disposed parallel to a heating wire, e.g. in a heating blanket
• CPC Class Codes: H05B 1/0227 Applications
• CPC Class Codes: H05B 2203/014 Heaters using resistive wires or cables not provided for in H05B3/54
• CPC Class Codes: H05B 2203/017 Manufacturing methods or apparatus for heaters
• CPC Class Codes: H05B 2203/035 Electrical circuits used in resistive heating apparatus
• CPC Class Codes: H05B 3/342 heaters used in textiles

Abstract

An electric blanket control circuit is provided which includes an overheat protection circuit to detect an overheat condition as well as a fail-safe testing circuit to assure that the electrical components in said overheat protection circuit are properly functioning. A simulation circuit is provided to electrically simulate an overheat condition in the blanket. An on-off switch is provided which will consecutively activate the overheat simulation circuit and then the fail-safe testing circuit so that said circuits are activated each time the electric blanket is turned off by the user.

Claims

1. An overheat protection circuit for an electric blanket having a heating means and a sensing means to detect an overheat condition comprising switch means to electrically activate said heating means;

said switch means having at least two mechanically stable positions;

circuit means to electrically simulate an overheat condition; and

said simulating circuit means activated each time said switch means is switched to one of its said stable positions.

2. An overheat protection circuit according to claim 1 wherein said switch means has two stable mechanical positions, an "on" position and an "off" position;

and said switch means having three electrical positions.

3. An overheat protection circuit according to claim 2 wherein the first of said three electrical switch positions corresponds to said "on" stable mechanical position;

said third electrical switch position corresponding to said "off" stable mechanical position; and

said second electrical switch position being made when said switch is between said two stable mechanical positions so that when the electric blanket is mechanically switched from its "on" to its "off" mechanical position, said switch will connect said second electrical position momentarily.

4. An overheat protection circuit according to claim 3 wherein said simulating circuit means is activated when said switch is in the second of said three electrical positions.

5. An overheat protection circuit according to claim 1 comprising circuit means electrically connected to said sensing means to deactivate said heating means when an overheat condition is detected;

and testing means to test for a malfunction in said deactivation circuit means.

6. An overheat protection circuit for an electric blanket according to claim 5 wherein said testing means includes a thermistor;

a fuse electrically connected in series with said thermistor; and

said thermistor and fuse being electrically connected across an input voltage source whereby in the event a malfunction occurs in said deactivation circuit means said fuse will break down.

7. An overheat protection circuit for an electric blanket having a heating means and a sensing means to detect an overheat condition comprising switch means to electrically activate said heating means;

said switch means having at least two stable mechanical positions;

circuit means electrically connected to said sensing means to deactivate said heating means when an overheat condition is detected;

testing means to test for a malfunction in said circuit means;

said testing means being operative each time said switch means is switched to one of its said stable mechanical positions; and

simulating circuit means to electrically simulate an overheat condition.

8. An overheat protection circuit according to claim 7 wherein said switch means has two stable mechanical positions, an "on" position and an "off" position;

and said switch means having three electrical positions, two of which correspond to said stable mechanical positions.

9. An overheat protection circuit according to claim 8 wherein the first of said three electrical switch positions corresponds to said "on" stable mechanical position;

said third electrical switch position corresponding to said "off" stable mechanical position; and

said second electrical switch position being made when said switch is between said two mechanical positions so that when the electric blanket is mechanically switched from its "on" position to its "off" position, the second electrical position will be momentarily established therebetween.

10. An overheat protection circuit according to claim 9 wherein said simulating circuit means is activated when said switch is in the second of said three electrical positions.

11. An overheat protection circuit according to claim 9 wherein said testing circuit means is activated when said switch is in the third of said three electrical positions.

12. An overheat protection circuit for an electric blanket having a heating means and a sensing means to detect an overheat condition comprising deactivation circuit means electrically connected to said sensing means and including switch means to deactivate said heating means when an overheat condition is detected;

a fuse separate from said sensing means connected in circuit with said heating means; and

testing means connecting said switch means and said fuse in series across the input voltage source whereby said fuse will break down if said switch means has malfunctioned to test for a malfunction in said deactivation circuit means.

13. An overheat protection circuit according to claim 12 wherein said switch means comprises electrical components including a neon light and a light sensitive resistor positioned to respond to said light and a relay activated by current through said resistor.

14. An overheat protection circuit for an electric blanket having a heating means and a sensing means to detect an overheat condition comprising deactivation circuit means electrically connected to said sensing means to deactivate said heating means when an overheat condition is detected;

testing means to test for a malfunction in said deactivation circuit means;

said deactivation circuit means comprising electrical components including a neon light and a light sensitive resistor positioned to respond to said light and a relay activated by current through said resistor;

said testing means comprises a fuse;

a thermistor electrically connected in series with said fuse; and

said fuse and thermistor electrically connected across an input voltage whereby in the event a malfunction occurs in one of said components in said deactivation circuit said fuse will break down.

15. An electric blanket having a heating means and an overheat protection circuit comprising a sensing means to detect an overheat condition;

first switch means to electrically energize and deenergize said heating means;

circuit means including second switch means to deenergize said heating means when an overheat condition is detected by said sensing means;

testing means to test for proper functioning of said deenergizing circuit means;

said testing means being connected in circuit each time said first switch means is operated to deenergize said heating means;

said testing means including circuit means to simulate an overheat condition and to disable said heating means if said second switch means failed to deenergize said heating element in response to the simulated overheat condition.