PWM controller for DC powered heating blanket

• US 6,770,853 B2
• Filed: 10/22/2002
• Issued: 08/03/2004
• Est. Priority Date: 10/22/2002
• Status: Expired due to Fees

• Current Assignee: Vector Products Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Vector Products Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Krieger, Michael, Randolph, Bruce
• Primary Examiner(s): Paschall, Mark
• Application Number:
  US10/277,031
• Publication Number:
  US 20040074897A1
• Time in Patent Office: 651 Days
• Field of Search: 219/212, 219/494, 219/497, 219/499, 219/501, 219/505, 219/535, 219/483-486, 290/5, 290/6
• US Class Current: 219/497
• CPC Class Codes: H05B 1/0272 For heating of fabrics
• CPC Class Codes: H05B 2203/035 Electrical circuits used in resistive heating apparatus
• CPC Class Codes: H05B 3/342 heaters used in textiles
• CPC Class Codes: Y10S 2/905 Electric

Abstract

A PWM-based controller for controlling a voltage applied to a DC-powered electric heating blanket from a power source includes a square wave producing circuit for connection in the circuit with the battery and the blanket. The square wave producing circuit produces a variable duty cycle square wave for controlling application of power to the blanket in accordance with the duty cycle of the square wave. The square wave producing circuit has a control input for varying the duty cycle of the square wave in response to a voltage at the control input. The voltage at the control input may be set manually using a voltage varying circuit connected to the power source. A low voltage detection circuit may also be connected to the power source and coupled to the control input of the square wave producing circuit for automatically producing a voltage that decreases the duty cycle of the square wave when the battery voltage decreases to or below a predetermined level.

Claims

1. A pulse-width modulation (PWM) controlled electric heating blanket comprising:

electric heating means of the electric heating blanket;

a square wave generator producing a square wave output, a duty cycle of the square wave output being controllable by a control input, the square wave output being coupled to the electric heating means;

manual control means for varying a control signal input to the control input of the square wave oscillator and thereby controlling the duty cycle of the square wave output; and

a low voltage detection circuit for monitoring the voltage level of a power source and providing a control signal to the control input of the square wave oscillator, to thereby decrease the duty cycle of the square wave output when the voltage level of the power source decreases below a predetermined level.

2. The electric heating blanket according to claim 1, wherein the control signal provided by the low voltage detection circuit is provided to the control input of the square wave oscillator via the manual control means.

3. The electric heating blanket according to claim 1, wherein the low voltage detection circuit comprises a control transistor, wherein the control transistor is gradually turned off as the voltage level of the power source decreases below the predetermined level.

4. The electric heating blanket according to claim 1, wherein the square wave generator comprises a comparator circuit having a threshold level set by the control input.

5. The electric heating blanket according to claim 4, further comprising:

a triangular wave oscillator producing a triangle wave signal, wherein the triangle wave signal is provided as input to the square wave generator for comparison to the threshold level by the comparator circuit.

6. The electric heating blanket according to claim 1, further comprising a switching means to which the square wave output is provided, to thereby control application of power to the electric heating means.

7. The electric heating blanket according to claim 6, wherein the switching means comprises a transistor.

8. The electric heating blanket according to claim 1, wherein the power source comprises a battery.

9. The electric heating blanket according to claim 1, wherein the power source comprises a rechargeable battery.

10. The electric heating blanket according to claim 1, wherein the manual control means comprises a potentiometer.

11. The electric heating blanket according to claim 1, wherein the manual control means comprises:

a plurality of transistors;

a plurality of resistor means, corresponding in number to the plurality of transistors, each having a different value, and each coupled to a different one of the plurality of transistors; and

a selector switch coupled to selected one or none of the plurality of transistors to be conductive.

12. The electric heating blanket according to claim 11, further comprising:

an integrated circuit coupled to the selector switch, wherein one or none of the plurality of transistors is enabled to conduct by an output of the integrated circuit generated in response to use of the selector switch.

13. The electric heating blanket according to claim 12, wherein the integrated circuit comprises a decade counter.

14. The electric heating blanket according to claim 12, wherein the integrated circuit includes a reset input coupled to reset the circuit upon any one of power-up, low power source voltage, and use of the selector switch to turn off the electric heating means, wherein the reset mode results in power to the electric heating means being cut off and the integrated circuit going to an initial state.

15. The electric heating blanket according to claim 1, further comprising a transistor coupled to the square wave generator and arranged so as to permit and shut off input to the square wave generator.

16. The electric heating blanket according to claim 15, further comprising:

an integrated circuit having an output coupled to the transistor to control the transistor to permit and shut off input to the square wave generator.

17. The electric heating blanket according to claim 16, further comprising:

a selector switch coupled to the integrated circuit;

wherein the integrated circuit includes a reset input; and

wherein the reset input is arranged so that the integrated circuit resets when at least one of a low power condition, a power-up condition, or a manual turn-off condition occurs.

18. The electric heating blanket according to claim 17, wherein, when the integrated circuit resets, the integrated circuit output coupled to the transistor causes the transistor to shut off input to the square wave generator.

19. A method of controlling an electric heating blanket, the method comprising the steps of:

generating a square wave signal having a controllable duty cycle, the square wave signal being coupled to an electric heating means of the electric heating blanket for controlling the electric heating means; and

controlling the duty cycle of the square wave signal, the step of controlling the duty cycle comprising;

monitoring a voltage level of a power source; and

decreasing the duty cycle of the square wave signal when the voltage level of the power source decreases below a predetermined level.

20. The method according to claim 19, wherein the step of decreasing the duty cycle of the square wave signal comprises the step of increasing a threshold voltage used in a signal comparison.

21. The method according to claim 20, further comprising the step of:

generating a triangle wave signal, wherein the triangle wave signal is used in the signal comparison to generate the square wave signal.

22. The method according to claim 19, wherein the step of controlling the duty cycle of the square wave signal further comprises the step of:

manually controlling the duty cycle of the square wave signals; and

wherein the step of decreasing the duty cycle of the square wave signal comprises the step of decreasing the duty cycle of the square wave signal below a duty cycle set by the step of manually controlling the duty cycle of the square wave signal.

23. The method according to claim 19, wherein the step of controlling the duty cycle of the square wave signal comprises the step of manually setting a threshold level for performing a signal comparison.

24. The method according to claim 23, further comprising the step of:

generating a triangle wave signal, wherein the triangle wave signal is used in the signal comparison to generate the square wave signal.

25. The method according to claim 23, wherein the step of manually setting a threshold level for performing a signal comparison comprises the step of manually selecting a threshold voltage from within a continuous voltage range.

26. The method according to claim 23, wherein the step of manually setting a threshold level for performing a signal comparison comprises the step of manually selecting a threshold voltage from among a discrete set of voltage levels.

27. The method according to claim 19, further comprising the step of:

using the square wave signal to switch power to the electric heating means on and off.