Heating pad controller with variable duty cycle for temperature adjustment

• US 5,708,256 A
• Filed: 12/18/1995
• Issued: 01/13/1998
• Est. Priority Date: 12/18/1995
• Status: Expired due to Term

• Current Assignee: Helen of Troy Limited
• Original Assignee: Kaz Incorporated (Helen of Troy Limited)
• Inventors: Montagnino, James G., Polonchak, John, Lerner, Ronald, Sherwood, Robert
• Primary Examiner(s): Paschall, Mark H.
• Application Number:
  US08/573,948
• Time in Patent Office: 757 Days
• Field of Search: 219/494, 219/497, 219/501, 219/505, 219/508, 219/212, 219/216, 219/483, 219/486, 307/117, 323/288
• US Class Current: 219/497
• CPC Class Codes: G05D 23/1913 delivering a series of pulses
• CPC Class Codes: G05D 23/24 the sensing element having a resistance varying with temperature, e.g. a thermistor

Abstract

A heating pad controller is provided which varies the duty cycle during which power is applied to a heating pad heating element. In one embodiment according to the present invention, an oscillator circuit is used to vary the off-time of the duty cycle, with the on-time portion being fixed. User control of the off-time is provided by way of a rotary control knob connected to a potentiometer. The potentiometer is part of the oscillator circuit and is used to vary the resistance through which a capacitor in the oscillator circuit charges up. The output of the oscillator circuit is used to control the gate of a silicon controlled rectifier (SCR), which acts as a power switch through which power is applied to the heating element. During power up, the oscillator circuit is overridden and a continuous control signal is applied to the SCR to provide constant power to the heating element to thereby achieve rapid heating. In an alternative embodiment according to the present invention, a digital heating pad controller is provided to vary the duty cycle during which power is applied to a heating pad heating element. User control is provided by way of a number of switches which are used to select one of a number of operating temperatures. Additionally, when the heating pad is first turned on or when the desired temperature setting is increased, continuous power, i.e., 100% duty cycle operation, is initiated in order to rapidly heat the heating pad to the desired temperature. Similarly, when the desired temperature setting is decreased, no power is applied to the heating element, i.e., 0% duty cycle operation.

Claims

1. A controller for a heating device for controllably applying power to a heating device and controlling the heating device temperature, comprising:

an oscillator circuit having a capacitor and producing a periodic control signal at the output of said oscillator circuit, said periodic control signal including a first logic level portion and a second logic level portion;

a power switch having a control input for receiving said periodic control signal and applying power to the heating device during one of said first and second logic level portions of said control signal, otherwise disconnecting power to the heating device;

a user controlled temperature adjustment circuit connected to the oscillator circuit, including means for varying one of said first and second logic level portions of said periodic control signal to thereby vary the heating device temperature wherein the means for varying includes a variable resistor connected to said oscillator circuit capacitor for varying the discharge time of the capacitor such that one of said first and second logic level portions of said periodic control signal is varied correspondingly;

a rapid heating control circuit connected to the control input of said power switch for continuously activating said power switch for a predetermined time period upon activation of the controller to thereby rapidly increase the temperature of said heating device;

. and

a diode connected to said power switch and a fuse connected to said diode such that said diode conducts a sufficient amount of current to trigger said fuse in the event of a failure of said power switch.

2. A controller according to claim 1 wherein the power switch comprises a silicon controlled rectifier.

3. A controller according to claim 1 wherein the heating device comprises a heating pad.

4. A controller for a heating pad for controllably applying power to a heating pad and controlling the heating pad temperature, comprising:

a microprocessor including a plurality of inputs connected to a plurality of user temperature setting devices;

a plurality of outputs connected to a plurality of temperature level indicators, each of said plurality of temperature level indicators corresponding to one of said plurality of temperature setting devices;

programmable means for producing at a control output a periodic control signal having a first logic level portion and a second logic level portion;

a power switch having a control input for receiving said periodic control signal and applying power to the heating pad during one of said first and second logic level portions of said control signal, otherwise disconnecting power to the heating pad;

a diode connected to said power switch and a fuse connected to said diode such that said diode conducts a sufficient amount of current to trigger said fuse in the event of a failure of said power switch; and

said microprocessor further including programmable means for varying one of said first and second logic level portions of said periodic control signal in response to the plurality of user temperature setting devices to thereby vary the heating pad temperature, programmable means for rapidly heating said heating pad by changing the periodic control signal to be continuously at one of said first and second logic levels for a first predetermined time, programmable means for rapidly cooling said heating pad by changing the periodic control signal to be continuously at the other of said first and second logic levels for a second predetermined time.

5. A controller according to claim 4, wherein said power switch comprises a silicon controlled rectifier.

6. A controller according to claim 5, further comprising:

power supply timing detection means operating in conjunction with said microprocessor for detecting zero crossings of a periodic power supply signal and adjusting a timing of said first and second logic level portions of said periodic control signal according to a predetermined relationship with respect to the power supply signal zero crossings.

7. A controller according to claim 4 wherein the heating device comprises a heating pad.