Heating pad controller with variable duty cycle for temperature

Details Heating pad controller with variable duty cycle for temperature Heating pad controller with variable duty cycle for temperature

1995-12-18

1998-01-13

Paschall, Mark H.

Electric heating

Heating devices

With power supply and voltage or current regulation or...

219492, 219212, 219501, 323288, H05B 102

Patent

active

057082561

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.

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