Patent ID: 8389908
Filing Date: 2013-03-05
Classification: H03K,H05B

Abstract:
1. A method for sourcing a heater, the method comprising: generating a ramping signal; generating a fixed frequency clocking signal; generating a variable ramp control signal from the ramping signal and the fixed frequency clocking signal, wherein a frequency of the variable ramp control signal is controlled by the fixed frequency clocking signal, and wherein a slope of the variable ramp control signal is controlled by the ramping signal; generating a root mean square (RMS) pulse width modulation (PWM) control signal based upon the variable ramp control signal, wherein the variable ramp control signal is based on an input voltage from a power source; controlling a switch in accordance with the RMS PWM control signal; wherein the RMS PWM control signal controls the switch to provide power to the heating resistor at a first duty cycle corresponding to the magnitude of a first input voltage, wherein the slope of the variable ramp control signal is set to a first value corresponding to the first input voltage while at the first duty cycle; wherein the RMS PWM control signal controls the switch to provide power to the heating resistor at a second duty cycle corresponding to the magnitude of a second input voltage distinct from the first input voltage, wherein the slope of the variable ramp control signal is set to a second value distinct from the first value and corresponding to the second input voltage while at the second duty cycle; sourcing a heater resistor from the power source in accordance with the controlling of the switch; and wherein power to the heating resistor is controlled by the switch to provide a substantially constant value of power to the heating resistor for varying values of the input voltage, wherein varying the slope of the variable ramp control signal between the first duty cycle and the second duty cycle causes the power provided to the heating resistor at the first duty cycle to be substantially the same as the power provided to the heating resistor at the second duty cycle.