PWM power supply with constant RMS output voltage control

Claim 2

A control system for supplying a constant RMS voltage to a load, said control system comprising: a pulse width modulator (PWM) configured to deliver a varying width pulse, said pulse representing a duty cycle of a drive signal to said load; a first control loop in communication with said PWM, said first control loop configured to monitor a characteristic variable and to generate a control signal to modulate said drive signal to said load, said control signal in response to a comparison of said variable with a predetermined reference point; and a second control loop configured to generate a control signal to said PWM, said control signal of said second control loop in accordance with a comparison of a duty cycle representation of a received input voltage to said system and a duty cycle representation of said drive signal.

Claim 3

The control system of claim 1 wherein said received input voltage comprises unregulated power received directly without conversion.

Claim 4

The control system of claim 1 wherein said first control loop includes a temperature sensing device and said characteristic variable comprises temperature.

Claim 5

The control system of claim 1 wherein said control signal of said second control loop comprises an instruction to vary the width of said pulse delivered by said PWM.

Claim 6

The control system of claim 1 wherein said second control loop comprises a filter configured to generate said duty cycle representation of said drive signal.

Claim 7

The control system of claim 1 wherein said second control loop comprises a function generator configured to receive said input voltage and to generate said duty cycle representation of said input voltage.

Claim 8

The control system of claim 6 wherein said function generator comprises a plurality of discrete components configured to generate a piece-wise linear approximation as a function of said input voltage.

Claim 9

The control system of claim 1 further comprising a switching device in communication with said PWM and said load, said switching device configured to receive said pulse from said PWM and in response to said pulse deliver a power to said load.

Claim 10

A control system for use in supplying a constant RMS voltage to a load, said control system comprising: a pulse width modulator (PWM) configured to deliver a varying width pulse, said pulse representing a duty cycle of a drive signal to said load; a first control circuit comprising a comparator section of said PWM and a temperature sensing mechanism, said comparator section configured to receive a temperature reading from said temperature sensing mechanism and compare said reading with a reference temperature, in response to said comparison, said first control circuit providing a control signal to said PWM; and a second control circuit comprising, a first function circuit configured to receive an input voltage and to generate a duty cycle representation in accordance with said input voltage, a second function circuit configured to receive said drive signal and to generate a duty cycle representation in accordance with said drive signal, and a comparator function circuit configured to receive and compare said duty cycle signal from said first function circuit with said duty cycle representation from said second function signal, and in response to said comparator function circuit comparison, said second control circuit providing a control signal to said PWM.

Claim 11

A control system for use in supplying a constant RMS voltage to a load, said control system comprising: a pulse width modulator (PWM) configured to deliver a varying width pulse, said pulse representing a duty cycle of a drive signal to said load; a first control circuit comprising a comparator section of said PWM and a temperature sensing mechanism, said comparator section configured to receive a temperature reading from said temperature sensing mechanism and compare said reading with a reference temperature, in response to said comparison, said first control circuit providing a control signal to said PWM; and a second control circuit comprising, a first function circuit configured to receive an input voltage and to generate a duty cycle representation in accordance with said input voltage, a second function circuit configured to receive said drive signal and to generate a duty cycle representation in accordance with said drive signal, and a comparator function circuit configured to receive and compare said duty cycle signal from said first function circuit with said duty cycle representation from said second function signal, and in response to said comparator function circuit comparison, said second control circuit providing a control signal to said PWM.

Claim 12

The control system of claim 9 wherein said input voltage comprises unregulated power received directly without conversion.

Claim 13

The control system of claim 9 wherein said load comprises a heating element and said temperature sensing mechanism is coupled to a luminescence device.

Claim 14

A circuit for controlling the power to a backlighting system of an electronic display, said backlighting system of the type having a lamp coupled to a heating element, said circuit comprising: a pulse width modulator (PWM) configured to deliver a varying width pulse, said pulse representing a duty cycle of a drive signal to said heating element; a first control loop in communication with said PWM, said first control loop configured to monitor the temperature of said lamp and to generate a control signal to modulate said drive signal to said heating element, said control signal in response to a comparison of the temperature of said lamp with a predetermined reference point; and a second control loop configured to generate a control signal to said PWM, said control signal of said second control loop in accordance with a comparison of a generated duty cycle representation of a received unregulated input voltage to said system and a generated duty cycle representation of said drive signal.

Claim 15

A circuit for controlling the power to a backlighting system of an electronic display, said backlighting system of the type having a lamp coupled to a heating element, said circuit comprising: a pulse width modulator (PWM) configured to deliver a varying width pulse, said pulse representing a duty cycle of a drive signal to said heating element; a first control loop in communication with said PWM, said first control loop configured to monitor the temperature of said lamp and to generate a control signal to modulate said drive signal to said heating element, said control signal in response to a comparison of the temperature of said lamp with a predetermined reference point; and a second control loop configured to generate a control signal to said PWM, said control signal of said second control loop in accordance with a comparison of a generated duty cycle representation of a received unregulated input voltage to said system and a generated duty cycle representation of said drive signal.

Claim 16

The circuit of claim 12 wherein said second control loop comprises a filter configured to generate said duty cycle representation of said drive signal.

Claim 17

The circuit of claim 12 wherein said second control loop comprises a function generator configured to generate said duty cycle representation of said input voltage.

Claim 18

The circuit of claim 14 wherein said function generator comprises a plurality of discrete components configured to generate a piece-wise linear approximation as a function of said input voltage.

Claim 19

The circuit of claim 12 further comprising a switching device in communication with said PWM and said heating element, said switching device configured to receive said pulse from said PWM and in response to said pulse to deliver power to said heating element.

Claim 22

The method of claim 17 wherein said monitoring step comprises obtaining a reading of said characteristic variable; and comparing said reading with a predetermined reference.

Claim 23

The method of claim 17 wherein said characteristic variable comprises temperature, said load comprises a heating element, and said generating a first signal comprises the steps of: determining whether said temperature of said device is less than a predetermined reference temperature; and generating said first control signal such that said heating element is caused to receive power and increase the temperature of said device if said temperature is less than said reference temperature.

Claim 24

The method of claim 17 wherein said receiving an input voltage comprises receiving an unregulated power directly without conversion.

Claim 25

The method of claim 17 wherein said modulating circuit comprises a pulse width modulator (PWM) and said third control signal comprises a pulse.

Claim 26

The method of claim 21 wherein said first and second control signals indicate an increase or decrease in a width of said pulse.

Claim 27

The method of claim 22 wherein an increase in said width of said pulse results in an increase in said first duty cycle representation of said control signal.

Claim 28

The method of claim 17 further comprising the step of receiving said third control signal at a switching circuit and in accordance with said third control signal providing a power to said load.

Claim 31

The method of claim 25 wherein said control signal configured to maintain a constant RMS voltage to said load.

Claim 32

The method of claim 25 wherein determining said duty cycle representation of said input voltage power comprises determining the ratio of an RMS value of said input voltage to a maximum value of said input voltage and squaring said ratio.