Patent ID: 7221133

Claim:
A switch mode power supply comprising: a semiconductor switching circuit connected to a source of DC; output circuitry coupled to the semiconductor switching circuit adapted to drive a load; a drive circuit operative to control the switching circuit; a control loop, the control loop being comprised of: an A/D converter which receives an analog input representative of the power supply output, and which provides a multiple bit output signal; a digitally implemented processing unit responsive to the output signal from the A/D converter to generate a multiple bit digital error signal; and a D/A converter which receives the multiple bit digital error signal as an input, and which provides an analog output signal representative of the digital error signal; and a PWM signal generator responsive to the analog output signal from the D/A converter to generate a variable duty cycle drive signal for the drive circuit, wherein the PWM signal generator further comprises: a first comparator operative to indicate a reference voltage that is independent of the actual operation of the power supply; and a second comparator receiving the reference voltage and the analog output signal from the D/A converter and operative to provide an output indicating the duty cycle of the variable duty cycle drive signal.