Patent ID: 7595624
Filing Date: 2009-09-29
Classification: H02M

Abstract:
1. A switching regulator system comprising: a switch that is coupled to a switching node; a control circuit that is coupled to the switch and that activates and deactivates the power switch to control; an inductor that is coupled between the switching node and an output node, wherein an output voltage is provided at the output node; a pulse-wide modulation (PWM) comparison circuit that is coupled to the control circuit, wherein the PWM comparison circuit controls at least one of an on-time and an off-time associated with a switching cycle of the at least one power switch based on a comparison of a feedback voltage associated with the output voltage and a reference voltage associated with a desired output voltage, and wherein the PWM comparison circuit including a ramp signal generator that provides a ramp signal having a non-zero slope that is combined with one of the feedback voltage and the reference voltage at a beginning of one of the on-time and the off-time, and wherein the PWM comparison circuit sets the slope of the ramp signal to zero during the off-time in a discontinuous conduction mode; a discontinuous conduction mode detector that is coupled to the inductor and to the PWM comparison circuit, wherein the discontinuous conduction mode detector determines a time at which the switching regulator has entered the discontinuous conduction mode based on the inductor current becoming equal to zero, and wherein provides a zero-crossing signal to the PWM comparison circuit upon the inductor current having a magnitude of zero, such that the PWM comparison circuit sets the relative slope to zero in response to the zero-crossing signal, and wherein the discontinuous conduction mode detector includes a counter that counts a number of successive zero-crossing signals provided to the PWM comparison circuit, such that the PWM comparison circuit sets the amplitude of the ramp signal to zero for successive switching cycles upon the number of zero-crossing signals exceeding a predetermined limit.