Patent ID: 6958594

Claim:
A DC-DC converter which produces a regulated output voltage and which uses the instantaneous output voltage to establish the duty ratio required for maintaining said output voltage, comprising: at least one switching element connected between an input voltage and a first node; an output inductor connected between said first node and an output terminal; and a switching control circuit which cycles said switching element on and off to maintain a desired output voltage at said output terminal, each of said switching cycles comprising an “on” time interval T on during which said switching element is on and connects said first node to said input voltage, and an “off” time interval T off during which said switching element is off and disconnects said first node from said input voltage, said switching control circuit comprising: a resistive network connected to produce a feedback voltage V fb at a feedback node representative of the instantaneous output voltage at said output terminal; a capacitance element connected between said feedback node and said converter's local ground; and a comparator which receives V fb at its first input and a voltage V2 which varies with a fixed reference voltage V ref at its second input, said switching control circuit arranged such that at least one of each switching cycle's “on” and “off” time intervals is terminated when V fb crosses V2 due to the natural discharge of the capacitance element through the resistive network, such a time interval being a “modulated” interval; and a switched noise filter circuit arranged to apply an offset voltage to said feedback voltage during at least one of each switching cycle's “on” and “off” time intervals and to disconnect said offset voltage from said feedback voltage by the beginning of the immediate modulated interval or shortly thereafter, thereby allowing V fb to decay toward V2, such that the noise margin between V2 and V fb is increased and the effect of extraneous electromagnetic noise coupled into said feedback voltage is reduced.