Patent ID: 6066943
Filing Date: 2000-05-23
Classification: H02M

Abstract:
A controller for a switch-mode power converter comprising:(a) a comparator having an output terminal and first and second input terminals;(b) a switch-mode power train coupled to said output terminal and operable to receive an unregulated input voltage and to provide a regulated output voltage;(c) a feedback network coupled to receive the regulated output voltage of said switch-mode power train and to provide a voltage to the first input of said comparator; and(d) a ramp circuit comprising:(i) a first input node, a first midpoint node and a first capacitor divider circuit comprising a first capacitor connected from said first input node to said first midpoint node and a second capacitor connected from said first midpoint node to a first reference voltage;(ii) a second input node, a second midpoint node and a second capacitor divider comprising a third capacitor connected from said second input node to said second midpoint node and a fourth capacitor connected from said second midpoint node to said first reference voltage;(iii) a first switch selectively coupling one of said first midpoint node or said second midpoint node to said second input of said comparator;(iv) a second switch coupling a current source to said first input node when said first switch connects said first midpoint node to said second input of said comparator and coupling said current source to said second input node when said first switch connects said second midpoint node to said second input of said comparator;(v) a third switch coupling said first input node to a first reference voltage when said second switch couples said current source to said second input node;(vi) a fourth switch coupling said second input node to said first reference voltage when said second switch couples said current source to said first input node;(vii) a fifth switch coupling said first midpoint node to a second reference voltage different from said first reference voltage when said second switch couples said current source to said second input node; and(viii) a sixth switch coupling said second midpoint node to said second reference voltage when said second switch couples said current source to said first input node.