Patent ID: 8446746

Claim:
A system for sensing an output voltage of a switch mode power supply (SMPS), the SMPS including a switched magnetic energy storage device for conveying power from a SMPS input to a SMPS output of said SMPS, said magnetic device having at least one winding, the system comprising; a sensing signal input to receive a sensing signal from said at least one winding of said magnetic device, said sensing signal having a waveform with a first, decaying portion during which power is supplied by said magnetic device to said SMPS output and a second portion during which substantially no power is supplied by said magnetic device to said SMPS output; a signal follower coupled to said sensing signal input to generate a decay signal approximating said decaying portion of said sensing signal waveform; a comparator to compare said decay signal with said sensing signal waveform to identify substantially a knee point on said sensing signal waveform when said sensing signal waveform decays faster than said decay signal; and a sampler to sample said sensing signal responsive to said comparator to provide an output signal sensing said output voltage of said SMPS, wherein said coupling of said signal follower to said sensing signal input is such that decay of said decay signal is dependent on said sensing signal waveform.