| 摘要 |
A switch mode power supply (SMPS) is regulated by sensing its output voltage at the primary side, from a winding of a switched magnetic energy storage device such as an inductor or transformer (fig 2,104). A sample/hold circuit 110 provides a control signal VSENSE, in response to a timing signal STATUS, when a decaying peak detector 109 detects that a sense signal waveform VAUX has a falling slope greater than a threshold. Decaying peak detector 109 may detect a knee point of the waveform VAUX for it to be sampled, between a flyback portion when power is supplied to an output and a portion when no power is supplied, and a secondary has zero current. The knee point may be identified by approximating a tangent to the decaying portion of the waveform VAUX and detecting when the waveform departs from the tangent, by means of a comparator (fig 4) that detects when the negative slope of signal VAUX exceeds a decaying signal slope set by a capacitor (fig 4, C1) discharged by a current (fig 4, I1) by more than a threshold (fig 4, V1). The detector may be reset by a signal RST that indicates a time (fig 8, T1) when the signal VAUX is greater than zero. |
