Switching power converter input voltage approximate zero crossing determination

Abstract

In at least one embodiment, the controller senses a leading edge, phase cut AC input voltage value to a switching power converter during a cycle of the AC input voltage. The controller senses the voltage value at a time prior to a zero crossing of the AC input voltage and utilizes the voltage value to determine the approximate zero crossing. In at least one embodiment, by determining an approximate zero crossing of the AC input voltage, the controller is unaffected by any disturbances of the dimmer that could otherwise make detecting the zero crossing problematic. The particular way of determining an approximate zero crossing is a matter of design choice. In at least one embodiment, the controller approximates the AC input voltage using a function that estimates a waveform of the AC input voltage and determines the approximate zero crossing of the AC input voltage from the approximation of the AC input voltage.

1 . An apparatus comprising:
 a controller having an input to sense a leading edge, phase cut alternating current (AC) input voltage to a switching power converter at least at a first time during a cycle of the AC input voltage, wherein the cycle of the AC input voltage is derived from a cycle of the AC input supply voltage, the first time is prior to an approximate zero crossing of the cycle of the AC input supply voltage, and at least some zero crossings of the AC input supply voltage are not directly observable by the controller, and the controller is configured to:
 determine the approximate zero crossing of the AC input supply voltage based on a voltage value of the phase cut AC input voltage sensed at the first time. 
   
     
     
         2 .- 31 . (canceled)