Patent ID: 8279634

Claim:
A circuit for predicting a valley timing for a voltage across a switching device, comprising: a voltage detector for detecting the voltage across the switching device to produce a detection voltage as a function of the voltage detected across the switching device; a first comparator for comparing the detection voltage with a first threshold to produce a first comparison signal; a second comparator for comparing the detection voltage with a second threshold to produce a second comparison signal; a logic circuit for producing a first logic signal and a second logic signal according to the first and second comparison signals; and, a timer for predicting the timing of a valley for the detection voltage according to the first and second logic signals, the timer thereby determining a valley signal corresponding to the detection voltage valley used to trigger turn on of the switching device, the valley signal being thereby generated responsive to the timing of detection voltage change between the first and second thresholds, said timer including a capacitor for providing a timer voltage, a first current source controlled by the first logic signal for determining a first current to charge the capacitor, a second current source controlled by the second logic signal for determining a second current to discharge the capacitor and a third comparator for comparing the timer voltage with a third threshold to produce the valley signal.