Patent ID: 7035122

Claim:
A switching power supply, comprising: a switch, configured to switch a switch-voltage; a bias sensor, configured to sense the switch-voltage and to generate a bias-voltage representative thereof; a zero-crossing detector, coupled to the bias sensor, configured: to sense time instances when the bias-voltage crosses zero; and to generate a zero-crossing detector (ZCD)-signal, which transitions between a first and a second level at the sensed crossing instances, the transitions of the ZCD-signal being delayed for a predetermined time interval relative to the sensed crossings instances; a blanking circuit, coupled to the zero-crossing detector, the blanking circuit configured: to receive the ZCD-signal from the zero-crossing detector; to generate a blanking-signal, which transitions between a first and a second level; and to generate a pulse-signal, wherein the pulse-signal is capable of: causing the turning on of the switch, for an on-time, at time instances when the ZCD-signal and blanking-signal are at their respective second levels; and causing the turning off of the switch for at least a blank-time, wherein the length of the blank-time is determined according to the on-time; and a pulse width modulation (PWM) signal generator, coupled to the blanking circuit and to the switch, the PWM signal generator configured: to turn on the switch, controlled by the pulse-signal of the blanking circuit; and to transmit a signal representing the on-time to the blanking circuit.