Patent ID: 8154269
Filing Date: 2012-04-10
Classification: H02M,Y02B

Abstract:
1. A control apparatus applied in a power-factor-correction (PFC) power converter comprising a primary winding, an auxiliary winding and a power switch, wherein the primary winding is coupled to receive a input voltage and is controlled by the power switch to increase or release the stored energy, the control apparatus comprising: a reference signal generator, for generating a reference signal having a rising portion and a falling portion, the slew rate of the reference signal being adjustable; a detection circuit, for determining whether the input voltage approaches a zero voltage and detecting whether the stored energy of the primary winding is almost completely released; and a driving circuit, for turning on the power switch to increase the stored energy of the primary winding when the stored energy of the primary winding is almost completely released and the falling portion of the reference signal reaches a predetermined condition; wherein the slew rate of the reference signal is reduced when the input voltage approaches the zero voltage.