Patent ID: 7859862
Filing Date: 2010-12-28
Classification: H02M

Abstract:
1. An apparatus for regulating constant output voltage and current on primary side in a flyback converter including a transformer having a primary winding coupled between a power input to receive an input voltage and a power switch, a secondary winding coupled to a power output to provide an output voltage through a rectifier diode, and an auxiliary winding on the primary side, the apparatus comprising: voltage detector circuitry coupled to the auxiliary winding to generate a first signal proportional to the input voltage when the power switch is on and a second signal related to the output voltage when the power switch is off; a knee voltage detector coupled to the voltage detector circuitry to detect a knee point of the second signal to generate a third signal proportional to the output voltage; and a current limit circuit coupled to the voltage detector circuitry and the knee voltage detector to generate a fourth signal according to the first and third signals to determine a current limit threshold for a switched current in the power switch; wherein the third and fourth signals are used to determine a duty of the power switch.