Patent ID: 6768655
Filing Date: 2004-07-27
Classification: H02M,Y02B,Y02P

Abstract:
A discontinuous mode power factor correction (PFC) controller, used in a PFC converter, wherein the PFC converter comprising a bridge, an inductor, a rectifier and a main capacitor, a plurality of switching cycles being applied to the PFC converter, wherein the PFC controller comprising:a VCC terminal, coupled to a first capacitor to supply power for the PFC controller; a RT terminal, coupled to a gate terminal of a first transistor; a GND terminal connected to the ground, a COM terminal; a FB terminal, wherein a second capacitor is coupled between the COM terminal and the FB terminal for the frequency compensation, the FB terminal is coupled to the output of the PFC converter through a second resistor; a DET terminal, coupled to an auxiliary winding of the inductor through a DET resistor for detecting a zero current state of the inductor, an OUT terminal, coupled to a gate terminal of a second transistor, wherein a drain terminal of the second transistor is coupled to a node between the inductor and the rectifier, a source terminal of the second transistor is coupled to the ground through a third resistor, wherein a switching signal is applied from the OUT terminal to the gate terminal of the second transistor; and a VS terminal, coupled between the source terminal of the second transistor and the third resistor, wherein a drain terminal of the first transistor is coupled to the second resistor through a fourth resistor and the FB terminal, wherein an off-time delay is inserted right before the start of each of the switching cycles, the off-time delay is modulated to be a function of a feedback voltage and a supply voltage, wherein the supply voltage is a voltage level in the VCC terminal, when the supply voltage is lower than a limit voltage, the off-time delay is decreased accordingly and a low supply voltage is prevented, and a switching frequency is decreased in accordance with the decrease of the load, and a first resistor is connected from the RT terminal to the ground, in which the first resistor determines the maximum on-time of the switching signal.