Clamp protection circuit and a PFC control circuit employing such clamp protection circuit

A PFC control circuit, which comprises:

• a boost module;
• a zero-crossing detection module used for detecting whether a current of a boost inductor in the boost module have crossed a zero point;
• a PFC control chip, and
• a clamp protection circuit connected to the ZCD pin of the PFC control chip;
• wherein, said clamp protection circuit comprises:
• a high voltage isolation module used for receiving power from a high voltage power supply;
• a voltage clamp module used for receiving an output low voltage from the high voltage isolation module and realizing a clamp protection;
• and
• a low voltage bias module used for providing bias voltage to the high voltage isolation module and the voltage clamp module, wherein,
• said low voltage bias module comprises a first bias module used for providing bias voltage to the high voltage isolation module and a second bias module used for providing bias voltage to the voltage clamp module, wherein
• a transistor in the second bias module detects a clamp current and produces a current fed back to the voltage clamp module based on changes of the clamp current, so that dynamic compensation is provided for the change of the clamp current, and high clamp voltage accuracy is guaranteed.