Control method and control circuit for switch in switching power supply

A control circuit for driving a power switch in a switching power supply, the control circuit comprising:

• a) a gate voltage detecting circuit configured to detect a gate voltage of said power switch, and to compare said gate voltage against a first threshold voltage;
• b) a drain voltage detecting circuit configured to detect a drain voltage of said power switch, and to compare said drain voltage of said power switch against a second threshold voltage;
• and
• c) a driving circuit configured to output a first drive current when said gate voltage of said power switch is less than said first threshold voltage or when said drain voltage of said power switch is less than said second threshold voltage, and during both a turning-on phase and a turning-off phase of said power switch, to output a second drive current when said drain voltage of said power switch is greater than said second threshold voltage and said gate voltage of said power switch is greater than said first threshold, wherein said first drive current is greater than said second drive current.