Synchronous rectification controller and switching power supply

A synchronous rectification controller, comprising a power switch transistor (Q0), a drive circuit (303), a power supply control circuit (304), and a switch circuit;

• wherein the switch circuit comprises a first switch transistor (Q1), a second switch transistor (Q2), a third switch transistor (Q3), and a fourth switch transistor (Q4);
• the first switch transistor (Q1) is connected to a third output terminal of the power supply control circuit (304);
• the third switch transistor (Q3) is connected to a first output terminal of the power supply control circuit (304);
• the second switch transistor (Q2) and the fourth switch transistor (Q4) are respectively connected to a second output terminal of the power supply control circuit (304);
• the drive circuit (303) is configured to control an on or off state of the power switch transistor (Q0), to make the synchronous rectification controller perform synchronous rectification or stop synchronous rectification;
• and
• the power supply control circuit (304) is configured to control an on or off state of each power supply switch transistor in the switch circuit;
• wherein the power switch transistor (Q0), the first switch transistor (Q1), the second switch transistor (Q2), the third switch transistor (Q3), and the fourth switch transistor (Q4) are N-Metal-Oxide-Semiconductor (NMOS) transistors;
• wherein a gate of the first switch transistor (Q1) is connected to the third output terminal of the power supply control circuit (304), a source of the first switch transistor (Q1) is connected to a source of the second switch transistor (Q2), and a drain of the first switch transistor (Q1) is connected to an external ground (VSS);
• a gate of the second switch transistor (Q2) is connected to the second output terminal of the power supply control circuit (304), and a drain of the second switch transistor (Q2) is connected to an internal ground (GND);
• a gate of the third switch transistor (Q3) is connected to the second output terminal of the power supply control circuit (304), a source of the third switch transistor (Q3) is connected to the internal ground (GND), and a drain of the third switch transistor (Q3) is connected to a source of the fourth switch transistor (Q4);
• and
• a gate of the fourth switch transistor (Q4) is connected to the second output terminal of the power supply control circuit (304), and a drain of the fourth switch transistor (Q4) is connected to an internal power supply (VDD).