Control circuit for switching power supply

A control circuit of a switching power supply having a high-voltage side switching element and a low-voltage side switching element connected in series between a positive potential end and a ground of a direct current power supply, the control circuit comprising:

• a central control circuit which has a first control port, a second control port, and a third control port, wherein the first control port and the second control port respectively output a control signal of turning on and off the high-voltage side switching element and the low-voltage side switching element, and an equivalent impedance between the third control port and the ground is used to set an output current value of the switching power supply;
• and
• a current selection circuit which is disposed between the third control port and the ground and has two or more selection terminals, a connection state between the selection terminals being switched between different connection states to adjust the output current value of the switching power supply,
• wherein the different connection states include disconnection, shorting, and connection with a resistor having a predetermined resistance value;
• and further
• wherein the current selection circuit also includes:
• at least one current selection subunit, and each current selection subunit is connected to the corresponding selection terminal,
• each current selection subunit includes at least two current selection branches connected in parallel, and
• each current selection branch includes a resistor and a switching element connected in series between the third control port and the ground, wherein trigger voltages required to turn on the switching element of each branch of the at least two current selection branches are made different from each other.