Transformer, flyback converter and switching power supply with the same

A flyback converter, comprising:

• a) a power switch being controlled to be turned on and off to control a current through a primary side;
• b) a first primary winding coupled between an input terminal and a first terminal of said power switch, wherein a dotted terminal of said first primary winding is coupled to said first terminal of said power switch;
• c) a second primary winding coupled between a second terminal of said power switch and a primary grounding terminal, wherein a dotted terminal of said second primary winding is coupled to said primary grounding terminal, and wherein said second primary winding is directly connected to said power switch with no other devices therebetween;
• d) a secondary winding configured between said first primary winding and said second primary winding in a radial direction of a magnetic core, wherein said first primary winding, said second primary winding, and said secondary winding are wound around said magnetic core;
• e) a rectifier bridge directly connected to a non-dotted terminal of said first primary winding, and to said dotted terminal of said second primary winding;
• f) a capacitor coupled in parallel with said rectifier bridge, wherein said non-dotted terminal of said first primary winding is only connected to said rectifier bridge and said capacitor;
• and
• g) a secondary rectifier and filter circuit coupled with said secondary winding, and being configured to generate a stable current/voltage.