Transformer, flyback converter and switching power supply with the same

1. 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.

2. The flyback converter of claim 1 , wherein:

a) said first primary winding and said secondary winding have a first turn ratio;

b) said second primary winding and said secondary winding have a second turn ratio; and

c) a displacement current from said first primary winding to said secondary winding is equal to a displacement current from said secondary winding to said second primary winding when said first turn ratio and said second turn ratio have a predetermined relationship.

3. The flyback converter of claim 1 , wherein:

a) said first primary winding has a first inductance value;

b) said second primary winding has a second inductance value; and

c) a displacement current from said first primary winding to said secondary winding is equal to a displacement current from said secondary winding to said second primary winding when said first and second inductance values have a predetermined relationship.

4. The flyback converter of claim 1 , wherein said secondary rectifier and filter circuit comprises:

a) a rectifier diode having an anode coupled to a dotted terminal of said secondary winding, and a cathode coupled to an output terminal; and

b) a filter capacitor coupled between said output terminal and a secondary grounding terminal.

5. The flyback converter of claim 1 , wherein said first primary winding, said secondary winding, and said second primary winding are configured from inside to outside in said radial direction of said magnetic core.

6. The flyback converter of claim 1 , wherein said first primary winding, said secondary winding, and said second primary winding are configured from outside to inside in said radial direction of said magnetic core.

7. The flyback converter of claim 1 , wherein said non-dotted terminal of said first primary winding, and said dotted terminal of said second primary winding are configured adjacent to said secondary winding in said radial direction of said magnetic core.

8. The flyback converter of claim 1 , wherein said capacitor is directly connected to said first and second primary windings.