Current detecting circuit AC/DC flyback switching power supply

A current detecting circuit for a AC/DC flyback switching power supply, the current detecting circuit being connected to a secondary side of a transformer of the AC/DC flyback switching power supply for detecting a current of a direct current (DC) output terminal, the secondary side of the transformer having a first output terminal, a second output terminal and a reference terminal, the current detecting circuit comprising:

• bipolar junction transistors, comprising a first transistor and a second transistor, the first transistor having a base connecting with a base and an collector of the second transistor to form a common base terminal, the first transistor having an emitter forming a first detecting terminal and having an emitter forming a feedback terminal, the second transistor having a collector forming a second detecting terminal;
• and
• a field-effect transistor (FET) having a source, a gate and a drain, the source connecting to the first output terminal of the transformer, the drain connecting to the DC output terminal;
• wherein the first detecting terminal is connected with the source of the FET, the second detecting terminal is connected with the drain of the FET, the feedback terminal is connected with the gate of the FET;
• via detecting the tiny current of the DC output terminal by using the bipolar junction transistors, the FET being turned on or off to release an energy stored in the transformer.