Three terminal type power switch power supply circuit

The invention relates to a circuit of a three-terminal type power switching power supply, comprising a transformer T1, a rectification circuit connected with the terminal 1 at the primary side of thetransformer T1, an output circuit connected with the secondary side of the transformer T1 and a feedback circuit which is connected with the terminal 3 at the primary side of the transformer T1 and the feedback terminal JK of the output circuit; wherein, the three-terminal type power switching power supply also comprises a three-terminal chip; the feedback signal control terminal VC of the three-terminal chip is connected with the output terminal of the feedback circuit, the chip high voltage terminal VD of the three-terminal type chip is connected with the rectification circuit and the terminal 2 at the primary side of the transformer, and the ground terminal VS thereof is connected with the terminal 4 at the primary side of the transformer T1. The invention has the advantage that the requirements can be satisfied by simple Y-shaped three-pin encapsulation, thus lowering the cost and being convenient for use.