Patent ID: 6137695
Filing Date: 2000-10-24
Classification: H02M

Abstract:
A self-oscillation type switching power supply comprising:a transformer having a primary winding, a secondary winding and a feedback winding;a switching transistor to interrupt current in said primary winding supplied with an input power supply voltage, the switching transistor performing an on-off operation having an on state and an off state, a feedback signal being provided by said feedback winding;a rectifying smoothing circuit being connected to said secondary winding for providing an output voltage and an output current;a controlling circuit controlling the on-off operation of said switching transistor in response to the feedback signal and a signal responsive to the output voltage, said controlling circuit including a first controlling transistor;a detector detecting a flyback voltage produced in said feedback winding when said switching transistor is turned off; anda second controlling transistor coupled to the detector and maintaining said switching transistor in the off state such that the output current becomes zero once the flyback voltage attains a predetermined value.