Patent ID: 6185112
Filing Date: 2001-02-06
Classification: H02M,Y02B

Abstract:
A switching power supply device comprising:a transformer having a primary winding, a secondary winding and a feedback winding, the feedback winding producing a feedback voltage including a same polarity voltage having a polarity the same as a voltage in said primary winding, a reverse polarity voltage and a kick voltage;a switching element connected in series with said primary winding, the switching element having a switching frequency and having an on-state and an off-state and switching the voltage in the primary winding;a controlling element connected to a control terminal of said switching element;a controlling circuit provided between said controlling element and said feedback winding;a rectifying circuit connected to said secondary winding; anda frequency limiting circuit including a charging circuit adapted to be charged by the reverse polarity voltage produced in said feedback winding, and further including a kick voltage absorbing circuit for absorbing a current developed by the kick voltage in said feedback winding, by discharge of said charging circuit, said frequency limiting circuit preventing said switching element from turning on due to the kick voltage generated in said feedback winding in correspondence to a light load signal provided by a load coupled to the power supply device when the load is light.