Switching power supply having a frequency limiting circuit

A method of reducing switching losses in a switching power supply device, wherein the power supply device comprises 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;
• the method comprising:
• limiting a frequency of operation of the switching element by charging a charging circuit with the reverse polarity voltage produced in said feedback winding and absorbing a current developed by the kick voltage in said feedback winding by discharging the charging circuit in a kick voltage absorbing circuit that prevents the switching element from going into the on-state due to the kick voltage, thereby 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.

A method of operating a switching power supply device having 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;
• and a rectifying circuit connected to said secondary winding;
• the method comprising charging a charging circuit with the reverse polarity voltage produced in said feedback winding and absorbing a current developed by the kick voltage in said feedback winding by discharge of said charging circuit, thereby preventing said switching clement 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.