Switching power converter for reducing EMI from ring oscillation and its control method

摘要

A switching power converter (200, 300, 400, 500) comprises a transformer (211) with a parasitic capacitance (212), a first switch (207) coupled to the transformer (211) and configured to couple or decouple a load (219) to or from a power source via the transformer (211), a switch controller (205) coupled to the first switch (207) and configured to generate a switch drive signal (206) for turning on or off the first switch (207) according to switching cycles, and a bypass circuit configured to provide a bypass path for the parasitic elements such as the parasitic capacitance (212). The bypass circuit may be coupled in parallel with the auxiliary winding (220), the primary winding (213), or the secondary winding (214) of the transformer (211). High frequency ringing and EMI/RFI is reduced when the bypass circuit is enabled.