EMI frequency spreading method for switching power converter

摘要

A controller of a switching power converter sets an actual turn-on time of a switch in the switching power converter in each switching cycle by selecting one of a plurality of valley points of the output voltage of the switching power converter occurring subsequent to the desired turn-on time of the switch. The desired turn-on time of the switch may be calculated according to the regulation scheme employed by the switching power converter. The controller selects one of the plurality of valley points randomly from switching cycle to switching cycle. The controller generates a control signal to turn on the switching power converter at the selected one of the plurality of valley points of the output voltage occurring subsequent to the desired turn-on time.

主权项

1. A switching power converter comprising:
a transformer including a primary winding coupled to an input voltage and a secondary winding coupled to an output of the switching power converter; a switch coupled to the primary winding of the transformer, current in the primary winding being generated responsive to the switch being turned on and not being generated responsive to the switch being turned off; and a controller coupled to the switch and configured to generate a control signal to turn on or turn off the switch, the switch being turned on responsive to the control signal being in a first state and the switch being turned off responsive to the control signal being in a second state, the controller being further configured to:
determine a desired turn-on time of the switch in each switching cycle according to a regulation mode employed by the switching power converter;select one of a plurality of predicted local minimums of a voltage across the switch that are predicted to occur subsequent to the desired turn-on time, the selection being made based on a value of a selection signal; andgenerate in said each switching cycle of the switching power converter the control signal in the first state to turn on the switch at an actual turn-on time corresponding to the selected one of the plurality of predicted local minimums of the voltage across the switch.