Disclosed examples include methods, power converters and damping circuits to control damping of an input filter circuit, in which a low-voltage secondary winding is wound around a common core with a primary winding connected between an AC input and a rectifier input of the converter, where the secondary winding is coupled in a series circuit with a damping resistor and a switch, and a controller selectively closes the switch with a controlled on-time at system power up and/or in response to detection of oscillation or transients in the power converter.