Hello, In a multi output flyback converter, the outputs are often cross regulated when only output of one winding is controlled by the feedback circuit. The bias winding is an additional output and the expectation is that the output will depend on the turns ratio between the output that is regulated and the bias winding. The regulation of the bias winding depends on a number of factors which includes the diode drop of the rectifiers on the output winding, the forward recovery time of the output rectifiers and the leakage reactance of the bias winding. A couple of simple fixes can resolve this problem. You could reduce the bias winding number of turns and also adde a small resistor in series with the bias winding. Please also note that winding sequence on the transformer will also affect the regulation of the bias output to some extent. As always when any changes are made, it is recommended that you verify the bias winding output at low line, high line and with no load at output and full load at output. Regards PI-Sarek