Abstract: For use with a power converter, a bias voltage generator samples a fraction of the input voltage Vin using a bias switch coupled to a tap on the power converter transformer input winding. The bias switch is driven from the same control circuit that drives the converter switch, and the fraction of Vin sampled by the bias switch is coupled to a low pass filter to generate the bias voltage Vbias. Vbias≈(Vin)·(Kf)·(Kdc), where Kf is the fractional location of the transformer tap, and Kdc is duty cycle of the power converter switch. Vbias enjoys automatic compensation against variation in Vin because the power converter will automatically compensate Kdc to correct for Vin variation. The resultant bias voltage generator requires no additional transformer winding.