Abstract: A preload circuit for a DC to DC converter which has main and auxiliary outputs. The circuit responds to the voltage in the auxiliary output circuit to provide a linearly varying preload at the converter's main output terminals. The preload is a maximum when the usual load at the main output terminals is at the no load condition and becomes zero when the usual load at the main output terminals reaches a predetermined load condition which depends on the amplitude of the auxiliary output voltage and the amplitude selected for a reference voltage. In response to the linearly varying preload the converter linearly increases the duty cycle of its switching device(s). That linear increase in duty cycle causes the voltage in the auxiliary output circuit to linearly increase to thereby linearly maintain the auxiliary output voltage in regulation over the usual load condition at the main output terminals for which the preload is active and for the entire auxiliary output load range.