Abstract: A resonant mode power supply includes a soft-start circuit for, at start-up, for sweeping the frequency of the power supply from a maximum value to a minimum value. The soft-start circuit performs this frequency sweep using the functionF(x)=1-e.sup.-tUsing this function, change in the frequency, and correspondingly the increase of the output voltage decreases over time, thereby allowing a feedback circuit of the resonant mode power supply to respond to the level of the output voltage and to begin regulation when the output voltage achieves the desired regulation level. As such, overshoot of the output voltage with respect to the regulation level is lessened, if not eliminated.

Abstract: A resonant mode power supply includes a d.c. voltage source and switching elements for alternatively connecting an oscillating circuit, including the primary winding of a transformer, to the d.c. voltage source and to ground. In order to detect faults in the load on a secondary side of the transformer which would cause the resonant mode power supply to attempt to supply and inordinate amount of power, the power on the primary side is detected and if this primary power exceeds a predetermined threshold value, the frequency of oscillation is increased to reduce the power. If the fault condition persists, the switching of the switching elements is discontinued.