I recently built a rather crude SMPS using two very powerful IGBT's and a SG3525 and IR2110 driving circuitry. It's a half bridge and even though it's unregulated the output voltage is quite stable , dropping only few volts as the power output goes up to 1KW and some more volts after that.but since i will be using it as a power supply for a power amplifier this voltage drop is fine with me because it was measured with a constant resistive load. now heres the problem.two IGBT's in half bridge are driving two separate transformers with the primaries in parallel. at the very powerup moment the secondary output voltage goes all the way up to 300 volts for a brief moment and only then goes to its intended 180v DC. it happens on both secondaries. the question is what could I use to limit this ? if it were AC , i'd simply use a triac but I guess on DC voltage surges and spikes are harder to stop? A varistor is built for voltage surges but i think it's not meant to be used as a regular voltage surge stopper , only for extreme cases and it also puts alot of load onto the power supply. basically the only real and simple way of getting rid of this for now to my mind would be to use a startup delay circuit with a relay which switches the power from the psu to the amplifier board with a delay.