I have a step-up transformer that has a 24 volt primary being driven by a digital network (pwm, H-bridge with linearizing LC filter). The secondary is 300 volts, with total capacity of 300mA. The output needs to be regulated within +/- 10%, from 50ma up to full load. The problem is I don't want to add another transformer to sample the output, and don't want to have any connection between the secondary output and the electronics driving the primary. I can increase the voltage to the primary side to about 35 volts, and then regulate it down using a comparator and the existing 25KHz PWM control frequency. Question: can the moment to moment secondary output voltage of a transformer, from no load to full load, be derived somehow from the current flowing thru the primary side, in some linear fashion (keeping in mind the presence of the LC filter network, with the L being the transformer primary)? Can this be used in turn to regulate the voltage to the primary via the H-bridge power, and thus regulate the secondary? As always, any guidance, direction, feedback or enlightenment would be greatly appreciated!