A transformer with DC well thats a new one.The only way I have ever heard of a transformer working with DC is if the DC is switched, with a transistor or some other means.
The old ignition systems of cars were DC and a set of points (contacts)the points broke the circuit everytime the high spot in the distributor came around.
For a regulated output they used to put a zener in the base-emitter circuit of a power transistor and take the output from the emittor side of the transitor but again these were filtered power supplies, but the output was always about .7 volts higher on the output because of the forward biased emmitter-base junction.
But as far as using pure DC with a transformer can not be done.
Mark
