I've been once again working on my TIG Welder design in my spare time. I determined back when I originally attempted to undertake this project that I just wasn't knowledgeable on SMPS design to be able to create this powerful of a supply. After over a year of research and simulating, I think I'm ready to start settling on a design that I will be able to prototype here. This will still be a hard-switched full-bridge(driven with GDTs) with CMC and the output will be constant-current regulated. I've recently stumbled upon some very fast, high power, low loss, IGBTs from Fairchild that should make this design much easier to implement from a DIY standpoint. I'm still a little bit unsure on the specific controller IC that I would like to use for the prototype, I've been considering the UC3846 as my initial selection and it seems as though it would be adequate for the task, although I'm open to any suggestions on this. I do have one main question about the controller and the bridge driving technique. I've done a little bit of research about Phase-Shift controllers for use in resonant SMPSs. One of the application notes I've found on this subject used a UC3875 controller driving a resonant full-bridge with GDTs. One interesting thing I noted about how the Phase-Shift controller works is that the GDTs are always driven at a near 50/50 duty-cycle(there is a little dead time to avoid shoot through on the bridge), but due to the way the phase-shift works, the main power transformer can see anywhere from 0 to 50-4xTd for it's duty cycle. Td being the turn-on delay for each of the IC's outputs driving the GDTs. My question is, since these converters often only achieve resonance above a certain load threshold, and below that load they usually run in either quasi-resonance or hard-switching; Is there any reason that a Phase-Shift controller could not be used for a strictly hard-switched application(The GDT 50/50DC could make the drive circuitry slightly easier to implement)? I've ran some simple, manually generated, simulations of just the bridge itself, and it seems that it's possible, but I know simulations are sometimes way off from how things really work. My main concern involves the fact that in a regular full-bridge, the dead-time that the main transformer sees is essentially an open circuit for the transformer, in that all four of the switches are off. This doesn't happen in the phase-shifted bridge except at 0%DC(this may extend slightly above 0% depending on the delay-times set for each side of the bridge but is still a very tiny margin) when both outputs are switching exactly in phase with each other, in which case it's irrelevant. Once the phase begins to shift, and the DC of the main transformer increases(in which the on-time is greater than either side's delay), at least one of the switches is on at all times(which switch depends on which part of the switching cycle you're looking at), and for the majority of the dead-time the main transformer sees, two switches are on connecting both legs of the primary to the same rail which gives zero volts across the primary and zero current being forced into the primary. So my question stands as, would this negatively effect, or prevent the use of, using a phase-shift controller for a strictly hard-switched full-bridge, given that the main transformer's dead time is essentially created by shorting both legs of the primary to the same rail? This doesn't pose a problem for the resonant bridge because there is a capacitor(along with the resonant inductor) connected in series with the primary and one side of the bridge.