I have been researching about designing a 3kW DC-DC Converter (Vin 12V from a battery, Vout 350VDC) and actually wired up a simple isolated Full-Bridge based DC-DC converter a few days back converting 12VDC to 140VDC. However, I noticed that it was difficult to vary the output voltage using the duty cycle of the switches. Reducing the duty cycle from 50% to 25% only changed the output DC voltage by 10V or so.
Instead, what worked far better was if I varied the input voltage to the Full-Bridge. So I came up with the idea: why not feed the Full-Bridge with a Boost Converter? I have seen a Buck-Converter feeding a Full Bridge, such as the circuit below, but never a Boost Converter feeding a Full-Bridge. Searching about the issue on the web didn't turn up any schematics or app. notes either.
Is it feasible to feed a Full-Bridge Converter with a Boost Converter and control the output voltage by modulating/controlling the Boost Converter rather than modulating the Full-Bridge switches? I am not very familiar with control (yet) and would rather not go into a design that's a dead-end. If there were some schematics or app. notes on the web, I'd know that the topology would work.
I could go with the Buck fed topology, but then I'd just be stepping down my 12V source and then boosting it back with my Full-Bridge so the logical solution seems to be to first boost the 12V to 48V or so and then drive the Full-Bridge at 50% fixed duty cycle which in turn drives a 48V to 240V high-frequency transformer (30-40KHz). The stepped up voltage is then rectified and smoothed out via a few caps.
The main reason I want feedback in the circuit is that my source voltage is a battery that will vary from 10V to 14V. Without a feedback loop, this will cause rather variations in the output voltage.