Current Fed Full-Bridge Isolated Boost Converter / Current Fed Step Up

What is the range of the duty cycle in your design?

I is able to vary from 50% to no more than 85%

you can use a push pull controller like 3526 or 3825 and invert the outputs.these controllers have 0 to near 50% duty cycle and when inverted it become 50 to 100%.

if using transformer drive, you can do it easily by reverse winding direction...

Inverting the output would also mean an increasing duty cycle, with a decreasing error signal..

This is not something that i want, then i have to add more components than needed.. 

There must be a pwm controller that meets these requirements.

Anyways thx for the fast response.  

You just need to swap the + and - input of error amplifier. no additional component needed.

aahh, at first i didn't notice that is did not have an internal error reference.

Then comes the next question, how do i go about phase shifting a controller or an output 180 deg? 

Also looks like the UCC3895 could do the job.

http://www.ti.com/lit/ds/symlink/ucc3895.pdf

I don't think its a good choice for current fed application. I know 3895 and did some projects with that.(all were voltage fed)

by the way  the output duty is less than 50% and you need to invert the signal to have time overlap on your switches.(negative dead time)

of course you can do it with transformer driving and reverse connection.

something like tl494 will fit your application. You can use outputs inverted or non inverted and have 2 error amplifier....

Thx for the fast reply and useful feedback.

I'm currently building a prototype and i'll let you know if and how well it works.

Hi All

After messing a bit with the tl494 i fount that it is working, but not as great as hoped, i'm still looking for a good alternative, something similar to the UC28023 but with tow phase shifted output that would go above 50%, I see that it has a "brother" the UC28025 but is does not offer variable current reference.

I were thinking of using something like LM5046, but i'm not quit confident about the feedback part, and if summing the outputs to obtain two phase shifted outputs with higher than 50% duty will work..

Hi Kristian,

I have similar topology. For MOSFET driving I choiced FPGA as it gives me full flexibility. As driver I got ISL2111 half bridge driver, but due to spikes I found in prototyp, for safety reason I moved to IRF2184S.

My design assume little higher currents at input., but from design point of view is similar. 

During bring-up, the main problem I got is leackage inductance of primary transformer. This produce pretty high overshoot when converter going from boost to energy transfering mode. 

If you follow with your LTSpice simulation, try to add something about 60nHr - 100nHr as leackege inductance to primary.

Good luck, Janusz

you need the LM5041B which can be programmed to exceed 50% duty cycle.Inductor value is determined by many factors.Check the data sheet for your starting point.