[SOLVED] 700W dcdc converter topology selection

[dhan_pow]

Input is variable from 30 to 70V. Output is 120V, 700W. Which variant of full bridge converter is preferable? Normal one or phase shifted with zvs

 

[Easy peasy]

easy - 700W could be half bridge hard switched, or, full bridge, 4 diode bridge, o/p choke ... 70kHz

 

[dhan_pow]

Thank u for the reply. At this watt whether phase shifted full bridge with zvs be advantageous?

--- Updated Jul 2, 2020 ---

Why four diode bridge?

 

[biswaIITH]

Thank u for the reply. At this watt whether phase shifted full bridge with zvs be advantageous?

--- Updated Jul 2, 2020 ---

Why four diode bridge?

You can try with PSFB topology which will be having ZVS for better efficiency & EMI.

For Low output voltage & High current PSFB :- Output should be Center Tap Configuration
For High output voltage & low current PSFB:- Output should be A diode bridge configuration

 

[Easy peasy]

at 700W, PSFB introduces extra circulating currents in the H bridge and the Tx primary, at a modest sw freq, the net losses in the hard switched equivalent are actually lower - snubbing takes care of RFI - just need a reasonably low leakage transformer - also PSFB is not soft switched at light load - unless you add extra parts - so you may need snubbers anyway on the PSFB for this --- so you see - not totally clear cut if you want a nice simple solution ...

 

[treez]

As the following shows, the PSFB, to be used in its optimal form, needs diodes to the rail, and extra series primary inductors to be added…even capacitors across the FETs......

https://www.edaboard.com/threads/phase-shift-full-bridge-smps-is-massively-over-hyped.342663/

The Plain Full Bridge also means you avoid those nasty failure modes which can lurk in the PSFB as attached. Infineon do special FETs for PSFB, with ultra fast, soft switched intrinsic diodes, because they do not believe that exposure to such harsh conditions can be avoided in the PSFB.

--- Updated Jul 2, 2020 ---

Here is an basic LTspice of a full bridge 30v to 120v at 700w...notice how the leakage means you need higher duty cycle than expected otherwise.

--- Updated Jul 2, 2020 ---

Due to the high 50A peak primary current at 30Vin, you could do two full bridges in parallel, both controlled by a single external error amplifier.

 

[treez]

The unique switching strategy of the PSFB, means that compared to the regular Full Bridge, the PSFB presents the danger of severe reverse recovery of the primary side diodes.

 

[sabu31]

Two Switch Forward Converter is also a suitable contender if efficiency is not critical. It is a robust topolgy. Developing PSFB also depends upon experience with power electronics