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Hi,
I am designing one High power density isolated DC DC converter with following specification.
Input voltage = Max 100Vdc
Output voltage = 12Vdc
Output current = 50Adc
I am at the beginning stage of design, could you please help me to select the right topology for above specification?
Also, after selection of topology I will be interested in filters and transformer selection aspects and finally selection of right part from the TI power portfolio.
Thank you
Regrads,
Rajesh
Hi Rajesh
There are a number of options here -
1/ The LM5045 is limited to 105V AbsMax - 100V recommended max. If you were to use it on a 110V input then you would have to find a way to limit the V_IN pin to less than 100V - a relatively simple zener regulator could do this. The high side gate drives HD1 and HD2 could not be used to drive the MOSFETS directly but they could be used as ground referenced outputs along with some external drivers - probably both high side and low side drivers would be needed to equalise the propagation delays but this is something the designers would have to look into. The UCC27714 high side and UCC27524A1 low side would be a good choice for gate drives in this case.
2/ You could put the LM5045 controller on the secondary side of the system. UCC25120 isolated drivers could drive the primary side MOSFETs. A secondary side controller can be designed to give a higher loop bandwidth than a primary side controller because you don't need an optocoupler to bring Vout information into the controller. You would also need both primary side and secondary side Aux supplies - normally a low power flyback works well - something like our PMP8787 design using the UCC28700
3/ A hard switched full bridge is a good option for low input voltages but the Phase Shifted Full Bridge is much better for high input voltages. It's difficult to know exactly where the boundary lies where one is better than the other but at 100V they are both fairly equally matched. At 400V the PSFB is clearly better because it can achieve ZVS for much lower switching losses.
4/ If you use a PSFB then the options are the UCC28951 or the LM5046. The LM5046 has the same input voltage limits as the LM5045 so the same considerations apply if you are using it on a 110V bus.
5/ The UCC28951 is a secondary side controller and the PSFB topology can be used from 100V up to 400V and beyond - with appropriate component selection and PCB clearances. The UCC21520 isolated driver is a good choice for primary side MOSFET drive.
6/ The UCC3895 is a primary side PSFB controller - similar to the UCC28951 but without the SR drive outputs. This would eliminate the need for a secondary side Aux supply, although you would still need one on the primary side.
BTW - you can normally get a higher loop bandwidth with a secondary side controller and interfacing to downstream system level circuits (monitoring etc..) is simpler.
Regards
Colin
