High Power SMPS for NiMH charger, Help!

Discussion in 'General Electronics Chat' started by SpikeFiend, Jun 20, 2008.

  1. SpikeFiend

    Thread Starter New Member

    Jun 16, 2008
    1
    0
    Hello all,

    I'm looking to build a very high power smps NiMH charger for an electric motorcycle I'm building. I'd like to use a front-end power factor correction module like the lambda PF1000A-360, which outputs 1000/1500W at 110/220 VAC respectively (eventually I would like to put two of these in parallel and run a 2000W/3000W charger). Each PFC module is about $215. http://www.lambdapower.com/ftp/Specs/pr_pf.pdf

    Now, I would like to build a DC-DC converter that can take the 360VDC from the PFC module and step it down to about 70V (max, I need to run the charger in constant current mode to charge NiMH's) but I'm having some issues in a few areas:

    1) Which topology to use?
    *Buck-you don't see many coming down from 360V, is there a reason? Also, the high drive is something of an issue.
    *1-transistor forward-Has isolation and a low side drive, but the fet needs to be rated for double the input voltage
    *2-transistor forward-FET voltage is lowered from the 1-transistor version but introduces a high side drive again.
    *Full bridge-most complicated, and still has high side drive.

    (basic schematics of topologies here)
    http://schmidt-walter.eit.h-da.de/smps_e/smps_e.html

    ->I've seen many conflicting reports on what power level each topology is suited for.

    2) High side drive
    High side drive is becoming a problem for me. I've found some driver IC's from IR (http://www.irf.com/product-info/cic/fsgatedriverics.html) but the switching frequency seems to top out at 100KHz. I was hoping for faster switching to keep component size down, but then, I don't really know what frequency is acceptable to start with.

    3) Component selection
    When I use an online calculator to get an inductance for the circuit, I can't seem to locate a part (say from Digikey) that matches both the inductance and the current rating. This leaves me thinking I might have to wind my own? Isn't that like voodoo magic?

    Most of my issues seem to stem from the high voltage/high current requirements (my NiMH's are 95Ah, so you need to charge them with 40-70A to get a really well defined peak termination, I'm still at the low end of that range).

    So if anyone has any pro tips or other suggestions on how to pin down a few of the loose ends that would be greatly appreciated!

    Thanks.
     
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