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
    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)

    ->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!