> From: Ian McLean [SMTP:ianmclean@OPTUSHOME.COM.AU]
> > Sent: Wednesday, February 05, 2003 3:06 PM
> >
> > The problem I see with an LC filter is picking a good inductor value.
> > Because I am drawing large amounts of current, the inductor cannot be
> too
> > small.  But it cannot be too large either or I will getting ringing on
> my
> > power supply side.  Any suggestions for a good combo for cap and choke
> to
> > do
> > the job ?
> >
> >
> What sort of current are you talking about?  You can get some high current
> surface mount inductors that are still quite physicaly small.  Obviously
> the
> higher the PWM frequency the better, as smaller value components can be
> used.
>
        From:   Ian McLean [SMTP:ianmclean@OPTUSHOME.COM.AU]
        Sent:   Wednesday, February 05, 2003 3:17 PM

        8 to 16 amps at 12V PWM with duty cycles between 50 and 100%.  I am
using a
        cascaded Mosfet switch to both drive the current and to isolate the
12V side
        from the logic side.  I am keeping the frequency at 5kHz - well
above the
        2kHz stress point.

Hmm, that's quite a bit, certainly inductors for that level aren't going to
be very tiny.  The TEC's I deal with take around 1.2 Amps at no more than
3.3 volts, so getting SM parts for filtering isn't such a problem.  Check
out the PDF at http://www.scanti.ru/docs/datasheets/slos365.pdf which is the
datasheet for a PWM TEC power driver from TI.  It contains a lot of design
theory for LC filtering and has an equation to work out the efficiency loss
from rippple in the TEC supply.

Vishay make a reasonable range of high power inductors
http://www.vishay.com/inductors/dc-more-5A/

Regards

Mike

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