Re: Searching for engineer experienced in 24V vehicle electrical design.

From: Winfield Hill (hill_a_at_t_rowland-dotties-harvard-dot.s-edu)
Date: 03/12/05

  • Next message: kell: "pwm chip" 
    Date: 11 Mar 2005 19:11:04 -0800

    GerberMultit00l wrote...
    >
    > 10.) Winfield Hill wrote:
    >
    >> Nah. Just plop an Infineon PROFET Smart SIPMOS switch in there.
    >> Get raw performance, short-circuit and thermal protection, and
    >> an error indication, all at a low cost. For example, use a
    >> BTS443, BTS432, BTS442, etc.
    >
    > I would love to use a solid state solution. I wanted to do this in a
    > bad way. Problem though. I can't keep a FET cool enough. My product
    > must operate up to 70C ambient. The FET would be passing up to 30A for
    > 2=2E5 minutes. Even if I could use a ultra low RDSON part of say 4
    > mohm it would still be dissipating 3.6W. Stack a few in parallel and
    > I still won't be able to remove the heat. My electronics are embedded
    > in a small sealed glass filled Nylon box (sealed from the elements that
    > is). Even if I could fit a heat sink inside my packaging space I still
    > don't have a way to get the hot air out and cool air in. We cannot
    > re-tool the housing to accomodate a heat sink at this point.

     Well, what a crazy set of requirements; you might try spelling them out
     for us at the get-go, so efforts aren't wasted on non-starter solutions.
     Your "port our 12V automotive product design to 24V" description doesn't
     convey much of the reality.

     But back to Infineon's PROFETs, there's their 800-pound gorilla, the
     BTS555. This little 5-lead TO-218 baby has an Ron of only 2.5 milliohms
     max at 25C and 2.7 milliohms typ at 85C. Therefore it should dissipate
     under 2.5W at 30A at 70C. That's a trivial amount of heat to get rid
     of with a small bit of modestly-heat-conductive material.

    > That and then there is the issue of reverse battery connection and the
    > internal body diode of the FET(s). I would need to add a rather large
    > diode in series with the load to prevent damaging reverse current flow.
    > This diode would take up even more space.

     The BTS555 shouldn't be damaged by reverse wiring, because the "Reverse
     battery protection by self turn on of power MOSFET" feature means that
     while current will flow (just as in the forward direction), the FET
     will turn on, shorting out the intrinsic diode with its high voltage
     drop, and thereby preventing any BTS555 switch-overheating damage. 

    -- 
 Thanks,
    - Win
  • Next message: kell: "pwm chip"

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