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From: Carl Smith
Subject: Re: Where do they get those MOSFETS?
X-Newsreader: Forte Agent 1.92/32.572
Date: Sun, 15 Dec 2002 06:34:23 GMT
NNTP-Posting-Date: Sat, 14 Dec 2002 22:34:23 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
On 14 Dec 2002 16:49:36 -0800, firstname.lastname@example.org (Bob Arnold)
>I have designed/built H-bridge PWM motor controllers with inexpensive
>MOSFETS ($5) and I am now trying to beef up my design to match the
>characteristics of say a Curtis golf cart motor controller (48V @ 650A
>cost:$574) I assume they use an H-bridge configuration using IGBTs or
>MOSFETs, however I cannot see how they can because the components are
>either much to expensive(IGBT) or not capable of withstanding such
>high currents (MOSFETS);
>- IGBT - GA600GD25S - $248 - Vce 250, Ic 1200
>- MOSFET - IXFN200N07-ND - $35 - 70V, 200A (pulse width not obvious)
>- MOSFET - IRFP2907-ND - $6.60 - 75V, 209A (from the datasheet, the
>device can only withstand a 75V pulse of 200A for 100 uS)
>Am I misunderstanding the specs of the Curtis controller? What power
>technology do these (Curtis) controllers use?
Like someone else already mentioned, it looks like you are
missing a decimal point in your amp spec. A golf cart motor
controller would be more in the 65 amp range, not 650A.
A 650A controller is more typical of what would be found in an
electric forklift. I used to design such controllers at a past
job at an electric fork lift manufacturer, and we used the
IXFN200N07 you mention above. (Actually another engineer
designed this particular one.) The controller used 6 of them in
parallel to get the necessary current. What made it affordable
is that the price comes down drastically when you buy tens of
thousands of the mosfets at a time. I think we were paying
somewhere in the $13 a piece range.
Right before getting downsized out of that company I designed a
smaller controller that would do 125A. I used three TO-220 parts
that cost about $3 each. $9 to control 125A. For the mosfets,
that is. The die inside these fets actually has a far higher
current rating than the leads of the TO-220 package could handle.
I think the part number was HUF75345.
The controllers we designed were just run of the mill Pulse Width
Modulation controllers. Just big banks of fets and really high
current diodes. Most of the complexity was actually in the
overcurrent protection circuits and the current sensing circuits
that were needed for our motor control methods. Probably similar
for the Curtis controllers.
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