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From: firstname.lastname@example.org (Bob Wilson)
Subject: Re: Help - Power mosfets - difficult load
Date: Mon, 21 Oct 2002 04:05:18 -0000
Organization: Your Organization
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References: <email@example.com> <firstname.lastname@example.org>
In article <email@example.com>,
>On Sun, 20 Oct 2002 18:34:07 +1000, "Phil Allison"
>>"Bill Allison" wrote in message
>>> Be aware I'm not an electonics professional - advanced enthusiast is
>>> about accurate.
>>> Problem: I have to drive an automotive starter motor at variable
>>> speed. The motor is used to drive a large model glider winch and
>>> tow-line tension must be smoothly controlled. Tension is sensed by a
>>> spring and potentiometer arrangemnent. Power is supplied by a 12v car
>>> Solution? Use the pot to control pulse width (NE544 or similar) of
>>> 50Hz pulse train fed via gate drive IC to bank of paralleled SMPS
>>> mosfets (IRF3703 or similar).
>> ** Why 50 Hz ?? A couple of kHz or so would be much more
>>fficient - smooth DC drive results.
>> Use enough low on resistance fets and you should be OK. It may be
>>possible to use only a small heatsink if the Ron is under 1 milliohm . The
>>motor stall current is the big worry - can be a hundred amps or more.
>> Regards, Phil
>> BTW Are we related ??? ................. :-)
>Gawd I hope not - one is enough! :)
>I would also suggest you use one of the MOSFET gate drive ICs,
>Maxim do some I think, they will minimise power dissipation
>in the MOSFETs.
Why? With an N-channel FET, with source grounded, all you need is s simple
NPN-PNP totempole pair as a driver, driven by a logic gate or similar. There
is really no special magic in this. Not every problem needs a special IC as
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