At 01:55 PM 8/23/02 -0500, you wrote:
>Hi all,
>Once in the past I needed to switch a lot of current so I paralleled a few
>BJT power transistors together.  I am currently switching 24VDC through a
>coil(a couple ohms) through an IRF840LC FET with an on time of 200us every
>2ms (500hz).  The FET gets pretty hot.

Do you really need the 500V rating? That FET has a fairly high Rds(on),
because of the high voltage rating.

>I need to increase the on time to
>1ms so I anticipate it is going to get extremely hot.  I'm wondering if any
>of you with experience can tell me if its possible to parallel FETs to
>spread the load?

Yes. Reasonably matched devices parallel well, and the positive tempco
of Rds(on) prevents current hogging, but guaranteeing it in production
is something else again.

>I'm wondering if the lower capacitance (the LC in 840LC) will be increased.

Yes, of course it will be increased proportional to the number of devices
paralleled (plus stray capacitance, but that shouldn't much matter).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body