From: "Michael Brown"
Subject: Re: Fan controller
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Mon, 14 Oct 2002 19:53:14 +1300
NNTP-Posting-Date: Mon, 14 Oct 2002 19:53:44 NZDT
First of all, thanks for the replies people :)
"petrus bitbyter" wrote in message
> I consider a microcontroller quite a heavy hammer for so small a pin but
> that's up to you.
Well, I'm extending my (homemade) watchdog timer, which uses an 8535, so I
thought I might as well make it completely programmable :) Also so I can do
stuff like coil-burnout protection, switch on/off fans based on absolute
temperature, numerical temperature difference between two places, percentage
difference, all of the above, etc ...
> A micro can drive a Mosfet directly. That's where Mosfets are known for:
> Very high input impedance. A transistor between them will not do any good.
Oh, cool :) I'm using a few ideas from a design for a stepper-motor
(http://lerch.yi.org/atm/The%20Circuit.htm) and trying to understand what's
going on ...
> You have to realise your fans are an inductive load. You will need a
> freewheel diode to protect your Mosfet.
Yup. The stepper motor design which had these in, though I'm taking the more
simplistic method of just dumping the power back to the fan as I don't need
to be rapidly switching on and off the fans.
> "Michael Brown" schreef in bericht
> > Hello all,
> > I'm in the process of designing a fan controller for my computer, and
> > it's going to be situated quite close to my hard-disk, I'm wary about
> > relays to do the switching for the fans (as I have done with my other
> > control circuits). The load is going to be 12V and not more than 2A, and
> > controller is going to be a AT90S8585 microcontroller. After reading up
> > bit, it seems the best way to go is to use a decent MOSFET to do the
> > switching, and have another (smaller) transistor between the MOSFET and
> > microprocessor to keep the current requirements on the microprocessor
> > Is this the right approach and are there any things I should watch out
> > Thanks in advance,
> > Michael Brown
> > --
> > My inbox is always open (remove the obvious):
> > emboss1@i4free.NOSPAM.co.nz
My inbox is always open (remove the obvious):