----- Original Message ----- 
From: "Jinx" <joecolquitt@clear.net.nz>
To: "pic microcontroller discussion list" <piclist@mit.edu>
Sent: Tuesday, January 16, 2007 2:51 PM
Subject: [EE] B+ disconnect


> Can anyone recommend an on-line crash-course in FETs ? I hadn't
> realised how many types there are until I had to look
>
> Attached is what I want to do. Basically the 12F monitors the
> battery and disconnects it from some loads when too low. An
> over-ride comes from another part of the circuit to stop the
> disconnect happening if a particular process is in progress
>
> I found a B+ disconnect here, using the BSP171, described as
> a SIPMOS FET in its pdf
>
> http://www.edn.com/archives/1994/090194/18di1.htm
>
> http://www.edn.com/archives/1994/090194/graph/18di1fg1.htm
>
> My problem is choosing a FET based on what voltage will work
> on its gate. The only other time I used big P-ch FETs was as the
> top half of a FET H-bridge. In that case 2 x V+ was needed to
> turn them on
>
> In this circuit I don't want to fiddle about making another voltage
> for the gate (although the 12F would be capable of that), so would
> like to be edumacated about FETs so I can pick one the engineer's
> way instead of wussing out and going bipolar with a TIP
>
> TIA
>


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