Lpc2000

At 02:45 PM 11/2/05 -0500, Tom Walsh wrote:
>Rob Jansen wrote:
>
> >>For that kind of drive I'd go for a MOSFET myself.  They are resistance
> >>devices.  You might be able to drive them from the I/O pin.  If you use a
> >>logic level FET and drive them at 5V you certainly will be able to.
> >>
> >>
> >
> >And do not forget to add a diode accross the FET, some MOSFETs have a
> >diode built in but it may be too small, depending on your load.
> >Solenoids and things like motors have huge coils - keep this in mind
> >when designing.
> >
> >
>
>I generally use a 2N7000 or 2N7002 FET for driving relays.  They can
>sink up to 100ma easily and have an internal clamping diode to protect
>the gate when the coil (de)energizes.


Well the original post did say they had a 2 Ohm coil.  That in turn would 
suggest a multiamp drive was needed.  That diode in the 2n7000 won't 
protect against inductive spikes though, it's in the wrong part of the 
circuit.  You are probably getting avalanche breakdown and I don't think 
I've seen a data sheet for either of these parts with an avalanche rating.

Robert

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