PICdude wrote:
> I need to switch a number of solenoids from a PIC, and the solenoids
> will be normally-off unless told otherwise.  I'm considering on-board
> relays vs. MOSFETs.  MOSFETs would be nicer due to the smaller space
> requirement, but I understand that in case of failure, MOSFETs usually
> fail closed whereas relays usually fail open (unless contacts get
> welded, etc).

A mechanical system like a relay is going to be less reliable than a
transistor IF the transistor is not being abused.  A properly used
transistor should last indefinitely for most practial purposes.  With a
inductive load like a solenoid, you have to make really sure the stored
energy in the coil is handle properly when shut off.

The best thing would be to use transistors and make sure they are allways
run well within specs.  What are the voltage and current requirements of th=
e
solenoids?  Why do you think you need FETs?  Why wouldn't a bipolar be able
to do the job just fine?  How fast do the solenoids need to respond to off
and on switch commands?


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