MOSFET/circuit troubleshotting :-\

From: Danny T (danny_at_nospam.oops)
Date: 01/09/05 

Date: Sun, 09 Jan 2005 12:31:22 +0000

Things just aren't going that well *sigh* :(

I've got a simple circuit with an IC controlling a motor via a MOSFET.
The motor has a diode for back emf protection, two caps, etc., etc.

Anyway... When I power it up, the motor doesn't spin as expected. If I
replace the source/drain legs of the MOSFET with a piece of wire, the
motor runs, suggesting to me either the MOSFET is bust or the chip isn't
outputting a high.

If I wire the pin up to an LED instead of the MOSFET, the LED lights
fine. This suggests the MOSFET...

I replaced the MOSFET with a new one - same problem. I tried
disconnecting the gate and connecting it to 4.5V via a 10M resistor -
motor spins fine!

I'm at a loss... The MOSFET seems to respond to being connected directly
to something, but not to the IC's output. It definately worked at some
stage this morning (until I started fiddling)...

:-( 

-- 
Danny