> > Wouldn't you need an extra diode with a bipolar transistor that you
> > don't need with a MOSFET (built-in)? That's the reason I suggested a
> > MOSFET.
> 
> Unless the MOSFET is avalanche-rated for the coil energy you need a
> diode anyway. The parasitic body diode should never conduct.

True. In other words the MOSFETs parasitic body diode is in the wrong place to be 
useful in this circuit. It won't become forward biased. It would be ok however if, as 
Spehro says, the parasitic body diode is suitably avalanche rated (behaves like a 
zener diode when reverse biased). Some power MOSFETs do have this feature.

-- 
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  brent.brown@clear.net.nz


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