Driving Injectors

[Bohdan L Bodnar]

The fuel injector firing tool I'm finishing building uses a Phillips
enhancement mode power MOSFET with integral suppression diode (I don't
remember the part number off of my head);  it will easily drive a 3 ohms
peak-and-hold injector or low impedance saturated switch injector (I use a
10 ohms 5 W series resistor in series for the latter).  With MOSFETs the
main problem is that turn-off time is so low that a large back EMF kick
develops across the injector -- I've measured about 500 volts (yes, 1/2 kV).
I tried using a NE-2 bulb as a surge suppressor but that didn't help (it
was, however, the *brightest* neon bulb I've ever seen in my life).  I now
use a reverse-biased LED as a surge suppressor since it not only suppresses
the kick but also gives a visual indication of magnetic field collapse.

Incidently, the component was recommended by a friend who used to design
high voltage power supplies for Zenith's color television sets.  Send me
e-mail if you want a copy of the spec sheets (bohdan.l.bodnar at att.com).

Regards,

Bohdan