Injector Driver Module

[Jose Rodriguez]

  You will lower the drive voltage from 14V to 5V. And will use a pass transistor, to handle the 5V switching power supply current.

  To be able to conduct 4A, the drive voltage should be at least 10 volts (10V divided by 2.3 ohms = 4.3A).

  So how are you going to conduct the 4A peak, using only the 5V supply?
  The way I would do it is to briefly apply the battery voltage when the 4A peak is needed, and then switch back to the reduced (5V) power supply.

>>> Lawrence King <lawrence at promobility.net> 08/12/98 01:06PM >>>
Peak operating current is 4A for the injector that is opening now, plus
up to 7A to hold open the other 7 injectors, grand total 11A. I have
assumed that you only open one injector at a time.

The switcher chips can use an external pass transistor (or FET). The
switcher should operate at about 50% duty cycle at full load. The pass
transistor will be either ON or OFF, and will need to conduct 22A when
ON (11Amps/50%). The power disipation of the pass transistor is the ON
resistance (0.01ohm?) times 22A squared, or about 5W (actually 0.484W).

For the pass transistor I don't expect you would choose a bi-polar
device, probably something like the injector driver transistors on the
EFI-332 driver board.

Greg Hermann wrote:
> 
> How are you going to get the peak opening current?
>                                 Greg
> 
> >Hmmm... Why go to all of the trouble to switch the injectors from
> >+14V. This would be a very tricky switch mode power supply design. Why
> >not simply lower the drive voltage. If you drive the injectors from a
> >lower voltage (say +5V) then your power dissipation will drop to a
> >mangeable level.
> >
> >National Semiconductor builds chips which are switch mode power
> >supplies (I think the family is called "simple-switcher") or you can
> >buy a commercial module (try PowerTrends http://www.powertrends.com/ )
> >to drop the voltage. This also solves the problem of not having enough
> >volts to fire the injectors while cranking.

--
Lawrence King   lawrence at promobility.net    Ottawa Ontario Canada
70 Buick Wildcat,        71 Lotus Elan,          92 Nissan NX2000
I am a three car family (four if you count the Buick as two cars)