Injector Drivers - Block P


        Here we can drive our eight (8) Fuel Injectors.  Both High and Low Impedance injectors can be driven.



        The popular LM1949 Injector Drive Controller is used in our application.  Primarily designed to control low impedance injectors in Sample-N-Hold operation this circuit will drive high impedance units just fine also.  The key point here is that when the controller goes into hold mode it will try to maintain 940ma through the current sense resistor.  Actually it tries to maintain 94mv across the sense resistor.  In our case it is a .1 ohm unit so ohms law will gets us to the 940 ma.  Well a high impedance injector with a DC resistance around 15 ohms there isn't enough potential across the injector and the driver to ever even get to 940ma.  So what we end up with is a saturated style driver.
        For low impedance operation the timer (R300/C300) is set to just under 5ms.  This timer is used to drop the output current to 940ma if the 3.85 amps can not be achieved before the timer times out.  This condition can occur during cranking or anytime the battery voltage is too low to achieve the trip current.
        This circuit has been bread boarded so there is waveforms and more information there.