[Diy_efi] High-voltage P&H IDM

[David Allen]

> While there are single-chip solutions for running
> either saturated with high-Z injectors or
> peak-and-hold with low-Z injectors, I don't know of
> anything commercially available to drive a high-Z
> injector in a peak-and-hold mode, especially above
> Vbatt (since most injector drivers seem to ground the
> injector rather than switch the +12v side).
>
> One disadvantage is that there is more moving mass and
> a stiffer spring inside of a high-Z injector, meaning
> that you'd have to create a much larger amount of heat
> in the injector coil (and use more wattage) to open a
> high-Z pintle injector as quickly as you could open a
> low-Z disc injector using only Vbatt in a 12V system.

  I see.  Would be interesting to try with a single injector in a test rig
to see it a full-scale unit would have any benefits.
A MCU with on-chip comparators could provide the basis for a switching DC-DC
power supply for the high voltage; as well as process the timing of the
peak/ hold/ precharge currents.
  A MCU crcuit is only as delicate as the support circuitry on the board
with it. The datasheet shows the temperature ranges and they are respectable
for even cheap PIC micros.
  Currently my car doesn't need this.  The Malpassi regulator reduces fuel
pressure at idle to where the injectors are within their design minimum PW
and everything works fine. The transmission is at its limit (maybe
beyond...) at 12 PSI. The fuel system is not a limiting factor at this time.
In the future I might want to build an all-out insanity motor that would
need somthing like this.
  Thanks for the comments!
David