Poweroutput to injectors

[Tommy.Palm at oron.ds.sll.se]

Hi!

I wonder if anyone here has worked with optimizing the outputstage to
injectors.
I need to get a outputstage that is as fast as possible and also freqvec=
y
linear to drive fuelinjectors. At first i thought this was no problem at=
 all,
most people have not even digged deep into this problem. I have a 4cyl t=
urbo
with
DIY_EFI and found that i need as fast open close time as possible. At fi=
rst i
tried just a freeweel diod to protect the transistor but it slowed down =
the
injector too much. The best thing yet was using 4 high voltage >300v
transistors but they can (the ones i afford) just handle 1 Amp and the p=
eak
hold system needs about 2,5 amp max (tested with oscilloscope, 5.5 amp
according ohms law)
I testrunned it for 2 days in bench w/o destroying the transistor but it=
 should
theoretically not last very long.

I have with oscilloscope found out that 330-470uF is perfect for the pea=
k
current (gives 10-13 volt slope for 2ms) and 8-10ohm is optimum for the =
hold
current on 2,4ohms injectors (they need just 1.3 volts to open). The vol=
tage
drop is
only <0.1v over transistor. The next best system was a capacitance paral=
ell
with the resistor and injector to decrease voltage over the transistor b=
ut see
mes too slow the opening. What i have seen on commercial low ohm inj sys=
tem is
condensator to cut the HV. Have anyone tried a varistor? Is the lifetime=

limited? One don't want a short here (flooded cylinder)!

I need injectioncycles down to 1,5 ms it was possible with HV-transistor=
=2E

Here is a circuit pic in windows paint of one of the tested curcuits:

Thankfull for any ideas and help! I am not interested in special curcuit=
s to
solve this.

Tommy Palm
tommy.palm at oron.ds.sll.se
Sweden

[jsg -- I deleted the bit map since it was about 1000K bytes. Please
contact Tommy if you would like a copy.]