Adding a resistor to raise injector impedance - Comments?

[Murphy, Ian]

The Burr-Brown / TI part DRV103 will drive injectors up to 3A peak without
any external parts other than a couple of resistors a cap and a flyback
diode.

Ian

-----Original Message-----
From: tim.van.setten at acssd.L-3com.com
To: diy_efi at diy-efi.org
Sent: 10/04/01 16:18
Subject: RE: Adding a resistor to raise injector impedance - Comments?

> Obviously, this resistor would need to be large to handle the current,
> but is this considered a bad practice?
> 
	Yes it is.  Injectors are driven by current, not voltage.  When
adding a resistor you lower the current and slow down the turn-on time.
	Someone earlier mentioned about reversing the voltage when
turning
off the injector to help it close faster.  The problem is the armature
inside the injector is not magnetically charged, or to say, there is no
polarity involved.  Any current in any direction will turn it back on.
To
close the injector faster you must allow the magnetic field to collapse
as
fast as possible.  This is why the "Peak-and-Hold" drivers were
developed.
They use the peak to turn it on fast, which means there is a large
magnetic
field built up, then the hold part is to allow the magnetic field to
collapse, but not fully.  Just enough to keep it turned on.  Now when
it's
time to turn it off, it can be done rather quickly because most of the
field
energy has already been dissipated.
	 
> I am curious if anyone else has run into this issue, or do you guys
> avoid this by using saturated injectors?
> 
	All the time. 

> Would it be possible to use the injector outputs from the ECU to drive
> a second set of injector drivers?  I watched the thread about
> peak-and-hold injector drivers, but nothing seemed to materialize, and
> according to one of the webpages on the DIY-EFI site, the Motorola
> MC3484 injector driver is no longer in production.  Web searches, so
> far, haven't yielded much on 'injector drivers'.
> 
	Some of us use additional injector drivers.  Up until about a
couple
of months ago, the Cherry CS452, and CS453 were available.  Now they're
out
of production.  The only alternative so far is to use the LM1949 and all
the
associated external parts.  The MC3484S2-1 and the CS452 were nice
because
all of this was inside one neat little package.

	If anybody else knows of any other Peak-and-Hold drivers. Please
let
us know........Tim.  
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