Driver Boards (Cherry Driver Load Resistor)

[David Rhoads II]

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Date: Mon, 18 Sep 2000 13:07:40 -0700
From: Garfield Willis <garwillis at msn.com>
Subject: Re: Driver Boards

SNIP...

Yous guys contemplating using DR's driver boards on your OEM TPI or
TBI setups, ought to make sure to check with DR as to whether these
are going to work for you if you drive all (or even half) of those INJ
drivers all at once on his board, ala batch or bank mode.

This issue was raised on EFI332, but I doubt if it made it to the
GMECM list; DR's particular design makes use of a shortcut in sharing
multiple Cherry drivers on ONE "load resistor" (if you're familiar
with the Cherry Driver circuit, that's the 300ohm 2W big R, normally
assigned one per driver); hence, there was some concern about too much
VR drop across these resistors if many/multiple drivers were to be
turned on at once. Since the common usage on EFI332 is SEFI I guess it
was assumed this would be OK, but since it's usually batch or bank on
GMECM, this might be something to get cleared up before you launch.

I haven't looked at the design since it was first reported, so I dunno
if any of this has changed; just thot I should interject a caveat
since the application is a tad different. If this old/stale/dated
news, I beg pardon.

Gar
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You're right Gar, the initial design made use of only 1 5W load resistor
rather than the 2W recommended in the data sheet.  The 5W would have
been cutting it close but jumping to a single 10W would have taken up
too much space.  So I went to a parallel pair of 620 ohm / 5W load
resistors to give a total of 310 ohms at 10 Watts.

So bank firing up to 4 injectors at a time would be a max of 8 watts
leaving 2 watts of overhead, and batch firing of 2 injectors at a time
would be a max of 4 watts.

Of course depending on the application it is possible to turn on more
than 4 injector drivers at a time.  Pushing the power limits of these
load resistors requires that the end user apply some caution and common
sense.  This is one caveat that I've stated in the past regarding this
combo driver board.

For automotive applications, the combo driver board should work well.

--
. David Rhoads II
. Applied Dynamics International
. 3800 Stone School Road, Ann Arbor, Mi 48108
. (734) 973-1300
. rhoads at adi.com   web site:  http://www.adi.com


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